The immensity of the impact of Superstorm Sandy on the Eastern U.S. is difficult to comprehend, and the scenes of devastation coming from the impact zone are stunning and heart-wrenching. To help understand the extraordinary scale of this historic storm, I’ve put together a list of notable statistics from Sandy:
Death toll: 160 (88 in the U.S., 54 in Haiti, 11 in Cuba)
Damage estimates: $10 – $55 billion
Power outages: 8.5 million U.S. customers, 2nd most for a natural disaster behind the 1993 blizzard (10 million)
Maximum U.S. sustained winds: 69 mph at Westerly, RI
Peak U.S. wind gusts: 90 mph at Islip, NY and Tompkinsville, NJ
Maximum U.S. storm surge: 9.45′, Bergen Point, NJ 9:24 pm EDT October 29, 2012
Maximum U.S. Storm Tide: 14.60′, Bergen Point, NJ, 9:24 pm EDT October 29, 2012
Minimum pressure: 945.5 mb, Atlantic City, NJ at 7:24 pm EST, October 29, 2012. This is the lowest pressure measured in the U.S., at any location north of Cape Hatteras, NC (previous record: 946 mb in the 1938 hurricane on Long Island, NY)
Destructive potential of storm surge: 5.8 on a scale of 0 to 6, highest of any hurricane observed since 1969. Previous record: 5.6 on a scale of 0 to 6, set during Hurricane Isabel of 2003.
Diameter of tropical storm-force winds at landfall: 945 miles
Diameter of ocean with 12′ seas at landfall: 1500 miles
Figure 1. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite acquired this image of Superstorm Sandy around 3:35 a.m. Eastern Daylight Time (7:35 Universal Time) on October 30. This image is from the “day-night band” on VIIRS, which detects light wavelengths from green to near-infrared. The full Moon lit up the tops of the clouds. Image credit: NASA.
Figure 2. Preliminary death and damage statistics for Sandy as compiled by Wikipedia on November 1, 2012.
Figure 3. Precipitation from Superstorm Sandy for the 7-day period ending at 8 am EDT Thursday, November 1, 2012. Image credit: NOAA/NWS/AHPS.
Figure 4. Top five weather-related power outages in the U.S.
Figure 5. Strong winds from Sandy blow snow in West Virginia on October 30, 2012. Image credit: Facebook/Cheryl Clay
Sandy’s snows
Several cities set records for snowiest October day on record during Sandy: Elkin, WV (7″, previous record, 4.6″ in 1917) and Bluefield (4.7″, previous record 3.2″ in 1993.) Heavy snows caused roof collapses in West Virginia, and snows of two feet or more fell in four states–West Virginia, Tennessee, Maryland, and Virginia. However, Sandy fell short of setting the all-time record for snowfall from a hurricane. The Vermont Journal estimated that the Snow Hurricane of 1804 dumped up to 4 feet of snow in Vermont.
Charities mobilize for Sandy
The outpouring of charitable donations in the wake of the devastation wrought by Hurricane Sandy has been one of the bright spots in the gloomy aftermath of the storm. The main owners of The Weather Channel have agreed to match donations of up to $1 million to the American Red Cross, if you text SANDY to 90999 ($10). I also recommend my favorite disaster relief charity, Portlight.org. They are focusing their response efforts exclusively on the post-Sandy neeeds of people with disabilities.Check out the Portlight blog to see what they’re up to; donations are always needed.
Sandy’s greatest devastation occurred in Haiti, where rains of up to 20 inches in 24 hours unleashed rampaging flood waters that killed at least 54, left 200,000 homeless, wiped out thousand of acres of crops, and killed massive numbers of livestock. For impoverished families in Haiti still struggling to recover from the earthquake in 2010 and Hurricane Isaac in August, Sandy was devastating. These crops are the very essence of rural Haitian’s livelihoods, and there are fears widespread starvation will result. A disaster relief charity in Haiti that I’ve contributed to for many years, The Lambi Fund of Haiti, is seeking donations to help farmers purchase local seeds so that they can replant their crops in the wake of this latest terrible Haitian catastrophe.
We’re used to seeing hurricane-battered beaches and flooded cities in Florida, North Carolina, and the Gulf Coast. But to see these images from the Jersey Shore and New York City in the wake of Hurricane Sandy is a shocking experience. New Jersey only rarely gets hit by hurricanes because it lies in a portion of the coast that doesn’t stick out much, and is too far north. How did this happen? How was a hurricane able to move from southeast to northwest at landfall, so far north, and so late in hurricane season? We expect hurricanes to move from east to west in the tropics, where the prevailing trade winds blow that direction. But the prevailing wind direction reverses at mid-latitudes, flowing predominately west-to-east, due to the spin of the Earth. Hurricanes that penetrate to about Florida’s latitude usually get caught up in these westerly winds, and are whisked northeastwards, out to sea. However, the jet stream, that powerful band of upper-atmosphere west-to-east flowing air, has many dips and bulges. These troughs of low pressure and ridges of high pressure allow winds at mid-latitudes to flow more to the north or to the south. Every so often, a trough in the jet stream bends back on itself when encountering a ridge of high pressure stuck in place ahead of it. These “negatively tilted” troughs have winds that flow from southeast to northwest. It is this sort of negatively tilted trough that sucked in Sandy and allowed the hurricane to take such an unusual path into New Jersey.
Figure 1. Inlet section of Atlantic City, N.J., after Hurricane Sandy. Image credit: 6 ABC Action News.
The 1903 Vagabond Hurricane
The only other hurricane to hit New Jersey since 1851 besides Sandy was the 1903 Category 1 Vagabond Hurricane. According to Wikipedia, the Vagabond Hurricane caused heavy damage along the New Jersey coast ($180 million in 2006 dollars.) The hurricane killed 57 people, and endangered the life of President Theodore Roosevelt, who was sailing on a yacht near Long Island, NY, when the hurricane hit. However, the Vagabond Hurricane hit in September, when the jet stream is typically weaker and farther to the north. It is quite extraordinary that Sandy was able to hit New Jersey in late October, when the jet stream is typically stronger and farther south, making recurvature to the northeast much more likely than in September.
Figure 2. The path of the 1903 Vagabond Hurricane, the only other hurricane to hit New Jersey since 1851.
