Posted by: JeffMasters, 4:06 PM GMT on February 03, 2012
+21
Brutal winter cold continues over most of Europe, where at least 200 people have died in a cold wave that began January 26. Hardest hit has been Ukraine, where the temperature bottomed out at -17°F (-27°C) at the capital of Kyivthis morning. It was the second coldest day of the cold wave, behind the -28°C reading of February 2. These temperatures are the coldest winter weather in six years in Ukraine, and at least 101 deaths are being blamed on the cold there. Also hard-hit has been Poland, where 37 people, most of them homeless, have died from the cold. Rome, Italy experienced a rare snowfall today, only its second day with snow during the past fifteen years. Very cold temperatures 10 – 20°C below average will continue for another seven days in Europe before gradually moderating late next week.
Figure 1. Departure of temperature from average as analyzed by the GFS model, for February 2, 2012. Remarkably cold air was present over Europe and western Alaska, while very warm air was over central North America and Siberia. This image is being generated experimentally by wunderground, and will be regularly available on our web site in the future.
Meanwhile, a snow drought for the U.S.
In the U.S., it’s been the opposite story, with temperatures 10 – 15°F above average continuing this week over much of the nation. January 2012 is in the weather record books as the 3rd least-snowy January for the contiguous U.S. since snow records began in 1966, and December 2011 ranked as the 11th least snowy December on record. With no major snow storms in the offing over at least the next ten days, it’s looking probable that the non-winter of 2011 – 2012 will set numerous record-low seasonal snowfall totals. The National Weather Service sends out a daily “Weather and Almanac” product for several hundred major U.S. cities that we make available on wunderground. I went through yesterday’s statistics for those cities that reported measurable snow this winter. Only nine cities out of 166 major U.S. cities in the lower 48 states reported above-average snowfall as of February 1; 157 cities received below-average snowfall. The big winner in the snow sweepstakes has been Alaska, which is boasting 8 of the top 10 locations for heaviest snowfall this winter. While the 27.75 feet of snow that has fallen on Valdez has gotten a lot of attention, more remarkable is the 18.8 feet of snow Yakutat has received. That’s more than 12.5 feet above what they usually have by this time of year.
The big losers in the snow stats for this winter are the cities along the lake effect snow belts on the Great Lakes. Most notably, Syracuse, New York is nearly four feet of snow below average for this time of year. Perhaps more exceptional is Williston, North Dakota, which has received just 1.8″ of snow this winter–more than two feet below their average for February 1.
Have a super weekend, everyone, and I’ll be back Monday with a new post.
Posted by: JeffMasters, 3:07 PM GMT on January 11, 2012
+4
Rains unprecedented in 117 years of record keeping set new yearly precipitation totals in seven states during 2011, NOAA’s National Climatic Data Center revealed in its preliminary year-end report for 2011. An extraordinary twenty major U.S. cities had their wettest year on record during 2011. This smashes the previous record of ten cities with a wettest year, set in 1996, according to a comprehensive data base of 303 U.S. cities that have 90% of the U.S. population, maintained by Wunderground’s weather historian Christopher C. Burt. Despite the remarkable number of new wettest year records set, precipitation averaged across the contiguous U.S. during 2011 was near-average, ranking as the 45th driest year in the 117-year record. This occurred because of unprecedented dry conditions across much of the South, where Texas had its driest year on record.
Figure 1. Precipitation rankings for U.S. states in 2011. Seven states had their wettest year on record, and an additional ten states had a top-ten wettest year. Texas had its driest year on record, and four other states had a top-ten driest year. Image credit: NOAA’s National Climatic Data Center.
Figure 2.Wettest, driest, and warmest year records set during 2011 for major U.S. cities. No major cities had their coldest year on record during 2011. Image credit: NOAA’s National Climatic Data Center.
2011 sets a new U.S. record for combined wet and dry extremes
If you weren’t washing away in a flood during 2011, you were probably baking in a drought. The fraction of the contiguous U.S. covered by extremely wet conditions (top 10% historically) was 33% during 2011, ranking as the 2nd highest such coverage in the past 100 years. At the same time, extremely dry conditions (top 10% historically) covered 25% of the nation, ranking 6th highest in the past 100 years. The combined fraction of the country experiencing either severe drought or extremely wet conditions was 58%–the highest in a century of record keeping. Climate change science predicts that if the Earth continues to warm as expected, wet areas will tend to get wetter, and dry areas will tend to get drier–so 2011’s side-by-side extremes of very wet and very dry conditions should grow increasingly common in the coming decades.
Figure 3. Percentage of the contiguous U.S. either in severe or greater drought (top 10% dryness) or extremely wet (top 10% wetness) during 2011, as computed using NOAA’s Climate Extremes Index. Remarkably, more than half of the country (58%) experienced either a top-ten driest or top-ten wettest year, a new record. Image credit: NOAA/NCDC.
23rd warmest year on record, and 2nd hottest summer for the U.S.
