Dr. Jeff Masters' WunderBlog

Tropical Storm Agatha one of the top ten deadliest Eastern Pacific storms on record

By: JeffMasters, 1:56 PM GMT on May 31, 2010

The Eastern Pacific hurricane season of 2010 is off to a bad start. The mounting death toll from Central America's Tropical Storm Agatha has made that storm one of the top ten deadliest Eastern Pacific tropical cyclones on record. Agatha was a tropical storm for just 12 hours, making landfall Saturday on the Pacific coast of Guatemala as a 45 mph tropical storm. However, the storm brought huge amounts of moisture inland that continue to be wrung out as heavy rains by the high mountains of Guatemala and the surrounding nations of Central America. So far, flooding and landslides have killed at least 83 people in Guatemala, 13 in neighboring El Salvador, and one in Honduras. Guatemala is also suffering from the Pacaya volcano in Guatemala, which began erupting four days ago. At least three people have been killed by the volcano, located about 25 miles south of the capital, Guatemala City. The volcano has destroyed 800 homes with lava and brought moderate ash falls to the capital.


Figure 1. Flood damage in Zunil, Quetzaltenango, in Guatemala on May 29, 2010, after heavy rains from Tropical Storm Agatha. Image credit: Sergio Huertas, climaya.com

Agatha is the deadliest flooding disaster in Guatemala since Hurricane Stan of 2005, which killed 1,513. In a bizarre coincidence, that storm also featured a major volcanic eruption at the same time, when El Salvador's Santa Ana volcano blew its top during the height of Stan's rains in in that country on October 1. The eruption killed two and injured dozens, and worsened the mud flow damage from Stan's rains. The deadliest Eastern Pacific tropical cyclone on record for Guatemala was Hurricane Paul of 1982, which made landfall in Guatemala as a tropical depression. Flooding from Paul's rains killed 620 people in Guatemala.


Figure 2. Two-day rainfall totals for Central America as estimated by satellite, for the period 7pm EDT Friday May 28 - 7pm EDT Sunday May 30, 2010. Rainfall amounts of 350 mm (14 inches, orange colors) were indicated for portions of Guatemala. The Guatemala government reported that rainfall exceeded 36 inches in some regions. Image credit: Navy Research Lab, Monterey.

Oil spill update
Light onshore winds out of the south to southwest are expected to blow over the northern Gulf of Mexico all week, resulting increased threats of oil to the Alabama and Mississippi barrier islands, according to the latest trajectory forecasts from NOAA. These persistent southwesterly winds will likely bring oil very close to the Florida Panhandle by next weekend.

Oil spill resources
My post, What a hurricane would do the Deepwater Horizon oil spill
My post Wednesday with answers to some of the common questions I get about the spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
Gulf Oil Blog from the UGA Department of Marine Sciences
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami
The Deepwater Horizon Oil Spill and its Aftermath
What You Need to Know about Mercury in Fish and Shellfish

Jeff Masters

Hurricane

Updated: 6:54 PM GMT on May 14, 2014

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Tropical Storm Agatha, Pacaya volcano kill 15 in Guatemala; oil spill update

By: JeffMasters, 2:39 PM GMT on May 30, 2010

Tropical Storm Agatha, the first Eastern Pacific named storm of 2010, was short lived but deadly. Agatha was a tropical storm for just 12 hours, making landfall Saturday on the Pacific coast of Guatemala as a 45 mph tropical storm. However, the storm brought huge amounts of moisture inland that continue to be wrung out as heavy rains by the high mountains of Guatemala and the surrounding nations of Central America. So far, flooding and landslides have killed twelve people in Guatemala, and one person in neighboring El Salvador. According to the excellent Guatemala weather site, climaya.com, rainfall amounts of up to 152 mm (six inches) in 24 hours have occurred in some regions of Guatemala. The National Hurricane Center is warning that rainfall amounts of up to 30 inches may fall the next few days in some mountainous regions near where the storm has dissipated. Adding to the mayhem is fallout from the Pacaya volcano in Guatemala, which began erupting three days ago. At least three people have been killed by the volcano, located about 25 miles south of the capital, Guatemala City. The volcano has destroyed 800 homes with lava and brought moderate ash falls to the capital.


Figure 1. Visible satellite image of Tropical Storm Agatha at landfall. The storm was intensifying right up until landfall, and had an impressive "hot tower" of building cumulonimbus clouds near its center that brought heavy rains to Guatemala.


Figure 2. Flooding in Quetzaltenango, Zone 2, in Guatemala on May 29, 2010, after heavy rains from Tropical Storm Agatha. Image credit: Carlos Diaz, climaya.com

Oil spill update
Light onshore winds out of the south are expected to blow over the northern Gulf of Mexico today through Tuesday, resulting increased threats of oil to the Alabama and Mississippi barrier islands, according to the latest trajectory forecasts from NOAA. Winds are expected to shift to southwesterly on Wednesday and continue through Friday, increasing in force to 10 - 20 knots late in the week as a cold front approaches the Gulf. These persistent and strengthening southwesterly winds will likely bring oil very close to shore from Mississippi to the Florida Panhandle by next weekend.

Oil spill resources
My post, What a hurricane would do the Deepwater Horizon oil spill
My post Wednesday with answers to some of the common questions I get about the spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami

Join the "Hurricane Haven" with Dr. Jeff Masters: a new Internet radio show
Beginning next week, I'll be experimenting with a live 1-hour Internet radio show called "Hurricane Haven." The show will be aired at 4pm EDT on Tuesdays, with the first show June 1. Listeners will be able to call in and ask questions. Some topics I'll cover on the first show:

1) What's going on in the tropics right now
2) Preview of the coming hurricane season
3) How a hurricane might affect the oil spill
4) How the oil spill might affect a hurricane
5) New advancements in hurricane science presented at this month's AMS Conference on Hurricanes and Tropical Meteorology
6) Haiti's vulnerability to a hurricane this season

I hope you can tune in to the broadcast, which will be at http://www.wunderground.com/wxradio/wubroadcast.h tml. If not, the show will be recorded and stored as a podcast.

I'll probably be back Monday with a quick update. Have a great holiday weekend!

Jeff Masters

Hurricane

Updated: 11:05 PM GMT on January 03, 2012

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Loop Current Eddy cuts off; oil danger to Keys now greatly reduced

By: JeffMasters, 2:24 PM GMT on May 28, 2010

A major ocean current re-alignment is underway the Gulf of Mexico right now, and the new configuration that is developing greatly reduces the threat of oil entering the Loop Current and affecting the Florida Keys and U.S. East Coast. As I explain in my Loop Current Primer, the Loop Current is an ocean current that transports warm Caribbean water through the Yucatan Channel between Cuba and Mexico. The current flows northward into the Gulf of Mexico, then loops southeastward just south of the Florida Keys (where it is called the Florida Current), and past the western Bahamas. Here, the waters of the Loop Current flow northward along the U.S. coast and become the Gulf Stream. With current speeds of about 0.8 m/s, the Loop Current is one of the fastest currents in the Atlantic Ocean. Every 6 - 11 months, the top bulge of the Loop Current cuts off, forming a 250-mile diameter circular eddy in the middle of the Gulf of Mexico. This clockwise-spinning eddy is filled with warm water from the Loop Current, and is called a Loop Current Eddy. The main body of the Loop Current then takes a fairly direct eastward path from the Yucatan Channel to the Florida Keys.

Over the past two days, surface currents in the Gulf of Mexico have aligned to form a Loop Current Eddy, as seen in the analysis of surface currents done by the U.S. Navy (Figure 1, and see also a 30-day animation of the eddy forming.) It remains to be seen if the deep water currents have followed suit, and a stable Loop Current Eddy cannot exist until the deep water currents also cut off into a clockwise-rotating ring of water at depth. A NOAA Hurricane Hunter aircraft is out over the Gulf of Mexico today dropping expendable buoys and current probes to determine if a stable Loop Current Eddy has formed. Roffer's Ocean Fishing Forecast Service has a nice discussion on the Loop Current Eddy formation.


Figure 1. Comparison of surface currents in the Gulf of Mexico on May 19 (top) and May 27 (bottom) as simulated by the HYCOM model. On May 19, the Loop Current made a large northward loop into the Gulf, and was able to transport oil from the near the spill location southwards through the Keys. By May 27, this loop had cut off, and new oil moving southwards from the spill will now be trapped in the clockwise rotating Loop Current Eddy that is cut off from the Loop Current. Note on the west side of the Gulf of Mexico, off the coast of Texas, there is an old Loop Current Eddy that cut off from the Loop Current in July 2009. This eddy cut off in the same location as this week's eddy, and has drifted west-southwestward at 3 - 5 km per day over the past ten months. Image credit: U.S. Navy.

If the eddy does remain in place, it will greatly reduce the chances of oil making it to Cuba, the Florida Keys, and beyond. Any oil moving southwards from the spill location will now become entrained in the eddy, and will move in a 250 mile-wide clockwise circle in the east-central Gulf of Mexico. A small portion the oil will get shed away from the eddy's periphery and make it into the Loop Current and waters surrounding the eddy, but the concentrations of oil doing so will be small. Keep in mind, though, that during the first 1 - 2 months that a Loop Current Eddy forms, it is common for the eddy to exchange substantial amounts of water with the Loop Current, and in some cases get re-absorbed into the Loop Current. A 1-year animation of the Loop Current shows that the last Loop Current Eddy, which cut off in mid-July 2009, experienced a 2-week period in early August when it re-attached to the Loop Current. A significant portion of any oil entering the eddy during a period of re-attachment will be able to enter the Loop Current and flow past the Keys.

One bad result of the eddy breaking off is that now we have an extra source of heat energy for passing hurricanes during the upcoming hurricane season. Loop Current eddies have high-temperature water that extends to great depth, and hurricanes passing over such eddies often undergo rapid intensification. Hurricanes Katrina and Rita of 2005 both underwent rapid intensification as they passed over warm Loop Current eddies in 2005. The formation of a Loop Current Eddy during hurricane season means that a much greater portion of the Gulf of Mexico has deep, warm water capable of fueling rapid intensification of hurricanes.

Oil spill update
Light offshore northwesterly winds are expected to blow over the northern Gulf of Mexico today through Saturday, resulting decreased threats of oil to the Louisiana shore, according to the latest trajectory forecasts from NOAA. These offshore winds may be able to transport oil southwards into the Loop Current Eddy that just formed; a streamer of oil moving southeastward into the Loop Current Eddy is visible in yesterday's NASA MODIS imagery (Figure 2). Winds will shift to onshore out of the south on Saturday night, then shift to southwesterly by Tuesday. The long-range forecast from the GFS model indicates continued southwesterly winds all of next week. If this forecast verifies, we will see our greatest chances yet of significant amounts of oil reaching the beaches of Mississippi, Alabama, and the Florida Panhandle.


Figure 2. Visible satellite image of the Gulf of Mexico taken at 2:55pm EDT Thursday May 27, 2010, by the MODIS instrument on NASA's Aqua satellite. Thin streaks of oil can be seen moving southeast and then southwest around the eastern side of the new Loop Current Eddy. Image credit: NASA.

Oil spill resources
My post, What a hurricane would do the Deepwater Horizon oil spill
My post Wednesday with answers to some of the common questions I get about the spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami

Central American disturbance
The Atlantic is currently quiet, with none of our reliable global forecast models predicting tropical cyclone development over the next 6 days. There is an area of disturbed weather (90E) just off the Pacific coast of Mexico that will be a major concern for southern Mexico and much of Central America over the next 3 - 4 days. The disturbance will bring heavy rains to Central America during the weekend, potentially bringing serious flooding rains to portions of Mexico, Guatemala, El Salvador, Honduras, and Nicaragua. NHC is giving the disturbance a high (>60% chance) of the disturbance developing into a tropical depression by Sunday. Wunderbloggers Weather456 and StormW have more on the tropics.


Figure 3. Satellite image of the Central American disturbance 90E this morning.

Join the "Hurricane Haven" with Dr. Jeff Masters: a new Internet radio show
Beginning next week, I'll be experimenting with a live 1-hour Internet radio show called "Hurricane Haven." The show will be aired at 4pm EDT on Tuesdays, with the first show June 1. Listeners will be able to call in and ask questions. Some topics I'll cover on the first show:

1) What's going on in the tropics right now
2) Preview of the coming hurricane season
3) How a hurricane might affect the oil spill
4) How the oil spill might affect a hurricane
5) New advancements in hurricane science presented at this month's AMS Conference on Hurricanes and Tropical Meteorology
6) Haiti's vulnerability to a hurricane this season

I hope you can tune in to the broadcast, which will be at http://www.wunderground.com/wxradio/wubroadcast.h tml. If not, the show will be recorded and stored as a podcast.

I'll be back with at least one update over the coming 3-day Memorial Day weekend. Have a great holiday!

Jeff Masters

Air and Water Pollution

Updated: 5:18 PM GMT on August 16, 2011

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NOAA's forecast: a very active, possibly hyperactive Atlantic hurricane season

By: JeffMasters, 3:29 PM GMT on May 27, 2010

The National Oceanic and Atmospheric Administration (NOAA) issued its 2010 Atlantic hurricane season forecast today. NOAA forecasts a very active and possibly hyperactive season. They give an 85% chance of an above-normal season, a 10% chance of a near-normal season, and just a 5% chance of a below-normal season. NOAA predicts a 70% chance that there will be 14 - 23 named storms, 8 - 14 hurricanes, and 3 - 7 major hurricanes, with an Accumulated Cyclone Energy (ACE) in the 155% - 270% of normal range. If we take the midpoint of these numbers, NOAA is calling for 18.5 named storms, 11 hurricanes, 5 major hurricanes, and an ACE index 210% of normal. A season with an ACE index over 175% is considered "hyperactive." An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The forecasters note that in regards to the oil spill in the Gulf of Mexico,

"Historically, all above normal seasons have produced at least one named storm in the Gulf of Mexico, and 95% of those seasons have at least two named storms in the Gulf. Most of this activity (80%) occurs during August-October. However, 50% of above normal seasons have had at least one named storm in the region during June-July."

The forecasters cited the following main factors that will influence the coming season:

1) Expected above-average SSTs in the hurricane Main Development Region (MDR), from the Caribbean to the coast of Africa. SSTs in the MDR are currently at record levels, and the forecasters note that several climate models are predicting record or near-record SSTs during the peak portion of hurricane season (August - October.) "Two other instances of very warm SSTs have been observed in the MDR during February-April (1958 and 1969). In both years, the SST anomaly subsequently decreased by roughly 50% during the summer months. For 2010, although the record SST departures may well decrease somewhat, we still expect a continuation of above average SSTs throughout the Atlantic hurricane season. "

2) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO). "During 1995-2009, some key aspects of the tropical multi-decadal signal within the MDR have included warmer than average SSTs, reduced vertical wind shear and weaker easterly trade winds, below-average sea-level pressure, and a configuration of the African easterly jet that is more conducive to hurricane development from tropical waves moving off the African coast. Many of these atmospheric features typically become evident during late April and May, as the atmosphere across the tropical Atlantic and Africa begins to transition into its summertime monsoon state."

3) There will either be La Niña or neutral conditions in the Equatorial Eastern Pacific. El Niño is gone, and it's demise will likely act to decrease wind shear over the tropical Atlantic, allowing more hurricanes to form. "La Niña contributes to reduced vertical wind shear over the western tropical Atlantic which, when combined with conditions associated with the ongoing high activity era and warm Atlantic SSTs, increases the probability of an exceptionally active Atlantic hurricane season (Bell and Chelliah 2006). NOAA's high-resolution CFS model indicates the development of La Niña-like circulation and precipitation anomalies during July."

How accurate are the NOAA seasonal hurricane forecasts?
A talk presented by NHC's Eric Blake at the 2010 29th Annual AMS Conference on Hurricanes and Tropical Meteorology studied the accuracy of NOAA's late May seasonal Atlantic hurricane forecasts, using the mid-point of the range given for the number of named storms, hurricanes, intense hurricanes, and ACE index. Over the past twelve years, a forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Using another way to measure skill, the Mean Squared Error, May NOAA forecasts for named storms, hurricanes, and intense hurricanes had a skill of between 5% and 21% over a climatology forecast (Figure 2). Not surprisingly, NOAA's August forecasts were much better than the May forecasts, and did significantly better than a climatology forecast.