The blocking ridge that steered Sandy into New Jersey
A strong ridge of high pressure parked itself over Greenland beginning on October 20, creating a “blocking ridge” that prevented the normal west-to-east flow of winds over Eastern North America. Think of the blocking ridge like a big truck parked over Greenland. Storms approaching from the west (like the fall low pressure system that moved across the U.S. from California to Pennsylvania last week) or from the south (Hurricane Sandy) were blocked from heading to the northeast. Caught in the equivalent of an atmospheric traffic jam, the two storms collided over the Northeast U.S., combined into one, and are now waiting for the truck parked over Greenland to move. The strength of the blocking ridge, as measured by the strength of the North Atlantic Oscillation (NAO), was quite high–about two standard deviations from average, something that occurs approximately 5% of the time. When the NAO is in a strong negative phase, we tend to have blocking ridges over Greenland.
Figure 3. Jet stream winds at a pressure of 300 mb on October 29, 2012, as Hurricane Sandy approached the coast of New Jersey. Note that the wind direction over New Jersey (black arrows) was from the southeast, due to a negatively tilted trough of low pressure over the Eastern U.S. caused by a strong blocking ridge of high pressure over Greenland. Image credit: NOAA/ESRL.
Arctic sea ice loss can cause blocking ridges
Blocking ridges occur naturally, but are uncommon over Greenland this time of year. According to NOAA’s Climate Prediction Center, blocking near the longitude of Greenland (50°W) only occurs about 2% of the time in the fall. These odds rise to about 6% in winter and spring. As I discussed in an April post, Arctic sea ice loss tied to unusual jet stream patterns, three studies published in the past year have found that the jet stream has been getting stuck in unusually strong blocking patterns in recent years. These studies found that the recent record decline in Arctic sea ice could be responsible, since this heats up the pole, altering the Equator-to-pole temperature difference, forcing the jet stream to slow down, meander, and get stuck in large loops. The 2012 Arctic sea ice melt season was extreme, with sea ice extent hitting a record lows. Could sea ice loss have contributed to the blocking ridge that steered Sandy into New Jersey? It is possible, but we will need to much more research on the subject before we make such a link, as the studies of sea ice loss on jet stream patterns are so new. The author of one of the new studies, Dr. Jennifer Francis of Rutgers, had this say in a recent post by Andy Revkin in his Dot Earth blog:“While it’s impossible to say how this scenario might have unfolded if sea-ice had been as extensive as it was in the 1980s, the situation at hand is completely consistent with what I’d expect to see happen more often as a result of unabated warming and especially the amplification of that warming in the Arctic.”
Massive and dangerous Hurricane Sandy has grown to record size as it barrels northeastwards along the North Carolina coast at 10 mph. At 8 am EDT, Sandy’s tropical storm-force winds extended northeastwards 520 miles from the center, and twelve-foot high seas covered a diameter of ocean 1,030 miles across. Since records of storm size began in 1988, no tropical storm or hurricane has been larger (though Hurricane Olga of 2001 had a larger 690 mile radius of tropical storm-force winds when it was a subtropical storm near Bermuda.) Sandy has put an colossal volume of ocean water in motion with its widespread and powerful winds, and the hurricane’s massive storm surge is already impacting the coast. A 2′ storm surge has been recorded at numerous locations this morning from Virginia to Connecticut, including a 3′ surge at Virginia’s Chesapeake Bay Bridge Tunnel and Sewells Point at 9 am EDT. Huge, 10 – 15 foot-high battering waves on top of the storm surge have washed over Highway 12 connecting North Carolina’s Outer Banks to the mainland at South Nags Head this morning. The highway is now impassable, and has been closed. The coast guard station on Cape Hatteras, NC, recorded sustained winds of 50 mph, gusting to 61 mph, at 5:53 am EDT this morning. In Delaware, the coastal highway Route 1 between Dewey Beach and Bethany Beach has been closed due to high water. Even though Sandy is a minimal Category 1 hurricane, its storm surge is extremely dangerous, and if you are in a low-lying area that is asked to evacuate, I strongly recommend that you leave.
Figure 1. A fright to behold: morning satellite image of massive Hurricane Sandy.
Sandy’s death toll now at 65
Sandy was a brutal storm for the Caribbean, the storm’s death toll now stands at 65. The death toll is highest in Haiti, with 51 deaths. Prime Minister Laurent Lamothe told the Associated Press that “This is a disaster of major proportions. The whole south is under water.” Approximately 8 – 10″ of rain (200 – 250 mm) fell in the capital of Port-au-Prince. Eleven people were killed in Cuba, where 35,000 homes were damaged or destroyed. Sandy is also being blamed for 1 death in Jamaica, 1 in Puerto Rico, and 1 in the Bahamas.
Figure 2. A resident carries a metal sheet from a house after heavy rains damaged by Hurricane Sandy in Port-au-Prince, Haiti, Thursday, Oct. 25, 2012. Sandy is being blamed for 51 deaths in Haiti. (AP Photo/Dieu Nalio Chery)
Figure 3. Satellite-estimated rainfall amounts from NASA’s TRMM satellite show that portions of Haiti received over 12.75″ (325 mm) of rain (pink colors) from Hurricane Sandy. The capital of Port-au-Prince received 8 – 10″ (200 – 250 mm.) Image credit: NASA.
Intensity and Track Forecast for Sandy
Sandy has a rather unusual structure, with the strongest winds on the southwest side of the center, but a larger area of tropical storm-force winds to the northeast of the center. Most of the storm’s heavy thunderstorm activity is on the storm’s west side, in a thick band several hundred miles removed from the center, giving Sandy more the appearance of a subtropical storm rather than a hurricane. Satellite loops show that the low-level center of Sandy is no longer exposed to view, and heavy thunderstorms are increasing in areal extent near the center, due to a reduction in wind shear from 35 – 40 knots last night to 25 – 30 knots this morning. Wind shear is expected to drop another 5 knots today, which may allow the storm to build an increased amount of heavy thunderstorms near its center and intensify by 5 – 10 mph over the next 24 hours. The NOAA Hurricane Hunters noted this morning that Sandy had a partial eyewall on the west through SE sides of the center, and the storm may be able to build a nearly complete eyewall by Monday morning. By Monday afternoon, though, Sandy will be moving over cool 25°C waters, which should slow down this intensification process. However, the trough of low pressure that will be pulling Sandy to the northwest towards landfall on Monday will strengthen the storm by injecting “baroclinic” energy–the energy one can derive from the atmosphere when warm and cold air masses lie in close proximity to each other. Sandy should have sustained winds at hurricane force, 75 – 80 mph, at landfall. Sandy’s central pressure is expected to drop from its current 951 mb to 945 – 950 mb at landfall Monday night. A pressure this low is extremely rare; according to wunderground weather historian Christopher C. Burt, the lowest pressure ever measured anywhere in the U.S. north of Cape Hatteras, NC, is 946 mb (27.94″) measured at the Bellport Coast Guard Station on Long Island, NY on September 21, 1938 during the great “Long Island Express” hurricane. The latest set of 00Z (8 pm EDT) and 06Z (2 am EDT) computer model runs are in agreement that Sandy will make landfall between 10 pm Monday night and 4 am Tuesday morning in New Jersey.