The year 2011 ranked as the 23rd warmest in U.S. history, with sixteen states recording a top-ten warmest year on record. Delaware had its warmest year on record, and Texas its second warmest. However, these statistics don’t convey the extremity of the summer of 2011–the hottest U.S. summer in 75 years. The only hotter summer–and by only 0.1°–was the Dust Bowl summer of 1936, when poor farming practices had turned much of the Midwest into a parking lot for generating extreme heat. The June – August 2011 average temperatures in Texas and Oklahoma were a remarkable 1.6°F and 1.3°F warmer than the previous hottest summer for a U.S. state–the summer of 1934 in Oklahoma. The U.S. Climate Extremes Index (CEI), which is sensitive to climate extremes in temperature, rainfall, dry streaks, and drought, indicated that an area nearly four times the average value was affected by extreme climate conditions during summer 2011. This is the third largest summer value of record, and came on the heels a spring season that was the most extreme on record. When averaged over the entire year, 2011 ranked as the 8th most extreme in U.S. history, since the fall weather was near-average for extremes. The CEI goes back to 1910.
Figure 4. Average temperatures for the summer in Texas and Oklahoma, at 86.8 degrees F (30.4 degrees C) and 86.5 degrees F (30.3 degrees C), respectively, exceeded the previous seasonal statewide average temperature record for any state during any season. The previous warmest summer statewide average temperature was in Oklahoma, during 1934, at 85.2 degrees F (29.6 degrees C). Image credit: National Climatic Data Center.
Wunderground’s weather historian Christopher C. Burt has a more detailed look at the U.S. extremes observed during 2011 in his latest post. His selection for the most remarkable yearly record set during 2011:
Perhaps, most astonishing is the total annual rainfall of just 1.06” at Pecos, Texas (normal annual precipitation is 11.61”). If confirmed this would be a Texas state record for least amount of precipitation ever recorded in a calendar year, the current record stands at 1.64” at Presidio in 1956.
I’m wrapping up my stay in San Francisco for the annual Fall Meeting of the American Geophysical Union (AGU), the world’s largest gathering of Earth Scientists. Over eighteen thousand scientists from all over the world, including most of the world’s top climate scientists, were in town this week to exchange ideas to advance the cause of Earth Science. It’s been a great opportunity to learn about climate change topics I don’t know much about, and I attended a fascinating (and somewhat unnerving) lecture on how global warming is expected to affect insects, titled “The Impact of Global Warming on global crop yields due to changes in pest pressure”. Global warming is expected to bring a variety of impacts to agriculture, both positive and negative. Extra CO2 in the atmosphere will tend to increase crop yields, but crop losses due to insect pests are expected to double by 2100, according to a insect pest/crop model designed by David Battisti of the University of Washington. These losses will occur in addition to the expected 35 – 40% decrease in crop yields due to higher temperatures by the end of the century.
When temperature increases, the metabolic rate of insects goes up, requiring that they eat more to survive. In the mid-latitudes, the predicted 2 – 4°C temperature increase by 2100 will require insects to eat double what they do now, in order to survive. The increase in temperature is also expected to enable insect populations to rise by 20%. However, insect populations will fall by 20% in the tropics, where insects have evolved to tolerate a much narrower range of temperatures. Let’s look at the world’s three most important crops: rice, wheat, and corn. In the four largest rice producing countries–China, India, Bangladesh, and Thailand–Insects currently cause a loss of 10- 20% of the crop, and this is expected to double to 20 – 30% by 2100. These nations have 40% of the world’s population, and make 60% of the world’s rice. For corn, the world’s four largest producers–the U.S., China, France, and Argentina–are expected to see insect pest losses double from 6% to 12%. The story is similar for wheat; pest losses are expected to double from 10% to 20% by 2100. The total increased damage to global agriculture is predicted to be $30 – $50 billion per year by 2100. This will likely contribute greatly to food costs and potential food shortages. The model made a number of simplifications that could greatly change this outcome, though. The model assumed that there would be no change to the number of insects that survive winter, and this number is likely to increase in a warmer climate. Precipitation was not changed to reflect what is expected to happen in a changed climate, and this will cause increases in crop yields in some areas, and decreases in others. Farmers are likely to change growing practices and utilize new pesticides to combat the expected increase in pests, and this was not considered, either. It is interesting to note that during the great natural global warming event of 55 million years ago–the Palecene-Eocene Thermal Maximum (PETM)–fossil records of plant leaves show greatly increased levels of damage from insects, supporting the idea that a warmer climate will drive an explosion in the insect population.
