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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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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Good afternoon folks

It looks like Erika is still having problems with her COCs and is now developing a new one. This seems to be her 5th COC so far. Hopefully this will be the last one.
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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.

The FIX mission is where the ARWO will direct the crew to the true center of the storm. In order to get a good overall look at the storm the unit flies the storm using an alpha pattern (see image below), which consists of intercardinal headings with legs 105 nautical miles in length. This alpha pattern is repeated 2 times during one mission.
During flight weather data is continuously collected and sent directly to the National Hurricane Center via satellite communications. Since the WC-130J is not equipped for aerial refueling, the alpha pattern will continue until bingo fuel is reached or the National Hurricane Center has received all the information it needs. We enter major hurricanes (category 3 or above) at 10,000 feet.
Alpha pattern:

From: http://www.hurricanehunters.com/mission.html
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Quoting ssmate:
Bring on Fred. I know a lot of Fred's. They are uncomplicated, simple, straightforward dudes. Ironincally, they all drink a lot of beer, which is just a side note I guess and not pertinent to my point.


hurricane Fred- he's gonna "yabdabadoo!" your house down. The name sounds so innocuous
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GOING GOING ...
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Quoting Squid28:


heck we are up to 48% post Ike occupancy here at the corner of Shoreacres & La Porte now (adjusted for those homes torn down already). Who knows maybe I will quit seeing demo trucks in another year or so.

LPSS Did you go to LPHS? If so what year for grad?


we still have homes being torn down in my subdivision. No i didnt go tp LPHS. I went to Dickinson HS. but got here as fast as i could.lol My kids have gone thru LP. Ages 23-16.
Member Since: July 17, 2008 Posts: 0 Comments: 385
Ed Rappaport
National Hurricane Center
Updated 10 December 1993 Hurricane Andrew Photos
a. Synoptic History
Satellite pictures and upper-air data indicate that Hurricane Andrew formed from a tropical wave that crossed from the west coast of Africa to the tropical North Atlantic Ocean on 14 August 1992. The wave moved westward at about 20 kt, steered by a swift and deep easterly current on the south side of an area of high pressure. The wave passed to the south of the Cape Verde Islands on the following day. At that point, meteorologists at the National Hurricane Center (NHC) Tropical Satellite Analysis and Forecast (TSAF) unit and the Synoptic Analysis Branch (SAB) of the National Environmental Satellite Data and Information Service (NESDIS) found the wave sufficiently well-organized to begin classifying the intensity of the system using the Dvorak (1984) analysis technique.

Convection subsequently became more focused in a region of cyclonic cloud rotation. Narrow spiral-shaped bands of clouds developed around the center of rotation on 16 August. At 1800 UTC on the 16th (UTC precedes EDT by four hours), both the TSAF unit and SAB calculated a Dvorak T-number of 2.0 and the "best track" (Table 1 and Fig. 1 [85K GIF]) shows that the transition from tropical wave to tropical depression took place at that time.

The depression was initially embedded in an environment of easterly vertical wind shear. By midday on the 17th, however, the shear diminished. The depression grew stronger and, at 1200 UTC 17 August, it became Andrew, the first Atlantic tropical storm of the 1992 hurricane season. The tropical cyclone continued moving rapidly on a heading which turned from west to west-northwest. This course was in the general direction of the Lesser Antilles.

Between the 17th and 20th of August, the tropical storm passed south of the center of the high pressure area over the eastern Atlantic. Steering currents carried Andrew closer to a strong upper-level low pressure system centered about 500 n mi to the east-southeast of Bermuda and to a trough that extended southward from the low for a few hundred miles. These currents gradually changed and Andrew decelerated on a course which became northwesterly. This change in heading spared the Lesser Antilles from an encounter with Andrew. The change in track also brought the tropical storm into an environment of strong southwesterly vertical wind shear and quite high surface pressures to its north. Although the estimated maximum wind speed of Andrew varied little then, a rather remarkable evolution occurred.