Figure 4. Predicted maximum storm surge from Hurricane Irene. There is a 10% chance that the storm surge could exceed the heights given here, so most regions will receive a surge lower than this forecast. The greatest surge is expected in the waters surrounding New York City, since the shape of the bays will act to funnel the water to higher levels.
Sandy’s storm surge a huge threat
Last night’s 9:30 pm EDT H*Wind analysis from NOAA’s Hurricane Research Division put the destructive potential of Sandy’s winds at a modest 2.6 on a scale of 0 to 6. However, the destructive potential of the storm surge was exceptionally high: 5.7 on a scale of 0 to 6. This is a higher destructive potential than any hurricane observed between 1969 – 2005, including Category 5 storms like Katrina, Rita, Wilma, Camille, and Andrew. The previous highest destructive potential for storm surge was 5.6 on a scale of 0 to 6, set during Hurricane Isabel of 2003. Sandy is now forecast to bring a near-record storm surge of 6 – 11 feet to Northern New Jersey and Long Island Sound, including the New York City Harbor. While Sandy’s storm surge will be nowhere near as destructive as Katrina’s, the storm surge does have the potential to cause many billions of dollars in damage if it hits near high tide at 9 pm EDT on Monday. The full moon is on Monday, which means astronomical high tide will be about 5% higher than the average high tide for the month. This will add another 2 – 3″ to water levels. Fortunately, Sandy is now predicted to make a fairly rapid approach to the coast, meaning that the peak storm surge will not affect the coast for multiple high tide cycles. Sandy’s storm surge will be capable of overtopping the flood walls in Manhattan, which are only five feet above mean sea level. On August 28, 2011, Tropical Storm Irene brought a storm surge of 4.13′ to Battery Park on the south side of Manhattan. The waters poured over the flood walls into Lower Manhattan, but came 8 – 12″ shy of being able to flood the New York City subway system. According to the latest storm surge forecast for NYC from NHC, Sandy’s storm surge is expected to be several feet higher than Irene’s. If the peak surge arrives near Monday evening’s high tide at 9 pm EDT, a portion of New York City’s subway system could flood, resulting in billions of dollars in damage. I give a 50% chance that Sandy’s storm surge will end up flooding a portion of the New York City subway system.
An excellent September 2012 article in the New York Times titled, “New York Is Lagging as Seas and Risks Rise, Critics Warn” quoted Dr. Klaus H. Jacob, a research scientist at Columbia University’s Earth Institute, on how lucky New York City got with Hurricane Irene. If the storm surge from Irene had been just one foot higher, “subway tunnels would have flooded, segments of the Franklin D. Roosevelt Drive and roads along the Hudson River would have turned into rivers, and sections of the commuter rail system would have been impassable or bereft of power,” he said, and the subway tunnels under the Harlem and East Rivers would have been unusable for nearly a month, or longer, at an economic loss of about $55 billion. Dr. Jacob is an adviser to the city on climate change, and an author of the 2011 state study that laid out the flooding prospects. “We’ve been extremely lucky,” he said. “I’m disappointed that the political process hasn’t recognized that we’re playing Russian roulette.”
Sandy’s winds
Sandy will bring sustained winds of tropical storm-force to a 1000-mile swath of coast on Monday and Tuesday. Winds of 55 – 75 mph with gusts over hurricane force will occur along a 500 mile-wide section of coast. With most of the trees still in leaf, there will be widespread power outages due to downed trees, and the potential for several billion dollars in wind damage. A power outage computer model run by Johns Hopkins University predicts that 10 million people will lose power from the storm.
Sandy’s rains
Sandy’s heavy rains are going to cause major but probably not catastrophic river flooding. If we compare the predicted rainfall amounts for Sandy (Figure 5) with those from Hurricane Irene of 2011 (Figure 6), Sandy’s are expected to be about 30% less. Hurricane Irene caused $15.8 billion in damage, most of it from river flooding due to heavy rains. However, the region most heavily impacted by Irene’s heavy rains had very wet soils and very high river levels before Irene arrived, due to heavy rains that occurred in the weeks before the hurricane hit. That is not the case for Sandy; soil moisture is near average over most of the mid-Atlantic, and is in the lowest 30th percentile in recorded history over much of Delaware and Southeastern Maryland. One region of possible concern is the Susquehanna River Valley in Eastern Pennsylvania, where soil moisture is in the 70th percentile, and river levels are in the 76th – 90th percentile. This area is currently expected to receive 3 – 6 inches of rain (Figure 4), which is probably not enough to cause catastrophic flooding like occurred for Hurricane Irene. I expect that river flooding from Sandy will cause less than $1 billion in damage.
Figure 5. Predicted 5-day rainfall for the period ending Friday morning, November 2, 2012, at 8am EDT. Image credit: NOAA/HPC.
Figure 6. Actual rainfall for 2011’s Hurricane Irene, which caused $15.8 billion in damage, most of it from river flooding due to heavy rains. Sandy’s rains are predicted to be about 30% less than Irene’s. Image credit: NOAA/HPC.
Sandy’s snows
You can add heavy snow to the list of weather frights coming for the Eastern U.S. from Sandy. A WInter Storm Watch is posted for much of southeastern West Virginia for Sunday night through Monday, when 2 – 6 inches of wet, heavy snow is expected to fall at elevations below 2000 feet. At higher elevation above 3,000 feet, 1 – 2 feet of snow is possible. With high wind gusts of 35 – 45 mph and many trees still in leaf, the affected area can expect plenty of tree damage and power outages. Lesser snows are expected in the mountains of Virginia, Tennessee, and North Carolina.
Sandy’s tornado threat is minimal
The severe thunderstorm and tornado threat from Sandy Sunday and Monday looks low, due to minimal instability.
Links for Sandy
To find out if you need to evacuate, please contact your local emergency management office. They will have the latest information. People living in New York City can find their evacuation zone here or use this map. FEMA has information on preparing for hurricanes.
People with disabilities and caregivers seeking information on accessible shelter and transportation can contact portlight.org
An impressive 1-minute resolution satellite loop of Sandy today is at the CSU RAMMB website.
This impressive 1-min GOES loop beginning at dawn Saturday shows Sandy’s heavy thunderstorms fighting against high wind shear, and the tilt of the vortex to the northeast with height.
The National Hurricane Center’s Interactive Storm Surge RIsk Map, which allows one to pick a particular Category hurricane and zoom in, is a good source of storm surge risk information.
Climate Central has a nice satellite image showing which parts of New York Harbor are below five feet in elevation.
