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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At 850mb...that's not at the surface. However, they could gust at times to those speeds.
It would definitely not hold 20"...Maybe somebody else can explain in detail
In 1998 a drought in San Antonio ended when we received 18 inches of rain in one day. There was some flooding of streams etc, but no big deal. We had to go to a b-day party across town.
; )
I went into a store on the south side of San Antonio to buy a part for a motorcycle and everyone is the store was speaking Spanish. At the time it was a culture shock. Now its no big deal.
looks like mode runs has this going right at FL or NC
I had to slap my own hand away from the keyboard.
I lived in San Antonio and Corpus Christ for many years.
Guess he was too busy on TV to look at the latest GFS run if you can believe the GFS!!!LOL
Plus, NC sticks out so much.
I was wondering if anyone would go there...lol
Cover childrens' eyes!
Next week, or the week after that, and if not then the week after that.....and on and on and on......Hang in there. It has to break sometime.
Sure
Link
Things will change when this closes!
But where will it go, no body knows!
Chewie,, turn us around,fast !!
The overall atmospheric pattern was different with Andrew. He was turned to the north by an extremely strong area high pressure that moved into the southeast U.S. and built pretty far eastward into the western Atlantic, with zonal flow to the north ensuring that no major troughs eroded any portion of the ridge. It's difficult to compare any historical storms with current storms because every single one is unique and comes with their own unique atmospheric conditions to work with.
Like VA needs another one, golly can't we catch a break from the bad weather, like Irene, and the earthquake, btw had another aftershock this morning, 3rd strongest one since the quake last week.
I agree 10-12" would just be right...
Same with the mets here. They would point it out but say what they should say. Too early to tell.
Question - has there ever been a year where the NC outer banks were hit by more than one hurricane?
Thanks guys... :P
That is true...sigh... but we need rain!
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
441 AM CDT THU SEP 1 2011
...AUGUST 2011 IS ONE FOR THE RECORD BOOKS...
...AUGUST 2011 IS THE WARMEST MONTH EVER RECORDED...
...AUGUST 2011 REMAINS DRY WITH RAINFALL
TOTALS LESS THAN AN INCH...
THE SUMMER OF 2011 CONTINUES TO INFLICT TREMENDOUS HEAT ACROSS
SOUTHEAST TEXAS. AUGUST 2011 WAS THE WARMEST MONTH EVER RECORDED
ACROSS SOUTHEAST TEXAS AND THE WARMEST AUGUST EVER RECORDED. THE
AVERAGE TEMPERATURE IN HOUSTON FOR AUGUST 2011 WAS 90.4 DEGREES.
THIS IS 2.5 DEGREES WARMER THAN THE PREVIOUS WARMEST MONTH (AUGUST
2010) WITH AN AVERAGE TEMPERATURE OF 87.9 DEGREES. COLLEGE STATION
CRUSHED IT'S PREVIOUS WARMEST MONTH BY 3.0 DEGREES AND GALVESTON
BEAT IT'S PREVIOUS WARMEST MONTH BY 1.2 DEGREES. COLLEGE STATION HAS
RECORDED A STAGGERING 58 DAYS WITH TEMPERATURES AT OR ABOVE 100
DEGREES THIS YEAR TYING IT'S ALL TIME RECORD OF 58 DAYS (1917).
THIS RECORD WILL LIKELY FALL THIS AFTERNOON.
THE DROUGHT HAS TAKEN A BACKSEAT TO THE INTENSE HEAT OF RECENT DAYS
BUT MAKE NO MISTAKE...THE DROUGHT IS ONGOING AND AUGUST 2011 WAS ONE
OF THE DRIEST ON RECORD. THE CITY OF HOUSTON RECORDED IT'S SECOND
DRIEST AUGUST ON RECORD. THE INTENSE HEAT PRODUCED NUMEROUS RECORDS.
