More WIld Weather for the Mid-West

It was yet another active day for tornadoes, flooding, and severe thunderstorms in the Midwest on Thursday, with NOAA’s Storm Prediction Center (SPC) logging 16 preliminary tornado reports. Twisters touched down in Oklahoma, Arkansas, and Illinois. The tornadoes missed heavily populated areas for the most part, but seven people were injured in Arkansas in two separate tornadoes, and two other people were hurt by lightning. The severe weather forced organizers of the outdoor Wakarusa Music Festival north of Ozark, Arkansas to delay the start of the festival. The band “Widespread Panic” was one of the groups scheduled to perform, leading to an Associated Press headline from yesterday titled, “Nine hurt in Arkansas storm; Widespread Panic delayed.” Heavy rains from this week’s thunderstorms have pushed the Mississippi River to major flood stage at most places from Burlington Iowa to Quincy Illinois, and the river is expected to crest near major flood stage at St. Louis early next week. In Iowa, the Cedar River at Cedar Falls, the Iowa River at Marengo, and the Skunk River near Sigourney and at Augusta are also in major flood. The latest forecast from NOAA’s Storm Prediction Center calls for a “Moderate Risk” of severe weather today (Friday) over much of Oklahoma and Southwest Missouri, including Oklahoma City and Tulsa in Oklahoma, and Joplin, Missouri, with the potential for several strong EF-2 and EF-3 tornadoes.

Figure 1. Lightning strike from a severe thunderstorm near Guthrie, Oklahoma on May 30, 2013, as photographed by KFOR-TV. (AP Photo/KFOR-TV)

Figure 2. Severe weather outlook for Thursday, May 30, calls for a “Moderate Risk” of severe weather over much of Oklahoma and Southwest Missouri, including Oklahoma City and Tulsa in Oklahoma, and Joplin, Missouri. You can follow today’s severe weather outbreak from our Severe Weather page.

A mostly quiet year for violent tornadoes
After a very quiet March, April, and first half of May, the U.S. tornado season has become very active during the last half of May, and is beginning to catch up to normal. TWC’s tornado expert Dr. Greg Forbes has a preliminary count of 181 tornadoes for the month of May, through May 29, which is 35% below the 10-year average of 279 through May 29th. May 2012 had only 121 tornadoes. The 2013 tornado tally has risen significantly in the last half of May, due to 7 of the last 15 days having above-average numbers of tornadoes. Fortunately, we are well below-average for strong and violent EF-3, EF-4, and EF-5 tornadoes so far in 2013. According to NOAA, the U.S. has averaged 43 EF-3 or stronger tornadoes per year during the period 1954 – 2012. With tornado season nearly half over, only twelve EF-3 and EF-4 tornadoes have been recorded so far in 2013. An average year should have had at least twenty of these tornadoes by this point in the year. Here are the twelve EF-3 and stronger tornadoes so far in 2013, as detailed in Wikipedia’s excellent Tornadoes of 2013 page:

EF-5, May 20, Moore, Oklahoma. 24 deaths, 377 injuries, $2 billion in damage.
EF-4, May 28, Ottawa County, Kansas. Intensity based on mobile Doppler radar data. See the Capital Weather Gang’s description of this tornado.
EF-4, May 19, Shawnee, Oklahoma. 2 deaths, 6 injuries.
EF-4, May 15, Granbury, TX. 6 deaths, 24+ injuries.
EF-4, May 18, Rozel, Kansas.
EF-4, February 10, Hattiesburg, MS. 0 deaths, 82 injuries.
EF-3, Corning, KS, May 28.
EF-3, May 27, Lebanon – Esbon, KS. 1 injured. Wind gust of 175 mph measured by TIV2 intercept vehicle.
EF-3, May 15, Cleburne, TX. No deaths or injuries.
EF-3, January 30, Adairsville, GA. 1 death, 17 injuries, 363 buildings damaged or destroyed.
EF-3, April 11, Kemper County, AL. 1 death, 9 injuries.
EF-3, May 19, Luther – Carney, Oklahoma.

Figure 3. The annual number of EF-3 and stronger tornadoes, 1954 – 2012. The greatest number of these dangerous tornadoes was 131 in 1974, the year of the notorious “Super Outbreak.” The minimum was just 15, set in 1987. The average is 43 per year. Image credit: NOAA.

Video 1. Impressive 2-minute timelapse of the Bennington, Kansas wedge tornado of May 28, 2013, as filmed by the Aussie Storm Chasers. As discussed in an excellent blog post by Jason Samenow of the Capital Weather Gang, the violent EF-4 tornado stood still for nearly an hour, and had wind gusts as high as 264 mph at an altitude of 300 feet measured by Doppler on Wheels.

