Erika dumping heavy rain on the Lesser Antilles

By: Dr. Jeff Masters , 2:12 PM GMT on September 03, 2009

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Tropical Storm Erika is hanging together despite strong wind shear, and is bringing high winds and much-needed heavy rain to the Lesser Antilles Islands. Winds on the south shore of Dominica Island were sustained at 37 mph this morning, and 8.03" of rain have been measured at the airport over the past two days. Winds and rain at nearby islands have been less, according to our wundermap for the region. The Hurricane Hunters are in the storm now, and have generally encountered top winds of 40 - 45 mph at the surface. They did find one spot of 50 - 65 mph winds, but that was likely due to outflow from a strong thunderstorm, and is not representative of Erika's wind field.


Figure 1. Radar image of Tropical Storm Erika at 9:15am EDT 9/3/09. Image credit: Meteo France.

Erika has improved in organization a bit since last night, but remains weak and disorganized, thanks to about 20 knots of shear at the 200 mb level, as seen on last night's Guadeloupe upper air sounding. Radar animations out of Martinique show plenty of heavy rain moving through the Lesser Antilles, but little organization of the echoes. Satellite imagery shows no low-level spiral bands and little upper-level outflow. Long range radar out of Puerto Rico is beginning to show rain echoes from Erika approaching the island.

The forecast for Erika
The computer models have come into better agreement about the track of Erika, taking the storm west-northwest over Puerto Rico and the Dominican Republic. This track will take Erika into a band of significantly higher wind shear of 25 - 35 knots, Friday through Saturday. Considering that Erika is barely maintaining itself as a tropical storm with 20 knots of shear, the combined effects of the higher shear and the encounter with the high mountains of Hispaniola and Puerto Rico should be enough to cause Erika to dissipate by Sunday. Erika's remains will still be capable of dumping very heavy rains of 3 - 5 inches over the Dominican Republic and 1 - 3 inches over Haiti and the Southeast Bahamas, due to the slow motion of the storm. By Monday, when the remains of Erika should be over the Bahamas, the storm will have penetrated through the band of high wind shear over the Greater Antilles, and shear may fall low enough for redevelopment of the storm. This is a scenario offered by the NOGAPS model, which then takes Erika northward towards North Carolina. The other models predict quite a bit more shear in the region than the NOGAPS, and any redevelopment of Erika early next week remains an iffy proposition. The GFDL and HWRF models continue to insist that Erika will brush off the high shear this weekend, avoid Hispaniola, and intensify into a Category 2 hurricane five days from now. These models have not been giving enough emphasis to how the current shear is affecting Erika, and are being discounted at this time.

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A number of wunderground users with the McAfee virus protection software installed were alerted yesterday that a possible Trojan virus existed on our web pages. After an investigation of the issue, we have determined that this is a false alarm. It appears McAfee updated their virus files yesterday, and included in their list of suspected viruses JavaScript web pages that are compressed using the packer compression system used by wunderground. We've changed the compression technique used on our web pages, and hopefully this will eliminate the bogus McAfee alert messages.

Elsewhere in the Atlantic
A large, strong tropical wave with plenty of spin emerged from the coast of Africa this morning. The wave is not yet generating much in the way of heavy thunderstorms, but has the potential to gradually develop into a tropical depression by early next week. NHC is giving this wave a low (less than 30% chance) of developing into a tropical depression by Saturday. The GFS model has been consistently developing this wave in its runs over the past few days.

I'll have an update this afternoon.

Jeff Masters

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We need stakes and holy water.

This thing doesn't want to die until it's literally becoming dust..
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Quoting Patrap:



Yeah,..been watching those 2 for a Day now,one will win,..or we could see a Double Barrel situ.
The GOM could turn interesting with all that warm water.Been a while since I have seen a double barrel low pressure area.
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Quoting cchsweatherman:
After watching yet another circulation center get ejected and what appears to be a new one forming over the Virgin Islands, I officially have no clue what the hell Tropical Cyclone Erika is doing and will do in the future. This has been one of the most unpredictable systems I have ever tracked in my young weather career.


The eastern COC will likely becoming become dominant, because it is under the convection. Sigh...this seems to be a repeat of yesterday. I'd be satisfy if Erika would die right now.
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The rain of Erika could fall Sunday or Monday in the Eastern region of Cuba to follow the slow movement towards the west.
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Quoting IKE:


Exactly.

