Unprecedented Hurricane Tomas pounding the Lesser Antilles

By: Dr. Jeff Masters , 3:38 PM GMT on October 30, 2010

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Hurricane Tomas, an unprecedented Lesser Antilles hurricane for so late in the season, is bearing down on the islands of St. Lucia and St. Vincent with Category 1 winds of 75 mph. Recent radar imagery from the Martinique radar shows that Tomas is still in the organizing stage, with an eyewall that just closed off, and a weak area of echoes on the south side, due to modest wind shear of 10 knots caused by southerly upper-level winds. The Hurricane Hunters reported top surface winds in the northern eyewall near 75 mph. St.Lucia figures to get the worst blow from Tomas, as this island will experience the strong right-front quadrant of the storm--the north eyewall. Winds on the island were sustained at 46 mph, gusting to 67 mph, at 11am EDT. Winds at Barbados peaked at 37 mph, gusting to 56 mph, early this morning, and the pressure bottomed out at 994 mb. Satellite loops of Tomas show a large and well-organized Cape Verdes-type hurricane, with good upper level outflow on all sides except the south, and an impressive amount of heavy thunderstorm activity. This is a very dangerous hurricane that is just beginning to get going. You can follow the progress of Tomas through the islands today with our wundermap zoomed in on St. Lucia.


Figure 1. Morning radar image from the Martinique radar shows the eye of Tomas moving between the islands of St, Lucia to the north and St. Vincent and the Grenadines to the south. The southern portion of the eyewall had just closed off with this image. Image credit: Meteo France.

Intensity forecast for Tomas
Now that the eyewall of Tomas has completely closed off, a period of steady and possibly rapid intensification lasting until Sunday afternoon is likely. The intensification rate may then be slowed by an increasing flow of southwesterly upper-level winds, which are expected to bring dry air and a moderate 15 - 20 knots of wind shear to Tomas Sunday through Tuesday, according to the latest SHIPS model forecast. Shear is then expected to relent, allowing more intensification on Wednesday. Water temperatures are a record warm 29.5°C and the Tropical Cyclone Heat Potential--a measure of the total heat content of the ocean--is a very high 100 kJ/cm^2, which is very favorable for rapid intensification. I expect the Tomas will strengthen to a Category 3 or 4 hurricane by Wednesday.


Figure 2. Hurricane specialists Robbie Berg (background) and Dan Brown (foreground) discuss the latest data on Tomas last night at the National Hurricane Center.

Track forecast for Tomas
The computer models have come into better agreement this morning that after Tomas reaches the central Caribbean 4 - 5 days from now, a turn to the north or northeast is likely, in response to a strong trough of low pressure expected to develop over the Eastern U.S. The exact timing of this turn to the north or northeast is difficult to predict at this time, as steering currents will be weak in the Caribbean after Tomas passes through the Lesser Antilles today and Sunday. At this time, is appears that the Dominican Republic and Haiti are most at risk from a strike by Tomas, though the storm could move as far west as Jamaica, or as far east as the northern Lesser Antilles Islands.


Figure 3. Hurricane specialist Dan Brown computes Tomas' radius of tropical storm force winds using the old-fashioned paper track plot and dividers technique. Hurricane specialists at NHC commonly use a paper track plot to mark all storm center fixes and compute the current motion of the storm. A storm's current heading and speed in NHC advisories is usually a 12-hour average of the motion up until the final fix position.

Tomas, Shary, and the 2010 hurricane season in perspective
Tomas' formation ties 2010 with 1995 and 1887 for 3rd place for most number of named storms in an Atlantic hurricane season. Only 2005 (28 named storms) and 1933 (21 named storms) were busier. Atlantic hurricane records go back to 1851, though there were likely many missed named storms prior to the beginning of satellite coverage in the mid-1960s. The intensification of Shary and Tomas into hurricanes today brings the total number of hurricanes this season to twelve, tying 2010 with 1969 and 1887 for second place for most hurricanes in a season. The record is held by 2005 with fifteen hurricanes, and I don't think we'll beat that record this year!

