Tropical Storm Leslie continues to struggle with moderately high wind shear of 15 – 20 knots, due to strong upper-level winds out of the northwest. The shear is keeping heavy thunderstorms confined to the southeast quadrant of the storm. These thunderstorms are as far removed from the center as we’ve so far with Leslie, as seen on satellite loops. According to the latest SHIPS model forecast, the shear is expected to stay moderately high through Tuesday night, then drop to the low category, 5 – 10 knots, by Wednesday night. At that time, Leslie will be over warm ocean waters of 29°C, and the reduction in shear and warm waters should allow Leslie to intensify into at least a Category 1 hurricane by Friday, as predicted by most of the intensity forecast models. Intensification to a stronger storm may be hampered by its slow motion, which will cause Leslie to churn up cool water from the depths that will slow intensification. Once Leslie begins moving more quickly on Saturday, this effect will diminish, and Leslie could be at Category 2 strength on Saturday, as predicted by the HWRF and LGEM models. Steering currents for Leslie are expected to be weak on Tuesday – Friday, as Leslie gets stuck between two upper level lows. The latest guidance from our top computer continues to show Leslie making a very close pass by Bermuda on Saturday, and that island can expect a 3-day period of rough weather Friday through Sunday. 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. This trough should be strong enough to pull Leslie quickly to the north on Saturday and Sunday, and Leslie may be close enough to the coast that the storm will make landfall in Canada on Monday, September 10. None of the reliable models have shown that a direct hit on New England will occur, but we can’t rule that possibility out yet. The most likely long-term fate of Leslie will be for it to miss land entirely and brush by the coasts of Nova Scotia and Newfoundland, but any forecast of what a tropical cyclone might do a full seven days in advance is pretty speculative. Regardless, Leslie will bring an extended period of high waves to Bermuda, the U.S. East Coast, and Nova Scotia and Newfoundland this week. These waves will be capable of causing significant beach erosion and dangerous rip currents.
Figure 1. Morning satellite image of Tropical Storm Leslie. The low-level circulation center is fully exposed to view, thanks to strong northwest winds creating 15 – 20 knots of wind shear.
Invest 99L in the Central Atlantic
A small extratropical low pressure system that got cut off from the jet stream and is now spinning away in the Central Atlantic, near 26°N 42°W, (Invest 99L), is headed west at 10 mph, and has developed a small amount of heavy thunderstorm activity. This storm is not a threat to any land areas, and in their 8 am EDT Tropical Weather Outlook on Monday, NHC gave 99L a 30% chance of developing into a tropical cyclone by Wednesday morning.
The top winds of Tropical Depression Isaac have fallen to 25 mph, but the storm continues to be a potent rain-maker as it heads north-northwest at 11 mph into Missouri. Isaac has spawned up to 20 suspected tornadoes, brought storm surges as high as 13.6′ to the coast (in Lake Borgne, LA), and dumped 20″ of rain at one station in New Orleans. The 13.27″ of rain that fell at Hattiesburg, MS broke the record for wettest August in the city’s history (previous record: 13.03″ in 1987.) Major flooding is occurring on seven rivers in Louisiana and Mississippi. Isaac is being blamed for at least four deaths in the U.S., 24 in Haiti, and five in the Dominican Republic.
A few notable rainfall totals from Isaac, through 11 am EDT on Friday:
20.08″ New Orleans, LA
15.02″ Marion, MS
13.99″ Pascagoula, MS
13.27″ Hattiesburg, MS
10.85″ Gulfport, MS
10.39″ Slidell, LA
10.17″ Biloxi, MS
9.85″ Mobile, AL
7.38″ Pine Bluff, AR
5.95″ Baton Rouge, LA
A major reason for Isaac’s heavy rainfall totals has been its very slow motion. This slow speed was due to the fact Isaac has been bumping into a ridge of high pressure that is unusually strong, due to the intense drought over the center of the U.S.; strong drought-amplified high pressure areas are very resistant to allowing any low pressure areas to intrude into their domain. The high pressure area was strong enough this week to allow several all-time records for heat this late in the year to be set:
112° on August 29 at Winner, SD
108° on August 29 at Valentine, NE
107° on August 29 at Corpus Christi, TX
97° on August 29 at Denver, CO (2nd highest so late in the year)
Figure 1. Nighttime view of Hurricane Isaac taken at 1:57 am CDT August 29, 2012, by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi-NPP satellite. The VIIRS day-night band detects light in a range of wavelengths from green to near-infrared, and uses light intensification to enable the detection of dim signals. In this case, the clouds of Isaac were lit by moonlight. Image credit: NASA.
Isaac’s beneficial rains falling in drought-stricken regions
Hurricanes get a lot of attention because of the billions in damage they cost, and the lives they disrupt. AIR Worldwide estimated today that insured damage from Isaac would cost up to $2 billion. This does not include damage to infrastructure or uninsured damage, so the final price tag of Isaac’s rampage will be more like $3 – $5 billion. However, Isaac is now dumping beneficial rains over Arkansas, Missouri, Illinois, Indiana, Ohio, and Kentucky–regions stricken by the worst drought since the 1950s or 1930s, depending upon the exact location. These regions need 9 – 18 inches of rain to pull them out of drought. Isaac’s 3 – 6 inches of rain will not end the drought, but will put a pretty good dent in it. I expect that 3 – 6 inches of rain for a wide swath of prime agricultural land in extreme drought is probably worth at least $5 billion, when you consider that a recent estimate by a Purdue economist put the cost of the great drought of 2012 at more than $77 billion. Only Hurricane Katrina ($146 billion) and the drought of 1988 ($78 billion) have been more expensive disasters, according to NOAA’s National Climatic Data Center. Unfortunately, Isaac’s arrival is poorly timed, as the storm is arriving during harvest season. The strong winds associated with the storm will flatten many crops, making it more difficult to harvest them, and Isaac’s winds may cost farmers several hundred million dollars due to unharvestable crops. Still, the rains from Isaac will be highly beneficial for the success of the upcoming winter wheat season, and for next year’s growing season.
Figure 2. Predicted precipitation for the five-day period ending on Tuesday evening shows that Isaac is expected to bring a large region of 3 – 6 inches of rain (red, orange, and brown colors) to Arkansas, Missouri, Illinois, Indiana, Ohio, and Kentucky. Image credit: NOAA/HPC.