Figure 7. Tide gauge in Kahului, Maui, Hawaii, showing the 2.5′ tsunami that hit at approximately 09 UTC Sunday, October 29, 2012. Image credit: NOAA Tides and Currents.
Three-foot tsunami his Hawaii after big quake in Canada
A major magnitude 7.7 earthquake hit 25 miles (40 km) south of Sandspit, British Columbia last night at 8:04 pm PDT. The quake generated a tsunami that raced across the Pacific Ocean and struck Hawaii six hours later. The tsunami reached a height of 2.5 feet in Kahului, Maui, 1.2′ at Hilo, and 0.5′ in Honolulu. The earthquake was Canada’s third largest since 1900. The last stronger quake was a magnitude 7.9 that hit in 1958. The other stronger quake was a magnitude 8.1 that hit in 1949, with an epicenter very close to last night’s trembler.
Hurricane warnings are flying for Jamaica and Eastern Cuba, as an intensifying Hurricane Sandy plows north-northeast at 13 mph towards landfall. The Hurricane Hunters are in the storm, and measured surface winds of hurricane strength–75 to 80 mph–in the storm’s northeast quadrant near 9:25 am EDT. Sandy’s pressure at the time of the 9:28 am center fix was 973 mb, and the temperature in the eye had warmed 2°C since the 7:48 am fix, a sign of strengthening. Intermittent rain squalls from Sandy have been affecting Jamaica since Monday night, and Kingston, Jamaica has picked up 2.12″ of rain from Sandy as of 9 am EDT. Winds in Jamaica have been below 20 mph as of 10 am EDT, but will start to rise quickly in the next few hours. The Hurricane Hunters found a large 55 mile-diameter eye that was open to the WNW this morning, and it is likely that Kingston will receive high winds of 55 – 65 mph from the western eyewall, which will cause considerable damage to Jamaica’s capital. The eastern tip of Jamaica will likely see the eye pass overhead, and will receive the strongest winds. The eye is beginning to appear on visible satellite loops, and Sandy is showing an increasing degree of organization as it closes in on Jamaica. Sandy is the tenth hurricane of the 2012 hurricane season, which is now tied for eighth place for most hurricanes in a year since record keeping began in 1851.
Figure 1. Morning microwave satellite image of Tropical Storm Sandy taken at 8:45 am EDT. The large 55-mile diameter eye was just south of Jamaica. Image credit: Navy Research Lab, Monterey.
Near-term forecast for Sandy
Wind shear is forecast to be in the moderate range and ocean temperatures will be a warm 28°C through Thursday morning, which will favor intensification. However, Sandy doesn’t have much time left over water before it encounters the high mountains of Jamaica this afternoon, which should interrupt the intensification process. The strongest Sandy is likely to be at landfall in Jamaica is a 90 mph Category 1 hurricanes. After encountering Jamaica, Sandy won’t have time to re-organize much before making landfall in Eastern Cuba near 10 pm EDT tonight, and the strongest the storm is likely to be then is a 90 mph Category 1. Passage over the rugged terrain of Cuba should weaken Sandy’s winds by 20 – 30 mph, and it will be difficult for the storm to regain all of that lost strength in the face of the high wind shear of 20 – 30 knots it will encounter Thursday and Friday. I expect that Sandy will be a 60 – 70 mph tropical storm as it traverses the Bahamas.
Figure 2. MODIS satellite image of Tropical Storm Sandy taken at 11:45 am EDT Tuesday, October 23, 2012. At the time, Sandy had top winds of 50 mph. Image credit: NASA.
Sandy: a potential billion-dollar storm for the mid-Atlantic and New England
On Friday, a very complicated meteorological situation unfolds, as Sandy interacts with a trough of low pressure approaching the U.S. East Coast and trough of low pressure over the Central Atlantic. The Central Atlantic trough may be strong enough to pull Sandy northeastwards, out to sea, as predicted by the official NHC forecast, and the 06Z GFS, 00Z UKMET, 00Z Canadian, and 06Z HWRF models (00Z is 8 pm EDT, and 06Z is 2 am EDT.) However, an alternative solution, shown by the 00Z ECMWF, 06Z GFDL, and 06Z NOGAPS models, is for Sandy to get caught up by the trough approaching the Eastern U.S., which will inject a large amount of energy into Sandy, converting it to a powerful subtropical storm that hits the mid-Atlantic or New England early next week with a central pressure below 960 mb and sustained winds of 60 – 70 mph. Such a storm would likely cause massive power outages and over a billion dollars in damage, as trees still in leaf take out power grids, and heavy rains and coastal storm surges create damaging flooding. The full moon is on Monday, which means astronomical tides will be at their peak for the month, increasing potential storm surge flooding. A similar meteorological situation occurred in October 1991, when Hurricane Grace became absorbed by a Nor’easter, becoming the so-called “Perfect Storm” that killed 13 people and did over $200 million in damage in the Northeast U.S.
Figure 3. The Wednesday morning 06Z (2 am EDT) run of the GFS model was done 20 times at lower resolution with slightly varying initial conditions of temperature, pressure, and moisture to generate an ensemble of forecast tracks for Sandy (pink lines). These forecasts show substantial uncertainty in Sandy’s path after Friday, with a minority of the forecasts taking Sandy to the northeast, out to sea, and the majority now predicting a landfall in the Northeast or mid-Atlantic states of the U.S. The white line shows the official GFS forecast, run at higher resolution.
When might Sandy arrive in the mid-Atlantic and New England?
The models vary significantly in their predictions of when Sandy might arrive along the U.S. coast. The 06Z NOGAPS model predicts Sandy’s heavy rains will arrive on North Carolina’s Outer Banks on Saturday, then spread into the mid-Atlantic and New England on Sunday. The 00Z ECMWF model predicts that Sandy’s rains won’t affect North Carolina until Sunday, with the storm making landfall in New Jersey on Monday night. The GFDL model is in-between these extremes, taking Sandy ashore in Delaware on Monday morning. The trough of low pressure that Sandy will be interacting with just moved ashore over the Western U.S. this morning, and got sampled by the 12Z (8 am EDT) set of land-based balloon-borne radiosondes for the first time. One of the reasons the models have been in such poor agreement on the long-term fate of Sandy is that the strength of this trough has not been very well known, since it has been over the ocean where we have limited data. Now that the trough is over land, it will be better sampled, and the next set of 12Z model runs, due out this afternoon between 2 pm – 4pm EDT, will hopefully begin to converge on a common solution. I’ll have an update this afternoon once the 12Z model runs are in.
Figure 4. Morning satellite image of Tropical Storm Tony.
