Gulf of Mexico low growing more organized

By: Dr. Jeff Masters , 1:51 PM GMT on May 21, 2009

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The large extratropical storm that has been drenching Florida over the past few days continues to pour rain on the state as it treks slowly west-northwestward over the Gulf of Mexico. Rainfall amounts as high as 23.75 inches have been measured in Northern Florida at the Flagler County Fairgrounds over the past four days, and Daytona Beach has seen over 14 inches, forcing closure of numerous roads. Another 1 - 3 inches are expected in Northeast Florida today from the storm, along with beach erosion, 7 - 10 foot waves, and tides 2 - 3 feet above normal. The bad weather in Northeast Florida should gradually subside Friday and the rains should diminish substantially on Saturday, when the center of the storm is expected to move ashore over Louisiana.


Figure 1. Storm total rainfall estimated from the Melbourne radar.

Latest visible satellite loops show that the circulation of the low has grown more circular and better defined, and heavy thunderstorm activity is starting to build off the Gulf Coast of Florida on the low's east side. These thunderstorms are beginning to form spiral bands characteristic of a developing tropical depression. Water vapor satellite imagery shows that the low is moving into an area of dry continental air, though, and this dry air will slow development. Wind shear is about 20 knots, which is low enough to allow development. While none of the computer models develop the storm, they generally predict the storm should move northwestwards towards Louisiana over the next two days, and the shear is lower to the north. The low is currently over Sea Surface Temperatures (SSTs) of about 27°C in the Loop Current, which is about 1°C (1.8°F) warmer than average. SSTs of at least 26°C are typically needed to support a tropical storm, so I expect the low will continue to develop through Friday. By Friday night, the low will be approaching the Louisiana coast, and SSTs will cool to 26°C. Still, with wind shear expected to drop, this low has a medium (30 - 50%) chance of developing into a subtropical or tropical depression before its expected landfall Saturday over Louisiana. Since there will be strong winds from the west creating wind shear over the storm, plus dry air to the storm's west, most of the heavy rain should be confined to the east of the storm's center, along a stretch of coast from New Orleans to Pensacola. Rainfall totals of 3 - 6 inches can be expected.


Figure 2. Latest satellite image of the Gulf of Mexico storm.

I'll have an update Friday morning, or sooner if NHC declares this storm an area of interest (an "Invest").

Jeff Masters

Majestic (earthlydragonfly)
Taken last night with a 16mm lense. Enjoy Mark www.shockpic.smugmug.com
Majestic

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547. JRRP
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Quoting Levi32:
Guys take a look at this map very very closely. Paste image url into your browser if you want to see it full-size:



Now look right where the big glob is that you're all talking about. I want you to see how to the left of the blob the wind barbs are aiming towards the NE. Now look to the right of the blob. The wind barbs point towards the east or ESE.

So what's happening is the upper-level air-flow is splitting in that area due to the ULL in the gulf of Mexico, causing two separate air streams to separate and pull away from each other. This is called diffluence. So think about it, air is getting transported away from that area, so new air needs to replace it. The only place that that air can come from is below (remember this is taking place in the upper atmosphere). This causes a bunch of air to rise from the surface, and we all know that when air rises it condensates, forms clouds, and when strong enough, thunderstorms. That is all that this is, it is baroclinic process not tropical process. There is no threat of development from this area of thunderstorms.


Great explanation!
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Tagged 91L, maybe...Named Ana, not very likely. Not enough time for it to develop.
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Quoting DDR:

Hi from trinidad,thats terrible,we could use some of that rain here.

yeah, the roads in St. Thomas are impassable hope you get the rain that you need. :)
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Lots of rain moving into Haiti...



Showers/t-storms affecting the Dominican Republic and Puerto Rico as well.

Member Since: November 24, 2005 Posts: 635 Comments: 26698
542. HCW
No doubt this one will get tagged 91L sometime tomorrow morning. After all they tagged 90L and it's looked horrible. Shear will relax and this thing should get named before landfall
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Quoting Levi32:
Hey Pat.....is there a shortcut to links that I am missing? I always have to type the whole code: href="url" target="_blank" text

You just seem to be able to do it so fast.