Figure 3. The great drought of 2012 has brought so little rain to the Midwest that some areas require over 15″ of rain (dark purple colors) to end the drought. Image credit: NOAA/CPC.
Unanswered questions about Hurricane Isaac
1. Did the passage of Hurricane Isaac stir up oil from the Deepwater Horizon oil spill? Isaac was the first hurricane to pass over the site of the 2010 Deepwater Horizon oil spill. We know that large hurricanes are capable of creating currents in deep water at the bottom of the Gulf of Mexico; Hurricane Ivan caused upwelling currents of 0.5 cm/s at a depth of about 500 meters. In an August 28 article in the Huffington Post, Nick Shay, professor of meteorology and physical oceanography at the University of Miami, said: “Winds will push water away from the center of a storm, which causes an upwelling as the ocean tries to adjust. It brings whatever is near the bottom up higher in the water column and currents can then push it towards the coast.” Up to 1 million barrels of oil from the spill are estimated to still be present in the deep water sediment, on beaches, and in the marshes of Louisiana, and it is possible some of this oil will wash up on the Gulf Coast in coming months. The storm surge of Isaac also likely flushed out oil lodged in the coastal marshes of Louisiana, but it is unknown how much of a concern this might be.
2. What’s the deal with these super-sized Category 1 and 2 hurricanes that have been hitting the U.S.? The past three landfalling hurricanes in the U.S.–Isaac (2012), Irene (2011), and Ike (2008)–have all been exceptionally large, among the top ten on record for horizontal extent of tropical storm-force winds. Each of these storms had an unusually low pressure characteristic of a storm one full Saffir-Simpson category stronger. Is this the new normal for U.S. hurricanes?
3. Did the new $14.5 billion upgrade to the New Orleans levee system cause worse flooding elsewhere? Whenever a new levee or flood control structure is created, you make someone else’s flood problem worse, since the water has to go somewhere. Where did the water was stopped by the new $1.1 billion, 1.8 mile-long Lake Borgne flood barrier on the east side of New Orleans go? Did it flow south and contribute to the overtopping of the levees near Braithwaite? Or did it go north and contribute to the 36 hours of storm surge in excess of 5′ observed along the Mississippi coast at Waveland? I posed this question to NHC’s storm surge expert Jaime Rhome, and he said it was impossible to know without doing detailed storm surge modeling studies.
4. Can only hurricanes beginning with the letter “I” hit the U.S. now? Isaac (2012), Irene (2011), and Ike (2008) are the last three hurricanes to hit the U.S. It turns out that hurricanes that begin with the letter “I” and “C” have more names on the list of retired hurricanes than any other letter (nine each.) I’m thinking Isaac will get its name retired, letting storms beginning with “I” take over sole possession of first place on the retired storms list.
Hurricane Kirk in the Central Atlantic Hurricane Kirk intensified into a 105 mph Category 2 hurricane this morning, becoming the 2nd strongest hurricane of the 2012 Atlantic hurricane season. Hurricane Gordon was the only stronger storm; Gordon hit sustained winds of 110 mph just before reaching the Azores Islands on August 18. Kirk has probably peaked in intensity, and is about to move over colder waters and gradually decay. Kirk is not a threat to any land areas.
Figure 4. Morning satellite image of Tropical Storm Leslie.
Tropical Storm Leslie a long-range threat to Bermuda, Canada, and the U.S. East Coast Tropical Storm Leslie formed on Thursday in the Central Atlantic. Leslie’s formation date of August 30 puts 2012 in 2nd place for earliest formation date of the season’s 12th tropical storm. Only 1995 had an earlier formation date of the season’s 12th storm. With records dating back to 1851, this year is only the second time 8 total storms have formed in August. The other year was 2004, when the first storm of the season formed on August 1 (Alex), and the 8th storm (Hermine) formed on August 29th. Satellite loops show that Leslie has a modest amount of heavy thunderstorm activity, and respectable low-level spiral bands and upper-level outflow. Conditions appear ripe to allow Leslie to intensify into a Category 2 hurricane by Sunday. Fortunately, Hurricane Kirk is weakening the ridge of high pressure to the north of Leslie, and Leslie is expected to turn to the northwest and miss the Lesser Antilles Islands. However, steering currents for Leslie are expected to collapse early next week, as Leslie gets stuck between two upper level lows. The storm will then slowly meander over the open ocean for many days, potentially threatening Bermuda. Leslie will stay stuck until a strong trough of low pressure approaches the U.S. East Coast around September 8. This trough should be strong enough to pull Leslie to the north and then northeast by September 9. At that time, Leslie may be close enough to the coast that the storm will make landfall in New England, Canada, or the Mid-Atlantic states. Leslie could also miss land entirely; this all depends upon the timing and strength of the September 8 trough of low pressure. Regardless, Leslie is expected to bring an extended period of high waves to the U.S. coast. According to NOAA’s Wavewatch III model, large swells from Leslie will reach Bermuda by Monday, and arrive along the U.S. East Coast on Tuesday. These waves will be capable of creating dangerous rip currents and beach erosion.
Portlight disaster relief charity responds to Issac
The Portlight.org disaster relief charity, founded and staffed by members of the wunderground community, are in Mississippi, helping out with Isaac relief efforts. You can check out their progress or donate to Portlight’s disaster relief fund at the portlight.org website.