Tropical Storm Tony forms in the middle Atlantic Tropical Storm Tony formed Tuesday night in the middle Atlantic, becoming the nineteenth named storm of this very busy 2012 Atlantic hurricane season. Tony has a modest area of heavy thunderstorms, as seen on visible satellite images, but is battling dry air , wind shear, and ocean temperatures that have fallen below 26°C. Tony will not threaten any land areas, and will likely be dead by Thursday night.
Tony’s place in history
Tony is the Nineteenth named storm of the 2012 Atlantic hurricane season, tying this year with 1887, 1995, 2010, and 2011 for third busiest Atlantic season since the HURDAT historical data base began in 1851. With five more weeks left before the November 30 end of hurricane season, 2012 is likely to move into second place for most named storms before the year is out, as all six prior Atlantic hurricane seasons with nineteen or more named storms have had at least one named storm form after October 24. Here, then, is a list of the seven busiest Atlantic hurricane seasons on record:
2005 (28 named storms) 1933 (20 named storms, according to a new re-analysis) 2012 (19 named storms) 1887 (19 named storms) 2010 (19 named storms) 2011 (19 named storms) 1995 (19 named storms)
It’s pretty remarkable that we’ve now had three straight years with nineteen named storms in the Atlantic. But how many of these storms might not have been counted in the pre-satellite era (before 1960)? Here’s a list of weak and short-lived storms from 2010 – 2012 that stayed far out sea, and would likely have gone unnoticed in the pre-satellite era:
Even if we correct for the possible over-count of approximately two named storms per year during the 2010, 2011, and 2012 hurricane seasons, compared to the pre-satellite era, there is nothing in the HURDAT data base that compares to the type of activity we’ve seen the past three years. One likely contributor to the unusual string of active years is the fact hurricane season has gotten longer, perhaps due to warming ocean temperatures. I discussed in a 2008 blog post that Dr. Jim Kossin of the University of Wisconsin published a 2008 paper in Geophysical Research Letters titled, “Is the North Atlantic hurricane season getting longer?” He concluded that yes, there is a “apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high”.
Jeff Mastersfrom: http://www.wunderground.com/blog/JeffMasters/article.html
A tropical wave embedded in a large trough of low pressure (Invest 99L) covers a large portion of the Central Caribbean between Hispaniola and the northern coast of South America. This storm has the potential to be a dangerous rainfall threat for Haiti, Jamaica, and eastern Cuba. The disturbance is headed west at less than 5 mph, is over very warm waters of 29°C, and is in a moist environment. 99L has a large area of heavy thunderstorms that have a good degree of spin. These thunderstorms are beginning to organize into spiral bands, as seen on visible satellite loops. However, the amount of heavy thunderstorm activity is about the same as yesterday, and there are no signs of a surface circulation. An Air Force hurricane hunter aircraft is scheduled to investigate 99L this afternoon, but I expect this flight will be rescheduled for later.
Figure 1. Morning satellite image of Invest 99L.
Forecast for 99L Wind shear is a low 5 – 10 knots, and is forecast to be in the low to moderate range, 5 – 20 knots, through Tuesday. This should allow for some steady development of 99L, and there has been a good deal of model support for 99L becoming a tropical depression by Wednesday. Steering currents favor a continued slow westward movement for 99L through Tuesday. On Wednesday, a strong trough of low pressure to the north of 99L is expected to turn the storm to the north or north-northeast, which should put 99L in the vicinity of Jamaica on Wednesday and Eastern Cuba on Thursday. By Friday, 99L should be in the Central or Eastern Bahamas. It is unclear at this point whether or not the trough pulling 99L to the north will be strong enough to pull the storm all the way out to sea to the northeast; a narrow ridge of high pressure has the potential to build in over 99L late this week and force the storm west-northwest, with a potential threat to the western Bahamas and U.S. East Coast by next weekend. In their 8 am EDT tropical weather outlook, NHC gave 99L a 70% chance of developing into a tropical cyclone by Tuesday morning. 99L will be capable of bringing heavy rains of 5 – 10 inches, with isolated amounts of up to 15 inches in mountainous areas, to Jamaica and Haiti, Monday through Wednesday. Heavy rains will begin on Tuesday in Eastern Cuba, and spread northwards into the Central and Eastern Bahamas by Wednesday.
Invest 90L in the middle Atlantic
A tropical wave (Invest 90L) about 830 miles east-northeast of the northernmost Lesser Antilles Islands is headed west-northwest at about 10 mph. The disturbance has a small amount of heavy thunderstorms, as seen on visible satellite images, and has gotten tangled up with an upper-level low pressure system. This upper-level low is providing 90L the spin it needs to become a tropical cyclone, but is also pumping cool, dry air into the disturbance, which will keep any development slow over the next few days. Wind shear is a moderate 10 – 20 knots, and is forecast to remain in the moderate range until Tuesday. This may allow for some slow development of 90L before it encounters high wind shear of 20 – 30 knots on Tuesday night through Thursday. None of the reliable computer models develop 90L into a tropical cyclone, and it’s unlikely that 90L will affect any land areas. In their 8 am EDT tropical weather outlook, NHC gave 90L a 30% chance of developing into a tropical cyclone by Tuesday morning.
The next name on the list of Atlantic tropical storms for 2012 is Sandy.
The first new tropical depression in the Atlantic since September 11 is here, Tropical Depression Fifteen. TD 15 is destined for a short life, though, and will not be a threat to any land areas. The storm is already showing signs that moderate wind shear of 10 – 20 knots is interfering with development, with most of the storm’s heavy thunderstorms displaced away from the center of circulation. Wind shear is expected to rise to the high range, above 20 knots, on Thursday and Friday as the storm turns north and then northeast. Ocean temperatures will cool from 28°C today to 25°C by Saturday, and all of the computer models show TD 15 ceasing to exist by Saturday, as the storm becomes absorbed by a large extratropical storm. TD 15 is a classic example of a weak, short-lived tropical cyclone that would have gotten missed before satellites came around. If TD 15 strengthens, it will be called Tropical Storm Oscar.
Figure 1. MODIS satellite image of TD 15 taken at 8:52 am EDT Wednesday, October 3, 2012. At the time, TD 15 was just forming and had top winds of 35 mph. Image credit: Navy Research Lab, Monterey.
