Gulf of Mexico disturbance 93L a Lousiana flood threat; Katia a hurricane
Surface winds over the northern Gulf of Mexico are rising, pressures are falling, and heavy thunderstorms are building today thanks to a tropical disturbance (Invest 93L) that is the product of a tropical wave interacting with an upper-level low pressure system. At 8:35 am CDT, winds at the Mississippi Canyon 711 oil rig were south-southeast at 38 mph. This is just 1 mph below tropical storm force, but the wind instrument was 348 feet (106 m) above the ocean surface, and winds near the surface were probably considerably lower, near 30 mph. Long range radar out of Mobile, Alabama shows heavy rain showers building along the northern Gulf Coast, but these rain showers are not organized into spiral bands and show no signs of rotation. Strong upper-level winds out of the west-northwest are creating 30 knots of wind shear over 93L, keeping the storm's heavy thunderstorms disorganized. Strong onshore winds raising tides to 1 - 2 feet above normal are likely along the northern Gulf Coast through the weekend, and coastal flood statements have been issued for the region.
Figure 1. Predicted rainfall for the 5-day period ending at 8am EDT Sep 6, 2011. A large region of rains in excess of 15 inches is expected over Southeast Louisiana. Image credit: NOAA/HPC.
Figure 2. U.S. drought conditions on August 30. The rains from 93L have the potential to bring major drought relief to drought-stricken portions of the coast. Image Credit: U.S. Drought Monitor.
By late tonight, wind shear is expected to drop to the moderate range, below 20 knots, and 93L should begin to organize into a tropical depression. Wind shear is expected to remain moderate, 10 - 20 knots, into Monday. There is some cold, dry air aloft that will retard this process, and I think the earliest we would see a tropical depression is Friday afternoon. NHC is giving 93L a 70% chance of developing into a tropical depression by Saturday morning. All of the major models develop 93L near the Louisiana coast, and show a slow and erratic movement due to weak steering currents. Coastal Louisiana, Mississippi, Alabama, and the extreme western Panhandle of Florida will likely receive very heavy flooding rains beginning this afternoon and intensifying Friday and Saturday. The latest rainfall forecast from NOAA Hydrological Prediction Center (Figure 1) shows that a large area of 15+ inches of rain is expected over Southeast Louisiana. The region is under moderate drought, so flooding problems will be delayed compared to what we'd normally expect from heavy rains of over a foot. Nevertheless, minor to moderate freshwater flooding is likely from 93L, and flash flood watches are posted for New Orleans and surrounding areas, and rainfall amounts of 1 - 3 inches per hour are possible in some of the heavier rain squalls. Ocean temperatures are near record warmth, 88°F (31.3°C), which will provide plenty of moisture for heavy rains, and plenty of energy to help 93L strengthen into a tropical storm. Most of the models predict 93L will have some motion to the west by Saturday, which would bring rains to the Texas coast near the Louisiana border. Steering currents will be weak in the Gulf this weekend and early next week, making it difficult to predict where the storm might go. If 93L stays over water through Tuesday, like the ECMWF model is predicting, the storm would be a threat to intensify into a hurricane. Most of the other models predict 93L will move ashore over Louisiana by Sunday, limiting the storm's development to just tropical storm strength. I think it at least 50% likely 93L will be a tropical storm with 40 - 60 mph winds along the coast of Louisiana by Sunday.
Hurricane Katia
Hurricane Katia intensified into the 2nd hurricane of the 2011 season last night, and continues its long trek across the Atlantic Ocean today. Katia is expected to arrive at a position several hundred miles north of the Northern Lesser Antilles Islands by Monday. The islands are not in the cone of uncertainty, and it appears unlikely that they will receive tropical storm-force winds from Katia. Satellite images show that Katia is a well-organized storm with plenty of heavy thunderstorms, but the storm has been struggling with dry air and moderate wind shear of 10 -20 knots, and is looking less organized than it did last night. These problems will likely diminish by Friday night, as the upper low bringing the wind shear moves away. It is still unclear how much of a threat Katia may post to the U.S. Dr. Bob Hart's Historical Tropical Cyclone Probability web page suggests shows that tropical storms in Katia's current position have an 16% chance of hitting North Carolina, a 21% chance of hitting Canada, a 12% chance of hitting Florida, and a 54% chance of never hitting land. I suspect that Katia will turn north before reaching the U.S. and potentially threaten Bermuda and Canada, based on what past storms in similar situations have done, and assuming the jet stream maintains its current pattern of bringing frequent troughs of low pressure off the coast of the U.S. It will be another day or two before the models will begin to have a handle on the long-term fate of Katia, though.