Remains of Hurricane Barbara bringing heavy rains to Mexico
Hurricane Barbara died on Thursday as it attempted to cross Mexico’s Isthmus of Tehuantepec into the southernmost Gulf of Mexico. While there is no low level circulation apparent on satellite loops this Friday morning, there is a bit of spin at middle levels of the atmosphere, and the remains of Barbara are kicking up some heavy thunderstorm activity over the southernmost Gulf of Mexico and adjacent land areas of Mexico. Wind shear is a high 20 knots in the region, and the area of disturbed weather is quite small, so I don’t expect any development to occur over the next few days. Wind shear is predicted to remain high over the Gulf of Mexico for the next six days, and none of the reliable computers models is calling for tropical cyclone development in the Atlantic during that period. Late next week, wind shear is predicted to drop, and there is a better chance for tropical cyclone development in the Gulf of Mexico or Western Caribbean. Both the GFS and ECMWF models suggest that a strong tropical disturbance with heavy rains may affect Mexico’s Yucatan Peninsula, Western Cuba, and the Southwest Florida by Friday next week.

Figure 4. Remains of Hurricane Barbara in the southernmost Gulf of Mexico as seen by MODIS at 12:05 pm EDT Thursday, May 30, 2013. Barbara had just been declared dead one hour prior to this photo. Image credit: NASA.

Saturday, June 1, is the first day of hurricane season, and I’ll post a quick look at what we might expect to see in June.


Hurricane Potential in The Gulf

Gulf of Mexico disturbance 96L poorly organized, but may develop
Posted by: Dr. Jeff Masters, on June 22, 2012 +27
An area of low pressure and heavy thunderstorms in the Southern Gulf of Mexico (designated 96L by NHC Thursday afternoon) is a threat to become a tropical depression this weekend, and all interests along the Gulf of Mexico coast should pay attention to the progress of this disturbance. The disturbance is bringing occasional heavy rains to Western Cuba, South Florida, and Mexico’s Yucatan Peninsula. Top winds measured in the surrounding ocean areas this morning were 27 mph, gusting to 34 mph, at the Yucatan Basin buoy between Mexico’s Yucatan Peninsula and the Cayman Islands. Our wundermap for the surrounding ocean areas show a ship that measured sustained winds of 30 mph near the western tip of Cuba this morning. Satellite-based surface wind measurements from the newly-available Oceansat-2 scatterometer, courtesy of India, show no signs of a surface circulation. Visible satellite loops show that 96L is less organized than it was Thursday evening, with only a little low-level spin apparent, and a modest area of disorganized thunderstorms. The decrease in organization is probably due to the moderate to high levels of wind shear of 15 – 25 knots over the region. Water vapor satellite loops show a modest region of dry air over the Central Gulf of Mexico, which is interfering with development. Ocean temperatures are 81 – 83°F in the Western Caribbean and Southern Gulf of Mexico, which is about 1°F above average, and warm enough to support formation of a tropical storm. A hurricane hunter mission is scheduled to investigate 96L this afternoon, but this mission will probably be cancelled due to the disturbance’s lack of organization.

Figure 1. Morning satellite image of the tropical disturbance 96L in the Southern Gulf of Mexico.

Forecast for 96L
Wind shear is predicted to remain in the moderate range through Saturday night, which is likely low enough to allow 96L to develop into a tropical depression; NHC gave 96L a 70% chance of developing into a tropical depression by Sunday morning, in their 8am EDT Tropical Weather Outlook. By Sunday, wind shear is predicted to increase, limiting 96L’s potential for intensification. Where the storm might go is anybody’s guess. The GFS model has consistently been predicting that a trough of low pressure pushing off of the U.S. East Coast will be capable of grabbing the disturbance and accelerating it to the northeast across Florida north of Tampa Bay on Sunday or Monday. However, an ensemble of forecasts from the model created by running the model with slight perturbations to the initial conditions shows a wide range of possible tracks, both to the east over Florida, and to the west towards Texas and Louisiana (Figure 2.) The latest ECMWF model run (00 UTC) predicts that the trough will not be strong enough to pull 96L northeastwards across Florida. The ECMWF predicts that a ridge of high pressure will build in over the Southern U.S., forcing the disturbance westwards across the Gulf of Mexico and into South Texas by Thursday. The UKMET model also favors a track west towards Texas. The NOGAPS model takes 96L to the northwest into Louisiana/Texas by Monday.

Figure 2. Which way will 96L go? The GFS model, when run at low resolution with 20 slightly different perturbations to the initial conditions in order to generate an ensemble of different forecasts, shows two distinct possibilities: a sharp east turn to move over Florida, or a west or northwest motion towards Louisiana or Texas. The high-resolution official GFS forecast is shown in white.

