Gulf of Mexico disturbance 93L a Lousiana flood threat; Katia a hurricane

By: Dr. Jeff Masters , 3:28 PM GMT on September 01, 2011

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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

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I like how one (only one!) of the ensemble models has it going straight through Charleston. (not *like* like, know what I mean)
this recurve is looking less likely, huh
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Quoting MississippiWx:


You should chime in more. Miss seeing you on the blog!


Agreed. Alec should stop by more!
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Quoting GTcooliebai:
And one must question why they call Florida the sunshine state in times like this...


Well, Florida gets typically a lot of sun yet more rain than most of the U.S. its hw tropical climates are. Many places in Central America get more sun but a much higher amount of rain than places in the northern U.S. which are cloudier on average.


In case you haven't noticed, there has been a lack of rain, much lower than forecast since yesterday over Florida because of high cloudiness, they said today would be sunnier but forecasters messed up again. Because the thick clouds are still here and keeping sun out which is causing well below what we should be getting
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recurve..schmeecurve I'm still wondering why they call the study of weather meteorology.. isn't that the study of meteors???
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Quoting GetReal:


We are Levi.... I am on the SW side of metro NOLA area.


Well...

New Orleans, Louisiana (Airport)
Updated: 2:53 PM CDT on September 01, 2011

81 °F / 27 °C
Light Rain
Humidity: 82%
Dew Point: 75 °F / 24 °C
Wind: 4 mph / 6 km/h / 1.5 m/s from the SE

Pressure: 29.98 in / 1015 hPa (Steady)
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MONTHLY TROPICAL WEATHER SUMMARY
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT THU SEP 1 2011

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

SEVEN NAMED STORMS AND A TROPICAL DEPRESSION FORMED IN THE ATLANTIC
BASIN DURING THE MONTH OF AUGUST. ONE OF THESE STORMS WAS MAJOR
HURRICANE IRENE THAT IMPACTED MUCH OF THE EAST COAST OF THE UNITED
STATES. THE NUMBER OF NAMED STORMS WAS WELL ABOVE THE LONG-TERM
(1944-2010) AVERAGE OF FOUR...BUT THE NUMBER OF HURRICANES...TWO...
WAS BELOW THE AVERAGE. IN TERMS OF ACCUMULATED CYCLONE ENERGY...
ACE...WHICH MEASURES THE COMBINED STRENGTH AND DURATION OF TROPICAL
STORMS AND HURRICANES...TROPICAL CYCLONE ACTIVITY WAS ABOUT AVERAGE.

REPORTS ON INDIVIDUAL CYCLONES...WHEN COMPLETED...ARE AT THE WEB
SITE OF THE NATIONAL HURRICANE CENTER...USE LOWER-CASE LETTERS...
HTTP://WWW.NHC.NOAA.GOV/2011ATLAN.SHTML

SUMMARY TABLE

NAME DATES MAX WIND (MPH)
------------------------------------------------- ---
TS ARLENE 29 JUN-1 JUL 65
TS BRET 17-22 JUL 65
TS CINDY 20-22 JUL 60
TS DON 27-30 JUL 50
TS EMILY 1-7 AUG 50
TS FRANKLIN 12-13 AUG 45
TS GERT 14-16 AUG 60
TS HARVEY 19-22 AUG 60
MH IRENE 20-28 AUG 120
TD TEN 25-26 AUG 35
TS JOSE 28-29 AUG 45
H KATIA 29 AUG- 75

$$
HURRICANE SPECIALIST UNIT
Member Since: July 6, 2010 Posts: 113 Comments: 32262
A weaker Katia. I wonder what that might do for its forecast track?
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... and up from Gulf came a Bubblin' Crude
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BULLETIN
TROPICAL STORM KATIA ADVISORY NUMBER 15
NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011
500 PM AST THU SEP 01 2011

...KATIA WEAKENS TO TROPICAL STORM...EXPECTED TO RESTRENGTHEN...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...16.1N 49.2W
ABOUT 930 MI...1495 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...990 MB...29.23 INCHES
Member Since: July 6, 2010 Posts: 113 Comments: 32262
Quoting quasigeostropic:
Hey MississippiWX, correct, I haven't posted here for a year or two I think...I'm very busy these days but haven't really followed tropical weather much lately(except for Irene). I'm mainly a lurker, I let Levi and others do a fantastic job explaining the weather:)

If people are interested in learning some basic hurricane 101, they are welcome to view my hurricane forecasting tutorial.