Satellite images suggest that Andrew produced deep convection only sporadically for several days, mainly in several bursts of about 12 hours duration. Also, the deep convection did not persist. Instead, it was stripped away from the low-level circulation by the strong southwesterly flow at upper levels. Air Force Reserve unit reconnaissance aircraft investigated Andrew and, on the 20th, found that the cyclone had degenerated to the extent that only a diffuse low-level circulation center remained. Andrew's central pressure rose considerably (Fig. 2 [87K GIF]). Nevertheless, the flight-level data indicated that Andrew retained a vigorous circulation aloft. Wind speeds near 70 kt were measured at an altitude of 1500 ft near a convective band lying to the northeast of the low-level center. Hence, Andrew is estimated on 20 August to have been a tropical storm with 40 kt surface winds and an astonishingly high central pressure of 1015 mb (Figs. 2 and 3 [87K GIF]).

Significant changes in the large-scale environment near and downstream from Andrew began by 21 August. Satellite imagery in the water vapor channel indicated that the low aloft to the east-southeast of Bermuda weakened and split. The bulk of the low opened into a trough which retreated northward. That evolution decreased the vertical wind shear over Andrew. The remainder of the low dropped southward to a position just southwest of Andrew where its circulation enhanced the upper-level outflow over the tropical storm. At the same time, a strong and deep high pressure cell formed near the U.S. southeast coast. A ridge built eastward from the high into the southwestern Atlantic with its axis lying just north of Andrew. The associated steering flow over the tropical storm became easterly. Andrew turned

I never post anything this big. Just for information.
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723. Relix
I want them to check the supposed new COC =(
Member Since: August 3, 2006 Posts: 0 Comments: 2741
Even a pressure of 1007mb now.

It may even make 1.0 on the Dvorak scale!
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Is a flare-up of thunderstorms tonight out of the question? Yesterday Erika looked really bad but at night it picked up quite a bit.
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Quoting btwntx08:
c'mon hh's go to the area of where its rotating just check that side of the storm and they will comfirmed and everything will change big time again


Huh?
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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.

The HH generally fly in an X pattern, but when the center isn't well defined, they will fly around until they find it (or the complete lack of it). As Orca commented yesterday, the HH flight into Erika made the HH pilot look like they were flying drunk.
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Quoting atmoaggie:

If they are from a sounding, 12 and 0 Z are we get. A lot of places in the Caribbean only give us one or the other, as well. Not sure about that from PR. Probably both 0 and 12. Not real likely to gives 6 or 18 Z.


Crap. I was hoping they would make exceptions for this event and send more up.
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Quoting katlbeach:


As a long-time resident of Florida (both SE and NE), I find that it is these "messy" storms that do the crazy things and cause the most damage. Erika looks like a storm that will wander around and then just sit over an area of land and dump a bunch of rain for days and days. Sometimes the lower level disturbances can cause worse flooding than a cat1 hurricane that blows through rather quickly. We HAVE to watch these storms whether they make it to hurricane strength or not.


Tru Dat! katlbeach. We've had ex tropical storms stall over us in the Keys and drop more precip than many of the formed/named systems
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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?

Dynamically I would think that is true. Once the TC motions are in place, I expect the convergence, and thus convection, overpowers the diurnal density difference.

Our surface pressure is diurnal by a few mb, but I don't think the central pressure of a system would be influenced that way.
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MAGIC BALL WE NEED TO CONTINUE THE PATH OF ERIKA. .... THE MOEL SAY ONE THING AND IT MAKES ANOTHER..
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Quoting MILLERTIME1:
Whats up with the flare up off the coast of Carolina?


remnant low
Member Since: August 2, 2006 Posts: 10 Comments: 9922
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?


If I recall, DMIN & DMAX activity is just behaviors disturbances cycle thru while they are getting kick started. Most of the time we look for that cycle to diminish to a constant production of t-storms, day or night.

In this case, this system is on the edge and it is trying to find it's grove that it had earlier when it was designated a TS (what little it had). It has a better LLC than a few days ago. This pulsing is a product of surface convergence forcing uplift to occur. T-storms erupt and shear prevents the system from becoming organized.
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Quoting IKE:


Okay...thanks. I've just never seen a tropical storm rev up and fall apart EVERY day like Erika has.