Alaska blizzard pushes 8-foot storm surge into Nome; Sean heads towards Bermuda
Posted by: JeffMasters, 2:47 PM GMT on November 10, 2011
+3
The most powerful storm to affect the Bering Sea coast of Alaska since 1974 is slowly winding down today, after pounding Alaska’s west coast and Eastern Siberia with hurricane-force winds, a destructive storm surge more than 8 feet high, waves up to 40 feet high, and heavy snow. The highest wind gust recorded during the storm, 89 mph, was at Wales at the western tip of the Seward Peninsula, which forms the U.S. side of the Bering Strait. Hurricane force gusts were observed at seven locations in Alaska:Cape Lisburne… 81 mph at 7 am Wed
Gambell… … … 74 mph at 6 pm Tue
Kotzebue… … ..74 mph at 6 am Wed
Point Hope… … 78 mph at 5 am Wed
Savoonga… … ..76 mph at 7 pm Tue
Tin City… … ..85 mph at 12 am Wed
Wales… … … ..89 mph at 1:42 am Wed
A storm surge of 8.6 feet hit Nome, Alaska near 9 pm EST last night, pushed inland by sustained winds that reached 45 mph, gusting to 61 mph. Large waves on top of the surge encrusted with sea ice battered the coast, causing extensive damage and coastal flooding. Significant wave heights at the Bering Sea buoy north of the Aleutian Islands reached 40 feet during the peak of the storm. The last time Nome, Alaska saw a storm this strong was November 11 – 12 1974,when the city experienced sustained winds of 46 mph with gusts to 69 mph, a pressure that bottomed out at 969 mb, and a storm surge of 13 feet. The center of yesterday’s storm moved ashore over eastern Siberia near 12 UTC with a central pressure of 945 mb. The storm’s central pressure had risen to 958 mb this morning, with the center of the storm now located north of Siberia over the Arctic.
Figure 1. Observed storm surge at Nome, Alaska (green line). MLLW = Mean Lower Low Water, the water level at the lowest tide of the month. The top storm surge of 8.6 feet occurred near 02 GMT this morning (9 pm EST November 9, 2011.) Image credit: NOAA Tides and Currents.
Tropical Storm Sean Tropical Storm Sean is on the move towards the northeast, towards a brush with Bermuda. Infrared satellite loopsreveal that Sean has not changed much in organization this morning. The storm has a respectable amount of heavy thunderstorm activity near its center that is relatively shallow, and Sean has at times been able to close off an eyewall, and has a ragged-looking eye. Bermuda radar shows one strong rain band from Sean has affected the island, with the bulk of Sean’s heavy thunderstorms well to the island’s southwest. Sustained winds at the Bermuda airport have been under 30 mph this morning, and Bermuda picked up 0.08″ of rain yesterday, and 0.24″ as of 9 am EST today. Sustained winds at buoy 41048, about 300 miles west of Bermuda were 40 mph at 7:50 am EST. Strong upper-level winds out of the west are creating about 20 knots of wind shear over Sean, which is low enough to allow some slow development. Ocean temperatures have fallen to 25°C (77°F), which just below the 26°C threshold typically needed for a tropical storm to maintain its strength.
Figure 2. Morning satellite image of Tropical Storm Sean.
Forecast for Sean
The latest SHIPS model forecast predicts wind shear will remain about where it is now through Friday morning. However, ocean temperatures will gradually cool to 24°C during this time, and it is questionable whether Sean will have a favorable enough environment to strengthen into a hurricane. The computer models show little development of Sean, with none of our reliable models predicting it will become a hurricane. Bermuda is the only land area that need concern itself with Sean, as the storm is now caught in a trough of low pressure that will accelerate the storm to the northeast. The center of Sean could pass close enough to Bermuda to bring the island heavy rain squalls and sustained winds of 40 – 45 mph on Friday. NHC is giving a 52% chance that Bermuda will receive tropical storm-force winds of 39 mph. Wind shear will rise to 30 – 50 knots on Friday, which should be able to rip the storm apart by Saturday.
Sean, rare Mediterranean hybrid, and AK superstorm forms; quakes and tornadoes in OK
Posted by: JeffMasters, 3:52 PM GMT on November 08, 2011
+16
Subtropical Storm Sean formed this morning between Bermuda and the Bahamas. Sean’s formation brings this year’s tally of named storms to eighteen, tying 2011 with 1969 as the 6th busiest Atlantic hurricane season since record keeping began in 1851. Only 2005, 1933, 1995, 1887, and 2010 have had more named storms. However, 2011 has had an unusually low percentage of its named storms reach hurricane strength. We’ve had an average number of hurricanes–six–meaning that only 33% of this year’s named storms have made it to hurricane strength. Normally, 55 – 60% of all named storms intensify to hurricane strength in the Atlantic. There have been three major hurricanes in 2011, which is one above average, and the total Accumulated Cyclone Energy (ACE)–a measure of the destructive potential of this season’s storms–has been about 20% above average. The rare combination of near-record ocean temperatures but unusually dry, stable air over the Atlantic is no doubt at least partially responsible for the unusually high count of named storms, but near-average number of hurricanes and ACE.
Figure 1. The subtropical disturbance that became Subtropical Storm Sean, as seen at 1 pm EST November 7, 2011. Image credit: NASA.
