Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 1:24 PM GMT on September 08, 2010
Major flooding is occurring in the Austin, Texas region after Tropical Storm Hermine dumped an estimated 10 - 15 inches of rain over the past 24 hours. The flash flood warning for Austin from the National Weather Service at 4am this morning summarized the danger:
"Areas along I-35 and the Balcones Escarpment in and around the Austin Metro area will continue to experience a very dangerous flash flood event over the next few hours. Numerous evacuations and high water rescues have already been reported by the media and law enforcement personnel."
As wunderground's Dr. Rob Carver reports in his blog this morning, hardest hit was the area ten miles north-northwest of Austin, where an NWS cooperative station measured 10.11" of rain yesterday. The rains have swollen the South Fork of the San Gabriel River at Georgetown, Texas to 50-year flood heights.
Hermine has dissipated, but its heavy rains live on, and are now affecting the Dallas/Fort Worth region, where 1 - 3 inch rainfall amounts have been common. Hermine's rains are still lingering over the hard-hit Austin area, but should remain under one inch for the remainder of the morning. However, this afternoon, additional significant rains are possible near Austin as the sun's heat drives thunderstorm development in the very moist airmass over Central Texas.
Figure 1. Radar estimated rainfall for the Austin, Texas area shows that over fifteen inches of rain may have fallen in the region ten miles north-northwest of the city.
Gaston's remains no longer a threat
Dry air has significantly disrupted the remains of Tropical Storm Gaston, which are now over the Dominican Republic. NHC is now giving Gaston a 0% chance of developing, and no models are calling for development. It appears Gaston is finally dead.
Invest 91 off the coast of Africa
A large, well-organized tropical wave (91L) is just off the coast of Africa, near the Cape Verdes Islands, and is bringing sustained winds of 30 mph this morning to Praia in the southeast Cape Verdes. 91L is under a high 20 - 30 knots of wind shear, but this shear will decline to the moderate range, 10 - 20 knots, by Thursday. Water temperatures are warm, 28°C, and 91L has plenty of spin. The Saharan Air Layer (SAL) is well north of 91L, and should not be an impediment to development over the next few days. The models are pretty unanimous about developing 91L into Tropical Storm Igor sometime in the next 1 - 3 days. NHC is giving 91L a 70% chance of developing into a tropical depression by Friday. The GFDL model predicts 91L will be Hurricane Igor five days from now. The storm will track west to west-northwest over the next week, with long range forecasts from the GFS and ECMWF models putting 91L several hundred miles northeast of the Lesser Antilles Islands 7 - 10 days from now. History shows that about 20% of all tropical cyclones that have existed at 91L's current position have gone on to hit the U.S. East Coast; these odds are 10% for the U.S. Gulf Coast, 5% for Puerto Rico, and 10% for Canada. The forecast steering pattern for the coming two weeks from the GFS model shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors a continuation of the sort of tracks we saw for Danielle, Earl, and Fiona, with threats to the northern Lesser Antilles, Bermuda, the U.S. East Coast, and Canada.
Figure 2. Morning satellite image of Invest 91L (Igor?)
Elsewhere in the tropics
The GFS and ECMWF models are predicting the development of a new tropical wave off the coast of Africa 5 - 6 days from now.
Death toll in Guatemala from Tropical Depression 11E rises to 54
In the Eastern Pacific, heavy rains from Tropical Depression 11E have killed at least 54 people in Guatemala, with many more missing and feared dead. The heavy rains triggered nearly 200 landslides and collapses, causing damages near $500 million. Fifteen landslides hit portions of the Inter-American Highway, burying a number of vehicles and a bus. Tropical Depression 11E formed on September 3, moved over Mexico and Guatemala, and dissipated by the next day. Remnants from the depression may have played a role in the formation of Tropical Storm Hermine in the Gulf of Mexico on September 5.
Guatemala is still recovering from the impacts of Tropical Storm Agatha, which killed 287 people in the country and did over $1 billion in damage in May. This September's heavy rains in Guatemala come on the heels of the rainiest August in Guatemala's history, according to preliminary data from the National Institute of Seismology, Volcanology, Meteorology and Hydrology (INSIVUMEH). Rain was more than 100% above average in many parts of the country, and more than 200% above average in some regions. September and October are historically Guatemala's rainiest months, and any additional tropical cyclones which affect the country can be expected to cause more serious flooding.
Figure 3. Satellite image from Friday, September 3, 2010, showing Tropical Depression 11E over Mexico and Guatemala. Image credit: NASA.
I'll have an update Thursday morning.
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