Slow-moving Tropical Storm Isaac continues to hammer coastal Louisiana, Mississippi, Alabama, and Florida’s Panhandle with tornadoes, torrential rains, high winds, and a damaging storm surge. Over the past 24 hours, destructive tornadoes have touched down in Biloxi and Pascagoula, Mississippi, and one person was killed by a tree falling on a car in Pearl River County, Mississippi. A major flood event is occurring in Slidell, Louisiana, where Isaac’s storm surge filled Bayou Bonfouca and the W-14 Canal, inundating portions of the city with 1 – 5 feet of water. While Isaac is now a weakening minimal-strength tropical storm, it is still a potent rainmaker, and will cause damaging floods all along its path for the next three days. Major river flooding is occurring or is about to occur on a number of rivers in the landfall area. In north central Tangipahoa Parish in southeast Louisiana and southwestern Pike County in southern Mississippi, a mandatory evacuation has been ordered for all low-lying areas and along the Tangipahoa River, due to the potential failure of the Lake Tangipahoa dam. Audubon Park in New Orleans, recorded 19.30″ of rain as of 7 pm Wednesday night, and 18.7″ of rain in a 24-hour period. This is the greatest 24-hour rainfall event at any official New Orleans site, with weather records extending back to 1871, according to wunderground’s weather historian, Christopher C. Burt. A few other rainfall totals from Isaac, through 11 am EDT on Thursday:
15.02″ Marion, MS
10.09″ Hattiesburg, MS
10.15″ Gulfport, MS
9.80″ Slidell, LA
9.74″ Biloxi, MS
8.52″ Mobile, AL
5.57″ Baton Rouge, LA
Figure 1. Isaac’s winds and storm surge overcomes the seawall and floods South Beach Boulevard in Waveland, Miss., Wednesday, Aug. 29, 2012, the seventh anniversary of Hurricane Katrina hitting the Gulf Coast. (AP Photo/Rogelio V. Solis). Waveland experienced a storm surge in excess of 5′ for 36 hours.
Isaac’s storm surge winds down
Storm surge levels along the coast of Mississippi and surrounding areas are gradually receding, and the surge has finally fallen below 5′ at Waveland, which experienced a storm surge in excess of 5′ for 36 hours. Isaac’s storm surge levels were characteristic of a Category 2 hurricane, and lasted for an exceptionally long period of time. Waveland, Mississippi experienced a peak surge of 8′ and peak storm tide of 9′ (surge plus the natural high tide), which beat the levels that occurred during Category 2 Hurricane Gustav of 2008 (7′ of storm tide.) The peak 11.06′ storm surge at Shell Beach, which is in Lake Borgne, 30 miles southeast of New Orleans, exceeded the 9.5′ surge recorded there during Gustav. According to an article in nola.com, Isaac pushed a storm surge of 13.6′ into Lake Borgne, on the east side of New Orleans. This is not far from the 15.5′ storm surge Hurricane Katrina brought to the location. It is quite possible that Isaac’s storm surge might have breached levees of the east side of New Orleans, flooding areas inhabited by tens of thousands of people, had the Army Corps of Engineers not completed their $14.5 billion upgrade to the New Orleans flood defenses this year. I estimate that storm surge damage from Isaac will exceed $2 billion. Isaac has likely caused $2.5 billion in insured damage not related to flooding, insurance firm Eqecat estimated yesterday. Here were some of the peak storm surge values that were recorded at NOAA tide gauges during Isaac:
11.1′ Shell Beach, LA
8.0′ Waveland, MS
3.5′ Pensacola, FL
4.6′ Pascagoula, MS
3.8′ Mobile, AL
Figure 2. A TRMM satellite 3-D view of rainfall on Aug. 28 showed a few very powerful thunderstorms near Isaac’s eye were reaching heights of almost 17 km (10.6 miles.) Intense bands of rain around Isaac were occasionally dropping rain at a rate of over 2.75 inches per hour. Image credit: SSAI/NASA, Hal Pierce.
Isaac’s storm surge on the Mississippi River
A storm surge estimated at 12′ moved up the Mississippi in Plaquemines Parish near Port Sulphur, LA, near 8:30 pm EDT Tuesday, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade New Orleans got after Hurricane Katrina, and were not rated to Category 3 hurricane strength, like the levees protecting New Orleans are. Since salt water is more dense than fresh water, the surge travelled along the bottom of the river, with the fresh water flow of the river lying on top. The surge continued upriver, and before reaching New Orleans, encountered an underwater barrier in Plaquemines Parish. This barrier was constructed by the Army Corps of Engineers beginning on August 15, in order to keep salt water from moving upstream and contaminating drinking water for Plaquemines Parish and New Orleans. Salt water had made it 90 miles upriver to the outskirts of New Orleans, due to the low flow rate of the river (which had dropped 7′ below average in height due to the drought of 2012.) According to a spokesperson for the National Weather Service River Forecast Office, this barrier was probably able to completely block the flow of salt water upriver due to Isaac’s storm surge, and no salt water made it as far as New Orleans. However, the massive intrusion of ocean water into the river channel caused the mighty Mississippi’s fresh water flow to back up for hundreds of miles. Water levels were elevated by 10′ in New Orleans (103 miles upstream from the mouth of the Mississippi), 8′ in Baton Rouge (228 miles upstream), and 1.4′ at Knox Landing, an amazing 314 miles upstream.
Hurricane Kirk in the Central Atlantic Hurricane Kirk intensified into a 75 mph Category 1 hurricane this morning, becoming the busy 2012 Atlantic hurricane season’s fifth hurricane. With the season’s mid-point of September 10 still almost 2 weeks away, we’ve already had 12 named storms and 5 hurricanes, which is close to what an entire season experiences in an average year (11 named storms and 6 hurricanes.) Kirk should stay well out to sea and not trouble any land areas.
Figure 3. Morning satellite image of Hurricane Kirk.
Tropical Depression Twelve forms in the Central Atlantic Tropical Depression Twelve has formed in the Central Atlantic, and appears destined to become a hurricane before the week is out. Fortunately, Hurricane Kirk is weakening the ridge of high pressure to the north of TD 12, and the storm is expected to turn to the northwest and miss the Lesser Antilles Islands. In the long term, it remains unclear if TD 12 will follow Kirk and fully recurve out to sea. The latest run of the GFS model predicts TD 12 will recurve out to sea and not threaten any land areas, but the latest run of the ECMWF model predicts that the trough of low pressure pulling Kirk to the norhteast will not be strong enough to recurve TD 12 out to sea. Instead, the ECMWF predicts that a ridge of high pressure will build in early next week, forcing TD 12 more to the northwest, making the storm a potential threat to Bermuda, the Northeast U.S., and Canada.
