Gaston still a threat to redevelop

By: Dr. Jeff Masters , 3:17 PM GMT on September 05, 2010

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For the first time since August 22, when Danielle became a tropical storm, there are no named storms active in the Atlantic. An extratropical storm absorbed Tropical Storm Earl last night, bringing an end to the 11-day life of the 2010 season's longest-lived storm. While Earl was mostly a non-event for North Carolina and New England, the storm gave Nova Scotia a solid pounding, reminding us of what could have easily happened to New England had the forecast track deviated slightly to the left. Kudos go to the computer models and NHC, who successfully predicted the path of Earl very accurately four days in advance. As we approach the climatological peak of Atlantic hurricane season, which occurs on September 10, there are no indications that today's break in the action represents a beginning of an extended quiet period in the Atlantic. Indeed, we have two systems that could become tropical depressions in the next day, and we also have model predictions of another storm to come late in the week.


Figure 1. Morning satellite image of the remains of Gaston, approaching the Lesser Antilles Islands.

Gaston near tropical depression status again
The remains of Tropical Storm Gaston, located about 700 miles east of the Lesser Antilles Islands and moving west at about 13 mph, are close to reaching tropical depression status again. Recent satellite imagery shows that Gaston's remains have developed a well-organized surface circulation, but not enough heavy thunderstorm activity to be considered a tropical depression. A large amount of dry air surrounds Gaston's remains on all sides, as seen on water vapor satellite loops. This dry air will continue to be a major impediment to development. The latest SHIPS model forecast predicts shear will remain moderate, 10 - 15 knots, for the next three days, then fall to the low range. The winds creating the shear are coming from the east, where a tongue of dry air has intruded. These easterly winds will be able to drive the dry air into Gaston's core, disrupting it, unless the storm can find a moister environment, or moisten its environment on its own by generating enough heavy thunderstorms. Gaston has managed to develop more heavy thunderstorms near its center of circulation late this morning, but the amount of dry air it is battling is formidable. Even if Gaston does manage to become a tropical depression today, development will be slow over the next few days, due to the dry air. When Gaston passes over or just to the northeast of the Lesser Antilles Islands early Tuesday morning, the storm is unlikely to have more than 50 mph winds. More significant development is possible later in the week, as the atmosphere should be moister for Gaston. Gaston may threaten Puerto Rico on Wednesday, the Dominican Republic on Thursday, and Haiti, Jamaica, and/or the Turks and Caicos Islands by Friday, depending upon the storm's interaction with a trough of low pressure expected to move off the U.S. East Coast later this week. The earlier Gaston develops into a tropical storm, the more likely it is to "feel" the upper-level winds of the approaching trough, and curve more to the northwest. The HWRF model predicts Gaston will develop by Monday, and pass just northeast of the Lesser Antilles Islands Tuesday morning. The GFDL model, on the other hand, delays development until Wednesday, keeping Gaston in the Caribbean. The GFDL has Gaston hitting Jamaica as a strong tropical storm on Friday morning. However, the GFDL forecast is dubious, because on Wednesday and Thursday, Gaston may have an encounter with the high mountains of the island shared by the Dominican Republic and Haiti, Hispaniola, which could easily destroy a system as fragile as Gaston. Gaston has a 70% chance of developing into a tropical depression by Tuesday, according to NHC.

Gulf of Mexico disturbance 90L
A concentrated area of heavy thunderstorms (90L) has developed over the extreme southwestern Gulf of Mexico, in the Bay of Campeche. Satellite imagery shows that this disturbance is disorganized, but has some modest spin to it. The disturbance is under a moderate 10 - 15 knots of wind shear, and has a 60% chance of developing into a tropical depression by Tuesday, according to NHC. The disturbance is headed northwest at 5 - 10 mph, and should bring heavy rains to the Texas/Mexico border region on Monday, according to the latest run of the GFS model. The main impediment to development will be the limited time 90L has over water; the storm will be ashore by Tuesday, which doesn't give it much time to develop.

Elsewhere in the tropics
The GFS and NOGAPS models are predicting development on Thursday of a tropical wave that will emerge from the coast of Africa on Tuesday or Wednesday.

Next post
I'll have an update Monday morning.

