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 , 5. syyskuuta 2011 klo 16:43 (GMT)
Texas' unprecedented heat wave and drought turned deadly yesterday when fires fanned by Tropical Storm Lee's gusty winds swept through East Texas, torching 300 homes near Austin, and killing a woman and her 18-month old daughter who couldn't escape the flames in Gladewater. At Austin Bergstrom Airport yesterday afternoon, the counter-clockwise circulation around Tropical Storm Lee brought sustained winds of 25 mph, gusting to 31. Lee didn't bring any clouds or moisture to Austin, and the afternoon high hit 102°, with a humidity of 22%. With the region enduring it's driest 1-year drought on record, yesterday's heat, dryness, and winds resulted in extremely critical fire conditions. The forecast today for Austin is marginally better--temperatures will be cooler, only reaching the upper 80s, but strong winds of 20 - 25 mph will continue to blow, and the atmosphere will be drier, with humidities in the 15 - 25% range. NOAA's Storm Prediction Center has declared a "Critical" fire weather danger area for East Texas today, one level below yesterday's "Extremely Critical" conditions. You can monitor today's fire activity by using our wundermap for Austin with the fire layer turned on. The summer of 2011 now holds every major heat record for the city of Austin, including most 100° days (67 so far), hottest month in recorded history (August, breaking the previous record by a remarkable 2.1°), hottest summer (by 1.1°), and hottest day in history (112°F, tied with Sep, 5, 2000.)
Texas' unprecedented heat
For as long as people have been taking weather measurements in Texas, there has never been a summer hotter than the summer of 2011. As wunderground's weather historian Christopher C. Burt documents in his latest blog post, seventeen major cities in Texas recorded their hottest summer on record in 2011. Most of these stations had records extending back more than 100 years, and several of the records were smashed by an amazing 3.4°F--at Lubbock and at Wichita Falls. Neighboring states also experienced unprecedented heat, with Oklahoma recording America's hottest month by any state in recorded history during July, and Shreveport, Louisiana breaking its record for hottest month by 3°F in August. Mr. Burt commented to me: " I do not believe I have ever seen a site with a long period of record, like Shreveport, where records go back to 1874, break its warmest single month on record by an astonishing 3°. This is unheard of. Usually when a site breaks its single month temperature record, we are talking about tenths of a degree, rarely a whole degree, let alone 3 degrees! Hard to believe, frankly." Texas has also had its worst fire season on record, with over 3.5 million acres burned this year, and it's driest 1-year period in recorded history.
Figure 1. Observed rainfall for the seven-day period ending at 8 am EDT Monday Sep 5, 2011. Tropical Storm Lee had dumped in excess of ten inches of rain sections of Louisiana and Mississippi (pink colors). Image credit: NOAA/AHPS.
Heavy rains from Lee creating dangerous flooding situation
Tropical Storm Lee has been absorbed by a cold front, and is no longer a tropical depression. However, the remnants of Lee are bringing torrential rains to the South and Appalachians today, and pose a serious flood threat. NOAA's latest Quantitative Precipitation Forecast warns that "an excessive and life-threatening rainfall event will be unfolding today and tonight across the Tennessee Valley and also the Southern Appalachians." A wide region of 4 - 8 inches of rain is expected along the path of Lee's remnants as they slide northeastwards along the front. These rains will likely accumulate later this week to 2 - 3 inches over New England regions devastated by Hurricane Irene's floods. Also of concern is the potential for tornadoes today. NOAA's Storm Prediction Center has logged 22 tornado reports so far from Lee, and today promises to be the most serious day for tornadoes yet, with SPC predicting a "Moderate Risk" of tornadoes across the South. Lee's heaviest rain amounts, by state, as of 10 am CDT today:
Holden, LA: 15.43"
Florence, MS: 13.45"
Mobile, AL: 11.35"
Milton, FL: 10.03"
Cumberland City, TN: 5.09"
Bridge City, TX: 3.12"
Plum Springs, KY: 3.10"
Figure 2. Predicted rainfall for the 5-day period 8am EDT Monday - 8 am EDT Saturday, Sep 10, 2011. Lee's remnants are expected to bring a large swath of 4+ inches of rain all the way to Pennsylvania. Image credit: NOAA/HPC.
Figure 3. Severe weather risk for Monday, September 5, 2011.
Hurricane Katia is close to major hurricane strength, and is now a high-end Category 2 hurricane with 110 mph winds. Latest satellite loops show a well-defined eye and good upper-level outflow on all sides, but the hurricane still has a lopsided appearance, due to the impacts of dry air and moderate wind shear on its south side.
The computer models have finally come into agreement on the long-range future of Katia, determining that the trough of low pressure that will develop over the Eastern U.S. later this week will turn the hurricane to the north well before the storm reaches the U.S. As the storm moves northwards past North Carolina, Katia will get caught up in west-to-east moving winds associated with the jet stream, and taken northeastwards out to sea. No land areas are in Katia's cone of uncertainty, though Newfoundland, Canada will need to watch future forecasts to see how close Katia may pass to the southeastern portion of that province. The main impact of Katia will be high surf leading to beach erosion and dangerous rip currents. Long period swells from Katia are arriving at the Southeast U.S. coast today, and the entire U.S. East Coast will receive an extended multi-day period of high surf.
Figure 4. Afternoon satellite image of Hurricane Katia.
95L off the coast of Africa
A large tropical wave with plenty of intense thunderstorm activity and spin is located about 500 miles southwest of the Cape Verde Islands off the coast of Africa. This wave, Invest 95L, is under a moderate 10 - 20 knots of wind shear, and is headed west at 15 mph. Water vapor satellite images show that 95L is embedded in a very moist environment. Ocean temperatures are near 28°C, which is 1.5°C above the 26.5°C threshold usually needed for a tropical storm to form. With wind shear predicted to drop to the low range tomorrow, I don't see anything that would keep 95L from becoming a tropical depression in two or so days. NHC is giving 95L a 20% chance of developing into a tropical depression by Wednesday; given the storm's rather impressive organization and spin apparent on recent satellite loops, I'd put these odds at 40%. The NOGAPS model predicts 95L will develop by Saturday, a few hundred miles north of the Northern Lesser Antilles Islands, but this storm could just as easily pass directly through the Lesser Antilles on Saturday or Sunday, and develop into a tropical storm much sooner. If you plan on being in the Lesser Antilles Islands this weekend, pay attention to 95L.
New Gulf of Mexico disturbance
A cold front swept into the Gulf of Mexico off the coast of Texas behind Tropical Storm Lee early this morning. The front is expected to continue to the east and stall out Tuesday and Wednesday along a line from Louisiana to Mexico's Bay of Campeche in the southern Gulf of Mexico. Several recent runs of the ECMWF and GFS models have given support to the idea that a tropical depression would form at the tail end of this front late this week, in Mexico's Bay of Campeche. The path such a storm might take would depend strongly on where the center forms. A more northerly formation location near the top of Mexico's Yucatan Peninsula would likely result in a northward motion towards the Florida Panhandle, while a more southerly formation location might lead to the storm getting trapped in a region of weak steering currents, resulting in a slow, erratic motion in the southern Gulf. NHC is currently not highlighting the Bay of Campeche in their Tropical Weather Outlook, and it will likely be Wednesday before enough heavy thunderstorms build to warrant mention.
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