The formation of Tomas so far south and east this late in the season is unprecedented in the historical record; no named storm has ever been present east of the Lesser Antilles (61.5°W) and south of 12°N latitude so late in the year. Hurricane Six of 1896 came close--it was also a tropical storm south of 12°N and east of 61.5°W on October 29, but nine hours earlier in the day. That storm recurved to the north and missed the Lesser Antilles. Tomas' track through the southern Lesser Antilles so late in the year is unprecedented. There have been only two other tropical storms that formed after October 15 south of 12°N and east of 61.5°W: Hurricane Jose, which was a tropical storm in that region on October 18, 1999, and Tropical Storm Nicolas, on October 16, 2003. Tomas most reminds me of a storm I flew into with the Hurricane Hunters--Hurricane Joan of 1988, which was a tropical storm on October 14 near Tomas' current location, and later strengthened into a Category 4 hurricane that hit Nicaragua. According to Chenoweth (2008), Tomas is the first tropical storm to cross through the Lesser Antilles Islands south of 16°N this late in the year since 1724. In that year, a tropical storm on 12 November crossed the islands at 13.7°N 61.5°W, and later became a hurricane that affected Jamaica. There was also a hurricane on 30 October 1671 that crossed 61.5°W at 13.3°N, and did damage on Barbados.

Another unusual aspect of Tomas' formation is that we now have two simultaneous hurricanes in the Atlantic Ocean on October 30. There has been only one hurricane season since 1851 that had had two simultaneous hurricanes later in the year--1932, when Hurricane Ten and Hurricane Eleven both existed November 7 - 10. Today is also the 5th latest date in the season that there have been two simultaneous named storms in the Atlantic. The record was set way back in 1887, when Hurricane Eighteen and Tropical Storm Nineteen were both active on December 8. There were three years that had simultaneous November named storms: 1932, 1961, and 2001.

References
Chenoweth, M. and D. Divine (2008), "A document-based 318-year record of tropical cyclones in the Lesser Antilles, 1690-2007", Geochemistry, Geophysics, Geosystems, 9, doi:10.1029/2008GC002066.

Next update
I'll have more on Sunday by 3pm EDT. I'm headed home to Michigan today, after a very valuable week here at the National Hurricane Center. The experience gave me a new appreciatation for just how good the forecasters are at what they do. NHC's hurricane experts are truly world-class, and we are very fortunate to have such a talented group of hard-working forecasters keeping us informed on the dangers we face from Atlantic hurricanes.

Jeff Masters

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Quoting kmanislander:


Good afternoon

Here is the correct steering layer for Tomas. Note the pressure range at the bottom right of the image.


Thanks Kmanislander. What are your thoughts in regards to his recent slowdown?
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Quoting cat5hurricane:
18z 700-850mb steering map:

Click To Enlarge


Good afternoon

Here is the correct steering layer for Tomas. Note the pressure range at the bottom right of the image.

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Quoting MiamiHurricanes09:
Yep. It will be interesting to see how far south the trough digs.

If he slows down considerably later in the track, then he'll have a better chance to catch it I think. A faster track would seem to mean he would sneak under the inbound trough and take advantage of the ridge's steering when it's the strongest before it's possibly eroded by the longwave. Timing is everything.
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340. SLU
Quoting GBguy88:
I have a question, and I'm not meteorology savvy, so be patient with me, hahaha. Given that Tomas does not appear to be moving very fast, and given the much improved presentation of the eye on radar, what are the odds that St. Lucia could experience winds that are a fair deal higher than what they've been warned for? If a strong burst of intensification takes place, isn't it plausible that they would be subject to the increasing winds? Do they warn for that possibility? I just imagine an island full of people expecting a minimal Category 1, and in reality experiencing something that could be a fair bit stronger than that. They didn't really have a lot of time to prepare in the first place...