Figure 1. Mean absolute error for the May and August NOAA seasonal hurricane forecasts (1999 - 2009 for May, 1998 - 2009 for August), and for forecasts made using climatology from the past five years. A forecast made using climatology was in error, on average, by 3.6 named storms, 2.5 hurricanes, and 1.7 intense hurricanes. NOAA's May forecast was not significantly better than climatology for these quantities, with average errors of 3.5 named storms, 2.3 hurricanes, and 1.4 intense hurricanes. Only NOAA's May ACE forecast was significantly better than climatology, averaging 58 ACE units off, compared to the 74 for climatology. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.

How do NOAA's seasonal hurricane forecasts compare to CSU and TSR?
Two other major seasonal hurricane forecasts will be released next week. On June 2, Phil Klotzbach and Bill Gray of Colorado State University (CSU) issue their forecast, and the British firm Tropical Storm Risk (TSR) will issue their outlook on June 4. A three-way comparison of the forecast accuracy of the three groups' forecast (Figure 2) reveals that all three organizations enjoy some success at making accurate seasonal forecasts, with NOAA and CSU making the best late May/early June forecasts overall. While the skill of these forecasts is low, they are useful for businesses such as the insurance industry.


Figure 2. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August). using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.

Central American disturbance
The Atlantic is currently quiet, with the non-tropical storm (90L) that we were watching now no longer a concern. There is an area of disturbed weather (90E) just off the Pacific coast of Mexico that will be a major concern for southern Mexico and much of Central America over the next 3 - 4 days. The disturbance will bring heavy rains to Central America during the remainder of the week, potentially bringing serious flooding rains to portions of Mexico, Guatemala, El Salvador, Honduras, and Nicaragua. NHC is giving the disturbance a high (>60% chance) of the disturbance developing into a tropical depression by Saturday. There is the potential for disturbed weather accompanying the disturbance--or the disturbance itself--to push into the Western Caribbean early next week and pose a threat to develop into a tropical depression. While there is high wind shear over the northern Caribbean, shear may be low enough to allow development should the disturbance stay in the southern reaches of the Caribbean. None of the models are currently calling for this to happen, and I think the threat is low. Any storm that develops in the Caribbean in the coming week would get steered to the northeast and will not pose a threat to the Gulf of Mexico. Wunderbloggers Weather456 and StormW have more on the tropics.


Figure 3. Visible satellite image of the Central American disturbance 90E this morning.

Oil threat for the coast of Louisiana to decrease this weekend
Light winds from the north or west are expected to prevail across the northern Gulf of Mexico through Friday, resulting in a lessened threat of oiling to the Louisiana shoreline, according to the latest trajectory forecasts from NOAA. However, the latest runs of the GFS model indicate a return to onshore winds out of the southwest for most of next week, which will likely bring oil back towards shore. At greatest risk will be the coast of Louisiana, and there will be heightened risk to Mississippi, Alabama, and the Florida Panhandle. I'll a have a more in-depth discussion of the oil spill forecast in Friday's blog.

Oil spill resources
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami

Join the Hurricane Haven with Dr. Jeff Masters: a new Internet radio show
Beginning next week, I'll be experimenting with a live 1-hour Internet radio show called "Hurricane Haven." The show will be aired at 4pm EDT on Tuesdays, with the first show June 1. Listeners will be able to call in and ask questions. Some topics I'll cover on the first show:

1) What's going on in the tropics right now
2) Preview of the coming hurricane season
3) How a hurricane might affect the oil spill
4) How the oil spill might affect a hurricane
5) New advancements in hurricane science presented at this month's AMS Conference on Hurricanes and Tropical Meteorology
6) Haiti's vulnerability to a hurricane this season

I hope you can tune in to the broadcast, which will be at http://www.wunderground.com/wxradio/wubroadcast.h tml. If not, the show will be recorded and stored as a podcast.

Jeff Masters

Hurricane

Updated: 11:05 PM GMT on January 03, 2012

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What would a hurricane do to the Deepwater Horizon oil spill?

By: JeffMasters, 1:57 PM GMT on May 26, 2010

Hurricane season is upon us next week, and the Deepwater Horizon blowout is still spewing a geyser of oil into the Gulf of Mexico. With this year's hurricane season likely to be a severe one, with much above average numbers of hurricanes and intense hurricanes, we have the unwholesome prospect of a hurricane churning through the largest accidental oil spill in history. A hurricane has never passed over a sizable oil spill before, so there are a lot of unknowns about what might happen. The closest call came in 1979, after the greatest accidental oil spill in history, the massive Ixtoc I blowout. That disaster dumped 3 million barrels (126 million gallons) of oil into the Southern Gulf of Mexico between June 1979 and March 1980. Category 1 Hurricane Henri passed just north of the main portion of the oil spill on September 16 and 17, generating 15 foot seas and southwest winds of 15 - 25 knots over the spill region on the 16th. Interestingly, the NOAA/AOML report on the spill found that the winds did not blow long enough or strongly enough to control the direction of oil flow, as evidenced by the fact that the wind direction was often 180° to the direction of plume flow. The main impact of the wind was to dilute the oil and weather it, converting it to a thick "mousse".

Oil and beaches
During the Ixtoc spill, prevailing currents circulating clockwise from the blowout carried a 60-mile by 70-mile patch of sheen containing a 300 foot by 500 foot patch of heavy crude 900 miles to the South Texas coast. On August 6, 1979, tarballs from the spill impacted a 17 mile stretch of Texas beach. Mousse patches impacted the shoreline north of Port Mansfield Channel on August 15 and again on August 18. On August 24, mousse impacted shoreline south of Aransas Pass. By August 26, most of North Padre Island was covered with moderate amounts of oil. By September 1, all of the south Texas coast had been impacted by oil. However, Hurricane Henri formed in the Gulf of Mexico's Bay of Campeche on September 17 - 18. At the same time, a strong non-tropical low pressure system formed along the Texas coast, bringing gale-force winds and rainfall amounts in excess of ten inches to the coast. The combination of swells from Hurricane Henri and wind-driven waves from the non-tropical low pressure system scoured the oiled beaches of over 90% of their oil (Gundlach et al., 1981). The oil washed over the barrier islands into the estuaries behind them, and much of it sank to the bottom of the ocean. According to NOAA, impacts to the estuaries were minor. However, Payne and McNabb (1984) noted that selected regions of the coast, most of the beached oil was heavily resistant to transport during storms. Oil/sediment mats were ultimately covered by clean sand, but the oil/sediment mats were re-exposed and washed into the lagoon behind the barrier islands one year later when Category 3 Hurricane Allen battered the coast. No transport of the oil/sediment mats from the lagoon bottom was observed in the 3-year period following Hurricane Allen.

So, the Ixtoc blowout experience shows us that if a sandy beach is already fouled by oil, a hurricane can help clean up the mess. However, the situation is different along shores with marshlands, where the many shoreline plants offer crevices and tangled roots for the oil to accumulate in. A hurricane will help scour some of the oil out of marshlands, but the majority of it will probably remain stuck. This is also true of rocky beaches. Rocky shores fouled by the great Exxon Valdez oil spill in Alaska in 1989 have been pounded by many hurricane-strength storms over the years, but these storms were not able to clean the beaches of oil like Hurricane Henri did for Texas' beaches in 1979.

Transport of oil by hurricanes
Shores that are already fouled by oil will probably benefit from a hurricane, but the oil cleaned off of those shores then becomes someone else's problem. The strong winds and powerful ocean currents that a hurricane's winds drive will bring oil to large stretches of coast that otherwise would not have gotten oil. This is my chief concern regarding a hurricane moving through the Deepwater Horizon oil spill. Consider the case of the Exxon Valdez disaster in 1989. The ill-fated tanker split open in Prince William Sound on March 24, and oil spill response crews were initially able to contain the spill behind booms and make good progress removing it. However, two days later, a powerful Gulf of Alaska storm with 70 mph winds roared through, overwhelming the containment booms and distributing the oil along a 90-mile stretch of coast. The oil went on to foul over 400 miles of Alaska coast, a far larger disaster than would have occurred than if the storm had not passed by. Similarly, a hurricane moving through the Gulf of Mexico spill will very likely make the disaster much worse, spreading out the oil over a larger region, and bringing the oil to shores that otherwise might not have seen oil. It is true that the oil will be diluted some by being spread out over a larger area, so some shores will not see a substantial oiling. But overall, a hurricane passing through the oil spill is likely to result in much higher damage to the coast.

I expect that during the peak portion of hurricane season (August - October), the clockwise-rotating eddy that is attempting to cut off from the Loop Current this week will be fully separated from the Loop Current. The separation of this eddy will substantially reduce the possibility that significant amounts of oil will reach the Florida Keys and Southeast U.S. coast, since the Loop Current will be much farther south, flowing more due east towards the Keys from the Yucatan Channel. Oil moving southwards from the spill location due to a hurricane's winds will tend to get trapped in the 250-mile wide eddy, potentially covering most of the surface of the eddy with oil. Thus we might have a 250-mile wide spinning oil slick in the middle of the Gulf of Mexico for days or weeks after a hurricane. This could potentially have a significant warming effect on the Gulf waters, since the oil is dark and will absorb sunlight, and the oil will prevent evaporation from cooling the waters underneath it. Since Loop Current eddies contain a large amount of very warm water that extend to great depth, they often act as high-octane fuel for hurricanes that pass over. The rapid intensification of Hurricanes Katrina and Rita were both aided by the passage of those storms over Loop Current eddies. Thus the warming of the Loop Current Eddy by oil pulled into it by a passing hurricane or tropical storm could lead to explosive intensification of the next hurricane that passes over the eddy.

The Loop Current Eddy will move slowly westwards toward Texas at about 4 miles per day after it fully cuts off. When it reaches the shallow waters near the Texas coast in early 2011, the eddy will turn northwards and gradually dissipate, By then, I expect that the vast majority of the oil in the eddy will have dispersed, sunk, or evaporated.

Storm surge and oil
One of the more unnerving prospects to consider if a hurricane hits the oil spill is what the hurricane's storm surge might do with the oil/dispersant mixture. The foul mix would ride inland on top of the surge, potentially fouling residential areas and hundreds of square miles of sensitive ecosystems with the toxic stew. The impacts of the oil and dispersant on vegetation may be too low to cause significant damage, since the hurricane would dilute the mixture with a large amount of sea water, and wash much of the toxic brew off the vegetation with heavy rain. We do have some limited experience with oil spills during Hurricane Katrina's storm surge to shed light on the subject. Katrina's storm surge caused over 8 million gallons of oil to spill into the storm surge waters. The largest spill occurred when the storm surge hit the Murphy Oil refinery in St. Bernard Parish, Louisiana. According to Santella et al. (2010), The refinery was inundated with 12 feet of water, and a partially filled 250,000-barrel above ground storage tank was dislodged and ruptured, releasing 25,100 barrels (1.05 million gallons) of mixed crude oil. Dikes surrounding the oil tanks at the refinery were flooded and breached and oil from the spill covered a residential area of approximately one square mile affecting approximately 1,800 homes. Front-end loaders were needed to remove the oily sediments from the area. A class action lawsuit resulted from the spill, ending in a $330 million settlement with a buy-out of properties closest to the spill and graded compensation in a larger zone. Katrina also caused a 139,000-gallon crude oil leak from a 20-inch pipeline at Shell Nairn Pipeline Company in Port Sulphur, Louisiana. Approximately 10,500 gallons of the spill reached the shoreline and coastal marshes, and only 10,700 gallons were recovered. This release resulted in a $5.5 million class action settlement to nearby property owners (http://www.nairnclaims.com). I haven't been able to find any information on how the marshlands fared after getting oiled by this spill.

Katrina's storm surge also destroyed an oil tank at Chevron's Empire facility, releasing oil into a retention pond in a region surrounded by marshland. Three and half weeks later, Hurricane Rita's storm surge hit the oily mess in the retention pond, washing 4,000 - 8,000 gallons of oil into nearby marshlands, which were heavily or moderately oiled. According to the EPA and Merten et al. (2008), the oiled marshlands were set on fire six weeks after the spill, resulting in 80-90% removal of the oil and contaminated vegetation. The marshland recovered fairly quickly, as seen in aerial photos taken five months after the burn (Figure 1)--though oil still remained in the roots, affecting burrowing crabs and the wildlife that feed on them. So, oiled marshes can recover somewhat from a storm-surge driven oiling, but it is uncertain if burning could be successfully used to restore a 100+ square mile region of marshland oiled by the storm surge from a major hurricane. Another big unknown is how toxic BP's dispersants might be to the vegetation.


Figure 1. Upper left: oiled marshlands as seen on October 10, 2005, near Chevron's Empire facility, after the storm surges of Katrina and Rita. Right: The marshlands on March 16, 2006, five months after the controlled burn. The marshlands had largely recovered. Bottom: the controlled burn in progress (October 12, 2005.) Image credit: Merten, A.A., Henry, C., and J. Michel, 2008, Decision-making process to use in-situ burning to restore an oiled intermediate marsh following hurricanes Katrina and Rita, 2008 International Oil Spill Conference.

Wind and oil
The winds from a hurricane hurl ocean sea spray miles inland, often causing major defoliation and tree damage far beyond where the storm surge penetrates. For example, Category 2 Hurricane Bob of 1991 blew sea spray inland 4 miles (7 km) inland over Cape Cod. The salt deposited defoliated nearly all the deciduous trees along the coast. Kerr, 2000 document the case of Category 2 Typhoon Gay of November 23, 1992, which hit the 15-km wide island of Guam with 95 - 100 mph winds. Interaction with another typhoon disrupted Gay's thunderstorm activity, resulting in a nearly rainless typhoon for Guam. As a result, heavy amounts of salt coated the entire island, resulting in nearly complete defoliation. The salt didn't actually kill many plants, and the island re-greened within a year. The Category 3 New England Hurricane of 1938 was able to cause salt damage to trees as far as 45 miles inland, due to wind-blown sea spray. Thus we can anticipate that a hurricane passing over the oil spill will be able to hurl oil and toxic dispersants many miles inland during landfall. In regions where little rain falls, the concentrations of the oil and dispersants may be a problem. Again, we have no experience with this sort of situation, so the potential risks are unknown.

Rain and oil
Hurricanes evaporate huge amounts of water from the ocean and convert it to rain. In general, we do not need to worry about oil dissolving into the rain, since the oil and water don't mix. Furthermore, about 50-70% of the oil that is going to evaporate from the spill does so in the first 12 hours that the oil reaches the surface, so the volatile oil compounds that could potentially get dissolved into rain water won't be around. Hurricanes are known to carry sea salt and microscopic marine plankton hundreds of miles inland, since the strong updrafts of the storm can put these substances high in the troposphere where they can be carried far inland as the hurricane makes landfall. The Eastern Pacific's Hurricane Nora of 1997, whose remnants passed over Southern California, brought traces of sea salt and marine microorganisms to clouds over the central U.S. similarly, we can expect any landfalling hurricanes that pass over the oil spill to pick up traces of Gulf of Mexico crude and transport it hundreds of miles inland. However, I doubt that these traces would be detectable in rainwater except by laboratory analysis, and would not cause any harm to plants or animals.

Lightning and oil
Could a lightning strike from a hurricane ignite oil from the spill, and the hurricane's winds hurl the flaming oil inland, creating a fiery maelstrom of water, wind, and flame? This would make a great scene in a typical bad Hollywood disaster movie, but it's not going to happen with the universe's current laws of physics. Lightning could set an oil slick on fire, in regions where the oil is most dense and very fresh. About 50-70% of the evaporation of oil's most flammable volatile compounds occurs in the first 12 hours after release, so fresh oil is the most likely to ignite. However, the winds of a hurricane are so fierce that any surface oil slick of flaming oil would quickly be disrupted and doused by wave action and sea spray. Heavy rain would further dampen any lightning-caused oil slick fires.

Bringing oil at depth to the surface
Hurricanes act like huge blenders that plow through the ocean, thoroughly mixing surface waters to depths as great as 200 meters (650 feet), and pulling waters from depth to the surface. Thus if sub-surface plumes of oil are located within 200 meters of the surface, a hurricane could potentially bring them to the surface. However, the huge sub-surface plumes of oil found by the research vessel Pelican were at depths of 2300 - 4200 feet, and a hurricane will not affect the ocean circulation at those depths.