Not that Im aware of.


Having multiple Tabs Opens allows me ez access to a Lot of er,stuff I have stashed.
Member Since: July 3, 2005 Posts: 427 Comments: 129435
Quoting CaicosRetiredSailor:


Levi,

Thanks for the "Baro" clinic, from here in the Turks and Caicos, (under the split between the two separate air streams) We don't need more rain.

CRS
[edit] ...I guess I could say that this evening I am "under the diffluence" ...NOT under the Influence.


Lol very funny CRS. I am sorry about the rain. Hopefully it will move on soon.
Member Since: November 24, 2005 Posts: 635 Comments: 26698
Hey Pat.....is there a shortcut to links that I am missing? I always have to type the whole code: href="url" target="_blank" text
You just seem to be able to do it so fast.
Member Since: November 24, 2005 Posts: 635 Comments: 26698
530. Pat beat me....lol
Member Since: November 24, 2005 Posts: 635 Comments: 26698
Quoting Levi32:

...the upper-level air-flow is splitting in that area due to the ULL in the gulf of Mexico, causing two separate air streams to separate and pull away from each other. This is called diffluence.


Levi,

Thanks for the "Baro" clinic, from here in the Turks and Caicos, (under the split between the two separate air streams) We don't need more rain.

CRS
[edit] ...I guess I could say that this evening I am "under the diffluence" ...NOT under the Influence.
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COC beginning to move west as expected

Popcorn thunderstorms still fizzling as soon as they form due to westerly shear from the ULL. You can see their cirrus debris being carried ESE over the center. The ULL is still displaced to the north of the surface low, and as a result the westerly winds on the southern side of the ULL are shearing the thunderstorms trying to form near the surface center. If this low can't get vertically stacked it will tear itself apart. Divided we fall....
Member Since: November 24, 2005 Posts: 635 Comments: 26698
THE REX BLOCK

METEOROLOGIST JEFF HABY


The Rex Block is a blocking pattern that in relation to the United States occurs most often in the spring and most often occurs along or near the West Coast. A Rex Block has two adjacent highs and lows. The most impressive Rex Blocks will have a strong low pressure next to a strong high pressure. The high pressure will be located in a generally north direction from the low pressure. The low associated with the Rex Block is not completely cut-off from the upper level flow, but does have little east-west movement. Strong ridging north of the low causes the airflow to move from high latitudes to low latitudes with little comparable west-east movement of the air. The airflow pattern follows a backward "S" trajectory. In the example image, air flowing into the West Coast of Canada then flows south into the Pacific off the Mexican West Coast

Member Since: July 3, 2005 Posts: 427 Comments: 129435


NexSat GOM
Member Since: July 3, 2005 Posts: 427 Comments: 129435
456, Levi,anyone else
What is a Rex Block?
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NEXRAD Radar
New Orleans, Composite Reflectivity Range 124 NMI




NEXRAD Radar
New Orleans, Storm Relative Mean Radial Velocity 0.50 Degree Elevation Range 124 NMI




Coastal Flood Warning

Statement as of 3:59 PM CDT on May 21, 2009

... Coastal Flood Warning in effect until 7 PM CDT Saturday...

The National Weather Service in New Orleans has issued a coastal
Flood Warning... which is in effect until 7 PM CDT Saturday. The
coastal Flood Watch is no longer in effect.

An area of low pressure will result in moderate to strong
northeast and easterly winds through Friday. These winds will pile
water along east facing shores from near Bay St. Louis to Port
Fourchon and increase tides further above normal over the next
couple days.

Tide levels were already running one to one and one half feet
above normal near Waveland Mississippi and Lake Borgne around the
time of high tide late this morning. The onshore winds will
continue to cause water levels to rise to 2 to 2.5 feet above
normal around the time of high tide Friday. Tides may reach one to
one and one half feet above normal farther west from Southwest
Pass of the Mississippi River to Port Fourchon.

Minor flooding of low lying roadways may occur in Hancock County
Mississippi... and minor flooding of low lying areas may occur
outside of hurricane protection levees from near Lake Catherine
and Lake Borgne... to Grand Isle and Port Fourchon.