Jeff Masters

Sunrise Surf was cranking (RIWXPhoto)
Sunrise Surf was cranking
Post Hurricane Earl surf photos at Newport, RI (RIWXPhoto)
Post Hurricane Earl surf photos at Newport, RI

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Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting stormwatcherCI:


COC definitely covered now and looks to be around 50.5W and 16.5N. MH09, help me out here please, am I seeing the coc in the right place ?
To the north and west of that location. It's near 17.0N 50.9/51.0W.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Now it has to persist for 6-12 hours.

Thats where I think it will struggle.
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AL, 90, 2010090506, , BEST, 0, 191N, 956W, 20, 1007,
AL, 90, 2010090512, , BEST, 0, 194N, 956W, 25, 1005

Pressure coming down quick
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A little persistance on the convection and "you betcha"

Quoting cirrocumulus:
Gaston has to be a depression already!

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Quoting cirrocumulus:
Gaston has to be a depression already!


A lil more convection is needed before the NHC upgrades ex-Gaston..
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Even though there is a lot of dry air on all sides of Ex-Gaston, most of this is Directly North & also to its East. There isn't a lot of dry air to its W, NW , & SW. 24 more hrs & we are going to get the all-clear signal to start ramping up. I See a ULL situated near Puerto Rico so I take it that this is moving Wesward away from Ex-Gaston.
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Yeah, Swirl....I know....(smiling). My comment sounded much harsher than it was meant. I was kinda pokin fun too, sorry bout that


Quoting HurricaneSwirl:


Well early in the season bloggers were longing for activity and used to pretend disturbances were doing better than they really were by saying "well this invest WOULD have a TCFA if this weren't the weekend", and I was just kind of making fun of that :)
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Gaston has to be a depression already!

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Thanks Dr. Masters!
Member Since: July 7, 2010 Posts: 0 Comments: 5690
Developing system off of Africa in 48 hours on the 12z GFS.
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Quoting Goldenblack:
I see where you are coming from, but that is like saying "...well I thought that weather didn't happen on the weekends...."




Well early in the season bloggers were longing for activity and used to pretend disturbances were doing better than they really were by saying "well this invest WOULD have a TCFA if this weren't the weekend", and I was just kind of making fun of that :)
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Quoting Goldenblack:
The GFS is a funny beastie....

Just a reminder that models are not to be trusted until a system actually develops


...And often after that, too... :)
Member Since: November 8, 2009 Posts: 4 Comments: 13571


COC definitely covered now and looks to be around 50.5W and 16.5N. MH09, help me out here please, am I seeing the coc in the right place ?
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The water vapor loop to which Dr. Masters linked definitely doesn't paint a pretty picture for ex-Gaston's future...but the air in front of it is black in that image, as opposed to the pure rust-colored desert it was yesterday. I feel shear will be more likely to do him in than the dry air will.
Member Since: November 8, 2009 Posts: 4 Comments: 13571
Quoting Stormchaser2007:

A weak TS over S Central TX is a good thing..We need the rain in Dallas-Ft Worth, TX & it looks like we're gonna get plenty :O)..
Member Since: August 25, 2009 Posts: 20 Comments: 6785
The GFS is a funny beastie....

Developed it well when it wasn't doing much better (Yesterday, Friday)..

and now that it is, and gaining a better enviroment.....GFS kills it...lol. Just a reminder that models are not to be trusted until a system actually develops..

Notice that some small convection is over the center of ex-Gaston for the first time in days...


Quoting Stormchaser2007:
The 12z GFS degenerates ex-Gaston into an open-wave in 33 hours.

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Quoting Stormchaser2007:
Vigorous T-wave emerging at 36 hours.
That should be future Igor...
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There's a few things I've been noticing about ex-Gaston that could explain the continued improvement in organization and convection this morning.

1) Wind shear seems to have slackened some allowing for the circulation to expand and become better defined.

2) In reviewing CIMSS data, some weak low level convergence and upper level divergence are stacked overhead allowing for convection to develop over the circulation center.

3) Its seems the moisture field associated with ex-Gaston has expanded some to try and combat dry air surrounding the system.

