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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http://weather.myfoxtampabay.com/maps/WTVT/custom/models/gfs_caribbean.html

not good, not good at all
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Quoting notverylikely:
The most worthless posts here do not come from the trolls. The most useless posts here are the ones that begin "As I said earlier" or "As I've been saying for three days" or any other manifestation of the "Look at me!!! See how smart I am?!?!?!" mentality of the amateur wannabes. Please go away. Your Great Leader has his own blog now.


The blog is a much better place without him too.
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Make me take out the big guns...

GREarth

FULL IMAGE


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Quoting notverylikely:


I would say your post is the most useless actually

Naturally the only thing more useless than beating of the chests is commenting about them lol. Funny thing is I have seen very little of that here, so I guess you wanted your 15 minutes of fame; you got it

now go away troll
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Wow

The eye has become MUCH better defined


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Quoting amd:
latest radar from Meteo France suggests that the eye is becoming much better defined in the past hour or so.

I agree. The eye has definitely contracted on radar.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting Jedkins01:


Of course, but I'm pretty sure you don't need perfectly saturated air parcels at all quadrants of a tropical cyclone to not call it dry air intrusion. To me its pretty obvious that blaming the convective collapse on dry air is jumping to conclusions, especially when atmospheric profiles indicate very high moisture in all levels within the circulation. There also isn't any dry air surrounding Tomas to pulled into the circulation either...

Tomas is a category 1 hurricane, you can't expect sustained deep convection, fluctuations in convective busts are normal in a hurricane of this intensity without effects from shear or dry air entrainment.

When you have lets say a major hurricane, and are seeing such an effect, you can usually blame it on dry air entrainment, because sustained deep convection is expected by then.


Outflow boundaries are not always observed in developing storms, and they usually indicate dry air. Why do you think a thunderstorm would collapse that fast in a tropical cyclone? Even in weakening hurricanes, outflow boundaries are not always seen. The only time I have ever seen them was when dry air entrainment was an obvious problem. It's not a big problem here, but this is a massive storm for this time of year, and dry air is usually very abundant by the time it gets this late. Water vapor satellite imagery doesn't always tell you whether the air is thoroughly moist around the storm. It's highly likely that a circulation this large pulled in at least some dry parcels which caused the collapse of some cells on the western side. No other explanation fits the details as well. Outflow boundaries are caused by dry air.
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Quoting ryang1994:


Stormchaser2007....
can you personal message me as to where you got this image...and the one below...and the loops associated with them? Thanks!!



NRL NAVY (Top)

RAMMB TC (Bottom)


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234. amd
latest radar from Meteo France suggests that the eye is becoming much better defined in the past hour or so.

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Quoting Bordonaro:

I know, however that St Kitts and St Lucia islands are one nation..


It's St. Kitts and Nevis. St. Lucia is seperate
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Stormchaser2007....
can you personal message me as to where you got this image...and the one below...and the loops associated with them? Thanks!!

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Thank goodness this storm isn't coming to Florida!
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Quoting Levi32:


Yes. It is not hard to imagine that a circulation this large pulled in some less than perfectly moist air parcels.


Of course, but I'm pretty sure you don't need perfectly saturated air parcels at all quadrants of a tropical cyclone to not call it dry air intrusion. To me its pretty obvious that blaming the convective collapse on dry air is jumping to conclusions, especially when atmospheric profiles indicate very high moisture in all levels within the circulation. There also isn't any dry air surrounding Tomas to pulled into the circulation either...

Tomas is a category 1 hurricane, you can't expect sustained deep convection, fluctuations in convective busts are normal in a hurricane of this intensity without effects from shear or dry air entrainment.

When you have lets say a major hurricane, and are seeing such an effect, you can usually blame it on dry air entrainment, because sustained deep convection is expected by then.
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Quoting Dakster:
St. Kitts and Nevis are one nation...

Looking at the 2pm cone - I still believe that the NHC thinks there is some chance Tomas will not get picked up by the trof. Since the coast of Colombia is almost in the 5 day cone.

BTW - Not wishcasting, just observing. I thought that the new cone ould show a more definitive turn toward the North. (Hoping it would've anyways)

Thoughts?

The NHC favors a gradual northward movement instead of a sharp turn.
Member Since: May 16, 2009 Posts: 1 Comments: 1231

Quoting GBguy88:


Yes, that's the information that was listed as of nearly two hours ago.
Station must be having problems.
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Quoting cat5hurricane:

Stick around. It's only the beginning.
I hope this situation does not turn out as bad as it looks...
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imo tomas is a CA bound tc..
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St. Kitts and Nevis are one nation...

Looking at the 2pm cone - I still believe that the NHC thinks there is some chance Tomas will not get picked up by the trof. Since the coast of Colombia is almost in the 5 day cone.

BTW - Not wishcasting, just observing. I thought that the new cone ould show a more definitive turn toward the North. (Hoping it would've anyways)

Thoughts?
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Quoting Stormchaser2007:

Wind out of the NE at 42 knots and gusts up to 60 knots.

Visibility is .5 miles


Yes, that's the information that was listed as of nearly two hours ago.
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219. SLU
Quoting GBguy88:
Does anyone have any updated weather reports out of St. Lucia? Looks as though the station hasn't updated in over an hour...wondering if they've seen any sustained winds approach hurricane force yet.