Well to be honest with you. The country wasn't adequately warned primarily as a result of the system's rapid overnight burst of intensification. And of course, some persons totally downplayed the severity of the situation as usual and went about their normal daily activities this morning.

It is now becoming a major disaster now given the lack of preparation and the strength of the winds which have caused some damage already. The worst is about to strike the island and the system has also suddenly stalled over the last few hours which means that there's going to be a mighty pounding from this strengthening hurricane.

This could be the worst disaster in St. Lucia since Major Hurricane Allen in 1980 based on reports coming through.
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Quoting Hurricanes101:


If I CAT 5 is predicted, GET OUT!! lol

When sunshine is predicted, bring an umbrella lol


I actually have one in the car, at home, and at work... I usually get out at Cat 3 anyways.
Member Since: March 10, 2006 Posts: 0 Comments: 10626
lightning is increasing around barbados


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first rains from tomas - related weather hittin south coast of pr? we got rain and wind here
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Quoting TropicalMan2010:
once the convection wraps around the eyewall then its uhh ohh time.

Think today and tonight might be the time for that.
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Quoting Hurricanes101:


It could also have the opposite effect, the front misses it entirely and it moves more west than forecast
Yep. It will be interesting to see how far south the trough digs.
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Quoting Dakster:
H101 - And when a Cat 5 is predicted?

And I guess when sunshine is predicted I should be prepared for a TS or Cat 1 storm?

just giving you a hard time... I get your point and it does make sense.


It just sparked my curiosity, because all the hurricanes I've been through have been the classic weaken-after-landfall scenario...I'm just trying to imagine what it would be like to have a slow moving hurricane rapidly intensify over top of you. Not saying it's rapidly intensifying just now, but it's a scary thought.
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once the convection wraps around the eyewall then its uhh ohh time.
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Quoting Dakster:
H101 - And when a Cat 5 is predicted?

And I guess when sunshine is predicted I should be prepared for a TS or Cat 1 storm?

just giving you a hard time... I get your point and it does make sense.


If I CAT 5 is predicted, GET OUT!! lol

When sunshine is predicted, bring an umbrella lol
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Quoting Stormchaser2007:


Keep 'em coming. Those are great visible shots.
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Quoting Relix:


The problem is it gives more time for the front to come down and pick it up. I am all for it hitting PR than going over Haiti. So many thousands of lives lost.


It could also have the opposite effect, the front misses it entirely and it moves more west than forecast
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Quoting Hurricanes101:
Steering shows it is on the SW side of a ridge now, could be why it slowed down


Looks like you beat me to it. But yeah, that's my only explanation right now.
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H101 - And when a Cat 5 is predicted?

And I guess when sunshine is predicted I should be prepared for a TS or Cat 1 storm?

just giving you a hard time... I get your point and it does make sense.
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Quoting sunlinepr:


Wow. Eyewall looking really solid on the eastern side.
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18z 700-850mb steering map:

Click To Enlarge
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325. Relix
Quoting Hurricanes101:


Remember how the NHC said the steering currents would collapse in about 4-5 days as Tomas went around the western edge of the ridge?

I am thinking that this is the opposite, the trough and Shary are rocketing out, but the ridge has not yet picked up Tomas yet, so its stuck for a bit until that ridge does pick it up


The problem is it gives more time for the front to come down and pick it up. I am all for it hitting PR than going over Haiti. So many thousands of lives lost.
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Steering shows it is on the SW side of a ridge now, could be why it slowed down

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Quoting MiamiHurricanes09:
Wow, this is interesting. The bulk of the 18z dynamical envelop shows Tomas cutting towards the east at the end of the plot. Models have come into larger disagreement in this run.