Infrared satellite loops reveal that Sean has developed a respectable amount of heavy thunderstorm activity near its center that is increasing in intensity and areal coverage. While the low-level circulation center is exposed to view, a band of thunderstorms is trying to wrap around and close of the center. If this occurs, more substantial strengthening can occur, since the center will be walled off from the dry air that is currently interfering with development. Bermuda radar shows weak rain bands from Sean rippling across the island, with the strongest rain showers well to the island’s southwest. Sustained winds at the Bermuda airport have been under 30 mph this morning. Sustained winds near tropical storm force were occurring this morning at buoy 41048, about 300 miles west of Bermuda. Winds at the buoy were 38 mph, gusting to 47 mph at 6:50 am EST. Strong upper-level winds out of the west are creating about 20 knots of wind shear over Sean, which is low enough to allow some slow development. Sean is a relatively shallow storm, and the tops of its thunderstorms extend up only to about the 300 mb level. Normally, a tropical storm extends up to about 200 mb. The shallow nature of Sean’s thunderstorms mean that the storm is less vulnerable to wind shear than normal, since the storm is not feeling the strongest winds aloft. Ocean temperatures are near 26.5°C (80°F), which is right at the boundary of being warm enough to support tropical storm formation.
Forecast for Sean
Sean will drift slowly west or northwest today and Wednesday. The latest SHIPS model forecast predicts wind shear will remain about where it is now through Thursday morning, which should allow Sean to slowly intensify to a 50 mph storm. If Sean can make the transition to a fully tropical storm, more significant intensification can occur. The computer models show little or no development of Sean, with none of our reliable models predicting it will become a hurricane. Bermuda is the only land area that need concern itself with Sean, as a trough of low pressure is expected to absorb the storm on Thursday and lift it quickly to the north or northeast. The center of Sean could pass close enough to Bermuda to bring the island heavy rain squalls and sustained winds of 40 – 45 mph on Thursday and Friday. NHC is giving a 28% chance that Bermuda will receive tropical storm-force winds of 39 mph. High wind shear should destroy Sean on Friday.
Figure 2. MODIS image of the hybrid low named “Rolf” in the Mediterranean Sea at 10:30 UTC November 8, 2011. Image credit: NASA.
Unusual tropical storm-like low forms off coast of France
An unusual hybrid low pressure system has formed in the Mediterranean Sea, about 100 miles south of the coast of France. The low began as an extratropical storm named “Rolf”, but has stalled out over the relatively warm waters of the Mediterranean over the past two days, and has acquired tropical characteristics. Heavy thunderstorms have built over the northeast portion of the low, and the storm has a symmetric spiral shape with a cloud-free center, like a tropical storm. The Navy is calling this system Invest 99L. The National Hurricane Center is not responsible for the Mediterranean Sea, so they are not issuing any products for 99L. NOAA’s Satellite and Information Service (NESDIS) is giving 99L a tropical classification based on its satellite presentation, with winds in the 40 – 45 mph range. French radarshows heavy rains from 99L are beginning to affect Southeast France and the island of Corsica. The Lion Buoy, located about 100 miles to the west of the center of 99L, recorded sustained winds of tropical storm force, 40 mph, at 00 UTC yesterday. Water temperatures at the buoy were 17°C (63°F), far below the 26°C threshold usually needed to sustain a tropical storm. The coldest waters I’ve seen a tropical storm form in were 22°C during Hurricane Epsilon of 2005. I doubt that NHC would name this system if they did have responsibility for the Mediterranean, due to the cold water temperatures.
“Rolf” is expected to move slowly northwards into the coast of South France by Wednesday night. Meteo France is predicting heavy rains of 30 – 40 mm/hr (1.2 – 1.6″/hr) will affect the coast Tuesday night through Wednesday, with sustained winds of 50 mph, gusting to 75 mph.
Figure 3. Hybrid subtropical storm of October 8, 1996, off the coast of Italy. According to Reale and Atlas (2001), the storm had characteristics similar to a hurricane, but formed over water of 21.5°C. “The maximum damage due to wind occurred over the Aeolian Islands, at 38.5°N, 15°E, to the northeast of Sicily: assistance for disaster relief was required. Unfortunately, no weather station data were available, but the media reported sheds, roofs and harbor devices destroyed, and houses and electric lines damaged, due to “extremely strong westerly wind.” The perfect agreement between the observations at Ustica, the storm scale, the eye-like feature position and the damages over the Aeolian Island reasonably suggest that the hurricane-level intensity of 32 m/s (72 mph) was reached over the Aeolian Islands.” A similar hybrid low affected Algeria on 9 – 10 November 2001. This storm produced upwards of 270 mm (10.6″) of rain, winds of 33 m/s (74 mph), and killed 737 people near Algeirs, mostly from flooding and mud slides. Image credit:Dundee satellite receiving station.
According to research published by Gaertner et al. (2007), an increase in ocean temperatures of 3°C in the Mediterranean by the end of the century could lead to hurricanes forming there. Miguel Angel Gaertner of the University of Castilla-La Mancha in Toledo, Spain, ran 9 different climate models with resolutions of about 50 km and found that some (but not all) of the models simulated hurricanes in the Mediterranean in September by the end of the century, when ocean temperature could reach 30°C.
Though the Mediterranean may start seeing hurricanes by the end of the century, these storms should be rare and relatively short-lived for three reasons:
1) The Mediterranean is quite far north and is subject to strong wind shear from jet stream activity.