Nadine touring the Azores Islands–again
I’m-not-dead-yet Tropical Storm Nadine is back for a second tour of the Azores Islands, where tropical storm warnings are up for the storm’s expected arrival tonight. Nadine is struggling with cool 21 – 22°C waters and high wind shear of 20 – 30 knots, and could transition to an extratropical storm later today or on Thursday as it heads east at 14 mph. Nadine is up to 21 days as a tropical or subtropical cyclone as of 2 pm today, making it the fifth longest-lived Atlantic tropical cyclone of all-time (tropical cyclones include tropical depressions, tropical storms, and hurricanes, but not extratropical storms.) According to the official HURDAT Atlantic database, which goes back to 1851, only five previous Atlantic tropical cyclones have lasted 21 days or longer (thanks go to Brian McNoldy for these stats):
According to the Hurricane FAQ, the all-time world record is held by Hurricane John in the Eastern Pacific, which lasted 31 days as it traveled both the Northeast and Northwest Pacific basins during August and September 1994. (It formed in the Northeast Pacific, reached hurricane force there, moved across the dateline and was renamed Typhoon John, and then finally recurved back across the dateline and renamed Hurricane John again.) Of course, there may have been some longer-lived storms prior to 1961 that we didn’t observe, due to the lack of satellite data.
Figure 2. MODIS satellite image of Hurricane Nadine taken at 8:45 am EDT Wednesday, October 3, 2012. At the time, Nadine had top winds of 50 mph. Image credit: NASA.
August 2012 was the globe’s 4th warmest August on record, according to the National Oceanic and Atmospheric Administration’s National Climatic Data Center (NCDC).NASA rated August 2012 the 6th warmest on record. August 2012 global land temperatures were the 2nd warmest on record, and global ocean temperatures were the 5th warmest on record. August 2012 was the 330th consecutive month with global temperatures warmer than the 20th century average; the last time global temperatures were below average was February 1985. Global satellite-measured temperatures in August for the lowest 8 km of the atmosphere were 3rd warmest in the 34-year record, according to the University of Alabama Huntsville (UAH). Wunderground’s weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of August in his August 2012 Global Weather Extremes Summary.
Figure 1. Departure of temperature from average for August 2012. Most areas of the world experienced much higher-than-average monthly temperatures, including much of Canada, Southeast Europe, and Western Asia. Central Russia was much cooler than average. Image credit: National Climatic Data Center (NCDC) .
El Niño watch continues
Sea surface temperatures were at 0.5°C above average as of September 17 in the equatorial Pacific off the coast of South America, and have been near or above the 0.5°C above average–the threshold needed for a weak El Niño event–since the beginning of July. However, winds, pressures, and cloud cover over the region have not responded in the fashion typically associated with an El Niño, and NOAA’s Climate Prediction Center (CPC) classified conditions as being neutral in their September 6 El Niño discussion. They continued their El Niño watch, and gave a 69% chance that an El Niño event will be in place by the end of September. El Niño conditions tend to decrease Atlantic hurricane activity, by increasing wind shear over the tropical Atlantic. Wind shear has been close to average over the tropical Atlantic since the beginning of hurricane season in June. However, the past few runs of the GFS model have predicted a significant rise in wind shear over the Caribbean and tropical Atlantic by early October, which may represent El Niño finally beginning to kick in and affect the atmospheric circulation over the Atlantic.
Figure 2. Arctic sea ice extent as of September 18, 2012 (black line) compared to the previous record low years, in millions of square kilometers. This year’s extent is far below any previous year, and is close to its minimum for the year. Satellite measurements of ice extent began in 1979. Image credit: Danish Meteorological Institute.
Arctic sea ice falls to all-time record low during August
August 2012 Arctic sea ice extent reached its lowest August extent in the 35-year satellite record, according to the National Snow and Ice Data Center (NSIDC). The new sea ice record was set on August 26, a full three weeks before the usual end of the melting season. Every major scientific institution that tracks Arctic sea ice agrees that new records for low ice area, extent, and volume have been set (see the comprehensive collection of sea ice graphs here.) Satellite records of sea ice extent date back to 1979, though a 2011 study by Kinnard et al. shows that the Arctic hasn’t seen a melt like this for at least 1,450 years (see a more detailed article on this over at skepticalscience.com.) The latest September 18, 2012 extent of 3.5 million square kilometers is approximately a 50% reduction in the area of Arctic covered by sea ice, compared to the average from 1979 – 2000. The amount of open ocean exposed this September compared to September 1980 is about 43% of the size of the contiguous United States. The ice extent is close to its minimum for the year, and should start in increase within the next week or two, but that open water over the Arctic will provide a significant amount of heat and moisture to the atmosphere over the next few months that will significantly alter weather patterns. One possible impact may be an increase in the intensity and duration of extreme weather events during fall and winter.
Video 1. This animation shows the 2012 time-series of ice extent using sea ice concentration data from the DMSP SSMI/S satellite sensor. The black area represents the daily average (median) sea ice extent over the 1979-2000 time period. Layered over top of that are the daily satellite measurements from January 1 – September 14, 2012. A rapid melt begins in July, whereby the 2012 ice extents fall far below the historical average. Source: NOAA’s Environmental Visualization Laboratory.
Nadine approaching the Azores
Long-lived Tropical Storm Nadine is headed northeastwards on a track that will bring the storm close to the Azores Islands on Wednesday and Thursday. A tropical storm watch has been posted for the islands of Flores and Corvo in the northwestern Azores. Steering currents for Nadine are expected to weaken on Wednesday, and the storm will move slowly and erratically for many days in the Central Atlantic late this week and early next week. On Friday, Nadine will become tangled up with an upper-level low pressure system, and the storm may partially or fully convert to an extratropical storm. By this weekend, the GFS and ECMWF models predict Nadine will move southwestward over warmer waters, and it could become fully tropical again.
Elsewhere in the Atlantic, thunderstorm activity associated with a tropical wave that moved through the Lesser Antilles Islands yesterday (92L) has diminished, and this wave is no longer a threat to develop. None of the reliable computers models is showing development of a new tropical cyclone in the Atlantic through September 24.
A partial remnant of Hurricane Isaac off the coast of Louisiana, Invest 90L, was almost torn apart last night by wind shear, but is making a bit of a comeback today. Visible satellite loops and surface observations from buoys and oil rigs in the Gulf show that 90L has an sloppy, elongated surface circulation. The area covered by heavy thunderstorms is relatively modest, and has been pushed to the south side of the circulation center by strong northerly winds that are creating a high 20 knots of wind shear. There is a large amount of dry air that surrounds 90L on all sides that is interfering with development. A hurricane hunter aircraft scheduled to investigate 90L today was cancelled, and has been rescheduled for Saturday afternoon.
Figure 1. Visible satellite image of Invest 90L taken at 11:58 am EDT Friday September 7, 2012.
