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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If you run this water vapour loop you will see two ULLs , one immediately NNW of Katia and another much farther away to the NW in the upper left of the loop. In between those two is an induced ridge and once Katia passes below the ULL almost due North of it the induced ridge will force the track back to a westerly heading. Given that it is almost past the first ULL I do not expect it to make too much headway to the WNW before being shunted back to the West and this is reflected in the models bending the system to the left above PR.
If it does not gain enough latitude before the first ULL passes by to the North then IMO that would bring the Northern Leewards into play when the induced ridge takes over.
what "North" ?
Sure don't like the HIGH PRESSURE that builds over Katia at the end....thata not be good.
WTNT33 KNHC 020238
TCPAT3
BULLETIN
TROPICAL DEPRESSION THIRTEEN ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011
1000 PM CDT THU SEP 01 2011
...TROPICAL DEPRESSION MOVING VERY SLOWLY...EXPECTED TO DRENCH
PORTIONS OF THE NORTHERN GULF COAST...
SUMMARY OF 1000 PM CDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...26.6N 91.5W
ABOUT 225 MI...365 KM SW OF THE MOUTH OF THE MISSISSIPPI RIVER
ABOUT 270 MI...435 KM SSE OF PORT ARTHUR TEXAS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 2 MPH...4 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...
NONE
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* PASCAGOULA MISSISSIPPI WESTWARD TO SABINE PASS TEXAS...INCLUDING
THE CITY OF NEW ORLEANS...LAKE PONTCHARTRAIN...AND LAKE MAUREPAS
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
24 HOURS.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING POSSIBLE
INLAND WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED BY
YOUR LOCAL NATIONAL WEATHER SERVICE FORECAST OFFICE.
DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1000 PM CDT...0300 UTC...THE CENTER OF TROPICAL DEPRESSION
THIRTEEN WAS LOCATED NEAR LATITUDE 26.6 NORTH...LONGITUDE 91.5 WEST.
THE DEPRESSION IS MOVING TOWARD THE NORTHWEST NEAR 2 MPH...4 KM/H.
A SLOW NORTHWESTWARD MOTION IS FORECAST THROUGH FRIDAY...FOLLOWED
BY A TURN TOWARD THE NORTH FRIDAY NIGHT OR SATURDAY. ON THE
FORECAST TRACK...THE CENTER OF THE CYCLONE IS EXPECTED TO APPROACH
THE COAST OF SOUTHERN LOUISIANA DURING THE WEEKEND.
MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/H...WITH HIGHER
GUSTS. GRADUAL STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS
AND THE DEPRESSION COULD BECOME A TROPICAL STORM ON FRIDAY.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB...29.74 INCHES.
HAZARDS AFFECTING LAND
----------------------
RAINFALL...THE DEPRESSION IS EXPECTED TO PRODUCE TOTAL RAIN
ACCUMULATIONS OF 10 TO 15 INCHES OVER SOUTHERN LOUISIANA...SOUTHERN
MISSISSIPPI...AND SOUTHERN ALABAMA THROUGH SUNDAY...WITH POSSIBLE
ISOLATED MAXIMUM AMOUNTS OF 20 INCHES.
STORM SURGE...A STORM SURGE WILL RAISE WATER LEVELS BY AS MUCH AS 2
TO 4 FEET ABOVE GROUND LEVEL ALONG THE NORTHERN GULF COAST IN AREAS
OF ONSHORE FLOW.
NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...100 AM CDT.
NEXT COMPLETE ADVISORY...400 AM CDT.
$$
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011
1000 PM CDT THU SEP 01 2011
ALTHOUGH THE OVERALL SATELLITE PRESENTATION OF THE DEPRESSION HAS
CHANGED LITTLE THIS EVENING...NEW BANDS OF DEEP CONVECTION HAVE
DEVELOPED TO THE SOUTHEAST OF THE CENTER. SATELLITE
CLASSIFICATIONS AND RECENT BUOY OBSERVATIONS SUPPORT KEEPING THE
INITIAL INTENSITY AT 30 KT. A NOAA HURRICANE HUNTER AIRCRAFT IS
SCHEDULED TO INVESTIGATE THE CYCLONE OVERNIGHT. A SHEAR ANALYSIS
FROM UW-CIMSS SHOWS ABOUT 20 KT OF WESTERLY SHEAR OVER THE
CYCLONE. THIS SHEAR IS FORECAST TO RELAX DURING THE NEXT 12-24
HOURS AS AN UPPER-LEVEL ANTICYCLONE BUILDS OVER THE GULF. THIS IS
EXPECTED TO RESULT IN A FAVORABLE ENVIRONMENT FOR INTENSIFICATION.