Precautionary/preparedness actions...

A coastal Flood Warning means that flooding is occurring or
imminent. Coastal residents in the warned area should be alert
for rising water... and take appropriate action to protect life
and property.
Member Since: July 3, 2005 Posts: 427 Comments: 129435
Quoting DestinJeff:
that was a good explanation, Levi. i am just jabbing you about the baroclinic process thing.

i guess you just put on a baroclinic with that explanation


LOL
Member Since: November 24, 2005 Posts: 635 Comments: 26698
Thanx for the nice explanation Levi.
Member Since: July 3, 2005 Posts: 427 Comments: 129435
Quoting DestinJeff:
there is huge blowup of convection over central Iowa that probably could develop, if not for the 1000s of miles of land between it and water. shear is low and CSTs (Cornfield Surface Temperatures) support development otherwise.


LMAO
Member Since: Posts: Comments:
Guys take a look at this map very very closely. Paste image url into your browser if you want to see it full-size:



Now look right where the big glob is that you're all talking about. I want you to see how to the left of the blob the wind barbs are aiming towards the NE. Now look to the right of the blob. The wind barbs point towards the east or ESE.

So what's happening is the upper-level air-flow is splitting in that area due to the ULL in the gulf of Mexico, causing two separate air streams to separate and pull away from each other. This is called diffluence. So think about it, air is getting transported away from that area, so new air needs to replace it. The only place that that air can come from is below (remember this is taking place in the upper atmosphere). This causes a bunch of air to rise from the surface, and we all know that when air rises it condensates, forms clouds, and when strong enough, thunderstorms. That is all that this is, it is baroclinic process not tropical process. There is no threat of development from this area of thunderstorms.
Member Since: November 24, 2005 Posts: 635 Comments: 26698
Quoting CybrTeddy:


Shear isn't horrible, its about 20 kts.
SST's are acceptable.
Subtropical Storms have a looser range. I doubt this will ever be fully tropical.


I do believe Shear is more than 20Kts......the tops are being blowed off anything trying to gather..
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Quoting stormpetrol:


Covering a large area about 700 miles from East to west in my estimation.


or west to east.
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Quoting Relix:
That big blog is causing rain here in PR as well.


Covering a large area about 700 miles from East to west in my estimation.
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516. Relix
That big blog is causing rain here in PR as well.
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-- EMC Cyclogenesis Tracking Page --

Model Cycle: 2009052118

North America: Model Tracks for Mid-Latitude Cyclones


18Z GFS


18Z Multi-Model
Member Since: July 3, 2005 Posts: 427 Comments: 129435
Hmm low pressure in the central Caribbean. One of you guys has got to beat the doctor to the punch if were going to have new champion. Small joke.
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If shear were lower that large blob over E Jamaica, Haiti and parts of Cuba might have a chance to develop, feel very sorry those in Haiti , they always seem to get the worst of the rains & floods.
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512. DDR
Quoting weatherwatcher12:
Latest from the Jamaica meteorological service:

NEWS RELEASE

*** FLASH FLOOD WARNING REMAINS IN EFFECT FOR ALL PARISHES ***




The Meteorological Service has continued the Flash Flood Warning for low-lying and flood-prone areas of all parishes until 5:00 p.m. tomorrow.

This Warning means that flooding has been reported or will occur shortly.

Satellite imagery indicates a broad Area of Low Pressure has developed across the central Caribbean extending over Jamaica. The island continued to experience periods of moderate to heavy showers and thunderstorms throughout today especially over eastern and central parishes.

The forecast is for limited movement of this system; therefore, the general instability should persist through tonight into tomorrow; resulting in periods of showers, across most parishes. Further flash flooding of low-lying and a flood- prone areas is therefore expected.

Fishers and other marine interests are advised to exercise caution in areas of showers and thunderstorms as gusty winds and rough seas may be encountered north and south of the island.


The Meteorological Service will continue to monitor the situation.


