Caribbean wave develops a new circulation

By: Dr. Jeff Masters , 4:23 PM GMT on August 24, 2006

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A powerful tropical wave that has the potential to become a serious hurricane is sweeping through the southernmost Lesser Antilles Islands today, bringing tropical storm force wind gusts and heavy rains. An important development has occurred in the past two hours--a new circulation center developed near 12.5N 63W, about 100 miles north-northwest of the original center near the South American coast. This new center lies between St. Vincent and Grenada, and southwest winds observed last hour in Grenada confirms that a closed circulation now exists at the surface. The old center near the South American coast now looks likely to dissipate. Inflow of warm, moist air into its center was too restricted by the presence of the South American land mass, and thus a new center farther north along the axis of this tropical wave was able to form and take over.

Current conditions in the islands
Barbados reported sustained winds of 32 mph at 5am this morning, and wind gusts as high as 51 mph. Togabo had wind gusts to 36 mph, and sustained winds of 33 mph with wind gusts to 43 mph were observed on St. Lucia. A QuikSCAT satellite pass from 6:30am EDT shows a large area of 35 mph winds to the north of the center. Radar from Martinique shows the heavy bands of rain spreading over the islands. Winds on Martinique have gusted to 35 mph so far today.

Wind shear
What happens in the next few hours in crucial in determining if we have a serious hurricane to worry about in a few days, or just a another harmless tropical blob. The storm is very vulnerable to wind shear right now as it reorganizes. The center of circulation is almost completely exposed, with just one spiral band of heavy thunderstorms connected to the northeast side of the center. Upper level winds out of the west are creating about 10 knots of wind shear over the center, keeping the band of thunderstorms pushed to the downwind side of the center. If the shear can increase a little this afternoon, it may disrupt the storm enough to keep it from developing today. The new center location also puts the storm closer to the large area of dry air and Saharan dust that covers much of the eastern Caribbean. This may also help disrupt the storm.

However, I think 97L will overcome these obstacles. Wind shear is probably low enough to allow the storm to reform, and I wouldn't be surprised to see the center jump again more to the east, to be underneath the strongest thunderstorms. The shear is forecast to remain low through the next five days. There is a zone of very high shear to the system's north, but it is forecast to retreat to the west ahead of the developing storm.

The computer models
The latest 8pm and 2am EDT computer model runs were all initialized with the old center position, and thus are unreliable. The new set of model runs using data from 12 GMT (8am EDT) are not going to be any better, since the new center formed about 2 hours later. We'll have to wait until the 18 GMT (2pm EDT) model runs are available late tonight before we can put much stock in any of the computer model solutions. With this in mind, here is my summary from my previous blog about what the latest computer models say:

The Canadian model continues to be very consistent and very gung-ho, developing 97L into a strong tropical storm on Saturday, south of Jamaica, then taking the storm into the Gulf of Mexico as a hurricane. The NOGAPS model is also consistent, assuming a more southerly track will occur with no development due to close proximity to the South American coast. The GFS takes a weak tropical storm across the Dominican Republic on Saturday, then into the Bahamas. The GFDL has the same idea, but has a much stronger system that becomes a Category 1 hurricane in the Bahamas on Monday. The run-to-run consistency of the GFDL has been poor, and both the GFDL and GFS have not done a good job forecasting the initial track of the storm so far.

What the new center means for this storm
The separation of its center from the coast removes the primary impediment to intensification for 97L. It looks more likely that this storm will develop into at least a strong tropical storm, and probably a hurricane. The track such a hurricane might take is highly uncertain, but the more northerly center increases the risk for Haiti, the Dominican Republic, the Bahamas, and the U.S. East Coast.


Figure 1. Current satellite image of Invest 97L.


Figure 2. Preliminary model tracks for disturbance 97L approaching the Lesser Antilles Islands.

Debby
Tropical Storm Debby remains a minimal tropical storm today, but is expected to slowly intensify in response to some warmer waters along her path the next two days. By the time Debby turns north this weekend, she could attain hurricane status. Early next week, Debby is expected to get caught up in the jet stream and die in the North Atlantic.

Why the 2am run of the GFDL failed
The 2am EDT run of the GFDL model failed on 97L this morning, so I was quoting the results from the 8pm EDT run last night. I got an email from Morris Bender of the GFDL project this morning on why the 2am GFDL run failed:

The vortex initialized from our initialization was very weak as the initialization process spins up the storm to match the observed initial winds. Since the easterlies in the lower level were very strong in the GFS analysis, it initialized a disturbance with very weak vorticity.

As you can see at hour 0 there was almost no circulation initially. As a result, our grid movement shut down at 3 hours and the inner nests could no longer follow the storm for the rest of the forecast.

The previous runs also had a very weak initial disturbance but there was enough of a pressure gradient that the inner nests continued to follow the vortex and eventually with the high resolution it developed into a significant tropical cyclone.

In the 6z run, the weak disturbance moved out of the high resolution inner grid, into the coarse resolution, and so all we had left was a very weak disturbance that could not be resolved in the coarse outer mesh.


As you can see, getting the computer models to work on weak disturbances is a difficult business! We should not put too much faith in the computer models for any weak system; it is too difficult for the models to get the starting conditions of the storm correct.

I'll have an update this afternoon after the Hurricane Hunters check out 97L.