2) The waters are shallow, and have relatively low heat content. There is no deep warm water current like the Gulf Stream.
3) The Mediterranean has a lot of large islands and peninsulas poking into it, increasing the chances that a tropical storm would weaken when it encountered land.
References Meteo France has an interesting animation of the predicted winds and temperatures over the next few days.
Figure 4. Radar reflectivity image from the Tipton, OK tornado of November 7, 2011, showing a classic hook echo.
Shaken and stirred: an earthquake and tornado for Oklahoma
It was a rare multi-natural hazard day for Oklahoma yesterday, as the state experienced both a tornado and an earthquake, six hours apart. The damaging magnitude 5.6 earthquake that shook the state Saturday night spawned amagnitude 4.7 aftershock at 8:46 pm CST yesterday, 44 miles east of Oklahoma City. And at 2:47 pm CST, a tornado touched down in Southwest Oklahoma near Tipton. The tornado destroyed an Oklahoma State University agricultural office, and damaged a hay barn at a dairy farm. No injuries were reported. The UK MailOnline has an interesting article showing the radar image from Saturday’s quake, which captured a massive groups of birds and insects that took flight after the ground shook.
This afternoon, NOAA’s Storm Prediction Center has placed Southeast Oklahoma, East Texas, Southeast Missouri, and most of Arkansas in its “Slight Risk” area for severe weather, thanks to a strong low pressure system moving across the Plains. During the late afternoon, severe thunderstorms with high winds and large hail and expected over the region, and we cannot rule out an isolated tornado.
Bering Sea superstorm targets Alaska
A massive blizzard the National Weather Service is calling one of the most severe Bering Sea storms on record is gathering strength today to the west of Alaska. The storm is expected to “bomb” to a central pressure of 945 – 950 mb Tuesday night, and to 940 mb on Wednesday. These pressures, characteristic of a Category 3 hurricane, will be strong enough to generate sustained winds of Category 1 hurricane force over the waters to the west of Alaska, with winds of 50 – 70 mph expected along portions of the coast. Nome, Alaska is expecting a storm surge of 8 – 10 feet. Waves of 15 – 25 feet with ice on top will batter the shores, causing severe damage to the coast.
Ophelia strengthening; Typhoon Nalgae a new threat to the Philippines
Posted by: JeffMasters, 1:51 PM GMT on September 29, 2011
+4
Tropical Storm Ophelia is strengthening as it pulls away from the Lesser Antilles Islands and heads north-northwest. Recentsatellite loops show that Ophelia has developed a Central Dense Overcast (CDO) of high cirrus clouds over its core, which is characteristic of strengthening tropical storms that are nearing hurricane intensity. Dry air and moderate wind shear of 15 – 20 knots are slowing down Ophelia’s intensification, but by Friday morning, wind shear is expected to fall to 10 – 15 knots, and remain below 15 knots through Sunday morning. This should allow Ophelia to intensify into a hurricane on Friday. Most of the models agree that Ophelia will track far enough to the east of Bermuda that the island should see sustained winds below 45 mph, since it will be on the weak (left) side of the storm. We can’t rule out the possibility that Bermuda will receive hurricane force winds yet, but the odds are low–the 5 am wind probability forecast from NHC gave Bermuda just a 3% chance of receiving hurricane force winds. Ophelia’s closest approach to the island will be late Saturday night and early Sunday morning. Ophelia is likely to bring high winds and heavy rains to Southeast Newfoundland Sunday night, as a weakening tropical storm.
In the middle Atlantic, Tropical Storm Philippe is headed west-northwest, and is not expected to trouble and land areas.Satellite loops show Philippe is a small system with little heavy thunderstorm activity. Wind shear is expected to diminish some today over the storm, which should allow the storm to intensify. However, by Saturday, Philippe will be encountering very high wind shear of 30 – 40 knots associated with the upper-level outflow from Ophelia. This shear will probably be high enough to destroy Philippe by Monday. In the event Philippe does survive the shear, the storm could penetrate far enough west that Bermuda might need to be concerned with it.
Elsewhere in the Atlantic, none of the computer models is calling for a new tropical storm to form in the coming seven days. The large-scale environment over the Atlantic currently favors sinking air, due to the current phase of the Madden-Julian Oscillation (MJO). This situation will likely last well into next week, and will discourage formation of new tropical storms. The MJO is a 30-60 day cycle of thunderstorm activity that affects the tropics.
Figure 1. Morning satellite image of Ophelia, showing the large Central Dense Overcast (CDO) that has formed.
Typhoon Nesat battering China Typhoon Nesat hit China’s Hainan Island today as a Category 1 typhoon with 75 mph winds. While Nesat’s winds and storm surge will not cause major damage, it is a very wet storm, capable of dropping up to 8 inches of rain in 24 hours, according to latest satellite rainfall forecasts.Haikou on Hainan Island recorded a wind gust of 78 mph and 3.23″ of rain as the eyewall passed just to the north. Nesat will hit Vietnam near Hanoi as a tropical storm on Saturday.