Hurricane Isaac continues to lumber slowly northwestwards at 6 mph, as it pounds Louisiana, Mississippi, Alabama, and Florida’s Panhandle with torrential rains, high winds, and a damaging storm surge. The eye was partially over water for most of the 15 hours after Isaac’s official landfall at 7:45 pm EDT Tuesday night, but New Orleans radar shows the eye of the storm is now fully ashore near Houma. The radar echoes show some weakening on the west side of the eyewall, where dry air has infiltrated the storm. Wind shear remains light, and upper level outflow over Isaac is as impressive as we’ve seen so far, with a strong outflow channel to the north, and a respectable one to the south, as well. Infrared and visible satellite loops show a very large, symmetric, and well organized storm, and Isaac is going to be able to stay near Category 1 hurricane strength all day today. This will allow Isaac to drop rainfall amounts of 15 – 20″ in some areas of Louisiana before the storm is over. A few rainfall totals from Isaac through 11 am EDT:
9.26″ New Orleans Lakefront Airport
5.59″ Belle Chasse, LA
5.21″ Mobile, AL
3.65″ Hattiesburg, MS
3.42″ Gulfport, MS
2.81″ Biloxi, MS
Figure 1. Morning radar reflectivity image from New Orleans.
A dangerous storm surge event underway
Isaac is bringing a large and dangerous storm surge to the coast from Central Louisiana to the Panhandle of Florida. Late this morning was high tide along much of the coast, and the highest water levels of Isaac are likely being experienced at many locations. At 11:30 am EDT, here were some of the storm surge values being recorded at NOAA tide gauges:
8.0′ Waveland, MS
8.2′ Shell Beach, LA
2.0′ Pensacola, FL
4.6′ Pascagoula, MS
3.4′ Mobile, AL
The peak 11.06′ storm surge at 1:30 am EDT this morning at Shell Beach, which is in Lake Borgne, 20 miles southeast of New Orleans, exceeded the 9.5′ surge recorded there during Category 2 Hurricane Gustav of 2008. In general, the storm surge heights from Isaac have been more characteristic of a strong Category 2 hurricane, rather than the weak Category 1 hurricane one might suppose Isaac is, based on its top sustained winds of 75 – 80 mph. The Saffir-Simpson Scale for ranking hurricanes is only a crude measure of their potential impacts.
A storm surge estimated at 12′ moved up the Mississippi in Plaquemines Parish near Port Sulphur, LA, near 8:30 pm EDT Tuesday, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade New Orleans got after Hurricane Katrina, and were not rated to Category 3 hurricane strength, like the levees protecting New Orleans are. The surge continued upriver, elevating the water levels 10′ in New Orleans (103 miles upstream from the mouth of the Mississippi), 8′ in Baton Rouge (228 miles upstream), and 1.4′ at Knox Landing, an amazing 314 miles upstream. The river was 7′ low due to the great 2012 U.S. drought, and I suspect the near-record low flow rate of the river allowed the storm surge to propagate so far upstream. The salt water from the storm surge will be slow to leave the river, due to the continued winds of Isaac keeping the surge going, plus the very low flow rates of the river. One benefit of the heavy rains of 10 – 20 inches expected to fall over Louisiana over the next two days will be to increase the flow rate of the Mississippi River, helping flush the salt water out of the river. The low flow rates of the Mississippi had allowed salt water to move upriver to just south of New Orleans over the past few weeks, threatening the drinking water supply of Plaquemines Parish.
Figure 2. Tide gauge data from Waveland, Mississippi. The green line shows the storm surge. The red line is the storm tide, the height of the water above Mean Sea Level (MSL.) The storm tide at Waveland currently (9′) is 2′ higher than that of Category 2 Hurricane Gustav of 2008. Image credit: NOAA Tides and Currents.
Tropical Storm Kirk in the Central Atlantic Tropical Storm Kirk formed Tuesday night in the Central Atlantic. Kirk’s formation at 03 UTC on August 29 puts 2012 in 4th place for earliest formation date of the season’s 11th storm. Only 2005, 1995, and 1933 had an earlier formation date of the season’s 11th storm. Kirk should stay well out to sea and not trouble any land areas.
Figure 3. Morning satellite image of Tropical Storm Kirk.
Invest 98L in the Eastern Atlantic
A tropical wave (Invest 98L) is about 750 miles west-southwest of the Cape Verde Islands, and is moving west to west-northwest at about 15 mph. In their 8 am EDT Tropical Weather Outlook, NHC gave 98L a 50% chance of developing by Friday morning. Several of the models develop 98L into a tropical depression by this weekend, but none of the reliable models foresee that 98L will be a threat to the Lesser Antilles. The storm may be a threat to Bermuda next week, but it is too early to say if it may threaten the U.S.
Tropical Storm Isaac is pounding Haiti and the Dominican Republic with torrential rains that are causing extremely dangerous flooding and landslides. Isaac’s center passed over Haiti’s southwest peninsula early this morning, tracking about 50 miles west of the capital of Port-au-Prince. As the center pulled away to the northwest, Isaac’s heaviest thunderstorms moved ashore over Hispaniola near sunrise, and are now dumping heavy rains with rainfall rates approaching one inch per hour, according to recent microwave satellite estimates.Barahona on the south coast of the Dominican Republic had received 5.14″ of rain as of 8 am EDT this morning, and it is probable that some mountainous areas in Haiti and the Dominican Republic have already received up to 10″ of rain from Isaac. These rains will continue though much of the day, and have the potential to cause high loss of life in Hispaniola.
Figure 1. A river north of Port-au-Prince, Haiti in flood due to rains from Isaac. Image from Amélie Baron via Twitter.
Latest observations
Isaac built a partial eyewall last night as the storm approached Haiti, but passage over the rough mountains of Haiti has destroyed the inner core, and the surface center of the storm is now fully exposed to view on satellite images. Radar out of Guantanamo Bay, Cuba shows no sign of an organized center, but does reveal some very intense thunderstorms affecting Eastern Cuba, Western Haiti, and nearby islands. Latest data from the Air Force Hurricane Hunters confirm that Isaac has weakened; during their penetration to obtain their 7:08 am EDT center fix, the aircraft reported top surface winds of 55 mph with their SFMR instrument, top flight-level winds at 5,000 feet of 68 mph, and a pressure rise of 3 mb, to 998 mb. Infrared and visible satellite loops show that Isaac remains a large and well-organized storm, though it lacks an inner core. An analysis of upper level winds from the University of Wisconsin CIMSS shows that upper-level outflow is still good to the north, but is lacking elsewhere. An impressive large multi-day satellite animation of Isaac is available from the Navy Research Lab.