Comparisons of the Deepwater Horizon blowout with Exxon Valdez
One footnote to consider when comparing the Deepwater Horizon blowout to the disastrous March 24, 1989 Exxon Valdez spill: the amount of oil spilled in that disaster is usually quoted as 11 million gallons (260,000 barrels.) However, this is the number given by Exxon Mobil, and independent assessments by the State of Alaska came up with a much higher figure--24 to 36 million gallons, with state investigators stressing that the lower number was very unlikely. I'd be inclined to believe Exxon grossly understated the actual severity of the spill, much like BP is attempting to do with the Deepwater Horizon blowout. Steven Wereley, an associate professor at Purdue University, used a computer analysis (particle image velocimetry) to arrive at a rate of 95,000 barrels (4 million gallons) per day since the April 20 blowout, nearly 20 times greater than the 5,000 barrel a day estimate BP and government scientists have been citing. If he is correct, and the State of Alaska's figures on the Exxon Valdez disaster are correct, the Deepwater Horizon blowout so far has spilled five times the oil Exxon Valdez did.

References
Gundlach, E.R., Finkelstein, K.J., and J.L. Sadd, "Impact and Persistence of Ixtoc I Oil on the South Texas Coast", Proceedings: 1981 Oil Spill Conference (Prevention, Behavior, Control, Cleanup) March 2-5, 1981, Atlanta, GA. p 477-485.

Kerr, A.M., 2000, "Defoliation of an island (Guam, Mariana
Archipelago, Western Pacific Ocean) following a saltspray-laden
dry typhoon," Journal of Tropical Ecology 16:895901.

Merten, A.A., Henry, C., and J. Michel, 2008, Decision-making process to use in-situ burning to restore an oiled intermediate marsh following hurricanes Katrina and Rita, 2008 International Oil Spill Conference.

Payne, J.R. and D. McNabb, Jr., "Weathering of Petroleum in the Marine Environment", Marine Technology Society Journal 18, 3, Third Quarter 1984.

Santella, N., Steinberg, L.J., and H. Sengul, 2010,Petroleum and Hazardous Material Releases from Industrial Facilities Associated with Hurricane Katrina, Risk Analyis, Volume 30, Issue 4, Pages 635-649, Published Online: 16 Mar 2010

90L
I've been focused more on the oil spill, and will have just a limited discussion of (90L) off the South Carolina coast. The storm has changed little over the past 24 hours, and doesn't have time to develop into a subtropical storm, before an approaching trough of low pressure pulls the system out to sea Thursday and Friday. The National Hurricane Center (NHC) is giving 90L a less than 10% chance of developing into a depression or tropical/subtropical storm, and anticipates not writing any more special advisories on 90L. There presently isn't much to be concerned with about this storm, though Bermuda may get more heavy rain and high seas from the storm late this week as it moves out to sea. Wunderbloggers Weather456 and StormW have more on 90L.

Central American disturbance
An area of disturbed weather has developed just off the Pacific coast of Mexico. The disturbance will bring heavy rains to Central America during the remainder of the week, potentially bringing serious flooding rains to portions of Mexico, Guatemala, El Salvador, Honduras, and Nicaragua. There is the potential for disturbed weather accompanying the disturbance to push into the Western Caribbean early next week and pose a threat to develop into a tropical depression. While there is high wind shear over the northern Caribbean, shear should be low enough to allow development should the disturbance stay in the southern reaches of the Caribbean. Any storm that develops in the Caribbean in the coming week would get steered to the northeast and will not pose a threat to the Gulf of Mexico.

Jeff Masters

Air and Water Pollution Hurricane

Updated: 4:58 PM GMT on May 26, 2010

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Little change to 90L

By: JeffMasters, 1:33 PM GMT on May 25, 2010

The extratropical low pressure system (90L) approaching North Carolina has weakened some over the past 24 hours, and has a much reduced chance of developing into a subtropical storm. The National Hurricane Center (NHC) is giving 90L a less than 20% chance of developing into a depression or tropical/subtropical storm, and anticipates not writing any more special advisories on it. Last night's ASCAT pass saw a large area of 35 mph winds to the north and east of the center, and buoy 41048 to northeast of 90L's center was seeing sustained E winds of 31 mph, gusting to 36 mph this morning. Bermuda radar showing an area of moderate to heavy rain has now moved north of the island, and seas are running 10 - 15 feet in the outer waters of Bermuda today.


Figure 1. Visible satellite image of 90L and the Central American disturbance this morning.

Strong upper-levels winds out of the west are creating about 20 knots of wind shear over 90L, and the shear has been gradually decreasing over the past day. Visible satellite loops show that 90L has a well-defined surface circulation. The main thunderstorm activity is in a large curved band to the north and northeast of the center. This band is several hundred miles removed from the center, which is characteristic of subtropical storms. Sea surface temperatures are near 24°C today and will remain in the 23 - 24°C range the next two days. These relatively cool SSTs have hampered formation of much heavy thunderstorm activity, as has the presence of a large area of dry air to the west, as seen on water vapor satellite loops .

The system will move slowly towards the Southeast U.S. coast today, making its closest approach to the coast on Wednesday, when most of the models indicate the center will be 300 - 500 miles southeast of Cape Hatteras, North Carolina. All of the major models currently predict that 90L will not make landfall, but will move slowly eastward out to sea on Thursday, when a trough of low pressure moving across the Eastern U.S. picks up the storm. There presently isn't much to be concerned with about this storm, though Bermuda may get more heavy rain and high seas from the storm late this week as it moves out to sea. Wunderbloggers Weather456 and StormW have more on 90L.

Central American disturbance
An area of disturbed weather has developed just off the Pacific coast of Guatemala. The disturbance will move inland over Central America during the last half of the week, potentially bringing flooding rains to portions of Guatemala, El Salvador, Honduras, and Nicaragua. There is the potential for the disturbance to push into the Western Caribbean late this week and pose a threat to develop into a tropical depression. While there is high wind shear over the northern Caribbean, shear should be low enough to allow development should the disturbance stay in the southern reaches of the Caribbean. Any storm that develops in the Caribbean in the coming week would get steered to the northeast and will not pose a threat to the Gulf of Mexico.

Tornadoes rip through the Plains
The Storm Prediction Center logged 17 reports of tornadoes yesterday, with twisters reported in South Dakota, North Dakota, Nebraska, Oklahoma, and Texas. In addition, there were 158 hail reports and 126 reports of damaging winds. Fortunately, there were no deaths or injuries reported, and it was a good day for the Vortex2 tornado field research project. Former wunderblogger Mike Theiss caught up with a very picturesque tornado near Faith, South Dakota, and has posted some spectacular video of the tornado.


Figure 2. Large tornado near Faith, South Dakota on May 24, 2010 just misses hitting a church. Image credit: Mike Theiss, ultimatechase.com. Check out his spectacular video of the tornado.

I'll be back later today to discuss how a hurricane might affect the oil in the Gulf of Mexico.

Jeff Masters

Hurricane

Updated: 3:20 PM GMT on May 25, 2010

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90L heads for North Carolina, drenches Bermuda; oil spill changing little

By: JeffMasters, 2:54 PM GMT on May 24, 2010

An extratropical low pressure system (90L) between the Bahamas and Bermuda is moving north-northwest towards North Carolina and is close to tropical storm strength. Last night's ASCAT pass saw a large area of 35 mph winds to the north and east of the center, and buoy 41048 to northeast of 90L's center was seeing sustained ENE winds of 36 mph, gusting to 43 mph this morning. Bermuda is seeing some heavy weather from this storm, with winds blowing at 35 mph on the west end of the island, and the Bermuda radar showing an area of moderate to heavy rain moving over the island. Seas are running 5 - 10 feet in the outer waters of Bermuda today, and are expected to increase to 10 - 14 feet tonight before diminishing on Tuesday.


Figure 1. Visible satellite image of 90L this morning.

Strong upper-levels winds out of the west are creating about 25 knots of wind shear over 90L, but the shear has been gradually decreasing over the past day. Visible satellite loops show that 90L does not have a well-defined surface circulation. The main thunderstorm activity is in a large curved band to the north and northeast of the center. This band is several hundred miles removed from the center, which is characteristic of subtropical storms. I expect that 90L will continue to grow more subtropical in nature today through Wednesday as the shear continues to fall. Sea surface temperatures are near 25°C today and will fall to 23 - 24°C on Tuesday. This is warm enough to support a subtropical storm, but probably not a tropical storm. On Wednesday, 90L will be nearing the warm waters of the Gulf Stream, and SSTs will warm again, to the 24 - 25°C range. This is still pretty cool for a tropical storm, and I expect 90L will never become fully tropical. To understand the difference between a tropical and subtropical storm and why we care, see my subtropical storm tutorial.

The SHIPS model predicts that shear will fall to the medium 10 - 20 knot range by Tuesday. A large amount of dry air to 90L's southwest associated with the upper-level trough of low pressure on top of the storm, as seen on water vapor satellite loops , will hamper transition of 90L to a subtropical or tropical storm. The system will move slowly towards the Southeast U.S. coast over the next two days, making its closest approach to the coast on Wednesday, when most of the models indicate the center will be 200 - 400 miles southeast of Cape Hatteras, North Carolina. All of the major models currently predict that 90L will not make landfall, but will move slowly eastward out to sea on Thursday, when a trough of low pressure moving across the Eastern U.S. picks up the storm. There presently isn't much to be concerned with about this storm, as it appears that it will remain offshore and will become, at worst, a 40 - 50 mph subtropical storm. The National Hurricane Center (NHC) is giving 90L a medium (30% chance) of developing into a depression or tropical/subtropical storm. Wunderbloggers Weather456 and StormW have more on 90L.

Western Caribbean disturbance
A small region of disturbed weather has developed in the Western Caribbean, off the east coast of Nicaragua. Moisture is expected to increase across in this area in the coming days, and by Saturday, the GFS and NOGAPS models predict that shear will drop low enough to permit the possible development of a strong tropical disturbance or tropical depression. This storm would then move northeastward over eastern Cuba early next week. The other models keep the shear high in the Caribbean all week, and do not show anything developing. Thus, the Western Caribbean bears watching later this week, but the conditions appear marginal for development.

Moderate risk of severe weather today in northern Plains
The Storm Prediction Center has placed western Nebraska and portions of South and North Dakota under their "Moderate" risk for severe weather today. They warn that "a couple of strong and possibly long-track tornadoes appear possible given the forecast scenario." Keep an eye on the activity today with our Severe Weather Page.

Major oil threat continues for the coast of Louisiana
Light winds are expected to prevail across the northern Gulf of Mexico all week, resulting in continued oiling threats to the Louisiana shoreline from the mouth of the Mississippi River westward 150 miles, according to the latest trajectory forecasts from NOAA. There is no longer a flow of oil moving southwards towards the Loop Current, and the oil that did move southwards last week was mostly entrained into a counter-clockwise rotating eddy attached to the northern boundary of the Loop Current. Synthetic Aperture Radar (SAR) imagery over the weekend showed that most of this oil has dispersed, and very little of this oil is now visible from space (Figure 2.) Imagery from NASA's MODIS instrument and from NOAA aircraft did not show any oil in the Loop Current headed towards the Florida Keys over the weekend, so that is good news. NOAA comments that there may be some "scattered tar balls" in the Loop Current headed towards the Florida Keys. I expect these scattered tar balls have completed the full loop of the Loop Current and are now headed east towards the Keys, and will pass the Dry Tortugas and Key West sometime Wednesday - Saturday. My guess is that the oil and its accompanying plume of toxic dispersants will be too thin and scattered to cause significant problems in the Keys.


Figure 2. Synthetic Aperture Radar (SAR) image of the oil spill taken at 11:41am EDT Saturday May 22, 2010, by the European Envisat-1 satellite. Only scattered patches of oil are evident in the counter-clockwise rotating eddy on the northern boundary of the Loop Current. A small amount of oil appears to be in the Loop Current, and is moving southward. Image credit: Center for Southeastern Tropical Advanced Remote Sensing, University of Miami Rosenstiel School of Marine and Atmospheric Science. SAR images have a resolution of 8 - 50 meters, and can be taken through clouds and precipitation.

Future threats to the Keys
Mostly offshore winds are expected this week over the northern Gulf of Mexico, thanks to the approach of the 90L storm along the Southeast U.S. coast. It is uncertain if these winds will be strong enough to push oil southward into the Loop Current, though at least one ocean trajectory model does show this occurring. As I discussed in my post Wednesday, the Loop Current is very unstable right now, and is ready to cut off into a giant clockwise-rotating eddy, an event that occurs every 6 - 11 months. At least one ocean model (the Global HYCOM model from the HYCOM consortium) is predicting that such an eddy will form this week. In the event a Loop Current Eddy does break off, it would create a rotating ring of water 250 miles in diameter to the south of the oil spill. Oil moving southwards would tend to enter the giant eddy and circulate around it, not threatening any land areas. Roffer's Ocean Fishing Forecast Service has a nice discussion on the possibility of the Loop Current cutting off into a Loop Current Eddy. Keep in mind, though, that during the first month that a Loop Current Eddy forms, it exchanges a considerable amount of water with the Loop Current. Thus we can expect that a portion of any oil moving southwards into a Loop Current Eddy will find its way into the Loop Current and move past the Florida Keys.

Oil spill resources
My post Wednesday with answers to some of the common questions I get about the spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami

I'll be back with a new post Tuesday morning.

Jeff Masters

Air and Water Pollution

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Little change to 90L; flow of oil southwards towards Loop Current shuts off

By: JeffMasters, 7:57 PM GMT on May 22, 2010

An extratropical low pressure system a few hundred miles northeast of the Bahamas (90L), has changed little over the past day. (For those of you who were wondering, a discussion of what an "Invest" is can be found in the Tropical Cyclone FAQ). This low has the potential to develop into the season's first depression or subtropical storm, and could be a threat to the Southeast U.S. coast by Tuesday or Wednesday. The SHIPS model predicts that shear will be in the high 30 - 40 knot range through Tuesday, though. The high shear combined with the large amount of dry air to 90L's west seen on water vapor satellite loops will greatly hamper transition of this system to a subtropical storm. This system is expected to move slowly north and then northwestward towards the Southeast U.S. coast over the next three days, and could bring 20 - 30 mph winds and heavy rain to the coast of North Carolina by Tuesday night. Most of the models indicate that Wednesday will be when 90L gets closest to the coast, with a position just off the North or South Carolina coast. All of the major models currently indicate that 90L will not make landfall, but will move slowly northeastward out to sea late next week as a trough of low pressure moving across the Eastern U.S. picks up the storm. While the storm will initially form in a region of high wind shear and be entirely extratropical, it will move into a region of lower wind shear in a gap between the polar jet stream to the north and the subtropical jet stream to its south by Wednesday. At that time, the low will be positioned near the warm waters of the Gulf Stream, and will have the opportunity to develop a shallow warm core and transition to a subtropical storm. The counter-clockwise flow of air around this low will probably lead to offshore winds over the oil spill region Tuesday through Wednesday, keeping oil away from the coasts of Alabama and the Florida Panhandle, but pushing oil southwards towards the Loop Current. Wunderbloggers Weather456 and StormW have more detailed discussions of the potential development of 90L.


Figure 1. Visible satellite image of 90L this afternoon.

Heavy rainfall threat for Haiti diminishes
Moisture is expected to increase across most of the Caribbean next week, leading to seasonally heavy rains across much of the region. A concentrated tropical disturbance capable of bringing dangerous flooding rains to Haiti is no longer being indicated, but the normal heavy rains that we can expect this time of year will likely begin affecting the island over the next several weeks.

Flow of oil southward towards the Loop Current shuts off
Light southeast to east winds are expected to blow over the northern Gulf of Mexico today through Monday, resulting in potential oiling of Louisiana shorelines from the mouth of the Mississippi River westward 150 miles, according to the latest trajectory forecasts from NOAA. These winds shut off the flow of oil southwards towards the Loop Current, as seen in the latest SAR satellite imagery (Figure 2). However, winds will shift to offshore out of the north or northeast Tuesday and Wednesday, due to counter-clockwise flow of air around the approaching 90L storm. This wind direction change should give some relief to the hard-hit Louisiana coast. If 90L becomes strong and lingers off the Southeast U.S. coast for several days, a significant amount of oil could get pumped into the Loop Current late next week.


