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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A
broad area of low pressure south of Louisiana is producing
thunderstorms and gusty winds over the Central Gulf of Mexico this
afternoon. So far, shear has kept this system from developing, but that
is expected to change by Friday. A reconnaissance plane will
investigate the system later this afternoon. Late tonight after the
models have been run, we should start to have better data on where this
system will go and how strong it will be.
The
usually reliable European Model now develops this system into a
depression Saturday south of Sabine Pass. By Sunday, we may see
tropical storm Lee form. By Labor Day, Lee could become a hurricane.
Tuesday, the European takes Hurricane Lee into Southeastern Louisiana.
Let
me remind you that nothing has formed at this point and it may or may
not, but there is a pretty good indication that it will. Also, the
exact path is not set in stone and the strength of the system is not
known. So, keep abreast of the weather through the weekend and
remember, that the forecast could change for the better or worse.
YOU WIN.............NUTHIN!
20:52:30Z 25.100N 91.583W 959.1 mb
(~ 28.32 inHg) 447 meters
(~ 1,467 feet) 1008.5 mb
(~ 29.78 inHg) - From 299 at 12 knots
(From the WNW at ~ 13.8 mph)
Good 'cuz it's forecast to come right over my house and sit there.
This is very interesting...moves from la to Texas. hmmmm
hmmm
I'm bummed also, my Aunt has a huge boat and we all were going to get together for a family part at crab island. I guess it possibly won't happen.
Hey DFW. Yeah, just posted a update from out locals said the same thing. Looks like the NAM wanted to send some rain up the length of east TX/west LA. That would be nice. :)
roflmbo...i know right?! i found it a bit disturbing that the discussion on Katia said that a few models keep it going west when the other models have her being picked up...this time of year keeps my stomach in knots i swear....
geez...wish these things would make up their mind.
What I'm not sure about is his explanation behind the stronger surface winds being a result of baroclinic instability. The only baroclinic process I can think of is the ULL to the north inflicting strong divergence over the system...or is that not a baroclinic process? idk, someone feel free to teach me a lesson, I'm not met
20 inches for NO/MS is what one model forecasts, and BAMS has the Low going west to 100 miles from Corpus then go south parallel with Brownsville headed back east and then curve back up through central MS...LOL!!!
Kinda looks like it's showing a strong small ridge to the east? Interesting thanks. :)
Lol. I'm gonna need dramamine now. :)
I'd give them a call.
Pat, do me a favor, please. Grab your radar and move about 300 miles west. Bring the echoes with you. Thanks!
Wilma? 2005
AtHome - think about me, i won't get any of it up here
UPDATE 4.1 Earthquake in LA, CA
What up Kris? not looking good for your show Fri nite! We considering canceling our show sunday nite in Madisonville.
that is true only its not going to weaken or even stop intensification. the dry air will prevent RI. Irene became a cat 3 and she didnt go through RI. if lee stalls out in the gulf for 4 to 5 days is possible he becomes one although a cat 1 is more realistic but still not out of the book. we shouldnt discount this situation of lee becoming a major just yet right?
.SYNOPSIS...TROUGH FROM 30N91W TO 24N91W WITH EMBEDDED LOW PRES
1010 MB...POSSIBLE TROPICAL CYCLONE...AT 27N91W. MODEL SOLUTIONS VARY GREATLY IN TRACKING AND TIMING OF LOW PRES AS IT MEANDERS OFF LOUISIANA COAST...WITH DIFFERENCES IN LANDFALL FROM FRI NIGHT ON THE GFS TO MON NIGHT ON THE ECMWF. WINDS INCREASE TO NEAR GALE FORCE WITHIN 150 NM OF E LOW PRES CENTER WITH SEAS TO 12 FT. LOW PRES ACCOMPANIED WITH EXTENSIVE AREA OF HEAVY RAINFALL EXPECTED TO EVENTUALLY MOVE INLAND.
we pushing but itsa tuff ridge to budge
Right on Brock! We lived in the Fort Myers, Florida, area (65 miles north of Wilma's landfall) and Wilma took off half our roof. No minor storm.
you go mail..
I agree that we won't see a storm circulation covering the entire breadth of the Gulf of Mexico. However, light westerly to stationary winds may already extend up to 200 miles south of the center, which is impressive for an invest.
I'm going to disagree and assert the notion that the system will remain fairly large.
Who is that??
Tell me about it. I do appreciate your efforts though. ... Let me turn off some of these industrial heaters and we will see if that helps.
Like what happened with Irene? Remember all that excess convection it had on the west side for a while?
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