Figure 2. Rainfall rates estimated by the NOAA F-17 polar orbiting satellite at 6:21 am EDT August 25, 2012. Rainfall rates of 1 inch per hour (orange colors) were occurring in a large area to the south of Hispaniola, and these heavy rains have now moved onshore. Image credit: Navy Research Laboratory.
Latest model runs for Isaac
The latest set of 0Z and 06Z (8 pm and 2 am EDT) model runs are similar in spread to the previous set of runs. Our two best models, the GFS and ECMWF, are virtually on top of each other, with a landfall location in the Florida Panhandle between Fort Walton Beach and Panama City. It is likely that the trough of low pressure pulling Isaac to the north will not be strong enough to pull Isaac all the way to the northeast and out to sea, and Isaac has the potential to drop torrential rains capable of causing serious flooding over the Southeast U.S. The latest 8-day precipitation forecast from the GFS model (Figure 3) calls for 10 – 15 inches of rain over portions of Georgia and South Carolina from Isaac. The ECMWF model, however, predicts that a ridge of high pressure will build in and force Isaac to the west after landfall, resulting in a slow motion across the Tennessee Valley into Arkansas by Friday. Arkansas is experiencing its worst drought in over 50 years, so the rains would be welcome there.
Figure 3. Predicted precipitation for the 8-day period from 2 am Saturday August 25 to 2 am Sunday September 2, from the 2 am EDT August 25 run of the GFS model. This model is predicting a wide swath of 5 – 10 inches of rain (orange colors) will affect portions of Cuba, Florida, the Bahamas, and the Southeast U.S. Image credit: NOAA/NCEP.
Intensity forecast for Isaac
Isaac survived passage over Hispaniola relatively intact. It’s large size aided this, and this will also help it survive passage over Cuba today and Sunday. By the time Isaac pops off the coast of Cuba into the Florida Straits on Sunday, it will likely be a 50 mph tropical storm with a large, intact circulation. Isaac will be over very warm waters of 31°C (88°F) in the Florida Straits, wind shear will be light to moderate, and the upper-level wind pattern will feature an upper-level anticyclone over the storm, aiding its upper-level outflow. As I discussed in my previous post, Crossing Hispaniola and Cuba: a history, there have been five storms since 1900 with an intensity similar to Isaac, which crossed over both Haiti and Cuba, then emerged into the Florida Straits. These five storms strengthened by 5 – 20 mph in their first 24 hours after coming off the coast of Cuba. Given the relatively intact structure of Isaac so far, and the favorable conditions for intensification, I expect Isaac will intensify by 15 – 20 mph in 24 hours once the center moves off of the north coast of Cuba. If Isaac spends a full two days over water after passing the Florida Keys, it is possible that it will have enough time to develop a full eyewall and undergo rapid intensification into a Category 2 or 3 hurricane. The latest 06Z (2 am EDT) run of the GFDL model is calling for Isaac to intensify to Category 2 strength, then weaken to Category 1 at landfall in Mississippi on Tuesday. The 06Z HWRF run is calling for landfall in the Florida Panhandle near Fort Walton Beach as a borderline Category 2 or 3 hurricane. The 5 am EDT NHC wind probability forecast gave Isaac a 19% chance of becoming a Category 2 or stronger hurricane in the Gulf. I expect these odds are too low, and that Isaac has a 40% chance of becoming a Category 2 or stronger hurricane in the Northern Gulf of Mexico. I doubt the storm has much of a chance of hitting Category 4 or 5 status, though. While the surface waters in the Gulf of Mexico are very warm, near 30 – 31°C, the total heat content of these waters is unusually low for this time of year. We got lucky with the Gulf of Mexico Loop Current this summer, as it did not shed a big warm eddy during the height of hurricane season, like happened in 2005 (I discuss this in my Gulf of Mexico Loop Current Tutorial.) Without the type of super-high heat energy we had in 2005 in the Gulf of Mexico, Category 4 and 5 hurricanes in the Gulf of Mexico in 2012 will have difficulty forming.
Invest 97L off the coast of Africa
A tropical wave (Invest 97L) is located about 350 miles west-southwest of the Cape Verde Islands off the coast of Africa. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 30% chance of developing by Monday morning. The 8 am EDT SHIPS model forecast predicts moderate shear for the next 5 days over 97L, so some development is possible if 97L can fend off the dry air to its north. None of the reliable models foresee that 97L will be a threat to the Lesser Antilles Islands. However, both the GFS and ECMWF models predict that a tropical wave that has not yet emerged from the coast of Africa may develop next week, and potentially take a more westward track towards the Lesser Antilles.
A large tropical wave that emerged from the coast of Africa Thursday night (Invest 94L) is located a few hundred miles southwest of the Cape Verde Islands off the coast of Africa, and is headed west at 15 – 20 mph. This storm is a threat to develop into a tropical storm that will affect the Lesser Antilles Islands as early as Wednesday. The storm is under moderate wind shear of 10 – 20 knots, and is over waters of 27.5°C. A large area of dry air lies just to the north of 94L, as seen on the latest Saharan Air Layer (SAL) analysis. This morning’s 8:15 am EDT ASCAT pass caught the east side of 94L, and showed a partial surface circulation. Satellite images show just a modest amount of heavy thunderstorm activity, and I expect the earliest that 94L could develop into a tropical depression would be Sunday.
Figure 1. Morning satellite image of Invest 94L.
Forecast for 94L
The latest 8 am EDT run of the SHIPS model predicts that wind shear will be low, 5 – 10 knots, and ocean temperatures will gradually warm from 27.5°C to 28.5°C over the next four days, as 94L tracks westwards towards the Lesser Antilles. As is typical with storms making the crossing from Africa to the Antilles, dry air to the north will likely interfere with development. However, with shear expected to be low, dry air may be less of an issue for 94L than it was for Ernesto or TD 7. The storm should maintain a nearly due west track through Monday night, to a point near 50°W, about 700 miles east of the Lesser Antilles. At that point, a trough of low pressure passing to the north of 94L may be able to pull the storm more to the northwest, as suggested by the latest 06Z (2 am EDT) run of the NOGAPS model, and by three members of the GFS model ensemble forecast (Figure 2.) However, the models have been trending more towards a solution where this trough is not strong enough to influence 94L’s path. This scenario will be more likely if 94L takes its time to develop, since a weaker storm will be smaller and shallower, and less likely to respond to the trough passing to the north. Our two best performing models, the GFS and ECMFW, both take 94L through the Lesser Antilles. The ECMWF, which predicts that 94L will stay weak and not develop, is faster, bringing the storm through the Lesser Antilles on Wednesday. The GFS model is slower, bringing 94L to the Lesser Antilles on Thursday as a hurricane. The models have shown poor run-to-run consistency in both the timing and the track of 94L, so it is difficult to assess which land areas might be most at risk, and when. A database of historical probabilities of storms in the same location as 94L maintained by Dr. Bob Hart of Florida State University reveals that historically, 45% of storms in this location have eventually hit land, with Canada (13% chance) and North Carolina (15% chance) the most likely targets. In their 8 am EDT Tropical Weather Outlook, NHC gave 94L a 40% chance of developing into a tropical depression by Monday morning.