Forecast for 90L
Wind shear over 90L is predicted to stay in the moderate to high range, 15 – 20 knots, through Saturday morning, then drop to the low range Saturday afternoon through Sunday. Ocean temperatures in the Gulf are 28.5° – 29°C, which is plenty warm enough to support formation of a tropical storm. 90L is essentially stationary this morning, but should begin a slow motion to the east-northeast tonight, in response to the steering flow from a trough of low pressure and its associated surface cold front approaching the Gulf Coast from the northwest. This trough should be capable of pulling 90L to a landfall along the Florida Panhandle or west coast of Florida by Sunday morning. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Sunday morning. I put these odds higher, at 30%.
Leslie weakens to a tropical storm Tropical Storm Leslie continues to remain nearly stationary to the south of the island of Bermuda, and a NOAA hurricane hunter aircraft found this morning that Leslie had weakened below hurricane strength, to a 70 mph tropical storm. An ocean probe launched by the aircraft found that the ocean temperatures at one location in Leslie were 24.5°C, a full 5°C (8°F) drop from when the storm first reached the area two days ago. Moderate wind shear of 10 – 20 knots due to strong upper-level winds out of the west continue to drive dry air to Leslie’s west into the core of the storm. The combined effect of shear and cool waters have eroded away Leslie’s core, and the storm has no eyewall, as seen on satellite loops. A NOAA hurricane hunter aircraft will be in the storm tonight, and an uncrewed NASA Global Hawk aircraft finished an HS3 Hurricane Research Mission into Leslie this morning.
Figure 2. Hurricane Leslie as seen by NASA’s Aqua satellite at 10:45 am EDT Thursday, September 6, 2012. At the time, Leslie was a Category 1 hurricane with 75 mph winds. Image credit: NASA.
Forecast for Leslie
A strong trough of low pressure approaching the U.S. East Coast should make Leslie start moving to the north at 5 mph by Saturday morning. The models have stayed with their more eastwards solution to Leslie’s track, which keeps the threat of Bermuda receiving hurricane-force winds relatively low, since the island is expected to be on the weak (left) side of the storm. If the official NHC forecast verifies, tropical storm-force winds will just graze Bermuda Sunday morning through Sunday evening. According to the latest SHIPS model forecast, the shear is expected to fall to the low category, 5 – 10 knots, by Friday night. Leslie is over warm ocean waters of 29 – 30°C, and once the storm moves away from the large pool of cool waters it has stirred up, the reduction in shear and warm waters should allow the storm to intensify to at least a Category 1 hurricane by Sunday. The latest 11 am EDT NHC wind probability forecast calls for a 30% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT, when the storm will be beginning its closest pass to Bermuda. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 200 – 220 miles by Sunday.
Most of the models indicate Leslie is likely to make landfall in Newfoundland, Canada on Tuesday night or Wednesday morning. However, the models have been trending more to the east with Leslie’s track in recent runs, and given the uncertainty in 4-day hurricane forecasts, the storm could very well miss the island, passing to the northeast. Large swells from Leslie are pounding the entire Eastern Seaboard, and are creating beach erosion and dangerous rip currents.
Figure 3. Hurricane Michael as seen by NASA’s Aqua satellite at 12:20 pm EDT Thursday September 6, 2012. At the time, Michael was a Category 3 hurricane with 115 mph winds. Image credit: NASA.
Hurricane Michael weakens to Category 2
The only major hurricane of the 2012 Atlantic hurricane season, Hurricane Michael, has weakened, and is now a Category 2 storm with 105 mph winds. Satellite loops show that Michael is still an impressive storm with a well-developed eye, but the storm is not as symmetric, and the eye no longer as distinct as was the case yesterday. Michael is far out over the open Atlantic, and none of the models show that Michael will threaten any land areas during the coming seven days.
Elsewhere in the Atlantic
Most of the reliable computer models are predicting that a new tropical wave moving off the coast of Africa today will develop into a tropical depression by the middle of next week. This wave is predicted to exit Africa too far north to threaten the Lesser Antilles Islands.
Extraordinary melting of sea ice in the Arctic this summer has shattered the all-time low sea ice extent record set in September 2007, and sea ice continues to decline far below what has ever been observed. The new sea ice record was set on August 26, a full three weeks before the usual end of the melting season, according to the National Snow and Ice Data Center. Every major scientific institution that tracks Arctic sea ice agrees that new records for low ice area, extent, and volume have been set. These organizations include the University of Washington Polar Science Center (a new record for low ice volume), the Nansen Environmental & Remote Sensing Center in Norway, and the University of Illinois Cryosphere Today. A comprehensive collection of sea ice graphs shows the full story. Satellite records of sea ice extent date back to 1979, though a 2011 study by Kinnard et al. shows that the Arctic hasn’t seen a melt like this for at least 1,450 years (see a more detailed article on this over at skepticalscience.com.) The latest September 5, 2012 extent of 3.5 million square kilometers is approximately a 50% reduction in the area of Arctic covered by sea ice, compared to the average from 1979 – 2000. The ice continues to melt, and has not reached the low for this year yet.
Figure 2. Sea ice extent on September 5, 2012, showed that half of the polar ice cap was missing, compared to the average from 1979 – 2000. Image credit: National Snow and Ice Data Center.
Why the Arctic sea ice is important
Arctic sea ice is an important component of the global climate system. The polar ice caps help to regulate global temperature by reflecting sunlight back into space. White snow and ice at the poles reflects sunlight, but dark ocean absorbs it. Replacing bright sea ice with dark ocean is a recipe for more and faster global warming. The Autumn air temperature over the Arctic has increased by 4 – 6°F in the past decade, and we could already be seeing the impacts of this warming in the mid-latitudes, by an increase in extreme weather events. Another non-trivial impact of the absence of sea ice is increased melting in Greenland. We already saw an unprecedented melting event in Greenland this year, and as warming continues, the likelihood of these events increase.
Huge storm pummels Alaska
A massive low pressure system with a central pressure of 970 mb swept through Alaska on Tuesday, generating hurricane-force wind gusts near Anchorage, Alaska that knocked out power to 55,000 homes. Mighty Alaskan storms like this are common in winter, but rare in summer and early fall. The National Weather Service in Anchorage said in their Wednesday forecast discussion that the forecast wind speeds from this storm were incredibly strong for this time of year–four to six standard anomalies above normal. A four-standard anomaly event occurs once every 43 years, and a five-standard anomaly event is a 1-in-4800 year event. However, a meteorologist I heard from who lives in the Anchorage area characterized the wind damage that actually occurred as a 1-in-10 year event. A few maximum wind gusts recorded on Tuesday during the storm:
The storm has weakened to a central pressure of 988 mb today, and is located just north of Alaska. The storm is predicted to bring strong winds of 25 – 35 mph and large waves to the edge of the record-thin and record-small Arctic ice cap, and may add to the unprecedented decline in Arctic sea ice being observed this summer.