You should chime in more. Miss seeing you on the blog!
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Quoting atmoaggie:
I *think* that is going to be expected with this system for a while, yet. This is an odd one where the mid-level circulation isn't as developed as the surface circulation. Even the 5 knot flight level west wind had a 22 knot surface wind.

So far, all of the stronger areas of surface winds have been under a slower flight level wind.

This system is vorticity inverted...



Like a baroclinic system...or a tornado :)
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Quoting Levi32:


You must not be right near sea-level then. 1006mb is a bit low.


We are Levi.... I am on the SW side of metro NOLA area.
Member Since: July 4, 2005 Posts: 204 Comments: 8896
Hey MississippiWX, correct, I haven't posted here for a year or two I think...I'm very busy these days but haven't really followed tropical weather much lately(except for Irene). I'm mainly a lurker, I let Levi and others do a fantastic job explaining the weather:)

If people are interested in learning some basic hurricane 101, they are welcome to view my hurricane forecasting tutorial.
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...KATIA WEAKENS TO TROPICAL STORM...EXPECTED TO RESTRENGTHEN...
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Member Since: July 3, 2005 Posts: 426 Comments: 128639
...KATIA WEAKENS TO TROPICAL STORM...EXPECTED TO RESTRENGTHEN...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...16.1N 49.2W
ABOUT 930 MI...1495 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...70 MPH...110 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...990 MB...29.23 INCHES
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Quoting quasigeostropic:
Re-curve connotes that it has at least curved prior. A storm turning out to sea the FIRST time, I would use "curving". If a storm is going West and then starts turning northward but misses the trough, goes West again, then catches the second trough and turns north again, that SECOND turn would technically be considered a re-curve.

Not going to make a big deal about it though.:)



I think I'd rather listen to politics than the explanation of the word "recurve".....let it go already
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Quoting GetReal:
My home barometer has seen a significant drop over the last 2.5 hours; dropping from 29.85 inches to 29.73 inches!


You must not be right near sea-level then. 1006mb is a bit low.
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To be precisely mathematical.. any direction of heading is a "curve" .. the common WNW heading is a curve. When the storm bends NW,N,NE, this phenomenon is known as a recurve. The lay person term of "curve" wouldn't work because curve is any direction. If you were to say, however, that the storm is entering recurvature, then it is clear to all what you mean. It is a word, a term, nothing more.
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Still no renumber...Not expecting 5PM classification...
Member Since: July 6, 2010 Posts: 113 Comments: 32262
Quoting Neapolitan:
The term "recurve" is a word meaning "to bend backwards or down"; the "re" in "recurve" isn't a prefix indicating a repeat any more than the "re" in "regret" means that you "gret" something then "gret" it again. ;-) A recurve simply means a westbound storm at lower latitudes moves north toward the mid-latitudes, then gets picked up and recurves--that is, bends backward from its initial track--and moves to the northeast or east.
Exactamente

A good way to illustrate this point about recurving is in the epac where storms hardly ever make it far north enough to feel the effects of troughs. As a result, most of them begin heading west or west-northwest and then turn more toward the west-northwest or northwestward out to sea as they round the subtropical ridge. However, they rarely ever turn out toward the east since they usually dissipate before reaching the latitude at which a trough could turn them out



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Do you have to peat before you repeat? Ask the Packers...
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would we have any affects from 93L / TD / LEE,,,here in the Fla. panhandle over the holiday weekend??
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Quoting LargoFl:
I had heard they were or Are considering raising the max limit of categories to cat-7


I did hear that it was considered to make a cat6 (I think with winds > 175mph), but it was then determined that the damages from that high of a windspeed wouldn't be any worse than cat5 winds.

I really don't think that windspeed should be the main hurricane scale anyways...just look at Irene, Ike, and Katrina to name a few. The damages from each were typical for at least a category higher from each storm.
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Quoting Neapolitan:
The term "recurve" is a word meaning "to bend backwards or down"; the "re" in "recurve" isn't a prefix indicating a repeat any more than the "re" in "regret" means that you "gret" something then "gret" it again. ;-) A recurve simply means a westbound storm at lower latitudes moves north toward the mid-latitudes, then gets picked up and recurves--that is, bends backward from its initial track--and moves to the northeast or east.