BELOW IS A BRIEF SUMMATION:
CITY OF HOUSTON:
CONSECUTIVE DAYS WITH TEMPERATURES AT OR ABOVE 100 DEGREES
24 DAYS AUG 2011 NEW
14 DAYS JUL 1980 PREV
MOST 100 DEGREE DAYS IN A YEAR
41 DAYS 2011 NEW
32 DAYS 1980 PREV
MOST 100 DEGREE DAYS IN A MONTH
30 DAYS AUG 2011 NEW
18 DAYS JUL 1980 PREV
HIGHEST DAILY TEMPERATURE IN CITY HISTORY
109 DEGREES 08/27/2011 TIE
109 DEGREES 09/04/2000
WARMEST AVERAGE MONTHLY TEMPERATURE (ALL TIME)
90.4 DEGREES AUGUST 2011 NEW
87.9 DEGREES AUGUST 2010 PREV
WARMEST DAILY AVERAGE TEMPERATURE
95.0 08/27/2011 NEW
92.5 08/18/2011 PREV
92.0 08/07/2003 PREV BEFORE 2011
AUGUST RECORDS:
WARMEST DAILY TEMPERATURE
109 DEGREES 08/27/2011 NEW
108 DEGREES 08/18/1909 PREV
WARMEST AVERAGE MONTHLY HIGH TEMPERATURE
102.0 DEGREES - FIRST TIME IN CITY HISTORY THAT THE AVERAGE MONTHLY HIGH
TEMPERATURE HAS EXCEEDED 100 DEGREES
99.4 DEGREES - JULY 1980 PREV
98.5 DEGREES - AUG 1998 PREV
WARMEST AVERAGE MONTHLY LOW TEMPERATURE
78.7 DEGREES - 2011 NEW
78.4 DEGREES - 1964 PREV
MOST 100 DEGREE DAYS IN AUGUST
30 2011 NEW
14 1998 PREV
DAILY RECORDS
NEW PREV
101 08/06/2011 (TIE) 101 - 1948
102 08/11/2011 101 - 1907
102 08/16/2011 (TIE) 102 - 1925
104 08/26/2011 102 - 1990
109 08/27/2011 104 - 1990
107 08/28/2011 101 - 1902
107 08/29/2011 103 - 1909
THERE WERE ALSO SEVEN NEW OR TIED RECORD HIGH MINIMUM TEMPERATURES.
ALL TOLD FOR THE SUMMER...THE CITY OF HOUSTON ESTABLISHED 14 NEW OR
TIED HIGH TEMPERATURES AND 17 NEW OR TIED RECORD HIGH MINIMUM
TEMPERATURES. THE SUMMER OF 2011 HAS BEEN BRUTAL. JUNE 2011 HAD THE
EARLIEST 100 DEGREE DAY IN CITY HISTORY ON JUNE 2ND AND ALSO THE
WARMEST JUNE TEMPERATURE EVER RECORDED WITH A VALUE OF 105 DEGREES
ON JUNE 5TH AND AGAIN ON THE 6TH. HOUSTON RECORDED IT'S WARMEST
JUNE...3RD WARMEST JULY AND WARMEST AUGUST. THERE WERE FIVE DAYS
THIS SUMMER WITH A TEMPERATURE AT OR ABOVE 105 DEGREES WHICH TIES
THE SUMMER OF 2000.
well the GFS is out to 160 hrs on the site i use and no north yet
Lakes are low everywhere. A few years ago, a freak summer storm dumped 19 inches somewhere northwest of Austin and rapidly increased Lake Travis' lake level by a bunch. It was getting a bit on the low side...
Coordinates: 26.5667N 91.2667W
Acft. Static Air Press: 923.7 mb (~ 27.28 inHg)
Acft. Geopotential Hgt: 770 meters (~ 2,526 feet)
Extrap. Sfc. Press: 1007.7 mb (~ 29.76 inHg)
D-value: -
Flt. Lvl. Wind (30s): From 160° at 0 knots (From the SSE at ~ 0.0 mph)
Air Temp: 23.6°C (~ 74.5°F)
Dew Pt: 20.9°C (~ 69.6°F)
Peak (10s) Flt. Lvl. Wind: 1 knots (~ 1.1 mph)
SFMR Peak (10s) Sfc. Wind: 17 knots (~ 19.5 mph)
SFMR Rain Rate: 0 mm/hr (~ 0 in/hr)
(*) Denotes suspect data
probably the "center" of 93L
I was born in Corpus Christi in 1962 and in Houston now. Family still there.
I don't think Texas is getting the much needed rain.
:(
I like dat un.
Sorry, but I just don't see what you are. most of the models still take this thing clearly to the NW and that ULL still has a firm grip between the bermuda and atlantic highs. I'll be quite shocked if this thing gets anywhere near NC much less Florida.
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