Figure 2. Synthetic Aperture Radar (SAR) image of the oil spill taken at 8:53am EDT May 22, 2010, by the Canadian Radarsat-1 satellite, operated by MDA GeospatialServices of Richmond, Canada. The plume of oil being drawn south towards the Loop Current has been cut off. Image credit: Center for Southeastern Tropical Advanced Remote Sensing, University of Miami Rosenstiel School of Marine and Atmospheric Science. SAR images have a resolution of 8 - 50 meters, and can be taken through clouds and precipitation.

Oil threat to the Keys uncertain
Satellite imagery from today's pass of NASA's Terra satellite and the European Envisat satellite were inconclusive as to the presence of oil in the Loop Current. It is likely that the oil has dispersed significantly over the 500-mile course it has taken from the site of the Deepwater Horizon blowout. I expect some oil is close to completing the full loop of the Loop Current and is now headed east towards the Keys, as depicted in the "Uncertainty" area in the latest NOAA 72-hour offshore trajectory forecast. If this estimate is correct, the Keys could see oil as early as Wednesday. However, this is not a sure thing. As I discussed in my post Wednesday, the Loop Current is very unstable right now, and is ready to cut off into a giant clockwise-rotating eddy, an event that occurs every 6 - 11 months. This event could occur today or tomorrow, in which case the ribbon of southwestward-moving oil would turn due west and then north, eventually winding up back near the site of the Deepwater Horizon blowout. Roffer's Ocean Fishing Forecast Service has a nice discussion on the possibility of the Loop Current cutting off into a Loop Current Eddy, and they note in today's discussion that there appears to be a developing eastward flow of water directly from the Yucatan Peninsula to the Florida Keys. Keep in mind, though, that during the first month that a Loop Current Eddy forms, it exchanges a considerable amount of water with the Loop Current. Even if a Loop Current Eddy forms today, I still expect we will see some oil make the turn eastward and flow past the Florida Keys by Wednesday. My guess is that the oil will be too thin and scattered to cause significant problems in the Keys, but there is great uncertainty on this.

Oil spill resources
My post Wednesday with answers to some of the common questions I get about the spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami

I'll be back with a new post Monday morning.

Jeff Masters

Air and Water Pollution

Updated: 3:03 AM GMT on May 23, 2010

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First Atlantic Invest, 90L is here; oil now 350 miles west of Key West

By: JeffMasters, 8:40 PM GMT on May 21, 2010

An extratropical low pressure system has developed a few hundred miles northeast of the Bahamas today, and has been designated as the first "Invest" of the year (90L) by the National Hurricane Center. (For those of you who were wondering, a discussion of what an "Invest" is can be found in the Tropical Cyclone FAQ). This low has the potential to develop into the season's first named storm--Alex--and could be a threat to the Southeast U.S. coast by Tuesday. Wind shear is currently 40 knots over the low, and the high shear ripped apart a low level circulation that was attempting to form this morning. Water vapor loops show a large amount of dry, continental air exists to the west of the storm, and this dry air will hamper transition of 90L to a subtropical storm. This system is expected to move slowly northwestward towards the Southeast U.S. coast, and could bring 20 - 30 mph winds and heavy rain to the coast of North Carolina by Tuesday. While the storm will initially form in a region of high wind shear and be entirely extratropical, it will move into a region of lower wind shear in a gap between the polar jet stream to the north and the subtropical jet stream to its south early next week. At that time, the low will be positioned near the warm waters of the Gulf Stream, and will have the opportunity to develop a shallow warm core and transition to a subtropical storm. The models are divided on whether the storm will eventually make landfall on the Southeast U.S. coast 5 - 7 days from now, and it is too early to offer odds on this occurring. The counter-clockwise flow of air around this low will probably lead to northeasterly winds over the oil spill region Tuesday through Wednesday, keeping oil away from the coasts of Alabama and the Florida Panhandle, but pushing oil southwards towards the Loop Current. Wunderbloggers Weather456 and StormW have more detailed discussions of the potential development of 90L.


Figure 1. Visible satellite image of 90L this afternoon.

Potential heavy rainfall threat to Haiti next week
Long-range forecasts from the NOGAPS model, and to a lesser extent, the ECMWF and GFS models, continue to predict an increase in moisture and decrease in wind shear over the Western Caribbean 4 - 6 days from now, leading to development of a tropical disturbance with heavy rains in the Western Caribbean early next week. A strong subtropical jet stream over the southern Gulf of Mexico will steer the disturbance to the north and east, and the potential exists for heavy rains of 2 - 4 inches to affect eastern Cuba, Jamaica, Haiti, and the Dominican Republic in the Wednesday - Thursday time frame next week. The models are less enthusiastic about the prospects for tropical development than they were in yesterday's runs, and it currently appears that high levels of wind shear will make formation of a tropical depression improbable.

Oil spill continues to impact Louisiana shores
Light southeast to east winds are expected to blow over the northern Gulf of Mexico today through Sunday, resulting in potential oiling of Louisiana shorelines from the mouth of the Mississippi River westward 150 miles, according to the latest trajectory forecasts from NOAA. These winds may be creating strong enough surface currents that the flow of oil southwards towards the Loop Current may be significantly reduced or shut off over the next few days, as suggested by the latest SAR satellite imagery (Figure 2). However, winds will shift to offshore out of the north or northeast by Tuesday, due to counter-clockwise flow of air around the approaching 90L storm. If 90L becomes strong and lingers off the Southeast U.S. coast for several days, a significant amount of oil could get pumped into the Loop Current next week.


Figure 2. Synthetic Aperture Radar (SAR) image of the oil spill taken at 11:53pm EDT May 20, 2010, by the European Space Agency's ENVISAT satellite. The plume of oil being drawn south towards the Loop Current appears truncated, and very little oil may be flowing south. Image credit: Center for Southeastern Tropical Advanced Remote Sensing, University of Miami Rosenstiel School of Marine and Atmospheric Science. SAR images have a resolution of 8 - 50 meters, and can be taken through clouds and precipitation.

Oil now 350 miles due west of Key West
Satellite imagery from today's 12:15pm EDT pass of NASA's Terra satellite (Figure 3) shows that a narrow ribbon of oil is caught in the Loop Current. The oil has moved south and then southwest, and the leading edge of the oil is now about 350 miles due west of Key West, Florida. The oil is substantial enough to modify the cumulus clouds in the Gulf of Mexico, though NOAA characterizes this portion of the oil spill as "numerous light sheens with some emulsified patties and streams." The oil is now headed away from the Keys towards a major kink in the Loop Current. By Saturday, the oil should double back towards the Keys in a eastward flowing branch of the Loop Current, and will likely pass just south of Key West by Tuesday. However, this is not a sure thing. As I discussed in my post Wednesday, the Loop Current is very unstable right now, and is ready to cut off into a giant clockwise-rotating eddy, an event that occurs every 6 - 11 months. This event could occur today or tomorrow, in which case the ribbon of southwestward-moving oil would turn due west and then north, eventually winding up back near the site of the Deepwater Horizon blowout. Roffer's Ocean Fishing Forecast Service has a nice discussion on the possibility of the Loop Current cutting off into a Loop Current Eddy. Keep in mind, though, that during the first month that a Loop Current Eddy forms, it exchanges a considerable amount of water with the Loop Current. Even if a Loop Current Eddy forms today, I still expect we will see some oil make the turn eastward and flow past the Florida Keys by Wednesday.


Figure 3. Visible satellite image from NASA's MODIS instrument for 12:15pm EDT May 21, 2010. I've enhanced the region along the eastern boundary of the Loop Current showing the south and southwestward moving ribbon of oil. Note that the oil is substantial enough to be affecting the low level cumulus clouds along portions of the ribbon of oil. The oil has reached the latitude of the Florida Keys.

Oil spill resources
My post Wednesday with answers to some of the common questions I get about the spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
Synthetic Aperture Radar (SAR) imagery from the University of Miami

I'll be back with a new post Saturday afternoon.

Jeff Masters

Air and Water Pollution

Updated: 8:43 PM GMT on May 21, 2010

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Warmest April on record for the globe

By: JeffMasters, 12:13 PM GMT on May 21, 2010

The globe recorded its warmest April since record keeping began in 1880, according to the National Oceanic and Atmospheric Administration's (NOAA's) National Climatic Data Center. The April temperature anomaly of 0.76°C (1.37°F) beat the previous record set in 1998 by 0.05°C. The is the second consecutive warmest month on record. NASA's Goddard Institute for Space Studies also rated April 2010 as the warmest April on record. The year-to-date period, January - April, is the warmest such period on record, according to both NOAA and NASA. NASA also rated the last 12-month period (May 2009 - April 2010) as the warmest 12-month period on record. April 2010 global ocean temperatures were the warmest on record for the 2nd month in a row, while land temperatures were the 3rd warmest. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the 2nd warmest on record in April, according to both the University of Alabama Huntsville (UAH) and Remote Sensing Systems (RSS) groups.

For those interested, NCDC has a page of notable weather highlights from April 2010.


Figure 1. Departure of temperature from average for April 2010. Image credit: NOAA's National Climatic Data Center.

A very warm April for the U.S.
For the contiguous U.S., it was the 14th warmest April in the 116-year record, according to the National Climatic Data Center. California was the coldest state, relative to average, with its 12th coldest April. No state had a top-ten coldest April. Five states had their warmest April on record--Illinois, Maine, Rhode Island, Connecticut, and New Jersey. Sixteen other states had top-ten warmest Aprils.

U.S. precipitation and drought
For the contiguous U.S., April 2010 ranked as the 36th driest in the 116-year record. Louisiana, South Carolina, North Carolina, Virginia, Maryland, Connecticut, and Massachusetts all had top-ten driest Aprils. Only Oregon had a top-ten wet April. At the end of April, 2% of the contiguous United States was in severe-to-exceptional drought. This is the lowest April drought footprint in the U.S. in the past ten years.

El Niño is over
El Niño rapidly weakened during late April and early May, with sea surface temperatures over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", falling 0.65°C in just one month. This brought SSTs into "neutral" conditions, at 0.18°C above average, which is well below the 0.5°C above average threshold to be considered an El Niño, according to the Australian Bureau of Meteorology. The speed of the collapse of El Niño makes it likely that a La Niña event is on its way this summer. This is what happened during the last strong El Niño event in 1998--El Niño collapsed dramatically in May, and a strong La Niña event developed by hurricane season. Ten of the 23 El Niño models (updated as of May 19) are predicting La Niña conditions for hurricane season. The demise of El Niño, coupled with sea surface temperatures in the tropical Atlantic that are currently at record levels, have prompted two major hurricane forecasting groups (tropicalstormrisk.com and Colorado State University) to predict a significantly above average 2010 Atlantic hurricane season. Over the full 160-year period we have records of Atlantic hurricanes, La Niña years have typically had more hurricanes, and more strong hurricanes, compared to neutral years. However, since 1995, there hasn't been any difference between neutral and La Niña years in terms of hurricane activity.

April sea ice extent in the Arctic near average in April
April 2010 Northern Hemisphere sea ice extent was the 15th lowest (or 18th greatest) since satellite measurements began in 1979, so was near average. However, the ice volume anomaly was at a record low at the end of April, according to University of Washington Polar Ice Center. Wind patterns this spring have pushed a great deal of the oldest ice out of the Arctic, leaving mostly thin ice that is vulnerable to rapid melting. The first two weeks of May have seen unusual warmth in the Arctic, leading to rapid melting, and ice extent as of May 20 was the 2nd lowest on record, behind 2006, according to the National Snow and Ice Data Center (NSIDC).

I'll be back this afternoon to talk about the oil spill and the tropics. I'm working on a post about how a hurricane passing over the spill might affect the oil. I'll post it if I have time to finish it.

Jeff Masters

Climate Summaries

Updated: 6:30 PM GMT on May 21, 2010

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Oil continues impacting Louisiana coast; storms for Caribbean and SE U.S. waters?

By: JeffMasters, 3:01 PM GMT on May 20, 2010

Light southeast to east winds are expected to blow over the northern Gulf of Mexico today through Sunday, resulting in potential oiling of Louisiana shorelines from the mouth of the Mississippi River westward 150 miles, according to the latest trajectory forecasts from NOAA. Clouds over the Gulf of Mexico have cleared, and we should get a good view late this afternoon on how far south the oil spill has penetrated into the Loop Current. Statements from NOAA and Synthetic Aperture Radar (SAR) satellite data imply that most of the oil that was pulled southwards to the northern boundary of the Loop Current is now caught in a counter-clockwise rotating eddy just to the north of the Loop Current. Some oil has escaped this eddy and is on its way south towards the Florida Keys. This tongue of oil consists of "numerous light sheens with some emulsified patties and streams," according to NOAA. I wish they'd provide more information about what the sensitivity of various ecosystems may be to oil at these concentrations. It would also be good to have more information about what the concentration of the toxic dispersants are in the surface waters of the spill, but I expect no one knows. The oil will grow more dilute as it travels the 500 miles to the Florida Keys. My present expectation is that the oil entering the Loop Current this week will cause only minor problems in the Keys next week. However, there is a lot of uncertainty about what the oil may do to the fragile Keys ecosystem. SAR imagery from last night and this morning continue to show a large plume of oil being drawn southeastward from the oil spill location into the northern boundary of the Loop Current. With winds expected to remain light over the coming week, I expect oil will continue to be drawn southwards into the Loop Current and the counter-clockwise rotating eddy just to its north. Much of the oil caught in this eddy may circulate around the eddy in 3 or so days, and potentially enter the Loop Current early next week. As I discussed in my post Wednesday, the Loop Current is very unstable right now, and is moving chaotically 10+ miles in a single day, making prediction difficult.


Figure 1. Synthetic Aperture Radar (SAR) image of the oil spill taken at 7:56am EDT May 20, 2010, by the Canadian Space Agency’s (CSA) RadarSat-1 satellite. Image credit: Center for Southeastern Tropical Advanced Remote Sensing, University of Miami Rosenstiel School of Marine and Atmospheric Science. SAR images have a resolution of 8 - 50 meters, and can be taken through clouds and precipitation.


Figure 2. Latest oil trajectory forecast from NOAA for this Saturday.

Oil spill resources
My post Wednesday with answers to some of the common questions I get about the spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
HYCOM ocean current forecasts from LSU

Potential serious rainfall threat to Haiti next week
Long-range forecasts from the NOGAPS model, and to a lesser extent, the ECMWF and GFS models, continue to predict an increase in moisture and decrease in wind shear over the Western Caribbean 4 - 6 days from now, leading to development of a tropical disturbance with heavy rains in the Western Caribbean early next week. A strong subtropical jet stream over the southern Gulf of Mexico will steer the disturbance to the north and east, and the potential exists for heavy rains of 3 - 6 inches to affect eastern Cuba, Jamaica, Haiti, and the Dominican Republic in the Tuesday - Thursday time frame next week. It is possible that a tropical depression could form from this tropical disturbance, though most of the models indicate that high levels of wind shear will make this improbable.

Southeast U.S. coastal storm next week could become subtropical
A region of cloudiness and showers just east of the Bahama Islands will develop into a strong extratropical storm over the weekend. This storm is expected to move slowly northwestward towards the Southeast U.S. coast Sunday and Monday, and could bring 20 - 30 mph winds and heavy rain to the coast of North Carolina by Tuesday. While the storm will initially form in a region of high wind shear and be entirely extratropical, it will move into a region of lower wind shear in a gap between the polar jet stream to the north and the subtropical jet stream to its south early next week. At that time, the low will be positioned near the warm waters of the Gulf Stream, and will have the opportunity to develop a shallow warm core and transition to a subtropical storm. The models are divided on whether the storm will eventually make landfall on the Southeast U.S. coast 6 - 7 days from now, and it is too early to offer odds on this occurring. The counter-clockwise flow of air around this low will probably lead to northeasterly winds over the oil spill region Monday through Wednesday, keeping oil away from the coasts of Alabama and the Florida Panhandle, but pushing oil westwards towards Texas. Wunderblogger Weather456 has a more detailed discussion of the potential development of this system in his blog this morning.