HOWEVER...GIVEN THE LARGE SIZE OF THE CIRCULATION...STRENGTHENING
IS EXPECTED TO BE GRADUAL. THE NEW NHC INTENSITY FORECAST IS
NEARLY IDENTICAL TO THE PREVIOUS ADVISORY AND IS A BLEND OF THE
SHIPS/LGEM GUIDANCE.
THE DEPRESSION HAS NOT MOVED MUCH THIS EVENING...AND THE HIGHLY
UNCERTAIN INITIAL MOTION IS 315/2 KT. SINCE THE DEPRESSION IS
STILL IN THE FORMATIVE STAGE...THE CENTER COULD REFORM WITHIN THE
LARGE CIRCULATION DURING THE NEXT 12-24 HOURS. THIS POSSIBILITY
IS SUPPORTED BY THE GFS...WHICH SHOWS THE CENTER REFORMING FARTHER
NORTH WITHIN 24 HOURS. STEERING CURRENTS ARE EXPECTED TO REMAIN
WEAK DURING THE NEXT SEVERAL DAYS AS THE DEPRESSION REMAINS TO THE
SOUTH OF A WEAKENING MID/UPPER LEVEL RIDGE. AS THE RIDGE SLIDES
EASTWARD...IT SHOULD ALLOW THE CYCLONE TO MOVE SLOWLY NORTHWARD...
THEN NORTHEASTWARD. ALTHOUGH THE DYNAMICAL MODELS SHOWS LITTLE
OVERALL MOTION DURING THE NEXT 2-3 DAYS...THERE IS A LARGE SPREAD
IN THE GUIDANCE AND LOWER THAN NORMAL CONFIDENCE IN THE TRACK
FORECAST. THE UPDATED NHC TRACK IS A LITTLE SLOWER AND EAST OF
THE PREVIOUS FORECAST.
THE SLOW MOTION OF THE CYCLONE DURING THE NEXT 5 DAYS IS LIKELY
TO PRODUCE A PROLONGED PERIOD OF TROPICAL STORM CONDITIONS AND
HEAVY RAINFALL OVER PORTIONS OF THE NORTHERN GULF COAST.
FORECAST POSITIONS AND MAX WINDS
INIT 02/0300Z 26.6N 91.5W 30 KT 35 MPH
12H 02/1200Z 27.5N 92.2W 35 KT 40 MPH
24H 03/0000Z 28.0N 92.4W 40 KT 45 MPH
36H 03/1200Z 28.6N 92.4W 45 KT 50 MPH
48H 04/0000Z 29.2N 92.3W 50 KT 60 MPH
72H 05/0000Z 29.7N 92.1W 50 KT 60 MPH...NEAR THE COAST
96H 06/0000Z 30.5N 91.5W 35 KT 40 MPH...INLAND
120H 07/0000Z 31.5N 90.0W 25 KT 30 MPH...INLAND
$$
FORECASTER BROWN
NNNN
Very well said and good analysis!
we're never "wishcasters" we're "Texascasters"...LOL
no not north...it was an EXTEMELY vulgar comment made towards a plethera of races and nationalities that has been removed...had they been in front of me when that was said...they would be shy a few teeth
No problem, always willing to share.
+
Get in line tigger...
I agree with that point. If 93L was 500 miles out in the Atlantic is would never be numbered either for a lack of a well defined circulation or poorly organised convection. Currently the circulation is probably producing weak westerlies but it is very broad and ill-defined for a tropical cyclone. Storms near the US mainland do tend to get named/numbered more easily than those elsewhere even when there's evidence to suggest they should be classified as in the case of 94L today.
This argument has been going on for years and it isn't going to simmer down anytime soon.
oh ok, i guess that would highly understandable...
does it matter, the word shouldn't be used by any race...
+100
Wishcasting is not working, I guess it's time to use reverse psychology: Rain, rain go away...
94L is attached to a front & should not be organized..
does it matter? the color of one's skin has no bearing on the type of person...but i will put MONEY that my ancestors were here LONG before yours
*POOF*
She found 50W, which makes it no surprise...
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