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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Yeah. That's what I'm thinking. I went to the Dr. and had my fingers permanently crossed so I 'm hoping it wasn't all for nothing. Lol.
You are cracking me up!
7:00 PM CDT Thu Sep 1
Location: 26.6°N 91.4°W
Max sustained: 35 mph
Moving: NW at 6 mph
Min pressure: 1007 mb
All necessary conditions have been met for tropical cyclone formation. Warm core, a closed LLC (weak I know), persistent convection over or near the LLC for 12 hours or more (not a great deal but just enough), sustained winds of at least 30 mph measured by RECON instruments or observations from the ground.
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011
700 PM CDT THU SEP 01 2011
...TROPICAL DEPRESSION FORMS OVER THE CENTRAL GULF OF MEXICO...
...TROPICAL STORM WARNINGS ISSUED FOR PORTIONS OF THE NORTHERN GULF
COAST...
SUMMARY OF 700 PM CDT...0000 UTC...INFORMATION
----------------------------------------------
LOCATION...26.6N 91.4W
ABOUT 225 MI...360 KM SW OF THE MOUTH OF THE MISSISSIPPI RIVER
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...
A TROPICAL STORM WARNING HAS BEEN ISSUED FOR THE COAST OF THE
NORTHERN GULF OF MEXICO FROM PASCAGOULA MISSISSIPPI WESTWARD TO
SABINE PASS TEXAS.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* PASCAGOULA MISSISSIPPI WESTWARD TO SABINE PASS TEXAS
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
24 HOURS.
someone sedate him, please...his nonchalant hysteria is pushing me to the edge.
They just announced her TD 13 officially.
(~ 18.19 inHg) 4,225 meters
(~ 13,862 feet) 999.7 mb
(~ 29.52 inHg
FORECAST VALID 03/1800Z 29.3N 92.6W
MAX WIND 50 KT...GUSTS 60 KT.
50 KT... 30NE 60SE 0SW 30NW.
34 KT...150NE 90SE 30SW 100NW.
Are these two storms having or going to have a influence on each other. I've been shocked by the models so far...I really don't know what to expect from either:o
2009 has 5 named storms after September 1.
2008 had 8 named storms after September 1.
2007 had 9 named storms after September 1.
2006 4 named storms after September 1.
2005 15 named storms after September 1.
2004 8 named storms after September 1.
2003 10 named storms after September 1.
2002 7 named storms after September 1.
2001 10 named storms after September 1.
2000 11 named storms after September 1.
2000, 2001, 2003, 2004, 2005, 2007, 2008, 2010 are good indications of what I think we will see for the rest of the season.
The low level center is near the western edge of all that strong convection though. She is still a pretty sheared cyclone right now. Wait until this time tomorrow and things will have improved markedly for her.
WTNT43 KNHC 012342
TCDAT3
TROPICAL DEPRESSION THIRTEEN SPECIAL DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL132011
700 PM CDT THU SEP 01 2011
SATELLITE...SURFACE...AND NOAA RECONNAISSANCE AIRCRAFT DATA INDICATE
THAT THE LOW PRESSURE AREA OVER THE CENTRAL GULF OF MEXICO HAS
ACQUIRED A CLOSED CIRCULATION THAT IS DEFINED ENOUGH TO BE
CONSIDERED A TROPICAL DEPRESSION. HOWEVER...THE CENTRAL REGION
STILL CONSISTS OF A LARGE AREA OF LIGHT WINDS. THE AIRCRAFT DATA
AND BUOY OBSERVATIONS SUPPORT AN INITIAL INTENSITY OF 30 KT.
ALTHOUGH THERE IS WIND SHEAR OVER THE CYCLONE...AN UPPER-LEVEL
ANTICYCLONE IS FORECAST TO BUILD OVER THE GULF OF MEXICO DURING THE
NEXT DAY OR SO. THIS SHOULD PROVIDE A MORE FAVORABLE UPPER-LEVEL
ENVIRONMENT FOR STRENGTHENING. HOWEVER...SINCE THE CIRCULATION IS
LARGE ONLY GRADUAL STRENGTHENING IS ANTICIPATED. THE OFFICIAL
INTENSITY FORECAST FOLLOWS THIS REASONING AND IS CLOSE TO THE
SHIPS/LGEM GUIDANCE.
SINCE THE DEPRESSION IS IN ITS FORMATIVE STAGE THE INITIAL MOTION
IS HIGHLY UNCERTAIN. IN FACT...THE CENTER COULD REFORM WITHIN THE
LARGE CIRCULATION DURING THE NEXT 12-24 HOURS. THE DEPRESSION IS
CURRENTLY LOCATED TO THE SOUTH OF A MID/UPPER LEVEL RIDGE OVER THE
CENTRAL UNITED STATES. THE RIDGE IS FORECAST TO SLIDE EASTWARD AND
WEAKEN DURING THE NEXT 2-3 DAYS...LEAVING THE CYCLONE IN WEAK
STEERING FLOW. THE OFFICIAL FORECAST SHOWS A SLOW NORTHWESTWARD
MOTION DURING THE NEXT 24 HOURS...FOLLOWED BY A TURN TOWARD THE
NORTH AND NORTHEAST. THE NHC TRACK IS IN BEST AGREEMENT WITH THE
GFS AND ECMWF MODELS.
THE DEPRESSION IS EXPECTED TO MOVE VERY SLOWLY DURING THE NEXT 5
DAYS PROLONGING THE PERIOD OF TROPICAL STORM CONDITIONS AND HEAVY
RAINFALL OVER PORTIONS OF THE NORTHERN GULF COAST.
FORECAST POSITIONS AND MAX WINDS
INIT 02/0000Z 26.6N 91.4W 30 KT 35 MPH
12H 02/0600Z 27.5N 92.3W 35 KT 40 MPH
24H 02/1800Z 28.2N 92.6W 40 KT 45 MPH
36H 03/0600Z 28.7N 92.7W 45 KT 50 MPH
48H 03/1800Z 29.3N 92.6W 50 KT 60 MPH
72H 04/1800Z 30.1N 92.3W 40 KT 45 MPH...INLAND
96H 05/1800Z 31.1N 91.5W 30 KT 35 MPH...INLAND
120H 06/1800Z 32.0N 90.5W 25 KT 30 MPH...INLAND
$$
FORECASTER BROWN/AVILA
It's reasonable based on only 48 hours over water. That intensity will shift significantly if the track slows down at all.
Or relocates south, which is certainty possible.
Significantly?
TD 13 looks like a moderate Category 2 hurricane compared to No way Jose.
Not likely, one will overpower and absorb the other.. Worst case is a fujiwara affect... (I hate to use that word here as I am sure I will get flamed for it)
But that is rare.. Usually one just steals the mojo from the other.
Very unlikely unless TD 13 stays in or around the Gulf of Mexico for a really long period of time. I favor a quicker landfall time than many of the models have been calling for (3 days at most compared to 5 days).
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