Tornadoes and large hail pound Oklahoma
A significant severe weather outbreak occurred last night over Oklahoma and surrounding states, with 25 tornado reports, 8 reports of damaging winds, and 23 hail reports. Severe weather wunderblogger Dr. Rob Carver has the details in his wunderblog this morning. The Vortex2 field project had a perfect opportunity to intercept these tornadoes, since they were slow moving and occurred over relatively unpopulated regions. The University of Michigan students writing our Vortex2 featured blog will have an update when their schedule allows.


Figure 3. Baseball-sized hail pounds a suburban Oklahoma City swimming pool, making huge splashes, in this remarkable video. The action gets really intense about 90 seconds into the video.

I'll be back with a new post Friday.

Jeff Masters

Air and Water Pollution

Updated: 5:06 PM GMT on May 20, 2010

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El Niño is done; Haiti at risk of heavy rains next week; oil spill update

By: JeffMasters, 8:09 PM GMT on May 19, 2010

El Niño rapidly weakened during late April and early May, with sea surface temperatures over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", falling a significant 0.65°C in just one month. Temperatures in the region are now in the "neutral" range, just 0.18°C above average, and well below the 0.5°C threshold to be considered an El Niño, according to the Australian Bureau of Meteorology. The speed of the collapse of El Niño makes it likely that a La Niña event is on its way this summer. This is what happened during the last strong El Niño event, in 1998--El Niño collapsed dramatically in May, and a strong La Niña event developed by hurricane season. Six of the sixteen El Niño models (updated as of April 15) are predicting La Niña conditions for hurricane season, and I expect more models will jump on the La Niña bandwagon when the May data updates later this week. The demise of El Niño, coupled with sea surface temperatures in the tropical Atlantic that are currently at record levels, have prompted two major hurricane forecasting groups (tropicalstormrisk.com and Colorado State University) to predict a significantly above average 2010 Atlantic hurricane season. Over the full 160-year period we have records of Atlantic hurricanes, La Niña years have typically had more hurricanes, and more strong hurricanes, compared to neutral years. However, since 1995, there hasn't been any difference between neutral and La Niña years in terms of hurricane activity. La Niña conditions typically cause cool and wet conditions over the Caribbean in summer, but do not have much of an impact on U.S. temperatures or precipitation.


Figure 1. Oil spill edge over the Gulf of Mexico on Wednesday, May 19, as seen from NASA's M ODIS instrument. Note that a band of cumulus clouds formed along the edge of the oil spill. I theorize this is because the low level wind flow out of the southeast moves faster over the oil, since the oil suppresses wave action. As the winds cross the spill boundary into rougher, clean water, they slow down, forcing the air to pile up and create updrafts that then spawn cumulus clouds. See my post on what oil might do to a hurricane for more information on how oil reduces wave action.

Oil spill update
Clouds over the Gulf of Mexico have again foiled satellite imaging of the extent of the Deepwater Horizon oil spill, though through breaks in the clouds it appears that a significant amount of the oil that was pulled southwards towards the Loop Current is now caught in a counter-clockwise rotating eddy just to the north of the Loop Current. However, some oil has escaped this eddy and is on its way south towards the Florida Keys. According to the latest trajectory forecasts from NOAA, the tongue of oil flowing southwards has at most "light" concentrations. The oil will grow more dilute as it travels the 500 miles to the Florida Keys. My present expectation is that the oil entering the Loop Current this week will cause only minor problems in the Keys next week. However, there is a lot of uncertainty about what the oil may do to the fragile Keys ecosystem. See my post yesterday for answers to many of the common questions I get about the spill.

Oil spill resources
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
HYCOM ocean current forecasts from LSU


Figure 2. Precipitation forecast from today's 8am EDT run of the NAVY NOGAPS model, valid 7 days from now. Precipitation amounts in excess of 70 mm (2.8") in 12 hours are predicted over Haiti, due to a tropical disturbance in the Western Caribbean. Image credit: U.S. Navy.

Potential serious rainfall threat to Haiti next week
Long-range forecasts from the GFS and NOGAPS models over the past few days have consistently been predicting an increase in moisture and decrease in wind shear over the Western Caribbean 5 - 7 days from now, and I expect that a tropical disturbance with heavy rains will develop in the Western Caribbean early next week. A strong subtropical jet stream over the southern Gulf of Mexico will steer the disturbance to the north and east, and the NOGAPS model shows heavy rains in excess of six inches impacting Haiti Wednesday through Thursday of next week. Rains of this magnitude are capable of causing a serious emergency with high loss of life in earthquake-shattered Haiti, and all interests in that nation should closely monitor the situation over the coming week. It is too early to speculate on the possibility of the disturbance becoming a tropical depression. The wunderblogs of StormW and Weather456, who are now featured bloggers for the coming hurricane season, have more information on this potential development, plus the possible development of a subtropical storm between Florida and Bermuda next week.

Major severe weather outbreak over Oklahoma expected tonight
NOAA's Storm Prediction Center has put much of Oklahoma in its High Risk region for severe weather today, warning that "The setup appears most favorable for large, relatively slow moving intense storms with large hail. A couple strong tornadoes also may occur."

I'll be back with a new post Thursday morning.

Jeff Masters

Climate Summaries

Updated: 8:19 PM GMT on May 19, 2010

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Clouds, unstable Loop Current making oil spill prediction difficult

By: JeffMasters, 8:48 PM GMT on May 18, 2010

It's cloudy over the Gulf of Mexico today, so it is difficult to tell how far into the Loop Current the Deepwater Horizon oil has penetrated using visible satellite imagery. Satellite imagery yesterday from NASA's MODIS instrument confirmed that a tongue of oil moved southeast from the Deepwater Horizon oil spill and entered the Gulf of Mexico's Loop Current. However, Synthetic Aperture Radar imagery from the European Envisat satellite posted at ROFFS Ocean Forecasting Service shows that while some of the tongue of oil that entered the Loop Current appears to be circulating southwards towards the Florida Keys, perhaps 80% of the oil in this tongue is caught in a counter-clockwise circulating eddy along the north side of the Loop Current. This oil may eventually circulate around and enter the Loop Current, but not for at least three days.


Figure 1. Oil spill forecast for this Thursday night as simulated by the 6pm EDT Monday May 17 runs of the Navy Gulf of Mexico HYCOM nowcast/forecast system and the Global HYCOM + NCODA Analysis from the HYCOM Consortium. See the University of South Florida Ocean Circulation Group website for more information. There are considerable differences between the two models, due in part to the fact that they have much different depictions of the sea surface temperatures (SSTs) and ocean currents at the beginning of their runs. The warm Loop Current is visible as the red colors of the SST field that form a heart-shaped area in the Gulf.

How long will it be until oil reaches the Keys?
Once oil gets into the Loop Current, the 1 - 2 mph speed of the current should allow the oil to travel the 500 miles to the Florida Keys in 5 - 10 days. Portions of the Loop Current flow at speed up to 4 mph, so the fastest transport could be 4 - 5 days.

How much oil has made it into the Loop Current?
According to the latest trajectory forecasts from NOAA, the tongue of oil flowing southwards has, at most, "light" concentrations. The oil will grow more dilute as it travels the 500 miles to the Florida Keys, and most of the oil appears to be caught in a smaller counter-clockwise rotating eddy on the north side of the Loop Current. My present expectation is that the oil entering the Loop Current this week will cause only minor problems in the Keys next week. However, there is a lot of uncertainty regarding how much oil will get to the Keys, and we cannot rule out the possibility of an ecological disaster in the fragile Keys ecosystem.

How is the Loop Current changing?
The Loop Current has been highly chaotic and unstable over the past week, making it difficult to predict how the ocean currents near the spill will behave. According to ROFFS Ocean Fishing Service, which has done a tremendous job tracking the spill, the Loop Current surged 7 - 10 miles northward Sunday and Monday. The Loop Current has gotten more contorted since Friday, and may be ready to cut off into a clockwise-rotating Loop Current Eddy. This process occurs every 6 - 11 months, with the clockwise-rotating ring of water slowly drifting west-southwest towards Texas. The last eddy broke off ten months ago, so the Loop Current is due to shed another eddy in the next few months. The latest 1-month forecast from the U.S. Navy does not predict an eddy forming, but these forecasts are not very reliable. If a Loop Current Eddy does break off, oil getting entrained into it might orbit the center of the Gulf of Mexico for many months inside the eddy. However, this eddy will probably reattach and detach from the main Loop Current flow for at least a month following when it breaks off, so oil will continue to flow through the Keys during this initial month.

When will the flow of oil into the Loop Current shut off?
Winds over the oil spill location are expected to be light and onshore at 5 - 10 knots through Saturday. This means that the chaotic contortions of the Loop Current will primarily control how much oil gets into it, making it difficult to predict when the flow will shut off. The long range (and thus unreliable) forecast for next week from the GFS model calls for a continuation of light winds over the eastern Gulf of Mexico. Thus, the flow of oil into the Loop Current could occur intermittently for several weeks.

Who besides the Keys are at risk next week from the Loop Current oil?
As I discussed in an earlier post, the coast of Southwest Florida from Tampa Bay to the Everglades is a "Forbidden Zone" for surface-based transport of ocean water to the coast, and is probably not at risk from this week's Loop Current oil. The northwest coast of Cuba east of Havana and the coast of Southeast Florida from the Keys to West Palm Beach are at the most risk. The western shores of the western-most Bahama Islands and the U.S. coast north of West Palm Beach northwards to Cape Hatteras are at slight risk. It would likely take ocean eddies 2 - 9 weeks to transport the oil to these locations, and the oil would probably be so dilute that ecosystem damage would probably be minor, at most. At this point, I see no reason for cancellation of vacation plans to any of the beach areas that may potentially be affected by the oil.

What is happening to the plumes of oil at depth?
Two research missions over the past week have detected substantial plumes of oil at depth, moving to the southwest. The deepest of the these plumes, near the site of the blowout at 5,000 feet depth, is in a region of slow ocean currents and has not moved much. At depths closer to the surface, the currents get stronger, and oil within a few hundred feet of the surface--if there is any--could potentially have been dragged into the Loop Current. At this point, we don't have a very good picture of how much oil is at depth and where it might be headed.

Oil spill resources
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA trajectory forecasts
Deepwater Horizon Unified Command web site
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
HYCOM ocean current forecasts from LSU

The tropics
For those of you interested in a detailed look at the early season tropical weather outlook, consult the excellent wunderblogs of StormW and Weather456, who are now featured bloggers for the coming hurricane season. We have some models predicting a possible subtropical storm off the U.S. East coast next week, but this does not appear to be a significant concern for land areas at this time. More concerning is the possibility that an area of disturbed weather will develop across the Western Caribbean late next week. While wind shear will likely keep anything in the Western Caribbean from developing, several models are predicting that this disturbance may bring major flooding rains to earthquake-ravaged Haiti late next week.

I'll be back with a new post Wednesday afternoon.

Jeff Masters

Air and Water Pollution

Updated: 1:43 PM GMT on May 19, 2010

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Oil enters the Loop Current and is headed to the Florida Keys

By: JeffMasters, 7:38 PM GMT on May 17, 2010

Satellite imagery today from NASA's MODIS instrument confirms that a substantial tongue of oil has moved southeast from the Deepwater Horizon oil spill and entered the Gulf of Mexico's Loop Current. The Loop Current is an ocean current that transports warm Caribbean water through the Yucatan Channel between Cuba and Mexico. The current flows northward into the Gulf of Mexico, then loops southeastward just south of the Florida Keys (where it is called the Florida Current), and then along the west side of the western Bahamas. Here, the waters of the Loop Current flow northward along the U.S. coast and become the Gulf Stream. Once oil gets into the Loop Current, the 1 - 2 mph speed of the current should allow the oil to travel the 500 miles to the Florida Keys in 10 - 20 days. Portions of the Loop Current flow at speed up to 4 mph, so the transport could be just 4 - 5 days. It now appears likely that the first Florida beaches to see oil from the spill will be in the Lower Florida Keys, not in the Panhandle.


Figure 1. Satellite image of the oil spill taken at 12:40 EDT Monday May 17, 2010. The location of the Loop Current is superimposed. Image credit: University of Wisconsin and NASA.

Why is oil getting into the Loop Current?
The winds over the oil spill location are offshore out of the northwest today, and offshore winds will continue intermittently through Wednesday, which should allow a substantial amount of oil to enter the Loop Current. The major reason oil is moving southwards is because of the instability of the currents in the Gulf of Mexico. The Loop Current is not a stable feature, and tends to surge northwards and southwards in a chaotic fashion, and in response to changes in the prevailing winds. Over the past week, chaotic behavior of the Loop Current and a clockwise-rotating eddy just to its north, just south of the oil spill location, have combined to bring a current of southward-moving surface water to the oil spill location. As strong on-shore winds from the southeast slackened this past weekend, oil has been drawn southward into the Loop Current. The latest NOAA trajectory forecasts failed to anticipate the movement of the oil into the Loop Current. The latest surface current forecasts from NOAA's HYCOM model show that oil could continue pouring into the Loop Current for most of the rest of the week. It is highly uncertain how diluted the oil might get on its voyage to northwestern Cuba and the Florida Keys this week, but the possibility for a major ecological disaster in the fragile Keys ecosystem cannot be ruled out. Southeast to east winds of 10 - 15 knots are expected to develop late this week and extend into early next week, which may be strong enough to impose a surface current that will shut off the flow of oil into the Loop Current by Friday or Saturday.


Figure 2. Forecast made at 8pm EDT Sunday May 16, 2010, of the Gulf of Mexico currents by NOAA's HYCOM model. A persistent southward flowing surface current is predicted to occur this week between the oil spill location (red dot) and the Loop Current. Image credit: NOAA.

Likely areas of impact
Based on a study of 194 floating probes released into the Northeast Gulf of Mexico during a 1-year study in the 1990s (Figure 3), the west coast of Florida from Tampa Bay southwards to the Everglades is at minimal risk of receiving oil from surface currents. There is a "forbidden zone" off the southwest Florida coast where the shape of the coast, bottom configuration, and prevailing winds all act to create upwelling and surface currents that tend to take water away from the coast. This study implies that the greatest risk of land impacts by surface oil caught in the Loop Current is along the ocean side of the Florida Keys, and along the coast of Southeast Florida from Miami to West Palm Beach. Eddies breaking away from the Gulf Stream would also likely bring oil to northwest Cuba, the western Bahamas, and the U.S. East Coast as far north as Cape Hatteras, North Carolina, though at lesser concentrations. Southwest Florida cannot rest entirely, though--the "forbidden zone" is only true for surface waters, and there is onshore flow below the surface. Since recent ship measurements have detected substantial plumes of oil beneath the surface, southwest Florida might be at risk if one of these plumes gets entrained into the Loop Current. These subsurface plumes were also detected by current probes launched into the oil spill on May 8 by one of NOAA's hurricane hunter aircraft, according to one scientist I spoke to at last week's AMS hurricane conference. There are plans for the Hurricane Hunters to go out again tomorrow and drop more probes into the spill to attempt to get a better handle on where the oil is and where the currents are taking it.


Figure 3. Paths of 194 floating probes released into the yellow-outlined area in the northeast Gulf of Mexico between February 1996 and February 1997 as part of a study by the Mineral Management Service (MMS). The probes were all launched into waters with depth between 20 and 60 meters. Image credit: Yang, H., R.H. Weisberga, P.P. Niilerb, W. Sturgesc, and W. Johnson, 1999, Lagrangian circulation and forbidden zone on the West Florida Shelf, Continental Shelf Research Volume 19, Issue 9, July 1999, Pages 1221-1245 doi:10.1016/S0278-4343(99)00021-7

When will a Loop Current eddy break off?
Every 6 - 11 months, the looped portion of the Loop Current cuts off into a clockwise-rotating ring of water that then slowly drifts west-southwest towards Texas. When one of these rings breaks off at the peak of hurricane season, it provides a source of heat energy capable of providing fuel for rapid intensification of any hurricanes that might cross over. The Loop Current is not predicted to shed an ring over the next month, as predicted by the latest 1-month forecast from the U.S. Navy. However, the last eddy broke off in July of 2009, ten month ago, and it is unusual for the Loop Current to go more than eleven months without shedding an eddy. I expect we'll see the Loop Current shed an eddy in July or August, just in time to pose the maximum threat for hurricane season. According to an interesting February 2004 article published by offshore-engineer.com, reliable forecasts of these currents and eddies are not available yet. Keep in mind that surface currents are largely driven by winds, and wind forecasts are not reliable out more than about 10 days.