Figure 2. The 00Z (8 pm EDT) run of the GFS model from August 17, 2012, was done 20 different times at low resolution using slightly different initial conditions to generate an ensemble of forecasts (pink lines.) The high-resolution operational GFS forecast is shown in white.
Gordon becomes a hurricane
Hurricane warnings are flying for the central and eastern Azores Islands as Hurricane Gordon heads eastwards at 18 mph. Gordon became the third hurricane of the 2012 Atlantic hurricane season at 5 am Saturday morning, and is sporting an impressive-looking eye on visible satellite loops. Gordon should be able to maintain hurricane status until Sunday, when wind shear will rise steeply to 30 – 40 knots, and ocean temperatures will drop to 25°C. The combined effects of high wind shear, dry air, and cooler waters will likely act to weaken Gordon to a strong tropical storm by the time it arrives in the Azores Islands Sunday night, but the storm will be strong enough to bring damaging winds and heavy rain to the Azores Islands. Gordon is not a threat to any other land areas, and the extratropical remnants of Gordon will not bring any strong winds or significant rain to Europe. The last time the Azores were affected by a tropical storm was in 2009, when Tropical Storm Grace brought 65 mph winds on October 4. No significant damage was reported. Ironically, the last hurricane to affect the Azores was the 2006 version of Hurricane Gordon, which caused minor damage in the Azores, consisting of mostly fallen trees and power outages. However, after Gordon became an extratropical low, four injuries due to falling debris from high wind were reported in Spain, and Gordon brought high winds and rain that affected practice rounds at the Ryder Cup golf tournament in Ireland. About 126,000 homes were without power after the storm in Northern Ireland and one injury was reported.
Figure 3. Morning satellite image of Hurricane Gordon.
Helene makes landfall in Mexico
Tropical Storm Helene made landfall near 10 am EDT as a tropical storm near Tampico, Mexico, with 40 mph winds. Helene’s formation on August 17 ties 2012 with 1933 for the 2nd earliest appearance of the Atlantic’s eighth tropical storm. Helene’s rains should remain south of Texas, but moisture from Helene may feed into a stalled frontal system over the northern Gulf of Mexico and bring heavy rains to the northern Gulf Coast early next week.
The great U.S. drought of 2012 remained about the same size and intensity over the past week, said NOAA in their weekly U.S. Drought Monitor report issued Thursday, August 16. The area of the contiguous U.S. covered by drought remained constant at 62%, and the area covered by severe or greater drought also remained constant at 46%. However, the area covered by the highest level of drought–exceptional–increased by 50%, from 4% to 6%. Large expansions of exceptional drought occurred over the heart of America’s grain producing areas, in Kansas, Nebraska, Oklahoma, and Missouri. The new NOAA State of the Climate Drought report for July 2012 shows that the 2012 drought is 5th greatest in U.S. history, and the worst in 56 years. The top five years for area of the contiguous U.S. covered by moderate or greater drought:
1) Jul 1934, 80%
2) Dec 1939, 60%
3) Jul 1954, 60%
4) Dec 1956, 58%
5) Jul 2012, 57%
The top five years for the area of the contiguous U.S. covered by severe or greater drought:
1) Jul 1934, 63%
2) Sep 1954, 50%
3) Dec 1956, 46%
4) Aug 1936, 43% 5) Jul 2012, 38%
Figure 1. August 14, 2012 drought conditions showed historic levels of drought across the U.S., with 62% of the contiguous U.S. experiencing moderate or greater drought, and 46% of the county experiencing severe or greater drought. Image credit: U.S. Drought Monitor.
Comparison with the great Dust Bowl droughts of the 1930s
An important fact to remember is that the 2012 drought is–so far–only a one-year drought. Recall that 2011 saw record rains that led to unprecedented flooding on the Mississippi, Ohio, and Missouri Rivers. In contrast, the great droughts of the 1950s and 1930s were multi-year droughts. The Dust Bowl drought of the 1930s lasted up to eight years in some places, with the peak years being 1934, 1936, and 1939 – 1940. Once the deep soil dries out, it maintains a memory of past drought years. This makes is easier to have a string of severe drought years. Since the deep soil this summer still maintains the memory of the very wet year of 2011, the 2012 drought will be easier to break than the Dust Bowl droughts of the 1930s were.
During the 1920s, agriculture in the United States expanded into the central Great Plains. Much of the original, drought-resistant prairie grass was replaced with drought-sensitive wheat. With no drought plan and few erosion-control measures in place, this led to large-scale crop failures at the initiation of the drought, leaving fields devegetated and barren, exposing easily eroded soil to the winds. This was the source of the major dust storms and atmospheric dust loading of the period on a level unprecedented in the historical record.
Figure 2. Black Sunday: On April 14, 1935 a “Black Blizzard” hit Oklahoma and Texas with 60 mph winds, sweeping up topsoil loosened by the great Dust Bowl drought that began in 1934.