But being combobulated is so much fun...
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My home barometer has seen a significant drop over the last 2.5 hours; dropping from 29.85 inches to 29.73 inches!
Member Since: July 4, 2005 Posts: 204 Comments: 8896
With respect to the phrase recurve, I agree with those 930. Regardless, recurve is now a term of art with a specific meaning when discussing hurricanes. Whether or not the origins of this term of art is grammatically correct is now irrelevant. Everyone who follows hurricanes knows what recurve means.
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Another 96L??

Member Since: July 6, 2010 Posts: 113 Comments: 32262
93L Floater - RGB Color Infrared Loop
Member Since: July 3, 2005 Posts: 426 Comments: 128639
Quoting quasigeostropic:
Re-curve connotes that it has at least curved prior. A storm turning out to sea the FIRST time, I would use "curving". If a storm is going West and then starts turning northward but misses the trough, goes West again, then catches the second trough and turns north again, that SECOND turn would technically be considered a re-curve.

Not going to make a big deal about it though.:)


Hey, Alec (right?)! Long time no see!
Member Since: July 15, 2006 Posts: 17 Comments: 10284
My best and uneducated guess on where any kind of center position could be.
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Quoting TomTaylor:
A storm can recurve and still hit land, so Levi is correct. Here are some hypothetical tracks involving a recurve before landfall (don't mean to scare anybody, just trying illustrate a point):




Charley's re-curve
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Stopping by in between meetings for a quick catch up on 93L.
Is the consensus now for LA+MS with FL out of the loop?
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959. cdo13
looks like shear is keeping the west side from developing imo
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Member Since: July 3, 2005 Posts: 426 Comments: 128639
Quoting Neapolitan:
The term "recurve" is a word meaning "to bend backwards or down"; the "re" in "recurve" isn't a prefix indicating a repeat any more than the "re" in "regret" means that you "gret" something then "gret" it again. ;-) A recurve simply means a westbound storm at lower latitudes moves north toward the mid-latitudes, then gets picked up and recurves--that is, bends backward from its initial track--and moves to the northeast or east.


So recurve is actually a plausible word to use.
Member Since: July 6, 2010 Posts: 113 Comments: 32262
From the ATCF Descriptive Data:

Note: Track type is a subjective classification of the storm as a straight mover, recurver, or odd mover. A straight storm path is one which maintained a somewhat constant heading between 250o - 360o. A storm is considered a recurver if it turned from an initial path toward the west or northwest to a path toward the northeast. An odd moving storm, therefore, is one which did not fit in the other two categories or contained loops in the track. ).

Link
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8 Days ECMWF 12z Ensembles. East coast, you are by no means in the clear...

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Quoting angiest:

I wasn't aware that there was an actual rule to that effect. I have noticed it in practice, however.


I could be wrong, but I can't remember the NHC issuing watches when there was no classified storm at the time when the watch was issued. They issued nothing for the Antilles islands when Irene was 50 miles away with 45kt winds, because she wasn't yet classified.
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Re-curve connotes that it has at least curved prior. A storm turning out to sea the FIRST time, I would use "curving". If a storm is going West and then starts turning northward but misses the trough, goes West again, then catches the second trough and turns north again, that SECOND turn would technically be considered a re-curve.

Not going to make a big deal about it though.:)
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Quoting nrtiwlnvragn:


ATCF Data Formats


Thanks a bunch!
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Here...this is the 12z GFDL



Member Since: July 15, 2006 Posts: 17 Comments: 10284
The term "recurve" is a word meaning "to bend backwards or down"; the "re" in "recurve" isn't a prefix indicating a repeat any more than the "re" in "regret" means that you "gret" something then "gret" it again. ;-) A recurve simply means a westbound storm at lower latitudes moves north toward the mid-latitudes, then gets picked up and recurves--that is, bends backward from its initial track--and moves to the northeast or east.
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Quoting Levi32:


That's why I wonder why they don't change the rules so that they can issue watches if development near the coast is expected with TS conditions.
I wasn't aware that there was an actual rule to that effect.  I have noticed it in practice, however.
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Quoting atl134:




The cat of nine tails (or maybe cat o' nine tails) is the name given to a 9 pronged whip used by pirates if I remember correctly.
Well, ok then that would make since. Those damn pirates were real son's of B.....s then. I suppose they whipped their fellow sailors and women folk.
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Quoting TropicalAnalystwx13:


Remote-Linking-Is-Disabled-!-!-!

lol...seriously though, you can see the image, but other people cannot.


You must mote before you can remote!
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Member Since: July 3, 2005 Posts: 426 Comments: 128639

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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