References
Yang, H., R.H. Weisberga, P.P. Niilerb, W. Sturgesc, and W. Johnson, 1999, Lagrangian circulation and forbidden zone on the West Florida Shelf, Continental Shelf Research Volume 19, Issue 9, July 1999, Pages 1221-1245 doi:10.1016/S0278-4343(99)00021-7.

Oil spill resources
NOAA trajectory forecasts
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Surface current forecasts from NOAA's HYCOM model
HYCOM ocean current forecasts from LSU

Jeff Masters

Air and Water Pollution

Updated: 7:06 PM GMT on May 18, 2010

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Oil spill headed towards the Loop Current

By: JeffMasters, 4:01 PM GMT on May 17, 2010

Recent satellite imagery and flight over-passes of the Gulf of Mexico oil spill confirm that a surface tendril of oil has become entrained into a southward-moving current that threatens to pull oil into the Gulf of Mexico Loop Current late this week. The Loop Current is an ocean current that transports warm Caribbean water through the Yucatan Channel between Cuba and Mexico. The current flows northward into the Gulf of Mexico, then loops southeastward just south of the Florida Keys (where it is called the Florida Current), and then along the west side of the western Bahamas. Here, the waters of the Loop Current flow northward along the U.S. coast and become the Gulf Stream. Once oil gets into the Loop Current, the 1 - 2 mph speed of the current should allow the oil to travel the 500 miles to the Florida Keys in 10 - 20 days. Portions of the Loop Current flow at speed up to 4 mph, so the transport could be faster.

Why is oil getting close to the Loop Current?
The winds over the oil spill location are offshore out of the northwest today, and offshore winds will continue intermittently through Wednesday, helping push the oil southwards towards the Loop Current. However, the major reason oil is moving southwards is because of the instability of the currents in the Gulf of Mexico. The Loop Current is not a stable feature, and tends to surge northwards and southwards in a chaotic fashion, and in response to changes in the prevailing winds. Over the past week, chaotic behavior of the Loop Current and a clockwise-rotating eddy just to its north, just south of the oil spill location, have combined to bring a current of southward-moving surface water to the oil spill location. As strong on-shore winds from the southeast slackened this past weekend, oil has been drawn southward towards the Loop Current. An examination of the latest NOAA trajectory forecasts and surface current forecasts reveals the possibility that this tendril of southward-moving oil could make it into the Loop Current late this week. It is highly uncertain how much oil might make it into the Loop Current, or how diluted it might get on its voyage to the Florida Keys next week. Southeast to east winds of 10 - 15 knots are expected to develop late this week and extend into early next week, which may be strong enough to impose a surface current that will prevent oil from getting into the Loop Current this month. I predict a 30% chance that oil will make it into the Loop Current in the next two weeks.


Figure 1. Forecast made at 8pm EDT Sunday May 16, 2010, of the Gulf of Mexico currents by NOAA's HYCOM model. A persistent southward flowing surface current is predicted to occur this week between the oil spill location (red dot) and the Loop Current. Image credit: NOAA.

Likely areas of impact once oil gets into the Loop Current
Based on a study of 194 floating probes released into the Northeast Gulf of Mexico during a 1-year study in the 1990s (Figure 2), the west coast of Florida from Tampa Bay southwards to the Everglades is at minimal risk of receiving oil from surface currents. There is a "forbidden zone" off the southwest Florida coast where the shape of the coast, bottom configuration, and prevailing winds all act to create upwelling and surface currents that tend to take water away from the coast. This study implies that the greatest risk of land impacts by surface oil caught in the Loop Current is along the ocean side of the Florida Keys, and along the coast of Southeast Florida from Miami to West Palm Beach. Eddies breaking away from the Gulf Stream would also likely bring oil to northwest Cuba, the western Bahamas, and the U.S. East Coast as far north as Cape Hatteras, North Carolina, though at lesser concentrations. Southwest Florida cannot rest entirely, though--the "forbidden zone" is only true for surface waters, and there is onshore flow below the surface. Since recent ship measurements have detected substantial plumes of oil beneath the surface, southwest Florida might be at risk if one of these plumes gets entrained into the Loop Current. These subsurface plumes were also detected by current probes launched into the oil spill on May 8 by one of NOAA's hurricane hunter aircraft, according to one scientist I spoke to at last week's AMS hurricane conference. There are plans for the Hurricane Hunters to go out again tomorrow and drop more probes into the spill to attempt to get a better handle on where the oil is and where the currents are taking it.


Figure 2. Paths of 194 floating probes released into the yellow-outlined area in the northeast Gulf of Mexico between February 1996 and February 1997 as part of a study by the Mineral Management Service (MMS). The probes were all launched into waters with depth between 20 and 60 meters. Image credit: Yang, H., R.H. Weisberga, P.P. Niilerb, W. Sturgesc, and W. Johnson, 1999, Lagrangian circulation and forbidden zone on the West Florida Shelf, Continental Shelf Research Volume 19, Issue 9, July 1999, Pages 1221-1245 doi:10.1016/S0278-4343(99)00021-7

When will a Loop Current eddy break off?
Every 6 - 11 months, the looped portion of the Loop Current cuts off into a clockwise-rotating ring of water that then slowly drifts west-southwest towards Texas. When one of these rings breaks off at the peak of hurricane season, it provides a source of heat energy capable of providing fuel for rapid intensification of any hurricanes that might cross over. The Loop Current is not predicted to shed an ring over the next month, as predicted by the latest 1-month forecast from the U.S. Navy. However, the last eddy broke off in July of 2009, ten month ago, and it is unusual for the Loop Current to go more than eleven months without shedding an eddy. I expect we'll see the Loop Current shed an eddy in July or August, just in time to pose the maximum threat for hurricane season. According to an interesting February 2004 article published by offshore-engineer.com, reliable forecasts of these currents and eddies are not available yet. Keep in mind that surface currents are largely driven by winds, and wind forecasts are not reliable out more than about 10 days.

References
Yang, H., R.H. Weisberga, P.P. Niilerb, W. Sturgesc, and W. Johnson, 1999, Lagrangian circulation and forbidden zone on the West Florida Shelf, Continental Shelf Research Volume 19, Issue 9, July 1999, Pages 1221-1245 doi:10.1016/S0278-4343(99)00021-7.

Air and Water Pollution

Updated: 7:40 PM GMT on May 17, 2010

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Record Atlantic SSTs continue in the hurricane Main Development Region

By: JeffMasters, 8:03 PM GMT on May 15, 2010

Sea Surface Temperatures (SSTs) in the Atlantic's Main Development Region for hurricanes had their warmest April on record, according to an analysis of historical SST data from the UK Hadley Center. SST data goes back to 1850, though there is much missing data before 1910 and during WWI and WWII. The area between 10°N and 20°N, between the coast of Africa and Central America (20°W - 80°W), is called the Main Development Region (MDR) because virtually all African waves originate in this region. These African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) SSTs in the Main Development Region (10°N to 20°N and 20°W to 85°W) were an eye-opening 1.46°C above average during April. This is the third straight record warm month, and the warmest anomaly measured for any month--by a remarkable 0.2°C. The previous record warmest anomalies for the Atlantic MDR were set in June 2005 and March 2010, at 1.26°C.


Figure 1. The departure of sea surface temperature (SST) from average for May 13, 2010. Image credit: NOAA/NESDIS.

What is responsible for the high SSTs?
As I explained in detail in a post on record February SSTs in the Atlantic, the Arctic Oscillation (AO) and its close cousin, the North Atlantic Oscillation (NAO), are largely to blame for the record SSTs. The AO and NAO are climate patterns in the North Atlantic Ocean related to fluctuations in the difference of sea-level pressure between the Icelandic Low and the Azores-Bermuda High. If the difference in sea-level pressure between Iceland and the Azores is small (negative NAO), this creates a weak Azores-Bermuda High, which reduces the trade winds circulating around the High. During December - February, we had the most negative AO/NAO since records began in 1950, and this caused trade winds between Africa and the Lesser Antilles Islands in the hurricane Main Development Region to slow to 1 - 2 m/s (2.2 - 4.5 mph) below average. Slower trade winds mean less mixing of the surface waters with cooler waters down deep, plus less evaporational cooling of the surface water. As a result, the ocean heated up significantly, relative to normal, over the winter. Negative AO/NAO conditions have been dominant much of this spring as well, resulting in further anomalous heating of the MDR waters. This heating is superimposed on the very warm global SSTs we've been seeing over the past few decades due to global warming. Global and Northern Hemisphere SSTs were the 2nd warmest on record this past December, January, and February, the warmest on record in March, and will likely be classified as the warmest or second warmest on record for April, since NASA just classified April as the warmest April on record for the globe. We are also in the warm phase of a decades-long natural oscillation in Atlantic ocean temperatures called the Atlantic Multi-decadal Oscillation (AMO). This warm phase began in 1995, and has been partially responsible for the high levels of hurricane activity we've seen since 1995.

What does this imply for the coming hurricane season?
The high April SST anomaly does not bode well for the coming hurricane season. The three past seasons with record warm April SST anomalies all had abnormally high numbers of intense hurricanes. Past hurricane seasons that had high March SST anomalies include 1969 (0.90°C anomaly), 2005 (1.19°C anomaly), and 1958 (0.97°C anomaly). These three years had 5, 7, and 5 intense hurricanes, respectively. Just two intense hurricanes occur in an average year. The total averaged activity for the three seasons was 15 named storms, 11 hurricanes, and 6 intense hurricanes (an average hurricane season has 10, 6, and 2.) Both 1958 and 2005 saw neutral El Niño conditions, while 1969 had a weak El Niño.

The SSTs are already as warm as we normally see in July between Africa and the Caribbean, and we have a very July-like tropical wave approaching the Lesser Antilles Islands this weekend. However, wind shear is still seasonably high, and the tropical waves coming off of Africa are still too far south to have much of a chance of developing. The GFS model is indicating that shear will start to drop over the Caribbean the last week of May, so we may have to be on the watch for tropical storms forming in the Caribbean then.

For those of you interested in a more detailed look at the early season tropical weather outlook, consult the excellent wunderblogs of StormW and Weather456. I'll be back with a new post on Monday.

Jeff Masters

Hurricane

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Solar impacts on hurricanes

By: JeffMasters, 2:36 PM GMT on May 13, 2010

I'm in Tucson for the American Meteorological Society's 29th Conference on Hurricanes and Tropical Meteorology. This is the premier scientific conference on hurricanes, and is held only once every two years, so pretty much all of the world's greatest hurricane experts are here. One of the more intriguing posters presented at Tuesday's poster session was titled, Evidence linking solar variability with USA hurricanes, by Robert Hodges and Jim Elsner of Florida State University. They showed that the probability of three or more hurricanes hitting the U.S. during a hurricane season with warmer than average sea surface temperatures increases dramatically during minima in the 11-year sunspot cycle. The odds increase from 20% to 40% for years when the sunspot activity is in the lower 25% of the sunspot cycle, compared to years in the upper 25% of the cycle. Near the peak of the sunspot cycle, the odds of at least one hurricane hitting the U.S. are just 25%, but at solar minimum, the odds increase sharply to 64%. The authors studied the period 1851 - 2008, and controlled for other variables such as changes in sea surface temperature and El Niño. Such a large impact of the sun on hurricanes might seem surprising, given that the change in solar energy at all light wavelengths is only about 0.1%. This relatively small change causes just a 0.1°C change in Earth's mean surface temperature between the peak of the 11-year sunspot cycle (high solar activity) and the minimum of the sunspot cycle (where we are now.) However, variation in radiation between extrema of the solar cycle can be 10% or more in portions of the UV range (Elsner et al., 2008.) The strong change in UV light causes globally averaged temperature swings in the lower stratosphere of 0.4°C between the minimum and maximum of the sunspot cycle--four times as great as the difference measured at Earth's surface (Lean, 2009). This sensitivity of the stratosphere to UV light is due to the fact the ozone layer is located in the stratosphere. Ozone absorbs a large amount of UV light, causing the stratosphere to heat up when solar activity is high. The authors speculate that a warmer stratosphere then heats up the upper troposphere, making the atmosphere more stable. An unstable atmosphere--with hot temperatures at the surface and cold conditions in the upper troposphere--are conducive for stronger hurricanes. Thus, we would expect to see reductions in hurricanes during the peak of the sunspot cycle.

Previous research
The findings presented at this week's conference build upon earlier work published by Elsner et al. (2008) and Elsner et al. (2010). The first of these studies found that for every 100 extra sunspots in September, the temperature of the atmosphere at 16 km altitude over the Caribbean and Gulf of Mexico increased by about 0.5°C, and the number of hurricanes in this region was reduced by 26%. Interestingly, a reduction of hurricanes over the eastern Atlantic off the coast of Africa was not observed during solar maxima, which the authors attributed to the fact that hurricanes in this region are limited by sea surface temperature, not instability. Solar maximum brings a small increase in sea surface temperature to the globe, aiding hurricane development in regions where sea surface temperature is the limiting factor. The second of these studies (Elsner et al., 2010) computed that for a Category 2 hurricane affecting the U.S. during the most active 30% range of the solar cycle, the resultant heating of the upper troposphere would cause a 19% decrease in the stability, lowering the hurricane's winds by 10% (10 mph.) Stronger hurricanes would be affected even more, with a potential wind speed reduction of 23 mph for the most powerful hurricanes. The 27-day rotation period of the sun causes a change in UV light even larger than the change observed during the 11-year sunspot cycle, so perhaps we should be monitoring the phase of the sun's rotation to look for more favorable periods for hurricane formation.

Commentary
Considering that this year we are at the deepest solar minimum in more than a century, this research gives us yet another reason to expect a severe Atlantic hurricane season this year. My next post, which may not be until Monday, I'll discuss the sea surface temperatures in the Atlantic hurricane main development region, which set an all-time record last month for the warmest monthly anomaly for the 100+ years we have records. Also, El Niño now appears to be over, as sea surface temperatures in the Eastern Pacific have crossed the threshold into neutral territory.

References
Elsner, J. B., and T. H. Jagger, 2008, United States and Caribbean tropical cyclone activity related to the solar cycle, Geophys. Res. Lett., 35, L18705, doi:10.1029/2008GL034431.

Elsner, J. B., T. H. Jagger, and R. E. Hodges, 2010, Daily tropical cyclone intensity response to solar ultraviolet radiation, Geophys. Res. Lett., 37, L09701, doi:10.1029/2010GL043091.

Lean, J.L., 2009, Cycles and trends in solar irradiance and climate", Wiley Interdisciplinary Reviews: Climate Change, Volume 1, Issue 1, Pages 111-122 Published Online: 22 Dec 2009

Jeff Masters

Hurricane

Updated: 4:34 AM GMT on May 14, 2010

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Hurricane tracks, changes in hurricane clustering, and other notes from Tucson

By: JeffMasters, 2:44 PM GMT on May 12, 2010

I'm in Tucson for the American Meteorological Society's 29th Conference on Hurricanes and Tropical Meteorology. This is the premier scientific conference on hurricanes, and is held only once every two years, so pretty much all of the world's greatest hurricane experts are here. Below are some quick snapshots of four of the talks I attended yesterday; I hope to more more snapshots each day this week.

Angela Colbert of the University of Miami/RSMAS showed how different weather and climate patterns affect the Azores-Bermuda High, and thus the tracks of Atlantic hurricanes. She divided storms into straight-moving storms that move straight west-northwest through the Caribbean, recurving landfalling hurricane that hit the east coast of the U.S., and recurving ocean storms that miss land. Roughly 1/3 of all hurricanes between 1950 - 2009 fell into each of these three categories. These proportions stayed pretty constant during La Niña and neutral years, but El Niño caused a weakening of the high, resulting in far fewer hurricanes hitting the U.S. East Coast. These storms instead recurved out to sea.