Current visible satellite imagery shows a much improved system that appears to be regaining tropical depression and maybe even tropical storm status if convection continues to build to the east and over the circulation center as has been the case in the past couple hours.
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This is a great satellite loop to see how ex-Gaston is progressing. The latest image reveals that the circulation is no longer exposed since a deep convective cluster fired atop it. It also looks like it is entering into more favorable conditions are organization and deepening right...well, it is. Check out the water vapor imagery, notice how it is no longer surrounded by the deep oranges, but is now surrounded mainly by the blacks. The indicates that mid-level dry air has decreased. Tropical depression by 11pm EDT is my call.



Moving due west towards the islands of Antigua, Guadeloupe, St. Kitts and Nevis, Montserrat, Barbuda, etc...

Also notice the nice banding feature starting to develop towards the north of the circulation.

Member Since: September 2, 2009 Posts: 130 Comments: 21194
Vigorous T-wave emerging at 36 hours.
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Quoting TropicalAnalystwx13:
Not Miami, but:

Thank you.
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Quoting btwntx08:
wow 6 inches projected by the hpc right off the coast

Great news RAIN in TX, yee haw..from what may become a TS in the GOM..
Member Since: August 25, 2009 Posts: 20 Comments: 6785
I see where you are coming from, but that is like saying "...well I thought that weather didn't happen on the weekends...."


Quoting HurricaneSwirl:


I thought they didn't do those on weekends?
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The 12z GFS degenerates ex-Gaston into an open-wave in 33 hours.

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12z GFS running.. 24 hours 90L a TD.


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Quoting MiamiHurricanes09:
You better stay tuned. Check out these models. If it goes into the Caribbean...well, you know the rest.

I am watching him very closely. I put the computer on when I get up at 5am and when I go to work I am back on WU as much as possible. I don't know what he will do in the long run but not looking good for us.
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Quoting Stormchaser2007:
I don't think it'll go that far north.
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Sorry about that. I am outside on my laptop
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Not Miami, but:

Member Since: July 6, 2010 Posts: 113 Comments: 32286
The dynamic duo in action once again.



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Quoting 850Realtor:
Do any of the models go far enough out to give an idea of where Gaston might go if he makes it to the GOM? I know that's a long way out, just wondering.


The long-range GFS ensembles take it through the Gulf. Not really reliable at the moment though.

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Quoting SirTophamHatt:
Weather in Atlanta is unbelievably perfect today. Hope everybody is having a good Sunday.

Now get off your computers and go outside!
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Quoting stormwatcherCI:
NHC says he should pass south of Hispaniola on Wednesday. We shall see.
You better stay tuned. Check out these models. If it goes into the Caribbean...well, you know the rest.

Member Since: September 2, 2009 Posts: 130 Comments: 21194
Gaston's COC is no longer exposed.
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Quoting Stormchaser2007:


Well some people may not...


True.

lol
Member Since: July 6, 2010 Posts: 113 Comments: 32286
Quoting spathy:

Did I miss Hermine?
Edit
Or is the thinking that 90L is going to become Hermine?
Oh I meant the future wave about to emerge off of africa.The one miami is showing.Miami can you post a pic with the whole continent of africa thank you.
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Quoting HurricaneSwirl:


I thought they didn't do those on weekends?


LOL

Thats obviously false.
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Quoting ElConando:


Sorry my mind is a little fizzy right now.
I understand now.

And no it is not another phrase like "word".
I said "wait what?" as in I was confused about what you posted.

Anyways yes Gaston will be one to watch once development occurs which should be in the next 48 hrs. If it heads into the Caribbean and misses Hisp, look out.
NHC says he should pass south of Hispaniola on Wednesday. We shall see.
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Quoting TropicalAnalystwx13:


We know.


Well some people may not...
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Quoting CybrTeddy:
Much better organized than this morning. Should this continue, expect the percentage at 2pm increase.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
I think the last time they have re-named a storm as a named TD after it fell apart was Ivan in 2004 after it re-surfaced in the Atlantic.
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Quoting Stormchaser2007:
TCFA



I thought they didn't do those on weekends?
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Quoting Stormchaser2007:
TCFA



We know.
Member Since: July 6, 2010 Posts: 113 Comments: 32286
Weather in Atlanta is unbelievably perfect today. Hope everybody is having a good Sunday.

Now get off your computers and go outside!
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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.