I'll stick with the NHC track, I don't see what could cause that sharp a turn in the near term at least.
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Quoting MiamiHurricanes09:
ATCF Model Plots -- RaleighWx


Thanks :)
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Quoting MiamiHurricanes09:
Yeah, it looks like it stalled just east of St. Vincent. Radar shows it's been there for more than 2 hours. Not sure what's the cause.


scary. poor little island :(
Member Since: October 6, 2007 Posts: 0 Comments: 6453
Quoting MiamiHurricanes09:
Yeah, it looks like it stalled just east of St. Vincent. Radar shows it's been there for more than 2 hours. Not sure what's the cause.


Remember how the NHC said the steering currents would collapse in about 4-5 days as Tomas went around the western edge of the ridge?

I am thinking that this is the opposite, the trough and Shary are rocketing out, but the ridge has not yet picked up Tomas yet, so its stuck for a bit until that ridge does pick it up
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317. JLPR2
Quoting MiamiHurricanes09:
Wow, this is interesting. The bulk of the 18z dynamical envelop shows Tomas cutting towards the east at the end of the plot. Models have come into larger disagreement in this run.



Well, you just ruined my confidence. :\
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Still trying to wrap that convection around the inner-core region. That heavy convection off to the east perhaps creating some friction holding him up? Just a thought. Not sure why he slowed.

Click For Animation
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Quoting CaribBoy:


Do you have a link to them please?
ATCF Model Plots -- RaleighWx
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Quoting Relix:
Moving slooooooooooow. Maybe slower than forecast? Can anyone shed some light?
Yeah, it looks like it stalled just east of St. Vincent. Radar shows it's been there for more than 2 hours. Not sure what's the cause.
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Quoting Hurricanes101:


A great rule of thumb while preparing for a storm is to always expect and prepare for at least 1 or 2 categories higher than what is forecast

If St Lucia was forecast to get a CAT 1, they should have prepared for a CAT 2 or 3, just to be safe


Well I hope they did. That right front quadrant is starting to look pretty dangerous on the radar.
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Quoting MiamiHurricanes09:
Wow, this is interesting. The bulk of the 18z dynamical envelop shows Tomas cutting towards the east at the end of the plot. Models have come into larger disagreement in this run.



Do you have a link to them please?
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Quoting sunlinepr:

Good radar link
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Quoting MiamiHurricanes09:
Wow, this is interesting. The bulk of the 18z dynamical envelop shows Tomas cutting towards the east at the end of the plot.


So much for the <90 degree pivot. That's a screeching halt and abrupt turn.
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Quoting MiamiHurricanes09:
Wow, this is interesting. The bulk of the 18z dynamical envelop shows Tomas cutting towards the east at the end of the plot. Models have come into larger disagreement in this run.



Very interesting.
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Quoting GBguy88:
I have a question, and I'm not meteorology savvy, so be patient with me, hahaha. Given that Tomas does not appear to be moving very fast, and given the much improved presentation of the eye on radar, what are the odds that St. Lucia could experience winds that are a fair deal higher than what they've been warned for? If a strong burst of intensification takes place, isn't it plausible that they would be subject to the increasing winds? Do they warn for that possibility? I just imagine an island full of people expecting a minimal Category 1, and in reality experiencing something that could be a fair bit stronger than that. They didn't really have a lot of time to prepare in the first place...


A great rule of thumb while preparing for a storm is to always expect and prepare for at least 1 or 2 categories higher than what is forecast

