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
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.
Jeff Masters
Another wildfire this afternoon in Bridgeport, Tx... still burning!
Mandeville, Louisiana Lakefront during TS LEE (
hurricanep)
TS Lee still affecting Louisiana
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But what always bugged me is understanding why the air parcles (cars in the front) slow down on the back side of upper troughs?
Yes, that's a normal couplet and no doubt its happening here. But upstream you've got massive ridge building along the West Coast forced, in turn, by anomalously deep troughing over the Gulf of Alaska whic is in turn related to the extratropical transition of a TS near Japan. These "Snakes on a Rossby wave train" can amplify mass adjustments in the atmosphere a great distance from the originating disturbance, and at a speed well in excess of the long wave velocity.
Far southeast TX got some rain. The rest? Nope. There were some gusty winds, and they preceded the frontal passage. There were winds after the front, too. The front just dried things out even more.
removed
How many Alaskans would we believe have an interest in the Tropics?
That in itself is an impressive irony.
As to his importance; I think he along with several others, takes a sober minded approach to forecasting dangerous hurricanes.
Well...a lot of us argued that Jose shouldn't have been classifed....and this has triggered a lot of debate on this blog....I have mixed results personally on whether Jose should have been classified or not...
Lee didn't create the wildfires BUT his wind fanned the flames that burned 300+ homes
So he might have not created the wildfire but those 300 homes are his fault. The winds were just too fast for Texas wildfire personnel to get the upper hand on it. Only east texas got rain. Central and west text have gotten very little to nothing on rainfall this year.
They're getting squished together. The pressure gradient becomes largest at the base of the trough, and thus the stream flow becomes "thinner" if you will, because air flows roughly along geopotential height contours. It's a little confusing because often the jetstream actually flows faster at the base of the trough, which would imply divergence since things are speeding up. However, perhaps the car analogy doesn't work that well here because the air isn't so much slowing down as it is getting squished together, which causes it to pile up regardless of its speed.
1.) heightened downsloping from the southern Rockies attributes to a naturally drier air across TX during the summer months as strong troughs of low pressure have moved across the central Plains.
2.) Intense upper air convergence on the backside of the upper level mean troughs has allowed a large buildup of subsidence to occur and combine with the mountain downsloping winds,
3.) finally a large mean surface high has been over the region for awhile now given the overall synoptic 500mb mean ridging and eastern US troughing have all combined to allow sinking motion over most of TX.
All three of these factors have combined right now to produce some of the driest air we have seen in a long time over the state of TX.
Oh Great Wise One, please explain. Do not include wind, dry air, or static in your explanation. Help the mere mortals to understand.
They always update before 8PM.
click for loop
a record rainfall of 3.85 inch(es) was set at Knoxville today.
This breaks the old record of 2.09 set in 1933
Holiday Hills PWS
4.16" since mid-night, and 4.67" storm total.
09/05/2011 0212 PM
Knoxville, Knox County.
Flash flood, reported by law enforcement.
Flooding is occurring on numerous roads around Knoxville
including Sherrill Blvd... Walker Blvd and Mineral Springs
Rd... heiskel Ave... and Proctor St. Water rescues have
been made from stranded cars on cross park Dr.
25minutes before 8pm is a little too much. xD
It's usually out by 7:50pm.
Aaaah...now I see...but why is it the geopotential height contours get squished at the base of the upper trough. I have indeed noticed this many times when I look at upper-level pressure maps...
I think it may
It's a holiday. Give 'em a break!
They're like isobars on a surface map. The pressure gradient is stronger when the spacing between them is smaller. This is because over a certain distance, the pressure (or geopotential height) changes by a greater amount. Geopotential height contours (isohypses) are very analogous to isobars because the pressure gradient is also stronger when isohypses are closer together.
The reason why they get closer together at the base of the trough is because this is where the trough is imposing the most on the ridge south of it. It is encountering greater resistance there, and thus the pressure gradient is stronger.
lol, it happens every once in a while, but it is very rare this season. Last year, it was more common.
Well it had a closed circulation, TS Force winds, and a little convection, seemed enough to warrant a TS.
well I dont think it really matters. He was named and that is a past event. I say Emily and Don because they really were annoying. Emily because she did whatever she wanted to do and forecasting her was a pain.
105 kts at 11 p.m. sounds good to me.
I agree, with MAY being the key word.
I'm not doing a good job of explaining things today, so I'll just let my online textbook from last year do the talking.
Chapter 10
MUCH improved.
Edit: I see it now. the 8pm TWO
On the back side of a trough you have negative vorticity advection where air flows from a region of low vorticity to region of higher vorticity. As the air stream flows towards the based of the trough the winds converge which creates sinking air. In order for the winds to curve the base of the trough they have to slow down because the curve is not instantaneous. When you drive a car do you speed into a curve?
Wow. A little early for that... I don't like the model runs for 95L, but I didn't like them this early in the game for Katia or Irene either and they didn't directly hit Florida. (I will assume that Katia will not pull a fast one and hit Florida)
Wow, somepin to watch.
i heard that Lee's winds toppled a tree and it hit power lines. if that is true, then technically, Lee would be responsible for starting that fire.
2011SEP05 231500 6.5 934.6/ -0.4 /127.0 6.3 6.6 6.6 NO LIMIT ON OFF 5.54 -70.53 EYE 28 IR 25.58 63.87 COMBO
ADT says 6.5, or 145 mph. I do not believe the intensity it that high, but it is definitely a solid Category 3 right now. Eye temperature is 5.54, and the deepest of convection is -70.53.
Which they would reposition the satellite...
ask that question in about 3-5 days and you will get a better answer. It is too far to say for sure where 95L will go. However, you should keep an eye on it since earlier the GFS model showed the storm almost slamming into Florida before making a sharp turn to the north. It shows an Irene.
I see now, you are looking the 8pm TWO and see that there will be no level rise on 95L
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