Well, "Limits the diurnal effect", in a relative sort of way. Far less noticeable with a well-built system.
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Quoting caneluver:
With most models redeveloping Erica by the Bahamas nobody seems to believe them??? Why is this???


The models arent initializing on anything concrete... her coc is changing (AGAIN)... wait for the next run or 2 and see what they say then.
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Erika is a lady of the night.
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Quoting DellOperator:


When are the next Skew-T charts coming out for Puerto Rico?



Upper air soundings are done by most meteorological institutions (including the National Weather Service in Puerto Rico) at 12UTC and 00UTC or currently 8PM/AM EDT
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Quoting StormW:


Actually, 15-20 kts. TUTT over the GOMEX right now. Hard to get anything at the surface while it's sitting under a TUTT axis.

Now...one thought is, we get a work down, and that could always lead to a chance of subtropical with moderate shearing in place.



Shear isnt the Inhibator here I feel..time is.
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After watching yet another circulation center get ejected and what appears to be a new one forming over the Virgin Islands, I officially have no clue what the hell Tropical Cyclone Erika is doing and will do in the future. This has been one of the most unpredictable systems I have ever tracked in my young weather career.
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Quoting atmoaggie:

I think the big differentiation between Erika and what we are used to seeing is that Erika didn't cross some threshold in development that limits that diurnal effect.



DING DING DING...we have a winner!
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Quoting leelee75k:
out of lurkdom with another dumb question.

Does the hurricane hunters fly a regular pattern, like maybe a box with an X in it or do they just fly around willy nilly? Who decides which direction they should fly in?

btw it's raining sideways and criss cross in western broward.


They fly in a butterfly pattern over what they think or can figure out is the center of the storm. It helps with the dropsonde data...
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This is NOT a TS.

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Quoting hydrus:
I see a couple of low pressures PATRAP.One in the Gulf, and one off (dare I say it)- -the Carolina,s



Yeah,..been watching those 2 for a Day now,one will win,..or we could see a Double Barrel situ.
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810. IKE
Quoting OSUWXGUY:


All storms feel the influence of DMIN/DMAX due to the influence of long wave/short wave radiation at the cloud edges.

During the day, sunlight (short wave radiation) is bombarding the cloud tops/edges causing a slight warming. This slight warming makes the environment slightly more stable during the day and the thunderstorms are not quite as deep.

During the night, there is no sunlight (shortwave radiation) obviously, so the emission of longwave radiation by the clouds at the cloud tops/edges is the dominate process cooling the environment near the clouds, making it more unstable and causes stronger storms with higher cloud tops.


For a weak system like Erika, or other invests, a slight change in the environment's instability can be an important factor in getting thunderstorms to form and to help organize a system.

In a well developed storm, the structure of the storm is such that there is always strong convergence at the surface which fuels thunderstorm activity. However, if you watch major hurricanes a lot, their cloud tops in general are higher during the night than during the day (think red instead of black on the AVN loop). Both are still significant convection, but one is slightly stronger.

Obviously, going over a rocket fuel warm eddy like Katrina did, throw all this DMIN/DMAX crap out the window...


Thanks.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
For your Viewing Pleasure

View Of weather from Web Cam St Croix Harbor



href="http://www.gotostcroix.com/live/harborcam.php.html"
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Quoting Patrap:
I see a couple of low pressures PATRAP.One in the Gulf, and one off (dare I say it)- -the Carolina,s...
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Quoting IKE:


I have a question....a true tropical storm wouldn't be going through DMIN and DMAX like Erika is doing, would it? I've read on here tropical storms and hurricanes aren't influenced by DMIN and DMAX? True?


All storms feel the influence of DMIN/DMAX due to the influence of long wave/short wave radiation at the cloud edges.

During the day, sunlight (short wave radiation) is bombarding the cloud tops/edges causing a slight warming. This slight warming makes the environment slightly more stable during the day and the thunderstorms are not quite as deep.

During the night, there is no sunlight (shortwave radiation) obviously, so the emission of longwave radiation by the clouds at the cloud tops/edges is the dominate process cooling the environment near the clouds, making it more unstable and causes stronger storms with higher cloud tops.


For a weak system like Erika, or other invests, a slight change in the environment's instability can be an important factor in getting thunderstorms to form and to help organize a system.