If St Lucia was forecast to get a CAT 1, they should have prepared for a CAT 2 or 3, just to be safe
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Sky must be impressive looking in St Vincent right now with the eye entering the area!
Member Since: October 6, 2007 Posts: 0 Comments: 6453
HurricaneTomas's heading held*steady at (3.7degrees west of) WestNorthWest
H.Tomas's average speed moving between its last 2 reported positions decreased to ~7mph(~11.3km/h) from its previous travel speed of ~14.3mph(~23.1km/h)
* The 0.1degree difference fits well within rounding error
TS.Thomas
29Oct 06pmGMT - 10.8n56.8w - 35knots(~64.8km/h) - - 998mb - ATCF
29Oct 09pmGMT - 11.1n57.5w - 40mph(~64.4km/h) - . - 998mb - NHC.Adv.#1
30Oct 12amGMT - 11.6n57.6w - 60mph(~96.6km/h) - . - 999mb - NHC.Adv.#2
30Oct 03amGMT - 12.2n58.4w - 65mph(~104.5km/h) - - 997mb - NHC.Adv.#3
30Oct 06amGMT - 12.4n58.8w - 65mph(~104.5km/h) - - 997mb - NHC.Adv.#3A
30Oct 09amGMT - 12.9n59.5w - 70mph(~112.7km/h) - - 994mb - NHC.Adv.#4
30Oct 12pmGMT - 13.1n60.1w - 70mph(~112.7km/h) - - 993mb - NHC.Adv.#4A
H.Tomas
30Oct 03pmGMT - 13.3n60.7w - 75mph(~120.7km/h) - - 993mb - NHC.Adv.#5
30Oct 06pmGMT - 13.4n61.0w - 75mph(~120.7km/h) - - 992mb - NHC.Adv.#5A

Copy&paste 10.8n56.8w, 11.1n57.5w, 11.6n57.6w, 12.2n58.4w, 12.4n58.8w-12.9n59.5w, 12.9n59.5w-13.1n60.1w, 13.1n60.1w-13.3n60.7w, 13.3n60.7w-13.4n61.0w, cfg, kin, pos, 13.4n61.0w-17.87n76.3w into the GreatCircleMapper for a look at the headings and the distances traveled over the last 12^hours.

Using straightline projection upon the speed&heading averaged
over the 3hours spanning the last two reported positions:
H.Tomas should have passed ~4.2miles(~6.8kilometres)north of Fancy,St.Vincent,
and be ~6days&7hours from PortMorant,Jamaica


^ The westernmost line-segment is the straightline projection.
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Statistical models
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Hi from P.R. Thomas is will turn NE? no me gusta nada.
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303. Relix
Moving slooooooooooow. Maybe slower than forecast? Can anyone shed some light?
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Wow, this is interesting. The bulk of the 18z dynamical envelop shows Tomas cutting towards the east at the end of the plot. Models have come into larger disagreement in this run.

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I have a question, and I'm not meteorology savvy, so be patient with me, hahaha. Given that Tomas does not appear to be moving very fast, and given the much improved presentation of the eye on radar, what are the odds that St. Lucia could experience winds that are a fair deal higher than what they've been warned for? If a strong burst of intensification takes place, isn't it plausible that they would be subject to the increasing winds? Do they warn for that possibility? I just imagine an island full of people expecting a minimal Category 1, and in reality experiencing something that could be a fair bit stronger than that. They didn't really have a lot of time to prepare in the first place...
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the models have shifted south and west again
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298. MZT
He is really close to wrapping up. Could be don by the 5PM advisory.
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most of the models that take it north have the system very weak mabie a moderate ts and the ones that are supporting a more west motion are the ones suggesting a major hurricane
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Quoting Jedkins01:


LOL


I figured you would like that lol

I guess for me the best part of tracking is not really knowing where the storm will go

While the chances of a Florida hit are unlikely they are not impossible, I just hate seeing people say it won't hit here or there when it is just going through the Islands and will still be in the Caribbean 5 days from now.

Kind of takes the fun out of the chase for me

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Quoting Hurricanes101:
Well crap this isnt hitting Florida?

Why even track this storm then?

*Leaves*


LOL nice!! *leaves and slams the door*
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Quoting weatherlover94:


how do you know that?

I don't know anything for sure. But I am almost 100% certain that the strong mid-level longwave will dig far enough south and east to erode the western flank of the mid-level ridge that will steer Tomas up until mid-week. Timing is everything here.

Now things can chance and the NHC is the best bet...like always. But FL is safe imo.
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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.