Jim Kossin of the University of Wisconsin separated all Atlantic storms from 1950 - 2007 into 4 clusters, based on genesis location. Two of the clusters were more northerly-forming storms that tended to be less tropical in nature--Gulf of Mexico storms, and storms off the U.S. East Coast that tended to recurve. The other two clusters were more southerly tropical-origin systems--ones that tended to form in the Caribbean, and storms that form near the Cape Verde Island region off the coast of Africa. The more tropical Cape Verde and Caribbean storms dominated major hurricane frequency by a factor of four. In mid-1980s, there was an abrupt shift to more of these more dangerous tropical type storms--ten years prior to the active hurricane period that began in 1995. It is unknown what caused this shift. The shift is unlikely to be a result of measurement error, since we had good satellite imagery then. Independent of any trends in frequency, this shift caused an increase in intensity metrics of Atlantic hurricanes. A doubling of these tropical systems has also occurred since 1950. Interestingly, there has been no change in the number of Gulf of Mexico storms, and a slight increase in storms forming off of the U.S. East Coast. Since slight changes in track can make a big difference in what SSTs and atmospheric environment a storm sees, there is a lot of natural "noise" in the system that will make it difficult to get a clear sense of when climate change is having a substantial impact on hurricane intensity.

Bin Wang of the University of Miami studied the global number of storm days from 1965 - 2008, which should be a less sensitive quantity to data problems than the number of storms or their intensity. Storm days were defined as any day when a tropical cyclone of tropical depression strength or greater existed. However, there are still some data problems, as evidenced by a sharp drop in storm days observed in the North Indian Ocean beginning in 1978. Dr. Wang found that there was no global trend in storm days. The Atlantic was the only individual basin that showed an increase in storm days.

Greg Holland of NCAR looked at the distribution of the strongest hurricanes over time by using a mathematical description of the historical hurricane data. His analysis showed that during the period 1995 - 2008, we probably had about a 30% increase in Category 5 storms in the Atlantic, and an 18% increase in Category 4 hurricanes. Using a climate model, he predicted that by the years 2045 - 2055, we should see a 60% increase in Cat 5s, 32% increase in Cat 4s, and 16% increase in Cat 3s in the Atlantic.

Jeff Masters

Hurricane

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Tornadoes rip Oklahoma, killing 5; oil spill headed towards Texas

By: JeffMasters, 2:09 PM GMT on May 11, 2010

Oklahoma residents are picking up the pieces and surveying the damage after a devastating tornado outbreak that left at least five people dead, dozens injured, and hundreds of millions in damage. Our severe weather expert, Dr. Rob Carver, has some amazing images and videos of the tornadoes in his blog. One solace Oklahomans can take in the disaster is that the data taken by scientists during the tornado outbreak may help forecasters issue better tornado warnings in the future. Usually, a proven way to reduce the incidence of dangerous weather phenomena is to schedule a multi-million dollar field experiment to study the phenomena. This is what happened last year, when the largest tornado field study ever conducted, Vortex2, kicked off. The $10 million study deployed an armada of over 100 storm chasing vehicles across the Great Plains, and were disappointed by one of the quietest tornado seasons in history. But it's pretty tough to have two consecutive record quiet tornado seasons in a row, so the Vortex2 program scheduled the study to run this year as well, beginning on May 1. Unfortunately for the residents of Oklahoma, the atmosphere unleashed one of its classic tornado outbreaks yesterday, in a region NOAA's Storm Prediction Center had outlined at "High Risk" for severe weather. The Vortex2 team was ideally positioned to intercept the tornadoes, according to the team of University of Michigan students that has been writing our featured Vortex2 blog, and I am told that they successfully collected what is probably the best data set even taken of a tornado outbreak. This was no mean feat, since yesterday's storms were moving 60 mph, making it extremely difficult to position the chase vehicles to capture the storm's secrets.


Figure 1. The Wakita, OK multiple-vortex tornado of May 10, 2010.

Oil spill may approach Texas early next week
The Deepwater Horizon oil spill has pushed steadily westward along the Louisiana coast, and is expected to reach central Louisiana near Atchafalaya Bay by Thursday, according to the latest trajectory forecasts from NOAA. Winds over the Gulf of Mexico this week will blow from the southeast at 15 - 20 knots, threatening to bring oil to large portions of the Louisiana coast. The Mississippi and Alabama coasts will also be at risk, but the risk to the Florida Panhandle is lower. It appears quite unlikely that oil will get into the Loop Current anytime over the next two weeks, and spread to the Florida Keys and beyond. However, the strong southeast winds are expected to shift more easterly late this week, and drive a westward-moving ocean surface current with a speed of 1 - 2 mph along the west coast of Louisiana late this week (Figure 2). This current may be capable of transporting oil all the way to the Louisiana/Texas border by Monday. However, the concentrations of oil in the water will be much less than what is present close to the blowout, and it is unclear what the potential danger is for the western Louisiana and eastern Texas coasts. The greatest danger is to the Eastern Louisiana coast.


Figure 2. Surface ocean current in the Gulf of Mexico on Friday, May 14, at 8pm EDT as forecast by the 8pm EDT run of the NOAA HYCOM model at 8pm EDT on Sunday, May 9, 2010. Note that a strong ocean current near 1 m/s (about 2 mph) is forecast to set up along the Western Louisiana coast, which could take oil close to the Texas offshore waters by Monday. Image credit: NOAA RTOFS.

Next Post
I'm in Tucson for the American Meteorological Society's 29th Conference on Hurricanes and Tropical Meteorology. I'll be posting Wednesday morning on some of the latest findings presented at the conference, or discussing yesterday's tornado outbreak.

Jeff Masters

Tornado

Updated: 2:12 PM GMT on May 11, 2010

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How oil might affect a hurricane

By: JeffMasters, 12:59 PM GMT on May 07, 2010

There's no major changes to the forecast for the Gulf of Mexico oil spill. As I discussed in yesterday's post, on Sunday, the winds will begin increasing and shifting to the southeast. The latest run of the GFS model shows that this will be a week-long period of southeast winds, with wind speeds at times reaching 20 - 25 knots. These winds will threaten to bring oil to a large portion of the Louisiana coast, including regions of the central Louisiana coast west of the mouth of the Mississippi River. The Mississippi and Alabama coasts will also be at risk next week, but the risk to the Florida Panhandle is lower. Yesterday's post also has the long-range outlook for oil to get into the Loop Current and spread to the Florida Keys and beyond.

What will oil in the Gulf of Mexico do to a hurricane?
With hurricane season fast approaching and the oil spill in the Gulf of Mexico likely to still be around once hurricane season starts in June, we need to ask, how will oil affect any hurricanes that might traverse over the spill? And how might a hurricane's wind and storm surge affect the spill? Let's consider the first of those questions today.

From the time of the ancient Greeks to the days of the wooden ships and iron men, mariners dumped barrels of oil onto raging seas to calm them during critical moments of violent storms (Wyckoff, 1886.) Oil does indeed calm wind-driven waves, thanks to the reduction in surface tension of the water that oil causes. Ripples with a wavelength shorter than 17 mm are affected by surface tension, and these ripples then cause a feedback that reduces the height of larger waves with longer wavelengths (Scott, 1986.) The reduction of surface tension also impacts the flow of air above the water, and reduces the amount of sea spray thrown into the air, both of which could affect the wind speed. Oil also damps waves by forming a thick, viscous film at the top of the water that resists water motion (Scott, 1999.) Oil also helps calm raging seas by switching off of the wind energy input needed by the wave to break. This occurs because the surface film of oil prevents the generation of ripples on the exposed crests of the waves, and this smoother surface makes the wind less able to grab onto the wave and force it to break.

So, what would happen to a hurricane that encounters a large region of oily waters? A 2005 paper by Barenblatt et al. theorize that spray droplets hurled into the air by a hurricane's violent winds form a layer intermediate between air and sea made up of a cloud of droplets that can be viewed as a "third fluid". The large droplets in the air suppress turbulence in this "third fluid", decrease the frictional drag over the ocean surface, and accelerate the winds. According to this theory of turbulence, oil dumped on the surface of the ocean would reduce the formation of wind-whipped spray droplets, potentially calming the winds. The authors propose spraying oil on the surface of the ocean to reduce the winds of a hurricane. However, the turbulence theory championed by Barenblatt et al. has been challenged by other scientists. In a 2005 interview with Newscientist magazine, turbulence expect Julian Hunt at University College London, UK, remarks, "I am very doubtful about this approach." Hunt studies turbulence both theoretically and in the laboratory, and believes that the high wind speeds in a hurricane are not caused by sea spray. In an article he wrote for the Journal of Fluid Dynamics, Hunt suggests that variations in the turbulence between different regions of the hurricane cause sharp jumps in wind speed, which are responsible for the hurricane's strongest winds.

Oil reduces evaporation
Hurricanes are sustained by the heat liberated when water vapor that has evaporated from warm ocean waters condenses into rain. If one can reduce the amount of water evaporating from the ocean, a decrease in the hurricane's strength will result. Oil on the surface of the ocean will act to limit evaporation, and could potentially decrease the strength of a hurricane. However, if the oil is mixed away from the surface by the strong winds of a hurricane, the oil will have a very limited ability to reduce evaporation. According to a 2005 article in Popular Science magazine, Dr. Kerry Emanuel of MIT performed some tests in 2002 to see if oil on the surface of water could significantly reduce evaporation into a hurricane. He found that the slick quickly dissipated under high wind conditions that generated rough seas.


Figure 1. A comparison of the size of 2008's Hurricane Gustav with the size of the Gulf oil spill. The spill is only about 60 miles in diameter, while a hurricane like Gustav is typically 400+ miles in diameter.

Conclusion
A tropical cyclone in its formative stage--as either a tropical depression or a tropical storm with 40 mph winds--might be adversely affected if it encountered the Gulf of Mexico oil slick, due to the reduction of evaporation into the storm. However, a full-fledged hurricane would mix the oil into the ocean to such a degree that the storm would probably not see any significant reduction in evaporation. It remains unknown how the reduction of sea spray by oil might affect a hurricane. If the oil slick expands to a much larger size, there might be a significant reduction in strength of the hurricane, if theory of how a reduction of sea spray will decrease a hurricane's winds is correct. However, the oil slick is currently Delaware-sized, while a hurricane tends to be Texas-sized, and I doubt that the oil slick at its current size is large enough to have a significant impact on a hurricane's intensity. The slick is about 60 miles across, and it would take a hurricane about four hours to traverse the spill at a typical hurricane forward speed of 15 mph. Furthermore, the slick is within 50 miles land, and interactions with land will dominate the behavior of a hurricane that gets that close to the coast. Unfortunately, there is a decent chance that we'll get a real-world opportunity to see what will happen. June tropical storms tend to form in the Gulf of Mexico, and we've been averaging one June storm every two years since 1995. This year, the odds of a June Gulf of Mexico storm are probably a little lower than usual, shear from our lingering El Niño may bring wind shear levels a bit above average. I expect there is a 20% chance that we'll see a June tropical storm in the Gulf of Mexico that would interact with the oil spill.

References
Barenblatt, G.I, A.J. Chorin, and V.M. Prostokishin, 2005, A note concerning the Lighthill sandwich model of tropical cyclones, PNAS August 9, 2005 vol. 102 no. 32 11148-11150 doi: 10.1073/pnas.0505209102.

Hunt, J.C.R, and I. Eames, 2006, Mechanics of inhomogeneous turbulence and interfacial layers,, Journal of Fluid Dynamics, vol. 554, pp. 499519 doi:10.1017/S002211200600944X.

Scott, J.C., 1986, "The Effect of Organic Films on Water Surface Motions," in Oceanic Whitecaps, edited by E. C. Monohan and G. Mac Niocaill, D. Reidel Publishing Company.

Scott, J.C., 1999, Ocean Surface Slicks - "Pollution, Productivity, Climate and Life-saving", IEEE Proceedings of the International Geoscience and Remote Sensing Symp. IGARSS99, Hamburg, Germany, 28 June-2 July 1999, vol. 3, pp 1463-1468, 1999.

Wyckoff, A.B., 1886, The Use of Oil in Storms at Sea, American Philosophical Society, April 2, 1886.

http://www.archive.org/stream/proceedingsofamep23 amer/proceedingsofamep23amer_djvu.txt

First tropical wave of the season leaves the coast of Africa
Yesterday, the National Hurricane Center noted the first tropical wave of the year coming off the coast of Africa in their Tropical Weather Discussion. The first half of May is the typical time when the first tropical wave comes off the coast of Africa. The wave is currently positioned in the far eastern Atlantic near 5N 45W, and I don't expect it to develop, since it is too close to the Equator to leverage the Earth's spin to gain the rotation needed. The wave has quickly been joined by two new ones today, located at 15W and 36W off the African coast. Tropical waves serve as the seed that form most Atlantic and Eastern Pacific hurricanes.

Portlight delivers major aid shipment to Haiti
Portlight continues to focus its energy and funds on the situation in Haiti, where the rainy season is fast approaching the needs for shelter, medical supplies, food and water remain urgent. Their latest effort was a shipment of several thousand pounds of Durable Medical Equipment and 30,000 pounds of rice that arrived this week via the schooner Halie and Mathew.

Portlight.org is also preparing to respond the the Gulf Coast oil spill by deploying one of more mobile kitchens to feed the hundreds of volunteers likely to flood the coast when the oil finally comes ashore. Please visit the Portlight.org web site or the Portlight blog to learn more and to donate to Portlight's efforts in Haiti and the Gulf Coast.


Figure 2. Relief supplies from the schooner Halie and Mathew sitting at the Portlight Haiti warehouse, ready for distribution.

Next Post
I'm on my way to Tucson today for the American Meteorological Society's 29th Conference on Hurricanes and Tropical Meteorology, which will be held in Tucson next week. My next post will probably be on Monday night, when I plan to discuss the record SSTs observed last month in the tropical Atlantic. I'm excited to be catching up on and blogging about all the latest advancements in hurricane research!

Jeff Masters

Hurricane

Updated: 5:25 PM GMT on August 18, 2011

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Long-range prospects for oil to enter the Loop Current and hit the Keys

By: JeffMasters, 3:21 PM GMT on May 06, 2010

The oil slick from the April 20 explosion and blowout of the offshore oil rig Deepwater Horizon is moving little, thanks to the light winds of 10 knots or less that have affected the northern Gulf of Mexico over the past few days. According to the latest NWS marine forecast, winds will remain light through Saturday, which should result in little transport of the oil slick. The latest trajectory forecast from the NOAA Office of Response and Restoration continues to show that the mouth of the Mississippi River and the Chandeleur Islands will be the only land areas affected by the spill over the next two days.

On Sunday, the winds will begin increasing and shifting to the southeast. The latest run of the GFS model shows that this will be a week-long period of southeast winds, with wind speeds at times reaching 20 - 25 knots. These winds will threaten to bring oil to a large portion of the Louisiana coast, including regions of the central Louisiana coast west of the mouth of the Mississippi River. The Mississippi and Alabama coasts will also be at risk next week, but the risk to the Florida Panhandle is lower.


Figure 1. Forecast location of the oil spill for Friday, May 7, 2010. Image credit: NOAA Office of Response and Restoration. See also the trajectory maps available at State of Louisiana web site.

Long-range prospects for oil to enter the Loop Current
A major concern with the Deepwater Horizon oil spill is the possibility for the oil to move southwards and become entrained into the mighty Gulf of Mexico Loop Current, which would rapidly transport the oil through the Florida Keys, impacting northwest Cuba, South Florida, the western Bahamas, and the U.S. East Coast all the way to Cape Hatteras, North Carolina. However, there is no immediate danger of this happening. The latest forecast of Gulf currents from the NOAA HYCOM model (see also this alternative view of the HYCOM ocean current forecast) indicate that the currents will not be favorable for pulling any oil southwards into the Loop Current over the next five days. Oil will have to travel approximately 100 miles to the south-southeast to get entrained into the Loop Current, and we probably would need a 2+ day period of strong winds out of the north for this to happen. The long-range GFS model indicates that the earliest this might happen is 10+ days from now. As summer gets closer, the incidence of cold fronts making it far enough south to bring an extended period of offshore northerly winds to the Gulf of Mexico decreases. I think there is a 40% chance that the next cold front capable of pushing oil into the Loop Current will arrive by the end of June. However, I think it is more likely that the next such front will not arrive until October, when fall comes.