Jeff Masters


Hurricane Updates

Katia organizing; threat of a Gulf of Mexico storm
Posted by: JeffMasters, 4:38 PM GMT on August 31, 2011
Tropical Storm Katia 
Tropical Storm Katia continues its long trek across the Atlantic Ocean today, and is expected to arrive at a position several hundred miles north of the Northern Lesser Antilles Islands by Monday. At this time, it appears unlikely that the islands will receive tropical storm-force winds from Katia. Satellite images show that Katia is a well-organized storm with plenty of heavy thunderstorms. The storm has good upper-level outflow channels to the north and south, is under light wind shear, and is traversing warm waters, so it should be able to overcome any dry air problems by Thursday and intensify into a hurricane. It is looking less likely that Katia will affect land. Dr. Bob Hart’s Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia’s current position have an 11% chance of hitting North Carolina, a 12% chance of hitting Canada, a 5% chance of hitting Florida, and a 62% chance of never hitting land. It will be two more days before our computer models will be able to assess the threat to land, though, as Katia is currently still very far out at sea.

Figure 2. The morning run of the GFS Ensemble prediction. The ensemble prediction was done by taking a lower-resolution version of the GFS model and changing the initial distributions of temperature, pressure, and humidity randomly by a few percent to generate an ensemble of 20 different computer projections of where Katia might go. The operational (highest-resolution) version of the GFS model (white line) is usually more accurate, but the ensemble runs give one an idea of the uncertainty in the forecast. Very few of the ensemble members are currently showing a threat to the U.S. Canada is more at risk than the U.S., according to this model.

Gulf of Mexico disturbance a threat to develop
Surface winds over the Gulf of Mexico are rising today in advance of the approach of a tropical wave currently over the Western Caribbean, western tip of Cuba, and Mexico’s Yucatan Peninsula. This wave is headed west-northwest at 10 – 15 mph, and is under a high 20 – 30 knots of wind shear. The wave is slowly beginning to build an increased amount of heavy thunderstorms, and this process will accelerate on Thursday when the wave enters the Gulf of Mexico. By Friday, when the wave will be near the Louisiana or Texas coast, wind shear is expected to drop to low to moderate levels, and the wave may be able to organize into a tropical depression. This process will likely take several days, and formation of a tropical depression is more likely Saturday or Sunday. NHC is giving the wave just a 10% chance of developing into a tropical depression by Friday morning. Regardless, this system will spread heavy rains to portions of the Gulf Coast by Friday, with the Upper Texas coast and the coast of Louisiana the most likely recipients of heavy rain. Strong onshore winds raising tides to 1 – 2 feet above normal are likely over Louisiana beginning on Friday, and coastal flood statements have been issued for the region. Three of our four top models for predicting tropical cyclone development forecast that a tropical depression will form this weekend or early next week, and I think it is at least 50% likely we will have Tropical Depression 13 on our hands by Monday. However, steering currents will be weak in the Gulf, and it is difficult to predict where the storm might go.The GFS model has a possible tropical depression forming by Sunday off the coast of Mississippi, then moving east-northeast over the Florida Panhandle on Monday. The ECMWF model forms the storm on Monday off the coast of Texas, and leaves the storm stalled out there through Wednesday. The UKMET model forms the storm Saturday off the coast of Louisiana, and leaves it stalled out there through Monday. If the storm did remain in the Gulf of Mexico for three days as some of the recent model runs have been predicting, it would be a threat to intensify into a hurricane.

Update on Storm Activity in the Tropics

Posted by: JeffMasters, 2:25 PM GMT on August 14, 2011 +3
The latest in our unusual number of weak tropical cyclones this season, Tropical Depression Seven, has formed to the southeast of Bermuda. Unless you live in Bermuda, TD 7 is not going to be a concern. Radar out of Bermuda shows an area of rain on the northern side of TD 7 beginning to approach the island, and rain from the storm will likely affect the island tonight and on Monday. TD 7 is not well-organized, and has only limited heavy thunderstorms, as seen on visible satellite images. While wind shear is a low 5 – 10 knots, dry air surrounds TD 7, and is keeping the storm from intensifying. None of the computer models foresee that TD 7 will ever become more than a weak tropical storm.

Figure 1. Morning satellite image of TD 7.

TD 7 isn’t the only system Bermuda needs to watch, Invest 92L is a day behind it, and will follow a path very similar to TD 7’s. The disturbance will pass close to Bermuda on Tuesday, bringing the island a second round of tropical rains. However, Invest 92L is very disorganized, as seen on recent visible satellite loops. Dry air and close proximity to TD 7 will likely keep 92L from showing significant development over the next two days, with NHC giving the system just a 30% chance of developing into a tropical depression by Tuesday morning.

Elsewhere in the tropics
The disturbance midway between the Lesser Antilles Islands and the coast of Africa we’ve been tracking over the past few days, Invest 93L, has fallen apart and is no longer a threat to develop. This system will need to be watched once it enters the Caribbean later this week, though. None of the reliable models for predicting tropical cyclone formation predict development of this system or any new disturbances over the coming week.

Jeff Masters