She's pretty strange in that respect...the problem is that we don't really have good data from the 40s 50s and 60s...we could track other systems that acted this way, I'm sure of it..."Nothing new under the Sun" as it were
Member Since: August 2, 2006 Posts: 10 Comments: 9922
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.
Member Since: Posts: Comments:
With 10/10 models (CMC, GFDL, GFS, HWRF, mm5fsu-merge, mm5fsu-GFS, NOGAPS, ICON, ICVN, SHIPS) predicting regeneration then rapid restrengthening, with GFDL even bringing Erika up to a cat. 4, I really don't see why the NHC forecast degrades it into a remnant low before dissapating it over the warm waters of the Bahamas...
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Whats up with the flare up off the coast of Carolina?
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704. IKE
Quoting Floodman:


Nopem, theuy're all influenced by DMIN/MAX...depending on the strength of the system it may be able to amintain better...a TS gets it worse than a CAT2, say...


Okay...thanks. I've just never seen a tropical storm rev up and fall apart EVERY day like Erika has.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Bring on Fred. I know a lot of Fred's. They are uncomplicated, simple, straightforward dudes. Ironincally, they all drink a lot of beer, which is just a side note I guess and not pertinent to my point.
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Quoting DellOperator:


I concur. Even though, it doesn't take much forcing to steer that shallow swirl. It is probably safer to watch the typical cumulus cloud overall direction that is in the mean flow rather than take heed with model solutions.

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

If they are from a sounding, 12 and 0 Z are we get. A lot of places in the Caribbean only give us one or the other, as well. Not sure about that from PR. Probably both 0 and 12. Not real likely to gives 6 or 18 Z.
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i have noticed that erika seems to blossom at night. i can't wait to see what she will do tonight. it is a little weird. i usually see storms blow up with day time heating, but this one seems to like the night.
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Quoting Orcasystems:
Quick straw vote... do I post the HH track once per page as I update it about every 10 minutes (it auto updates the image thats already there).. or should I just post it on my blog and let who ever wants to see it go and look?




no
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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?


Nope, they're all influenced by DMIN/MAX...depending on the strength of the system it may be able to maintain better...a TS gets it worse than a CAT2, say...
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Erika is shrinking smaller, and smaller....... I'm guessing her days are few. When and if her remants make it to the Florida Keys, i'll shout out a eulogy to her for all of you.
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Quoting Floodman:


It's because the shear isn't at the top; more like the middle, say 500mb?


I see
Member Since: August 11, 2008 Posts: 0 Comments: 2315
693. eddye
it shows 62 knots troppical guidence
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Quoting Cotillion:


Per the current readings on UW - which are always subject to changing - she'd actually run into more.



Of course. Thanks!
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Another reason why Erika is having massive problems:

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Orca, I for one appreciate your images and I say post away...
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Quoting OSUWXGUY:
DRY AIR is the KILLING Erika...

I challenge ANYBODY to find sounding near decent tropical systems that have dewpoints of 50-52 at 1000 feet above the surface...

This is insane. Not only is the air dry, but it has been evaporatively cooled apparently...

No WAY air in the tropics in early September should have a temperature of 74.8 at 1000 feet. Think about it this way. The sea surface temperatures in this area according to SHIPS area 29.0 degrees or 84 degrees fahrenheit.

Normally in the atmosphere the temperature drops about 3.5 degrees fahrenheit for every 1000 feet and usually maxes out at about 5.5 degrees/thousand feet in very dry environments (dry adiabatic lapse rate).

In our example there is nearly a 10 degree/thousand feet lapse rate unless the air temperature is cooler than the ocean...which it probably is...

This air is stable stable stable...

Flight height: (~ 922 feet)
Flight temp: 23.8C (~ 74.8F)
Flight dewpoint: 10.2C (~ 50.4F)

That's what GFS was showing us with the Theta-e about a week ago through yesterday. This is why GFS continued to dissipate Erika.
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Quoting mrnicktou:
Question: Since some of us can agree that Erika wont go north like the models predict does that mean she will run into the same wind shear as if she went north?


Per the current readings on UW - which are always subject to changing - she'd actually run into more.

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Quoting StormChaser81:



But im pretty sure thye higher levels shouldnt be spinning after the center has moved away.


It's because the shear isn't at the top; more like the middle, say 500mb?
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Quoting iceman55:
i have a bad feel bad feel

you have a bad feeling or you don't have a good feel on the storm track?
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Question: Since some of us can agree that Erika wont go north like the models predict does that mean she will run into the same wind shear as if she went north?
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Quoting Elena85Vet:


Downgrade likely but not death. Fine silverware to be replaced with plastic sporks.


lol
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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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