Nesat roared across Luzon Island in the Philippines Monday as a powerful Category 3 typhoon with 120 mph winds, leaving35 people dead and 45 missing. The Philippines has a new worry today: Typhoon Nalgae has formed 700 miles to the east of Luzon Island, and is expected to follow a course just to the north of Nesat’s. Nalgae is expected to intensify into a major Category 3 typhoon and hit the northern portion of Luzon on Saturday afternoon, local time. With soils on the island already saturated from the heavy rains Nesat brought, the new typhoon promises to bring heavy flooding to Luzon this weekend.
Figure 2. True-color MODIS image of Typhoon Nesat over the South China Sea taken at 1:35 pm local time September 28, 2011. At the time, Nesat was a Category 1 typhoon with 75 mph winds. Image credit: NASA.
Invest 98L spinning up; outlook for remainder of hurricane season
Posted by: JeffMasters, 2:09 PM GMT on September 19, 2011
+6
A tropical wave midway between Africa and the Lesser Antilles (Invest 98L) continues to look well-organized on satellite imagery, with a modest amount of heavy thunderstorm activity and spin. An ASCAT pass from 8:08 pm EDT last night showed 98L was close to closing off a well-defined surface circulation. Wind shear as diagnosed by the SHIPS model is light, less than 10 knots, and is predicted to stay light to moderate through Friday. Ocean temperatures are 28 – 28.5°C, well above the threshold typically needed for a tropical storm to spin up. Water vapor satellite images show 98L is embedded in a moist environment, but there is dry air to the system’s northwest. However, given the light wind shear, this dry air may not pose a hindrance to development at this time. An analysis of upper level winds from the University of Wisconsin CIMMS group shows a pattern favorable for development, with an outflow channel open to both the north and south available to ventilate the storm and allow 98L to efficiently lift plenty of moisture to high levels.
Figure 1. Morning satellite image of 98L.
The models are not very aggressive about developing 98L into a tropical depression, but most of them do show some weak development. NHC gave the disturbance a 60% chance of developing into a tropical depression by Wednesday in their 8 am Tropical Weather Outlook. Given the recent increase in spin on visible satellite images and favorable environment for development, I’d bump these odds up to 70%. 98L is currently moving little, but is expected to begin a westward motion at 10 mph today. This motion would take 98L into the Lesser Antilles Islands by Friday or Saturday. The northern Lesser Antilles would be most likely to see the core of the storm, as has been the case for all of this year’s disturbances. However, a more southerly path across Barbados, as predicted by the GFS model, cannot be ruled out. Once 98L does reach the Lesser Antilles, all of the models indicate the storm will see a sharp increase in vertical wind shear due to strong upper-level winds out of the west. This shear should make it difficult for 98L to intensify as it moves though the islands.
Atlantic hurricane outlook for the rest of September
Ocean temperatures are starting to decline in the North Atlantic, though remain much above average in the Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America, between 10°N and 20°N latitude. The latest departure of sea surface temperature (SST) from average plot (Figure 2) shows a large area of ocean temperatures near 1°C above average. The water temperatures were 0.8°C above average in this region during August, which is the 4th highest such reading on record. These warm waters will allow for an above-average chance of African tropical waves developing through early October. By early October, the African Monsoon typically begins to wane, spawning fewer tropical waves that tend to be weaker, and we should stop seeing development of newly-emerged tropical waves off the coast of Africa.
Figure 2. Departure of sea surface temperature (SST) from average for September 19, 2011. Ocean temperatures were about 1°C above average over much of the Main Development Region (MDR) for hurricanes, from the coast of Africa to the coast of Central America, between 10°N and 20°N latitude. In the Pacific off the coast of South America, we can see the tell-tale signature of a La Niña event, with cooler than average waters along the Equator. Also note the cooler than average waters between Bermuda and Puerto Rico, due to the passage of Hurricane Maria and Hurricane Katia. Image credit:NOAA/NESDIS.
Wind shear has been near average over the tropical Atlantic this hurricane season, and is currently at its climatological low point, which occurs in mid-September. The latest 2-week run of the GFS model shows wind shear will remain at the sort of typical low levels we usually see this time of year. With ocean temperatures at near-record warm levels, this combination would tend to favor formation of at least two tropical storms between now and the beginning of October. One inhibiting factor, though, may be the continued presence of dry, stable air over the tropical Atlantic. Hurricanes like to have an unstable atmosphere, with moist, warm air near the surface, and cold, dryer air aloft. This situation helps the updrafts in the storm grow stronger. This year, we’ve had unusually stable air (Figure 3.) This has really put the brakes on intensification of most of the tropical storms that have formed. The current ratio of 14 named storms but only 3 hurricanes is unprecedented in the historical record, going back to 1851. Usually, just over half of all Atlantic tropical storms intensify into hurricanes. One other factor to consider, the 30-60 day pattern of increased thunderstorm activity known as the Madden-Jullian Oscillation (MJO), looks like it will have little influence over the coming week. The MJO has been weak all month, and is predicted to stay weak for the remainder of this week.