Figure 3. Morning satellite image of Katia.
94L
A well-organized low pressure system with a surface circulation and limited heavy thunderstorm activity has developed between Bermuda and the Canadian Maritimes. This disturbance, (94L), is headed out to sea, and is being given a 10% chance of developing into a tropical depression by NHC. 94L is under a very high 30 - 40 knots of wind shear, and will not be able to intensify very much. However, Tropical Storm Jose formed from a similar type of system, and we might get surprised by 94L.
I'll have more on Irene in tomorrow's post.
Jeff Masters
Reader Comments
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don't think so - think they are working on the graphics - may be wrong - but that is the only area i see that is not working....
25.6n88.7w, 26.1n90.0w, 26.6n91.4w have also been re-evaluated&altered
25.4n88.7w, 26.0n90.0w, 26.3n90.8w, 26.6n91.4w are now the most recent positions
Starting 1Sept_12amGMT and ending 2Sept_12amGMT
The eastern line-segment represents TropicalDepression13's path
and the westernmost line-segment is the straightline projection.
Using straightline projection of the travel-speed&heading derived from the ATCF coordinates spanning the 6hours between 6pmGMT then 12amGMT :
TD.13's travel-speed was 7.2mph(11.5k/h) on a heading of 299.2degrees(WNW)
TD.13 was headed toward passage over the SouthTexasNuclearGeneratingStation between Palacios and BayCity,Texas in a bit more than ~1day17hours from now
Copy&paste 24.5n87.5w, 25.4n88.7w, 26.0n90.0w, 26.3n90.8w-26.6n91.4w, psx, 26.3n90.8w-28.675n95.8w, bbc, 28.796n96.049w into the GreatCircleMapper for more info
I know...
North of no above average winds prolly 5 to 10 mph pressure is at 1012 an falling ts warnings up but it might take what three days to make landfall
There is a difference between an opinion and labeling....
TS BUSTED FORECAST ALIBI
not exactly true, the Western Florida Panhandle region still has some ensembles in play. Furthermore, If the storm came in as far East as Miss/Alabama line depending if there was a reformation of the center, that would put the Western Panhandle region on the Eastern side. Everybody remembers Ivan. Landfall in Alabama/Mississippi but devastated the region from Pensacola to Destin on the right hand side.
Katrina was bad, but did not flood anyone out there, that I know of (hey, is possible someone had a flood issue, just not prevalent, there).
Tropical Depressions are not attached to fronts..it has to cut off first...
if classifying it is the conservative action, why is it that big of deal?
You couldn't be more right.
Does anyone know what the spin is just onshore across mid-coastal LA? Is it just a vorticy coming out/off the low? An ULL? We were just curious. TIA!
I'll buy that. It can't hurt.
From a purely scientific standpoint... maybe it's up for debate whether 13 follows the letter of the law...
But if the object of the game is to keep the public informed (it IS the first thing in NHC's mission statement)... it's the right call.
For those who haven't seen NHC's mission statement:
The NHC mission statement is to save lives (my emphasis in bold), mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather, and by increasing understanding of these hazards.
(nods)
I'm not even sure that Gause flooded in the May '95 flood.
here's a story about the levee and the temp pumps
Link
I am going to take twins advice and ignore the troll... Labeling people "idiot's" for their opinion is like me labeling you an idiot for having an opinion in the first place.... Enough said...
You must not be from round here..we all say anything more than an inch an hour will overwhelm the pumps and the streets will flood... (lol) :-)
I just got back from Dauphin Island Alabama and the wind is steady at 20MPH with gust to 26mph.... Waves are at 5 to 7 feet.... No rain as of yet but I think we will get about 15 to 18 inches..... All I can say is I might need a bigger Boat :o)
Taco :o)
yep blowing pretty good over in Orange Beach also..
just going by what the army corp of engineers have said about the "new" temporary pumps..
We should have 14L if 13L was classified. I see that's the whole argument this evening, lol.
yeah, they have no clue(please note sarcasm)
Because the goal is to up the number of storms to correlate with the premise of "climate change" and all of its speculated DOOM. There can be no other explanation. If there is, I want to know it.
Stop bashing the NHC, which most of you were getting mad about with Irene because other people were bashing them. But what are you doing right now?
Awesome tidbit: The author of that article is the voice of 21 characters in The Simpsons.
Shearer is the man!
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