The Dust Bowl drought and heat of the 1930s: partially human-caused
Using computer models of the climate, the scientists found that the Dust Bowl drought was primarily caused by below-average ocean temperatures in the tropical Pacific and warmer than average ocean temperatures in the Atlantic, which acted together to alter the path of the jet stream and bring fewer precipitation-bearing storms to the Central U.S. However, the full intensity of the drought and its spatial extent could not be explained by ocean temperature patterns alone. Only when their model included the impact of losing huge amounts of vegetation in the Plains due to poor farming practices could the full warmth of the 1930s be simulated. In addition, only by including the impact of the dust kicked up by the great dust storms of the Dust Bowl, which blocked sunlight and created high pressure zones of sinking air that discouraged precipitation, could the very low levels of precipitation be explained. The Dust Bowl drought had natural roots, but human-caused effects made the drought worse and longer-lasting. The fact that we are experiencing a drought in 2012 comparable to the great Dust Bowl drought of the 1930s–without poor farming practices being partially to blame–bodes ill for the future of drought in the U.S. With human-caused global warming expected to greatly increase the intensity and frequency of great droughts like the 2012 drought in coming decades, we can expect drought to cause an increasing amount of damage and economic hardship for the U.S. Since the U.S. is the world’s largest food exporter, this will also create an increasing amount of hardship and unrest in developing countries that rely on food imports.
A searing heat wave rare even for the Desert Southwest sent temperatures soaring to record levels on Monday, with Needles, California tying its record high for the date of 118°F (47.8°C). The temperature might have gone higher in Needles, but a thunderstorm rolled in at 3:20 pm, and by 3:56 pm PDT, rain began falling at a temperature of 115°F (46.1°C). Most of the rain evaporated, since the humidity was only 11%, and only a trace of precipitation was recorded in the rain gauge. Nevertheless, Monday’s rain at 115° in Needles sets a new world record for the hottest rain in world history. I don’t think many people were outside to experience to experience the feeling of rain falling at 115°, but if they were, it must have been an uncomfortable, sauna-like experience! Thanks go to Dr. Warren Blier of the NWS Monterey office for pointing out this remarkable event to me.
It is exceedingly rare to get rain when the temperature rises above 100°F, since those kind of temperatures usually require a high pressure system with sinking air that discourages rainfall. Monday’s rain in Needles was due to a flow of moisture coming from the south caused by the Southwest U.S. monsoon, a seasonal influx of moisture caused by the difference in temperature between the hot desert and the cooler ocean areas surrounding Mexico to the south. According to weather records researcher Maximiliano Herrera, the previous record for hottest rain, which I blogged about in June, was a rain shower at 109°F (43°C) observed in Mecca, Saudi Arabia on June 5, 2012 and in Marrakech, Morocco on July 10, 2010. The 11% humidity that accompanied Monday’s rain shower at 115° in Needles was the lowest humidity rain has ever occurred at anywhere on Earth in recorded history, according to Mr. Herrera.
Figure 1. True-color MODIS satellite image of California and Arizona taken at 1:25 pm PDT August 13, 2012. Developing thunderstorms surround Needles, CA, and the line of clouds to the southwest of the city would develop into a thunderstorm that brought rain to the city at 4 pm PDT, at a temperature of 115°F. Image credit: NASA.
A “very rare” heat wave for Phoenix
The heat wave that brought Needles’ record hot rain has broken an exceptional number of heat records in Phoenix, Arizona the past two weeks. According to the Phoenix NWS office, the “almost unbearable heat” of the first two weeks of August is a “very rare” event, and August 1 – 14, 2012 was the warmest such 2-week period in city history. The average temperature on August 6 – 13 was 100°F or higher each of the eight days, tying the record for most consecutive days with an average temperature of 100°. The temperature peaked at 116° on August 8, just 6° below Phoenix’s all-time record of 122° set on June 26, 1990. The forecast for Phoenix call for a bit of relief–highs are expected to be a relatively modest 105° today, and down near 100° by Friday.
Figure 2. Morning satellite image of 93L over the Central Atlantic.
93L close to tropical depression status
A large tropical wave (Invest 93L) is located in the Central Atlantic about 700 miles east of Bermuda. Satellite loops this morning show a surface circulation has formed, and heavy thunderstorm activity has increased to the point where 93L should be considered a tropical depression, if the heavy thunderstorms can persist through this afternoon. Wind shear is light, and ocean temperatures are warm, near 28°C. The latest Saharan Air Layer Analysis from the University of Wisconsin shows that 93L has moistened its environment considerably, and dry air should no longer be a significant impediment to development. The 8 am EDT run of the SHIPS model predicts that wind shear will remain in the low range through the weekend, and I expect this system will become Tropical Storm Gordon by Friday. The storm will not affect Bermuda, but residents of the Azores Islands should keep an eye on 93L, which could pass through the islands as early as Sunday night. In their 8 am Tropical Weather Outlook, NHC gave 93L an 80% chance of becoming a tropical depression by Friday morning.
Elsewhere in the tropics
In the Gulf of Mexico, a fall-like cold front is expected to stall out early next week, and the GFS model is predicting something could start to spin up near the Texas/Mexico border on Monday. Wind shear is predicted to be low to moderate, and cold fronts stalled out over the Gulf of Mexico often serve as the seed for tropical storms.
Most of the models predict development of a new tropical wave off the coast of Africa 6 – 7 days from now.
Tropical Depression Seven continues westward across the central tropical Atlantic with little change in appearance. Looking remarkably like the tropical depression that became Tropical Storm Ernesto last week, TD 7 has a limited region of heavy thunderstorms, as seen on satellite loops. A large amount of dry air to the west and north is visible on water vapor satellite loops, and this dry air is interfering with TD 7’s heavy thunderstorms. Wind shear is a light 5 – 10 knots, which is favorable for intensification. Ocean temperatures are 26.5°C, which is a bit on the cool side, but these temperatures are 0.5° warmer than on Thursday. Winds at the Middle Atlantic buoy 41041 peaked at 29 mph, gusting to 38 mph, at 1:50 am EDT this Friday morning, when the center of TD 7 passed about 40 miles to the south. TD 7 will pass about 60 miles south of buoy 41040 near midnight tonight. The first hurricane hunter mission into TD 7 is scheduled for Saturday morning.
Figure 1. Morning satellite image of TD 7.