Figure 5. An unusually strong storm formed off the coast of Alaska on August 5 and tracked into the center of the Arctic Ocean, where it slowly dissipated over the next several days. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color mosaic image on Aug. 6, 2012. The center of the storm at that date was located in the middle of the Arctic Ocean. Image credit: NASA.
Arctic storms may be increasing due to climate change
This week’s Alaskan storm is the second unusually strong low pressure system to affect the Arctic in the past month. On August 4 – 8, a mighty storm with a central pressure of 963 mb raged through the Arctic, bringing strong winds that helped scatter and break up Arctic sea ice. According to a detailed post at NASA Earth Observatory, that storm was in the top 3 percent for strongest storms ever recorded north of 70 degrees latitude. A study of long-term Arctic cyclone trends authored by a team led by John Walsh and Xiangdong Zhang of the University of Alaska Fairbanks found that number and intensity of Arctic cyclones has increased during the second half of the twentieth century, particularly during the summer. Dr. Zhang explained that climate change has caused sea ice to retreat markedly in recent decades and has also warmed Arctic Ocean temperatures. Such changes may be providing more energy and moisture to support cyclone development and persistence. The strong storms of this week and a month ago would have had far less impact on the ice just a decade ago, when the sea ice was much thicker and more extensive.
A sea ice decline double-whammy
The monster Arctic storms like we’ve seen this year have sped up the rate of sea ice loss, but increased water temperatures and air temperatures due to human-caused global warming are the dominant reasons for the record melting of the Arctic sea ice. A July 2012 study by Day et al. found that the most influential of the possible natural influences on sea ice loss was the Atlantic Multi-decadal Oscillation (AMO). The AMO has two phases, negative (cold) and positive (warm), which impact Arctic sea ice. The negative phase tends to create sea surface temperatures in the far north Atlantic that are colder than average. In this study, the AMO only accounted for 5% – 31% of the observed September sea ice decline since 1979. The scientists concluded that given the lack of evidence that natural forces were controlling sea ice fluctuations, the majority of sea ice decline we’ve seen during the 1953 – 2010 period was due to human causes.
Tropical Storm Leslie is growing more organized and is approaching hurricane strength on its slow voyage northwards at 2 mph towards the island of Bermuda. Moderately high wind shear of 15 – 20 knots due to strong upper-level winds out of the northwest continues to keep most of Leslie’s heavy thunderstorms pushed to the east side of the storm, but satellite loops show that Leslie now has an impressive blow-up of heavy thunderstorms with cold cloud tops near its center. Leslie’s slow forward speed means that the storm is staying over the cold water stirred up by the storm’s winds, inhibiting intensification, but the waters underneath Leslie are warm to great depth, making this less of a factor than usual. According to the latest SHIPS model forecast, the shear is expected to fall steadily today, reaching the low category, 5 – 10 knots, by Thursday afternoon. Leslie is over warm ocean waters of 29 – 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Saturday night and early Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 48% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 42-hour period of tropical storm-force winds beginning Saturday morning near 2 am AST, and lasting until 8 pm AST Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, and Leslie will be capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize. NHC is predicting that hurricane-force winds will extend outwards from the center of Leslie by 35 miles on Thursday night, and I expect this will increase to at least 60 miles by early Sunday morning, when Leslie will be making its closest pass by Bermuda.
Figure 1. Morning satellite image of Tropical Storm Leslie. Heavy thunderstorms have built near the center of the storm, and Leslie is near hurricane strength.
Leslie’s impact on Canada
Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There are still significant differences among the models in the timing and speed of Leslie’s track over the weekend, but we can now dismiss the threat of Leslie making a direct hit on New England. The storm is likely to make landfall in Nova Scotia or Newfoundland, though there are significant differences in the models’ predictions of the timing of Leslie’s arrival in Canada. The GFS model predicts an early Tuesday landfall in Newfoundland, but the ECMWF model is much faster and farther west, predicting a Monday afternoon landfall in Nova Scotia. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in strength this week. The Hurricane Hunters are scheduled to make their first flight into Leslie on Thursday afternoon.
Figure 2. Morning radar image of Invest 90L off the coast of the Florida Panhandle.
Son of Isaac: Invest 90L emerges in the Gulf of Mexico
During Tropical Depression Isaac’s trek across the center of the U.S. during the Labor Day weekend, the storm was ripped in half. One portion of the storm moved over the Northeast U.S., bringing heavy rains there, and another portion sank southwards over Alabama. You can see this split by studying an animation of the vorticity at 850 mb (the amount of spin at low levels of the atmosphere, near 5,000 feet above sea level) from the University of Wisconsin. This remnant of Isaac, which still maintained some of Isaac’s spin, brought heavy rains of 5 – 10 inches that caused flooding problems over portions of Alabama on Tuesday. The storm has now emerged over the Gulf of Mexico near the Florida Panhandle, and was designated Invest 90L this morning by NHC. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Friday morning. According to NHC naming rules, “if the remnant of a tropical cyclone redevelops into a tropical cyclone, it is assigned its original number or name”. Since “the remnant” refers to the primary remnant, and 90L does not fit the definition of a “primary remnant”, the storm will be given a new name should it develop into a tropical storm, according to information posted on the NHC Facebook page. Esau or Jacob–the names of the sons of the biblical Isaac–would be fitting names for 90L, but the next storm on the list of Atlantic storms is Nadine.
Long-range radar out of Mobile, Alabama shows a large area of heavy rainfall along the coast due to 90L. The echoes do show some spiral banding behavior, but there is only a slight evidence of rotation to the storm. Infrared satellite loops show that the thunderstorms associated with 90L are not that vigorous and do not have particularly cold cloud tops, and the area covered by the thunderstorms is relatively small. Wind shear is a high 20 – 30 knots over the northern Gulf of Mexico, but is predicted to fall to the moderate range, 10 – 20 knots, by Thursday afternoon. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28 – 28.5°C. This is still plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization on Thursday and Friday as it moves slowly south or south-southwest. 90L could become a tropical depression as early as Thursday, though Friday is more likely. A hurricane hunter aircraft is scheduled to investigate 90L on Thursday afternoon. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday.
Figure 3. Morning satellite image of Tropical Storm Michael.
Tropical Storm Michael in the Central Atlantic Tropical Storm Michael has strengthened to 50 mph winds, and appears to have a favorable enough environment to become a hurricane later this week. Satellite loops show that this is a small tropical cyclone, far out over the open Atlantic, and none of the models show that Michael will threaten any land areas.
Elsewhere in the Atlantic
The GFS and ECMWF models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. It’s too early to tell if this system might threaten the Lesser Antilles Islands.
