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Posted at 12:54 PM ET, 10/30/2010

Tomas grows into season's 12th hurricane

By Greg Postel

* Four straight sunny days: Full Forecast *

Infrared satellite image of Hurricane Tomas over the Lesser Antilles.

The tropical system impacting the Lesser Antilles, just yesterday identified as 91L (pre-depression stage) by the National Hurricane Center, has quickly intensified into Hurricane Tomas. Its satellite presentation is unmistakable in its hurricane characteristics, with very cold (high) cloud tops radiating outward in all directions almost symmetrically.

Maximum sustained winds are estimated to be near 75 mph, and the storm is moving west-northwestward at 15 mph. The center of Tomas is passing near St. Lucia and St. Vincent this Saturday afternoon (see live radar), where hurricane warnings are in effect, and will enter the Caribbean Sea tonight. The National Hurricane Center predicts Tomas will intensify to major (Category 3) hurricane status next week.

For now, wind shear around Tomas is light. And the circulation is moving over unusually warm 85+ degree ocean waters that are capable of supporting a Category 5.

But as so often been the case this year over the Caribbean, an unfriendly environment is not far away. A large counterclockwise swirl associated with an upper trough sits right in the middle of the Caribbean, and is introducing relatively strong wind shear and dry mid-level conditions to that region.

If the weather aloft doesn't improve over the next couple of days as Tomas heads that way, the hurricane may struggle. In fact, if you want to be picky about Tomas' appearance right now in the satellite pictures, one could argue that some dry air is already working into the primary circulation, as indicated by the slight comma-shaped (rather than circular) distribution of tall thunderstorms near the center. Though this is probably something Tomas will be able to overcome in the near term, we will see how the large-scale environment moves with and against the hurricane in time.

Prospects for its longer term survival, beyond a week, particularly if it moves northward toward the Northern Caribbean and the Greater Antilles (e.g., Jamaica; Cuba; Hispaniola), are not especially good. The global weather models continue to advertise a solution that brings a large and very windy upper vortex over the Southern United States later next week. That could very well spell trouble for Tomas.

But in the larger context, the fact that we have a hurricane at this stage of autumn is really not unusual. Officially, we have another month to go the in the 2010 Atlantic season. Historically, 7 of the last 10 years have had named storms in November. Two of those years (08 and 01) saw major hurricanes in the Caribbean. And going back just a couple of years further to 1998, one of the more ferocious storms of modern times, Category 5 hurricane Mitch, tore across the Western Caribbean in the last few days of October.

This season, there's no reason to be convinced that Tomas will be the final one. Though the high-altitude conditions will gradually deteriorate, as hostile intrusions of dry and windy conditions from the north become more frequent with time, the southern-latitude water temperatures stay warm enough to support hurricanes even beyond November.

By Greg Postel  | October 30, 2010; 12:54 PM ET
Categories:  Tropical Weather  
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how's this hurricane season "ranking" now? - in terms of named storms and hurricanes.

like, what's the average # of named storms and named hurricanes as of the end of october, and how many do we have so far, etc...?

Posted by: walter-in-fallschurch | October 31, 2010 8:19 AM | Report abuse

Hi walter-in-fallschurch

Seasons with most named storms (data from Wx Underground):

1. 2005 28
2. 1933 21
3. 2010 19
3. 1995 19
3. 1887 19
6. 1969 18
7. 2008 16
8. 2003 16
9. 1936 16
10. 2007 15
10. 2004 15
10. 2001 15
10. 2000 15

Seasons with most hurricanes (data from Wx Underground):

1. 2005 15
2. 1969 13
2. 1887 13
4. 2010 12
5. 1950 11
5. 1998 11
7. 1995 10
7. 1933 10
7. 1916 10


Posted by: gregpostel | October 31, 2010 8:38 AM | Report abuse

I don't see how they can say Tomas is "better organized" (5AM report today). It had another burst of convection overnight, but no eye formation or anything close. Now (13:15 UTC) it looks very disorganized. Have they actually measured the central pressure or is it just an estimate?

Posted by: eric654 | October 31, 2010 10:10 AM | Report abuse

Hi eric654

I don't have the data NHC used for that discussion. But I trust them. They generally do excellent work. You're right, though, the burst of convection last night seems to have waned somewhat this morning. This kind of diurnal swing is typical.

The 5am NHC disc. does not appear to be based on GOES satellite appearances. Instead, they're relying on in-situ recon data. Rightly so. To your point, they also note that the vortex is getting sheared a bit, which is what we're seeing on the IR.


Posted by: gregpostel | October 31, 2010 10:48 AM | Report abuse

Good news: Tomas is weakening.
Bad news: it may reintensify and slam directly into Haiti, which could be catastropic. Even a minimal hurricane is the the last thing the Haitians need right now.

Posted by: JerryFloyd1 | October 31, 2010 5:32 PM | Report abuse

thanks for the data. looks like an extremely high ranking season after all. and shows how "off the charts" 2005 was.

Posted by: walter-in-fallschurch | October 31, 2010 9:49 PM | Report abuse

AM visible satellite shows the exposed low level vortex. Although very weak, it will be a big problem for Haiti even at the current strength.

Went to wxunderground and clicked on the 1850's years. It is pretty clear they had limited tracking (less than 1/2 looked like they might have a complete track). Sporadic reports from ships probably got some and others were missed. So I would take the "nth highest year since 1851" with a bit of skepticism.

Posted by: eric654 | November 1, 2010 7:32 AM | Report abuse

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