Forecast for TD 7
TD 7 formed about 400 miles east-northeast of where Ernesto became a tropical depression, as seen on our wundermap. Atmospheric and oceanic conditions are currently quite similar to what Ernesto experienced, and I expect TD 7 will struggle with dry air like Ernesto did. The SHIPS model predicts that shear will remain light through tonight, then rise to the moderate range on Saturday, when the storm will encounter upper-level southwesterly winds associated with a trough of low pressure. However, ocean temperatures will warm to 28°C, which may partially counteract the increase in shear, as far as maintaining a favorable environment for development. Dry air and shear may be significant enough to destroy TD 7 on Sunday, as predicted by the GFS and ECMWF models. These models tried to kill off Ernesto in a similar situation last week, so I am inclined to believe TD 7 will survive for the coming five days, but struggle. The official NHC forecast of a 45 mph tropical storm moving through the Lesser Antilles Islands Saturday night and Sunday is a reasonable one.
Figure 2. Morning satellite image of Invest 93L.
93L
A strong tropical wave in the far Eastern Atlantic that emerged off the coast of Africa Thursday night was designated Invest 93L by NHC. In their 8 am Tropical Weather Outlook, NHC gave 93L a 50% chance of becoming a tropical depression by Sunday morning. Satellite loops show a pronounced spin to the atmosphere at mid levels, but little in the way of heavy thunderstorm activity. The latest Saharan Air Layer Analysis from the University of Wisconsin shows that while the atmosphere immediately surrounding the disturbance is moist, there is a large area of dry air from the Sahara to the west and north. This dry air will be a significant impediment to development during the coming week. The ECMWF model shows some weak development of 93L over the coming week, and predicts a general west-northwesterly track. The storm may be something Bermuda needs to be concerned about in eight or so days.
Tropical Storm Ernesto lashed the Windward Islands with strong winds and heavy rain early this morning, as it passed over St. Lucia near 7 am AST. Ernesto brought sustained winds of 43 mph to Barbados at 7 am AST, and sustained winds of 41 mph, gusting to 63 mph to St. Lucia at 6:15 am AST. Ernesto looks moderately well-organized on Martinique radar, with spiral bands to the north and south feeding into an echo-free center. Ernesto is beginning to show more organization on visible satellite loops, with the very limited heavy thunderstorm activity near its center now expanding, spiral banding increasing, and an upper-level outflow channel developing to the north. Ernesto is fighting moderate wind shear of 10 – 20 knots, and water vapor satellite loops show a large area of dry air to the west. Strong upper level winds from the west are driving this dry air into the core of the storm, disrupting it. It appears, though, that Ernesto has fended off the most serious challenges to its survival, as the pressure has fallen to 1002 mb, and the storm’s appearance on radar and satellite is gradually improving. The latest 7:30 am center report from the Hurricane Hunters also indicated that Ernesto was beginning to build an eyewall.
Figure 1. Radar image of Ernesto at 9:15 am EDT August 3, 2012. Image credit: Meteo France.
Figure 2. Morning satellite image of Ernesto.
Forecast for Ernesto
Ernesto’s survival into today means that the storm now potentially poses a formidable threat to the Western Caribbean. Wind shear is expected to drop to the low range, 5 – 10 knots, later today, and remain low for the next five days, according to the 8 am EDT run of the SHIPS model. With the storm entering a moister environment with increasing heat energy in the ocean, the official NHC forecast of Ernesto reaching hurricane strength by early Monday morning near Jamaica is a reasonable one. The reliable computer models predict a west to west-northwest motion through the Caribbean, with the storm’s heavy rains staying south of Puerto Rico and the Dominican Republic. The more southerly path predicted by the usually reliable ECMWF model, which brings Ernesto to a landfall in Belize on Wednesday, is being weighted less heavily by NHC, since they are assuming Ernesto will stay stronger than the ECMWF model is forecasting. Once Ernesto enters the Central Caribbean on Sunday, the storm’s outer spiral bands will likely cause flooding problems in Southwest Haiti, Jamaica, and the Cayman Islands. Of the major dynamical models NHC uses operationally–the ECMWF, GFS, NOGAPS, UKMET, GFDL, and HWRF–none clearly show Ernesto reaching hurricane strength in the Caribbean. However, some of the best statistical models, such as the LGEM and SHIPS, do show Ernesto becoming a hurricane in the Caribbean. By Monday, a trough of low pressure passing to the storm’s north may be capable of turning Ernesto more to the northwest, resulting in the storm entering the Gulf of Mexico by the middle of next week.
New African tropical disturbance 90L
A strong tropical wave is located just off the coast of Africa, about 175 miles south of the Cape Verde Islands. This disturbance, designated Invest 90L by NHC Friday morning, is headed west-northwest at 10 – 15 mph. Wind shear is a high 20 – 30 knots over 90L, but is expected to drop, and water temperatures are warm enough to support development. NHC gave 90L a 30% chance of developing into a tropical depression by Sunday morning in their 8 am Friday Tropical Weather Outlook.
Kuwait hits 53.6°C (128.5°F): 2nd hottest temperature in Asian history
An extraordinary high temperature of 53.6°C (128.5°F) was recorded in Sulaibya, Kuwait on July 31, the hottest temperature in Kuwait’s history, and the 2nd hottest temperature ever measured in Asia. According to weather records researcher Maximiliano Herrera, Sulaibya is in a location well-suited for recording extreme high temperatures, since high sand dunes surround the site, keeping the wind low and hampering sea breezes from cooling the city. Most record books list the 54°C (129.2°F) recorded on 21 June 1942 in Tirat Zvi Israel as the site of Asia’s all-time maximum temperature, but this record is disputed. The previous second warmest temperature in Asian history was set 53.5°C (128.3°F) at MohenjuDaro, Pakistan on May 26, 2010.
Extreme heat in Oklahoma
The most intense and widespread heat wave in Oklahoma since August, 1936 brought more than half of the state temperatures of 110° or higher for the second consecutive day on Thursday. The temperature at the Oklahoma City airport hit 112°, for the 2nd day in a row. These are the city’s 2nd highest temperatures since record keeping began in 1890. The only hotter day was August 11, 1936, when the temperature hit 113°. Thursday’s temperatures in Oklahoma were generally a degree or two cooler than Wednesday’s, with the hottest temperature reported a 116° reading from a location just south of Tulsa International Airport. The highest reading Thursday at any major airport was a 114° temperature at Tulsa Jones Airport. Oklahoma’s all-time state record is 120°, set in Tipton on June 27, 1994, and at three locations in 1936. Freedom, in the northwest part of the state, hit 121° on Wednesday, but this reading will need to be reviewed to see if the sensor was properly sited.