In a well developed storm, the structure of the storm is such that there is always strong convergence at the surface which fuels thunderstorm activity. However, if you watch major hurricanes a lot, their cloud tops in general are higher during the night than during the day (think red instead of black on the AVN loop). Both are still significant convection, but one is slightly stronger.

Obviously, going over a rocket fuel warm eddy like Katrina did, throw all this DMIN/DMAX crap out the window...
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did any models pick that up in the GOM this week?
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800. IKE
Quoting atmoaggie:

I think the big differentiation between Erika and what we are used to seeing is that Erika didn't cross some threshold in development that limits that diurnal effect.


Exactly.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting lurkn4yrs:




You are 100% correct.. We just let the men think other wise..


Ya, i hear that! I'm either told what to do, or showed where i can go if any resistance is given.....LOL
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798. IKE
Quoting KEEPEROFTHEGATE:
first for me as well ike strange kinda reminds me of a chicken on a hot rock keeps bouncing around from one point to another iam not even posting anything in my blog anymore on the storm and surface reports dont even match what we are seeing on sat images



12Z ECMWF shows nothing on Erika...
Member Since: June 9, 2005 Posts: 23 Comments: 37858
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Quoting Keys99:


No, there's a NW component to the movement at that point...but before you get your undies all bunched up, remember that these models are anywhere from 144 hrs to 168hrs out and the data in those images is old...the 18Z run may show dissipation
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Quoting KEEPEROFTHEGATE:
first for me as well ike strange kinda reminds me of a chicken on a hot rock keeps bouncing around from one point to another iam not even posting anything in my blog anymore on the storm and surface reports dont even match what we are seeing on sat images

I think the big differentiation between Erika and what we are used to seeing is that Erika didn't cross some threshold in development that limits that diurnal effect.
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I know some of you aren't big fans of his, but even Bastardi thinks she might be trying to reform back to the east:

The usual morning mad dash of the low-level vortex out of thunderstorms is taking place, and if this be Erika, then that's it, it's over. However I think the center is reforming and means business near the island of Guadeloupe, and if this is the case, the storm is likely to survive perhaps thrive.
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@PATRAP yes that one!!
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792. Relix
Quoting StormW:


LOL!

You are also correct!


Any new comments about Erika, Storm? =)
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OK don't attack me, but what is that spot over Grand Anse that looks like an eye on visible?
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Quoting LUCARIO:
everything moves west

Erika looks to be getting sttonger, i think her winds will be 60 by 5pm


Okay.. youre officially a troll looking for a rise out of someone... Wheres that ignore button?? Oh yeah.. there it is.
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Quoting futuremet:


I never seen a storm developed this much COCs before lol.


Well considering your age, you probably havnt seen that many storms, no offense. Banned from WU here I come.lol
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Not much Shear in the GOM AOI today Chief..



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Quoting atmoaggie:

Well, if you're still here. Dad is on his way to run the Miata at Birmingham - Barber Motorsports.
Another new (to him) track...


Ok, last one for 20 minutes....
I have never been there. But I hear it is a nice facility and course to race on.
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Quoting ncweatherfolks:
My husband plots storms and the wobbling of Erica looks like Hurricane Hazel?????? Can Erica do that?


Erika can do what ever she wants, nobody is stopping the crazy lady...
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Quoting IKE:


Severely.

I've been following storms on here for 4, maybe 5 years. Never seen one do, daily, what this one has.
first for me as well ike strange kinda reminds me of a chicken on a hot rock keeps bouncing around from one point to another iam not even posting anything in my blog anymore on the storm and surface reports dont even match what we are seeing on sat images
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everything moves west

Erika looks to be getting sttonger, i think her winds will be 60 by 5pm
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Quoting leelee75k:
out of lurkdom with another dumb question.

Does the hurricane hunters fly a regular pattern, like maybe a box with an X in it or do they just fly around willy nilly? Who decides which direction they should fly in?

btw it's raining sideways and criss cross in western broward.


As previously posted they will fly the Alpha pattern for developed storms. For invest missions they also have additional patterns they may fly:





National Hurricane Operations Plan
Member Since: September 23, 2005 Posts: 14 Comments: 11179
has anybody noticed the L marked 1010mb on the GOM? press on NWS

Link
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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.