Figure 3. Vertical instability, as measured by the difference in temperature near the surface to the bottom of the stratosphere. The atmosphere in the Caribbean (left) and tropical Atlantic between Africa and the Lesser Antilles Islands (right) has been much more stable than average this year (average is the thick black line). Image credit: NOAA/CIRA.
Forecast of the rest of hurricane season
We are past the half-way point of the Atlantic hurricane season, which typically peaks on September 10. On average, about 60% of the activity has occurred by this point in the season. Since we’ve already had 14 named storms and 3 hurricanes, at the current rate, we would expect to see another 8 or 9 named storms, with 1 or 2 of them reaching hurricane strength. It’s pretty tough to maintain the sort of activity levels we’ve seen so far this year, so I am forecasting we’ll see 7 more named storms during the remainder of this season, taking us all the way to “W” in the alphabet. With the unusually stable air over the Atlantic showing no signs of abating, I predict that we’ll see just 2 of these storms reach hurricane strength. As far as steering currents go, the latest 2-week forecast from the GFS model doesn’t show any significant changes to the jet stream pattern we’ve seen all summer. There will continue to be a parade of troughs of low pressure moving off the U.S. East Coast that will tend to curve any storms northwards and then northeastwards out to sea, once they penetrate north of the Lesser Antilles Islands. This pattern favors strikes on North Carolina and New England, and discourages strikes on Texas. I doubt Texas will see a tropical storm this year given this steering pattern, and considering that Texas’ tropical cyclone season tends to peak in late August and early September. It is quite unusual for Texas to have a tropical storm or hurricane this late in the season, so they will probably have to look elsewhere for drought-busting rains.
No change to Nate; Maria fizzles; Katia headed to Britain
Posted by: JeffMasters, 3:47 PM GMT on September 10, 2011
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Tropical Storm Nate in Mexico’s Bay of Campeche continues to have trouble intensifying. Latest visible satellite loops show that Nate has a large, cloud-filled center, and the storm is probably pulling in dry air to its north into its center. Nate is also likely having trouble with all the cool waters it has stirred to the surface. Assuming Nate is able to close off its center from the dry air, it would take the storm at least a day to tighten up its rather large center, form a solid eyewall, and reach hurricane intensity. Nate doesn’t have enough time before landfall for that to happen, and it is unlikely Nate will ever become a hurricane. The latest wind probability forecast form NHC gives Nate a 13% chance of reaching hurricane strength on Sunday. Latest radar imagery from Alvarado, Mexico shows heavy rains from Nate are affecting the coast near Veracruz, and heavy rains of 4 – 6 inches will be the main threat from Nate.
Figure 1. True-color MODIS image of Tropical Storm Nate taken at 12:45 pm EDT Friday, September 9, 2011. At the time, Nate was a tropical storm with 50 mph winds. Image credit: NASA.
Nate is a small storm, and is not likely to bring significant rains to Texas; only extreme South Texas near Brownsville could see an inch or so of rain on Sunday from an outer spiral band of Nate. Our latest wundermap wind forecast map from the European Center model, with the fire layer turned on, shows that Nate’s wind field on Saturday and Sunday will not be large enough to fan the fires burning in Texas.
Tropical Storm Maria Tropical Storm Maria doesn’t look much like a tropical storm–on the latest satellite imagery it looks like a squashed question mark instead of a spiral. The surface circulation center is very poorly defined, and moderate wind shear of 15 – 20 knots has really done the Lesser Antilles Islands a big favor by ripping up Maria. It is doubtful this storm will generate any sustained winds of tropical storm force in the islands, and it is a 50/50 proposition that Maria will degenerate into a tropical disturbance and become ex-Tropical Storm Maria later today. Martinique radar shows heavy rains from Maria are mostly east of the islands, and the thunderstorms are not well-organized into spiral bands. The wind shear affecting Maria will probably last through Sunday. By Monday, wind shear is predicted to fall enough so that Maria could potentially organize again. However, the storm is expected to be far from land when that occurs. Bermuda could see a few rain showers from Maria on Wednesday, and Maria may be a threat to southeast Newfoundland late next week.
Figure 2. Morning satellite image of Tropical Storm Maria shows the the storm looks like a squashed question mark?
Hurricane Katia Hurricane Katia brushed by Newfoundland, Canada this morning, and is now racing east-northeast at 52 mph into the open Atlantic. With water temperatures 19°C (66°F) underneath it, Katia has lost its tropical characteristics, and has transitioned to a powerful extratropical storm. Extratropical Storm Katia will continue east-northeastward towards Europe, and on Monday, the storm will pass very close to northern British Isles. The offshore waters of Northern Ireland and Western Scotland can expect storm-force winds of 50 – 60 mph on Monday as Katia roars past to the north. The storm will bring 2 – 4 inches of rain to the coast, and likely cause significant tree damage and power failures.
Figure 3. Image of Hurricane Katia taken from the International Space Station at 15 GMT September 9, 2011, by astronautRon Garan. At the time, Katia was a Category 1 hurricane with 85 mph winds. Long Island, New York is visible at the lower left.