Well there are reports of damaged homes, blown of roofs, lot of fallen trees, stranded people, heavy rain, high seas
Member Since: July 13, 2006 Posts: 13 Comments: 5367
Quoting weatherman12345:
no not in the beginning of November. It will recurve one way or
Another.
So no threat to GOM?
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Quoting GBguy88:
Does anyone have any updated weather reports out of St. Lucia? Looks as though the station hasn't updated in over an hour...wondering if they've seen any sustained winds approach hurricane force yet.
Wind out of the NE at 42 knots and gusts up to 60 knots.

Visibility is .5 miles
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Quoting cat5hurricane:
Tomás is now at 83W? something is wrong with your longitudes..
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So we're at 19-12-5. Probably those "bustcasters" that we saw in August are weeping in shame.
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looks like some pretty impressive intensification going on. Crazy storm.
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the US is safe by 100% weatherlover94 don't worry the only people that do is us in the Carribean
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Does anyone have any updated weather reports out of St. Lucia? Looks as though the station hasn't updated in over an hour...wondering if they've seen any sustained winds approach hurricane force yet.
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Recon heading back into Tomas at 18z.

I. ATLANTIC REQUIREMENTS
1. SUSPECT AREA (WINDWARD ISLANDS)
FLIGHT ONE -- TEAL 70
A. 30/1200,1800Z
B. AFXXX 0221A CYCLONE
C. 30/0900Z
D. 11.5N 61.0W
E. 30/1030Z TO 30/1800Z
F. SFC TO 15,000 FT
Member Since: September 2, 2009 Posts: 130 Comments: 21194

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Quoting Stormchaser2007:
Extremely high top in the southern eyewall

You can even see the shadow:



Looks like a hot tower.

Usually when that happens we see increased organization.
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Look at those cloud tops in the southern eyewall. AMAZING!
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Quoting SLU:


No they're not.

Sorry I was wrong :O)
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Looks like some dry air intruding into the core, creating the lower-level outflow.
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Quoting weatherwatcher12:

No.

Sorry I was wrong :O)
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...TOMAS LASHING ST. LUCIA AND ST. VINCENT WITH STRONG WINDS AND HEAVY RAINS...
2:00 PM AST Sat Oct 30
Location: 13.4°N 61.0°W
Max sustained: 75 mph
Moving: WNW at 12 mph
Min pressure: 992 mb
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Extremely high top in the southern eyewall

You can even see the shadow:

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Pressure continues to fall.

000
URNT12 KNHC 301656
VORTEX DATA MESSAGE AL212010
A. 30/16:29:50Z
B. 13 deg 09 min N
060 deg 46 min W
C. 700 mb 3025 m
D. 54 kt
E. 299 deg 33 nm
F. 360 deg 58 kt
G. 295 deg 42 nm
H. 992 mb
I. 9 C / 3051 m
J. 13 C / 3043 m
K. 2 C / NA
L. RAGGED BANDING
M. C40

N. 12345 / 7
O. 0.02 / 1 nm
P. AF300 0221A TOMAS OB 26
MAX FL WIND 67 KT N QUAD 14:16:50Z
RADAR STRONG BAND SOUTH SEMI-CIRCLE RAGGED APPEARANCE OVERALL

LAST REPORT
;
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199. unf97
Quoting Orcasystems:


You mean just like most of the models show?



Of course. The model map analysis which Levi posted on this page illustrated all of what should happen with Tomas and the cooldown this upcoming next weekend over the Eastern CONUS.
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Quoting Bordonaro:

I know, however that St Kitts and St Lucia islands are one nation..

No.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
197. SLU
Quoting Bordonaro:

I know, however that St Kitts and St Lucia islands are one nation..


No they're not.
Member Since: July 13, 2006 Posts: 13 Comments: 5367
Quoting Levi32:


Yes. It is not hard to imagine that a circulation this large pulled in some less than perfectly moist air parcels.
Exactly. Looking at water vapor, Tomas could have easily ingested dry air in through the western or southern semicircles.

Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting unf97:
Tha

Thanks levi for providing that map analysis. Yeah, as I explained earlier, that trough currently on the U.S. West Coast will move east and really dig southeastward deep down all the way to the NW Carribbean Sea by the end of the week. That definitely will be the wall that will bring Tomas to a screeching halt on its approach southeast of Jamaica sometime mid week. A trough that deep should pull Tomas more NE and that will take him more towards Haiti and the SE Bahamas as he turns out to sea into the Atlantic. A bad situation for hait should this materializes and God knows those folks just can't take any more disaster. My prayers to all in those areas who may see Tomas' fury. Hope everyone is preparing.



You mean just like most of the models show?
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Quoting MiamiHurricanes09:
Something must have caused the downdrafts that resulted in the large lower-level outflow boundaries coming out of the western quadrant.


Down drafts are not always a result of dry air, those outflow boundaries do give that appearance you are right. But, there are no atmospheric profiles around the circulation that indicate dry air is present.

That being said, a conclusion can be made that the developing tropical cyclone is just going through a phase of change right now. As I said, Tomas is only a category 1 hurricane, and its very large size will limit explosive development. Such collapses in lower and hurricanes as well as tropical storms are common.

Down drafts in general are a result of collapsing convection, but not necessarily dry air, just changing of internal dynamics. This is completely typical in category 1 hurricanes, but as a tropical cyclone grows stronger, these low phases in convection decrease, to where convection becomes constant with a strong hurricane, unless disrupted by shear or dry air intrusion. But once again, since Tomas is a category 1 hurricane, you can't just blame convective collapse on dry air entrainment. Even more so when atmospheric profiles don't indicate any presence of dry air.
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193. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 6213

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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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