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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lol....
Well I am hoping never to see Hurricane Omega (the last)!
96 hours...
now just cut that out!! ;)
I can't open that- what did you see (may I ask)?
We don't want this to eject it's north llc and relocate further south or southeast. This would just give more time over water and be further away from dry contental air; however, I'd say 93L will kick out its northern most llc and its already evident now that its the process of doing so. The shear is just too high 30-40 knots.
I do not see a TD yet, not even close. Like you said way too many negatives going for it. I'm thinking Saturday, maybe late Friday we get our TD, but to where it forms remains the million dollar question.
intensifying....from day 3 to day 4.
Actually the last name on the greek alphabet would be zeta.
One would think that the NHC should get more funding to deal with these types of complexities, since the Return on Investment is great for hurricane prediction. Funny how politics play out.
IKE is that 984mb??
To be honest...looks to drop just slightly south from day 3 to day 4.
***runs from room screaming*** arrrrgghhhh!
Looks like 989mb's.
Last thing anyone needs is a 1-2 punch with Katia giving the finger to the troughs and slamming the SE CONUS while Lee drills the Gulf coast.
Thanks
No: http://www.nhc.noaa.gov/aboutnames_greek.shtml
As soon as I say that they are now finding south winds. Needs to now shift to SW, W, etc.
Yea they could have used that 535 million we wasted on Solyndra.
Actually Zeta is the 6th letter of the greek alphabet.
Im not tellin' Pat, you tell Pat
Yes, as Dr Masters suggested, return on investment is massive. It costs millions to evacuate areas needlessly. The amount "saved" by cutting funding to NOAA/NWS is trivial compared to what is saved through their forecasts.
AL, 93, 2011090118, , BEST, 0, 270N, 905W, 30, 1010, DB, 0, , 0, 0, 0, 0,
Good afternoon (or morning in Alaska)!
Talk about heartache on this blog! LOL.
Ike....am I seeing the reincarnation of Hurricane Ike on that map?....please say no.
IMHO, I do believe that the culprit LLC has formed near 27N and 90W.
Link
That is a scary picture..
no, Omega is the last letter in the greek alphabet.
I'd put it closer to 91W IMO GR, but yeah it's in that general area and starting to look a little more like a true low pressure center.
Viewing: 451 - 501
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