That makes a tropical storm or hurricane as perhaps the most likely weather event to push oil into the Loop Current over the next few months. A tropical storm hitting the Panhandle of Florida would do the trick, by bringing northerly winds over the oil spill location, thanks to the counter-clockwise flow of air around the storm. Looking ahead to June, June tropical storms tend to form in the Gulf of Mexico, and we've been averaging one June storm every two years since 1995. This year, the odds of a June Gulf of Mexico storm are probably a little lower than usual. While Gulf of Mexico sea surface temperatures are near average, wind shear from our lingering El Niño will probably be above average. Since 1995, there have been three June tropical storms in the Gulf of Mexico that have followed a track capable of pushing oil into the Loop Current. These storms were Hurricane Allison of 1995, Tropical Storm Allison of 2001, and Tropical Storm Arlene of 2005. Taking into account all these factors, I'll give a 20% chance that we'll get a June tropical storm capable of transporting oil into the Loop Current.


Figure 2. Tracks of all June tropical storms and hurricanes, 1851 - 2006.

Next Post
I'll have a new post Friday. Next week, I'm in Tucson for the American Meteorological Society's bi-annual conference on hurricane science, and will be updating you on all the latest advancements in hurricane research.

Jeff Masters

Air and Water Pollution

Updated: 3:53 PM GMT on May 06, 2010

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Flooding death toll in Southeast U.S. floods rises to 24; oil slick moving little

By: JeffMasters, 2:11 PM GMT on May 04, 2010

The death toll from last weekend's record flooding in Tennessee, Kentucky, and Mississippi has risen to 24, making it the deadliest non-tropical storm or hurricane flood disaster in the U.S. since the October 1998 Central Texas floods that killed 31 when a cold front stalled over Texas. As flood waters recede today, the toll from last weekend's floods is expected to grow higher. Particularly hard-hit was the Nashville, Tennessee area, where ten fatalities were reported. The city had its heaviest 1-day and 2-day rainfall amounts in its history over the weekend. A remarkable 7.25" of rain fell on the city Sunday, breaking the record for most rain in a single day (6.60", set September 13, 1979.) Nashville's third greatest day of rainfall on record occurred Saturday, when 6.32" fell. Nashville also eclipsed its greatest 6-hour and 12-hour rainfall events on record, with 5.57" and 7.20", respectively, falling on Sunday. And, only two days into the month, the weekend rains made it the rainiest May in Nashville's history.

Rainfall records were smashed all across Tennessee, Kentucky, and northern Mississippi over the weekend, with amounts as high as 17.73" recorded at Camden, TN, and 17.02" at Brownsville, TN. According to Chris Burt, the author of the excellent book Extreme Weather, the 13.30" that fell on Camden in 24 hours just missed eclipsing the state's all-time 24-hour precipitation record, the 13.60" inches that fell on Milan on September 13, 1982. Jackson, Tennessee had its rainiest day in its 63-year weather history on Sunday, 7.93". Bowling Green Kentucky had its heaviest 2-day precipitation event on record, 9.67". Records in Bowling Green go back to 1870.


Figure 1. Satellite-estimated precipitable water at 23 UTC (7 pm EDT) Sunday, May 2, 2010. Precipitable water is a measure of how much rain would be produced if all the water vapor and cloud moisture through the depth of the atmosphere were to fall as rain. Values above 50 mm (about 2 inches) are frequently associated with flooding. Sunday's precipitable water image showed a tropical disturbance crossed Mexico into the Gulf of Mexico, dragging a plume of very moist air northwards over the Southeast U.S. Image credit: University of Wisconsin GOES Satellite Blog.


Figure 2. Flood forecast for the Cumberland River in Nashville, Tennessee. Image credit: NOAA.

The record rains were accompanied by a surge of very warm air that set record high temperature marks at 21 major airports across the Eastern U.S. on Saturday. This is not surprising, since more moisture can evaporate into warmer air, making record-setting rainfall events more likely when record high temperatures are present. Accompanying this warm air was moisture from a tropical disturbance that crossed over Mexico from the tropical East Pacific over the weekend (Figure 1.)

The record rains sent the Cumberland River in downtown Nashville surging to 51.86' this morning, 12' over flood height, and the highest level the river has reached since a flood control project was completed in the early 1960s. The previous post-flood control project record level was 47.6', set on March 15, 1975 (the river hit 56.2' in 1929, before the flood control project was built.) The river has now crested (Figure 2) and is expected to recede below flood stage by Wednesday morning. There are no further rains in the forecast this week for Tennessee. At least four rivers in Tennessee reached their greatest flood heights on record this week. Most remarkable was the Duck River at Centreville, which crested at 47', a full 25 feet above flood stage, and ten feet higher than the previous record crest, achieved in 1948 (to check out the flood heights, use our wundermap for Nashville with the "USGS River" layer turned on.)

Funding issues to take 17 Tennessee streamgages offline
According to the USGS web site, seventeen Tennessee streamflow gages with records going back up to 85 years will stop collecting data on July 1 because of budget cuts. With up to eighteen people in Tennessee dying from flooding this weekend, now hardly seems to be the time to be skimping on monitoring river flow levels by taking 17 of Tennessee's 94 streamflow gages out of service. These gages are critical for proper issuance of flood warnings to people in harm's way. Furthermore, Tennessee and most of the northern 2/3 of the U.S. can expect a much higher incidence of record flooding in coming decades. This will be driven by two factors: increased urban development causing faster run-off, and an increase in very heavy precipitation events due to global warming. Both factors have already contributed to significant increases in flooding events in recent decades over much of the U.S. The USGS web site advertises that users who can contribute funding for the non-Federal share of costs to continue operation of these streamgages should contact Shannon Williams of the USGS Tennessee Water Science Center at 615-837-4755 or swilliam@usgs.gov. Tennessee is not the only state with streamgages at risk of closing down; fully 276 gages in 37 states have been shut down or will be shut down later this year. If you have questions about specific streamgages, click on the state of concern on the USGS web page of threatened stream gages.

Oil spill update
The oil slick from the April 20 explosion and blowout of the offshore oil rig Deepwater Horizon has retreated from the coast, thanks to a slackening of the persistent onshore winds that have affected the northern Gulf of Mexico over the past week. According to the latest NWS marine forecast, winds will be light and variable through Wednesday, resulting in little transport of the oil slick. Winds will then resume a weak onshore flow at 5 - 10 knots, Thursday through Friday, then reverse to blow offshore at 5 - 10 knots over the weekend. The net result of this wind pattern will be little transport of the oil slick. The only areas at risk of landfalling oil over the next five days will be the mouth of the Mississippi River in Louisiana, and the Chandeleur Islands. The latest forecast of Gulf currents from the NOAA HYCOM model (see also this alternative view of the HYCOM ocean current forecast) show weak ocean currents affecting the region during the remainder of the week. These currents will not be strong enough to push any oil southwards into the Loop Current over the next five days, so the Keys and South Florida are safe from oil for now. I'll have a post on the long-range prospects for oil to enter the Loop Current later this week, and a discussion of how a hurricane might affect and be affected by the oil spill.


Figure 3. Forecast location at 6pm CDT Tuesday, May 4, 2010, of the oil slick from the Deepwater Horizon blowout. Image credit: NOAA Office of Response and Restoration. See also the trajectory maps available at State of Louisiana web site.

Jeff Masters

Flood

Updated: 12:25 PM GMT on May 05, 2010

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Flooding from record rains kills 11 in Tennessee; oil spill update

By: JeffMasters, 1:52 PM GMT on May 03, 2010

Nashville, Tennessee remains virtually paralyzed this morning thanks to that city's heaviest recorded 1-day and 2-day rainfall in its history. A remarkable 7.25" of rain fell on the city Sunday, breaking the record for most rain in a single day (previously 6.60", set September 13, 1979.) Nashville's third greatest day of rainfall on record occurred Saturday, when 6.32" fell. Nashville also eclipsed its greatest 6-hour and 12-hour rainfall events on record, with 5.57" and 7.20", respectively, falling on Sunday. And, remarkably, only 2 days into the month, May 2010 is already the wettest May on record for Nashville.

Rainfall records were smashed all across Tennessee and Kentucky, with amounts as high as 17.73" recorded at Camden, TN, and 17.02" at Brownsville, TN. According to Chris Burt, the author of the excellent book Extreme Weather, the 13.30" that fell on Camden in 24 hours just missed eclipsing the state's all-time 24-hour precipitation record, the 13.60" inches that fell on Milan on September 13, 1982. Jackson, Tennessee had its rainiest day in its 63-year weather history on Sunday, 7.93". Bowling Green, Kentucky had its heaviest 2-day precipitation event on record, 9.67". Records in Bowling Green go back to 1870. The University of Wisconsin GOES Satellite Blog has some excellent imagery showing the remarkable plume of tropical moisture that crossed over Central America from the Eastern Pacific and fed the record rains.


Figure 1. Radar estimated rainfall for May 1 - 2, 2010 from the Nashville, Tennessee radar. A large region of the Tennessee and Kentucky received over ten inches of rain, with many areas receiving more than fifteen inches.


Figure 2. Flood forecast for the Cumberland River in Nashville, Tennessee. Image credit: NOAA.

The record rains triggered massive flooding that has killed at least eleven people in Tennessee, with two missing. The Cumberland River in downtown Nashville has surged to a height of 51', which is 11' over flood height, and the highest level the river has reached since a flood control project was completed in the early 1960s. The river is expected to crest this afternoon at 11.5' above flood stage, bringing flood waters to a large portion of the downtown area. The mayor has ordered all schools, parks, and libraries closed today, and commuter bus and train services have also been suspended. Five people died in Nashville due to the flooding. The Harpeth River at Bellevue, Tennessee to its greatest flood height since record keeping began in 1921. The river had a depth of 2 feet early Saturday morning before the rains began, and was running at a depth of 29' early this morning, breaking the record of 24.34' set in 1948. (To check out the flood heights, use our wundermap for Nashville with the "USGS River" layer turned on.) The Duck River at Hurricane Mills reached 28.7' yesterday morning before its streamgage stopped operating, its 2nd greatest flood height since record keeping began in 1926 (record: 30.7' in 1948.)

The record rains were accompanied by a surge of very warm air that set record high temperature marks at 21 major airports across the Eastern U.S. on Saturday; 19 more records were set on Sunday. This is not surprising, since more moisture can evaporate into warmer air, making record-setting rainfall events more likely when record high temperatures are present.


Figure 3. A portable classroom building from a nearby high school floats past submerged cars on I-24 near Nashville, TN on May 1, 2010. One person died in the flooding in this region of I-24. Roughly 200 - 250 vehicles got submerged on this section of I-24, according to wunderphotographer laughingjester, who was a tow truck operator called in to clear out the stranded vehicles.

Funding issues to take 17 Tennessee streamgages offline
According to the USGS web site, seventeen Tennessee streamflow gages with records going back up to 85 years will stop collecting data on July 1 because of budget cuts. With up to thirteen people in Tennessee dying from flooding this weekend, now hardly seems to be the time to be skimping on monitoring river flow levels by taking 17 of Tennessee's 94 streamflow gages out of service. These gages are critical for proper issuance of flood warnings to people in harm's way. Furthermore, Tennessee and most of the northern 2/3 of the U.S. can expect a much higher incidence of record flooding in coming decades. This will be driven by two factors: increased urban development causing faster run-off, and an increase in very heavy precipitation events due to global warming. Both factors have already contributed to significant increases in flooding events in recent decades over much of the U.S. According the landmark 2009 U.S. Climate Impact Report from the U.S. Global Change Research Program, "the amount of rain falling in the heaviest downpours has increased approximately 20 percent on average in the past century, and this trend is very likely to continue, with the largest increases in the wettest places." The USGS web site advertises that users who can contribute funding for the non-Federal share of costs to continue operation of these streamgages should contact Shannon Williams of the USGS Tennessee Water Science Center at 615-837-4755 or swilliam@usgs.gov. Tennessee is not the only state with streamgages at risk of closing down; fully 276 gages in 37 states have been shut down or will be shut down later this year (Figure 4.)


Figure 4. Streamgages that have been discontinued or are being considered for discontinuation or for conversion from continuous record discharge to stage-only stations. Funds for these 276 threatened streamgages are from the U.S. Geological Survey and other Federal, State, Tribal, and local agencies. For those streamgages that have already been discontinued, extensive efforts were made to find another funding source; however, when no funding was made available the streamgages had to be discontinued. For those streamgages at risk for discontinuation, the current funding source has indicated that it can no longer fund the streamgage. Efforts are currently underway to identify another funding source for the operation of these streamgages; however, if no funding is identified, then these streamgages will have to be discontinued also. If you have questions about specific streamgages, click on the state of concern on the USGS web page of threatened stream gages.

Oil spill update
The oil slick from the April 20 explosion and blowout of the offshore oil rig Deepwater Horizon has retreated from the coast, thanks to a slackening of the persistent onshore winds that have affected the northern Gulf of Mexico over the past week. Onshore winds of 10 - 15 knots will continue today, according to the latest NWS marine forecast, then shift to sideshore (out of the west) on Tuesday, as a cold front passes. Winds will then resume a weak onshore flow at 5 - 10 knots, Wednesday through Friday. These winds should cause only a slow transport of the oil slick towards the coast. I don't expect the spill will affect any land areas for the remainder of the week, with the possible exception of the mouth of the Mississippi River in Louisiana and the Chandeleur Islands. The latest forecast of Gulf currents from the NOAA HYCOM model (see also this alternative view of the HYCOM ocean current forecast) show weak ocean currents affecting the region during the remainder of the week. These currents will not be strong enough to push any oil southwards into the Loop Current over the next five days, so the Keys and South Florida are safe from oil for now.


Figure 5. Previous location and forecast location for tomorrow of the Deepwater Horizon oil spill. Image credit: NOAA Office of Response and Restoration. See also the trajectory maps available at State of Louisiana web site.

Jeff Masters

Flood

Updated: 4:04 PM GMT on May 03, 2010

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Gulf of Mexico oil spill slows its advance towards the coast

By: JeffMasters, 12:21 AM GMT on May 02, 2010

The oil slick from the April 20 explosion and blowout of the offshore oil rig Deepwater Horizon continues to affect the Louisiana coast near the mouth of the Mississippi River, and along the Chandelier Islands off the coast of Mississippi. Strong south to southeast winds blowing at 15 - 25 knots will continue through Monday, which will push oil onto portions of the eastern Louisiana coast from the mouth of the Mississippi River northwards towards the Mississippi border. However, the current trajectory forecasts now show the advance of the oil will slow over the next few days, despite the strong onshore winds. This is probably due to the fact that the shape of the Louisiana coast is setting up a counter-clockwise rotating eddy over the ocean regions between the Mississippi coast and the mouth of the Mississippi River, as seen on the latest forecast of Gulf currents from the NOAA HYCOM model (see also this alternative view of the HYCOM ocean current forecast.) Unfortunately, there are no buoys in this region of the Gulf to tell us what the currents are.


Figure 1. The oil spill on May 1, 2010, as seen by the MODIS instrument on NASA's Terra spacecraft. Image credit: NASA.

It now appears that the Mississippi, Alabama, and Florida Panhandle coasts will not see significant amounts of oil hitting their shores through at least Monday. On Monday night, the winds shift to southwesterly and weaken as a cold front approaches. The wind shift will allow oil to move eastwards towards Alabama and the Florida Panhandle, but at just 1 mph or so. The winds with then shift to offshore (northwesterly) on Tuesday as the cold front passes. This should blow the oil back out to sea a few miles. It is thus possible that only the Louisiana coast will see oil impacts over the coming seven days, though there is substantial uncertainty in this forecast. High pressure is expected to build in late next week, bringing relatively light onshore winds that should allow for slow transport of the oil towards shore. It appears very unlikely that oil will make it into the Loop Current during the next seven days and affect the southern Gulf of Mexico. The long range wind forecast beyond that time is too uncertain to say what might happen at longer time ranges.


Figure 2. Previous location and forecast location for today of the Deepwater Horizon oil spill. Image credit: NOAA Office of Response and Restoration.


Figure 3. Trajectory forecast for the Gulf of Mexico oil spill for 6 pm CDT Monday May 3, 2010. Image credit: State of Louisiana.

High risk of severe weather tonight
NOAA's Storm Prediction Center has outlined a "High Risk" region of severe weather potential over Arkansas tonight, and there are numerous tornadoes currently being reported over Arkansas. Our severe weather expert, Dr. Rob Carver, has radar images of yesterday's strongest storms in his blog today, including images of the tornado north of Little Rock that killed one person and injured several dozen.

Jeff Masters

Air and Water Pollution

Updated: 5:33 PM GMT on May 02, 2010

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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