Hi from trinidad,thats terrible,we could use some of that rain here.
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Quoting HURRICANECAT5:
THERE IS A BIG EXPLOSION OF CONVECTION EAST OF JAMAICA. IF WE LOOK AT SHEAR MAPS, SHEAR IS LESSENING IN THE VICINITY OF THIS AREA OF DISTRUBED WEATHER. WHAT DO YOU THINK?


LOL
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Member Since: Posts: Comments:
Latest from the Jamaica meteorological service:

NEWS RELEASE

*** FLASH FLOOD WARNING REMAINS IN EFFECT FOR ALL PARISHES ***




The Meteorological Service has continued the Flash Flood Warning for low-lying and flood-prone areas of all parishes until 5:00 p.m. tomorrow.

This Warning means that flooding has been reported or will occur shortly.

Satellite imagery indicates a broad Area of Low Pressure has developed across the central Caribbean extending over Jamaica. The island continued to experience periods of moderate to heavy showers and thunderstorms throughout today especially over eastern and central parishes.

The forecast is for limited movement of this system; therefore, the general instability should persist through tonight into tomorrow; resulting in periods of showers, across most parishes. Further flash flooding of low-lying and a flood- prone areas is therefore expected.

Fishers and other marine interests are advised to exercise caution in areas of showers and thunderstorms as gusty winds and rough seas may be encountered north and south of the island.


The Meteorological Service will continue to monitor the situation.

Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting TampaSpin:
The Low is not getting any better defined or organized...Still to much Shear and Low SST's for anything to take off. Just alot of rain!


Shear isn't horrible, its about 20 kts.
SST's are acceptable.
Subtropical Storms have a looser range. I doubt this will ever be fully tropical.
Member Since: July 8, 2005 Posts: 259 Comments: 24550
Tampa-when the low gets going, will it bring rain back over SoFl?
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505. DDR
Hello everyone,yet another hot, dry day again in Trinidad,i guess the rainy season is running late again just like last year.Below average rain in the sahel could means a greater chance of a prolonged dry season for us in the long run.
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Quoting jcpoulard:
From Haiti
It's raining since last saturday on the south of country. When I make a look on the satellite I can the system (Jamaica-Haiti-Cuba) is literaly explode. I would like to know if they are any chance for this system to develop on a named storm. If not how we can explain this explosion of energy... ?
Thank you every one.


Its all from the Low in the GOM. I don't see anything developing....We just need this LOW to move! You are stuck in a band that is not moving. This is very character of SubTropical like systems where often miles from the COC has problems.
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Quoting Patrap:
Dunno,never looked at the Map that Hard.

GW isnt an Issue ,really.

The warming is Occurring Globally,what is at issue however,is the cause.

Maybe I should have specified anthro =}
Just thought I'd point it out. I thought it was funny =P How bout that explosion of convection west of Haiti? Have to keep an eye on it, depending on it's direction it may can get to <25 knots shear, though I expect it will die down soon. another thing: Is the ULL pulling north away from the surface circulation?
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Thanks Pat is that sight on the front page of blog. It doesnt seem like satellite from that sight is current but they got the forecast right 100% rain.
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Current shear Map,Atlantic Basin

Member Since: July 3, 2005 Posts: 427 Comments: 129435
Quoting HURRICANECAT5:
THERE IS A BIG EXPLOSION OF CONVECTION EAST OF JAMAICA. IF WE LOOK AT SHEAR MAPS, SHEAR IS LESSENING IN THE VICINITY OF THIS AREA OF DISTRUBED WEATHER. WHAT DO YOU THINK?

Here there are clouds rolling and my mango tree fell down
Member Since: May 16, 2009 Posts: 1 Comments: 1231
I believe it was 456 that gave a good synopsis of what is occurring in Haiti and Below in the Caribbean.
Its Baroclinic divergence caused by the ULL in the GOM.

What do I know,..but its not a Tropical entity..that I do know.

But it matters not what it is that brings the deluge. The effects are still B-A-D.
Member Since: July 3, 2005 Posts: 427 Comments: 129435
shear has been dropping for a long time in the Caribbean.

Member Since: May 16, 2009 Posts: 1 Comments: 1231

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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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