TD 14 likely to become Maria; new Gulf of Mexico system brewing
Tropical Depression Fourteen formed yesterday from a strong tropical wave that moved off the coast of Africa early this week, and is headed west-northwest towards an encounter with the Northern Lesser Antilles Islands. Satellite loops show a large a steadily organizing system with plenty of heavy thunderstorm activity, good upper-level outflow to the north and west, and some respectable low-level spiral bands beginning to form. TD 14 is probably a tropical storm now, and is very likely to be named Tropical Storm Maria later today. Water vapor satellite images show that 95L is embedded in a very moist environment. Ocean temperatures are near 28.5°C, which is 2°C above the 26.5°C threshold usually needed to sustain a tropical storm. With wind shear predicted to remain low to moderate the next five days, the atmosphere expected to stay moist, and ocean temperatures predicted to gradually warm, TD 14 should generally show a strengthening trend. Curiously, most of the intensity forecast models show little strengthening of TD 14, so NHC is keeping their intensity forecast lower than is typical for a storm in these conditions at this time of year.
The track forecasts for TD 14 from the various models agree that the storm will affect the Northern Lesser Antilles Islands, though there are some differences in forward speed, resulting in some uncertainty whether the storm will arrive at the islands as early as Friday night, or as late as Saturday afternoon. After it passes the Lesser Antilles, TD 14 has the usual amount of high uncertainty in its 5 – 7 day track forecast. The models are split on how strong the steering influence a trough of low pressure along the U.S. East Coast will have. The ECMWF and UKMET models prefer a more southerly track for TD 14 through the Bahamas towards the U.S. East Coast, while the GFS, NOGAPS, and HWRF models predict a more northwesterly track, with a potential threat to Bermuda. It’s too early to guess which track the models will eventually converge on. Climatology favors a track that would miss land, with Dr. Bob Hart’s track history pages suggesting TD 14 has a 22% chance of hitting Canada, 19% chance of hitting Bermuda, and an 11% chance of hitting North Carolina.
Figure 1. Morning satellite image of TD 14.
Gulf of Mexico disturbance 96L
A cold front swept into the Gulf of Mexico off the coast of Texas behind Tropical Storm Lee on Monday, and has stalled out along a line from Tampa, Florida to Mexico’s Bay of Campeche in the southern Gulf of Mexico. Heavy thunderstorms have begun to build along the tail end of this front in the Bay of Campeche, and this disturbance has been designated Invest 96Lby NHC. Latest visible satellite loops do not show that 96L has a closed surface circulation yet, but buoy and surface observations along the coast of Mexico suggest that there may be a large-scale counter-clockwise circulation present over the Bay of Campeche. Sustained winds at Buoy 42055, about 100 miles to the northwest of the suspected center of 96L, were northeast at 27 mph at 6:50 am CDT this morning. Water vapor satellite loops show that here is a large area of very dry air from Texas to the north of 96L, and this dry air may interfere with 96L’s development. A hurricane hunter mission is scheduled for this afternoon into 96L.
Most of the computer models develop 96L into a tropical depression in the next 1 – 2 days, and these same models did very well at anticipating the formation of Tropical Storm Lee in the Gulf of Mexico last week. Given the moderate wind shear, warm waters, and presence of an old cold front to serve as a nucleus for development, I give 96L an 80% chance of becoming a tropical depression over the next tow days, a bit higher than the 60% probability NHC is going with. Steering currents are weak in the Bay of Campeche, making for a lot of uncertainty in where 96L might go. The only model predicting a U.S. landfall is the ECMWF, which predicts 96L might hit between Louisiana and the Florida Panhandle on Monday. A more popular solution is for the storm to meander in the Bay of Campeche for many days, and eventually make landfall on the coast of Mexico between Veracruz and Tampico. None of the models is hinting at a track towards Texas, and the intense dome of high pressure associated with their record drought and heat wave will tend to discourage any tropical cyclones from making a Texas landfall over the coming seven days.
Hurricane Katia Hurricane Katia continues to the northwest as a Category 1 hurricane with 90 mph winds. Latest satellite loops show that dry air has eaten into the southwest side of the storm. The computer models continue to agree that a low pressure system over the Eastern U.S. associated with the remnants of Tropical Storm Lee will turn Katia to the north. As the storm moves northwards past North Carolina, Katia will get caught up in west-to-east moving winds associated with the jet stream, and taken northeastwards out to sea. No land areas are in Katia’s cone of uncertainty, and Katia’s outer rainbands should remain just offshore from North Carolina, New England, and the Canadian Maritime provinces at the point of closest approach. Bermuda may see a few rain showers from Katia, but the storm will not cause hazardous weather there. The main impact of Katia will be a multi-day period of high surf leading to beach erosion and dangerous rip currents. The East Coast is lucky that Tropical Storm Lee came along, since Lee helped to create the steering pattern that will keep Katia from hitting the U.S.
Figure 2. GOES-13 image of Hurricane Katia and the remains of Tropical Storm Lee, taken at 11:45 am EDT Tuesday September 6, 2011. At the time, Katia was a Category 3 hurricane with 120 mph winds. Image credit: NOAA Visualization Laboratory.