Jeff Masters

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726. Baybuddy
9:16 PM GMT on August 24, 2006
Every time I say Ernesto I picture some lounge singer with a bad combover.
Member Since: June 26, 2006 Posts: 0 Comments: 1115
725. Baybuddy
9:15 PM GMT on August 24, 2006
I think, for sanitys sake everyone should concentrate on what is going to happen enroute to the GOM, right now the cone of uncertainty is well, uncertain.
Member Since: June 26, 2006 Posts: 0 Comments: 1115
723. 21N71W
8:05 PM GMT on August 24, 2006
new blog
Member Since: August 1, 2006 Posts: 0 Comments: 180
722. nash28
7:59 PM GMT on August 24, 2006
It's out on FSU 0741. But don't put much stock in this run. Wait for the next set of runs when they have been able to reposition the center.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
721. ihave27windows
7:59 PM GMT on August 24, 2006
The good Dr. has updated the blog.
Member Since: July 19, 2005 Posts: 108 Comments: 14933
720. silverstripes
7:58 PM GMT on August 24, 2006
New blog with TD5 confirmed by the Dr.
Member Since: July 26, 2006 Posts: 5 Comments: 595
719. SWFLdrob
7:58 PM GMT on August 24, 2006
STRONG RIDGING N OF THE SYSTEM WOULD KEEP
THE TC WELL AWAY FROM THE NE GULF.

I could see this happening...will have to wait and see, of course.
718. Levi32
7:57 PM GMT on August 24, 2006
NEW BLOG UP!!!
Member Since: November 24, 2005 Posts: 635 Comments: 26700
717. KShurricane
7:57 PM GMT on August 24, 2006
Hey Ernesto, glad to see you. You've been one of my best pals, now why don't you just spin yourself away from my continent like a good little disturbance.
716. 0741
7:57 PM GMT on August 24, 2006
i donot see gfdl on 97l yet their still run it on other system in pacific
715. franck
7:56 PM GMT on August 24, 2006
Now nearly all buoys report falling barometric pressure in northern Gulf.
Member Since: August 30, 2005 Posts: 0 Comments: 1150
713. HurricaneRoman
7:55 PM GMT on August 24, 2006
NATIONAL WEATHER SERVICE TALLAHASSEE FL
333 PM EDT THU AUG 24 2006

.LONG TERM...SUN THROUGH THU.
ALSO OF NOTE, TPC JUST
REPORTED IN A SPECIAL DISTURBANCE STATEMENT THAT THE RECONNAISSANCE
PLANE INVESTIGATING THE SYSTEM NEAR THE WINDWARD ISLAND FOUND A
CLOSED CIRCULATION. THE ENVIRONMENT AHEAD OF THE SYSTEM DOES NOT
LOOK CONDUCIVE FOR DEVELOPMENT, AND EVEN IF THE SYSTEM SURVIVES ALL
THE WAY TO THE YUCATAN, STRONG RIDGING N OF THE SYSTEM WOULD KEEP
THE TC WELL AWAY FROM THE NE GULF.
Member Since: February 25, 2006 Posts: 2 Comments: 959
711. nash28
7:54 PM GMT on August 24, 2006
No HurricaneRoman. No one can say with any certainty "who is out" right now. In fact, they should be ashamed of themselves for poo pooing this in an official statement.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
710. Patrap
7:54 PM GMT on August 24, 2006
..great post dacajun..But Nash did influence hiz neighbors last year to leave..His wife takes all his time due to her health..and when nash left with his wife for katrina last year...everyone..everyone on his Block left...and survived...
Member Since: July 3, 2005 Posts: 428 Comments: 129902
709. ProgressivePulse
7:54 PM GMT on August 24, 2006
2pm runs don't come out unitl later tonight.
Member Since: August 19, 2005 Posts: 5 Comments: 5458
708. SWFLdrob
7:53 PM GMT on August 24, 2006
Posted By: jphurricane2006 at 7:47 PM GMT on August 24, 2006.
but im thinking that if we see some steady strengthening it will get drawn further north and those models will change

Probably so...although the general idea that a high over or around Florida would keep the system from getting too far north and start shoving it more westerly (as seen with some of the newer models in days 4 and 5)..would it not?
707. southbeachdude
7:53 PM GMT on August 24, 2006
wow...thanks for the update....guess SE FL and others on the east coast need to watch this carefully
Member Since: July 29, 2005 Posts: 2 Comments: 697
704. HurricaneTracker01
7:53 PM GMT on August 24, 2006
ernesto could be bad... we'll have to wait and see
Member Since: August 1, 2006 Posts: 6 Comments: 126
703. nash28
7:52 PM GMT on August 24, 2006
That's ok Dacajun. I try to read everything that posts while I am typing, but when this blog really starts hopping, it become tedious.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
702. FlaRob
7:52 PM GMT on August 24, 2006
18Z is 2PM.
701. HurricaneRoman
7:52 PM GMT on August 24, 2006
Does that statement mean that florida is out???? I hope so
Member Since: February 25, 2006 Posts: 2 Comments: 959
700. dacajun
7:51 PM GMT on August 24, 2006
Sorry nash28...thought you saw Patrap's posting about Nash Roberts...a retired but beloved New Orleans meterologist. Postings are coming hot and heavy, so his comments are about 4 pages down by now.
Even after he retired, when things would get bad, they would pull Nash out the closet, dust him off, and stick his infamous grease pencil in his hand. He NEVER used green screen projections and all the nifty gadgets they use nowadays. He would draw where each high and low pressure system is with his grease pencil and write the temperature of each city as he referred to the prinouts in his hand.
Everyone in New Orleans knew...if Nash said it, then it was gospel (no matter how wrong or vague he was). Makes you wonder how many people would have left had he been on TV telling everyone to leave before Katrina!
Member Since: November 1, 2005 Posts: 0 Comments: 52
699. nash28
7:50 PM GMT on August 24, 2006
The models should change anyways JP. Remember, Dr. Masters said the 2pm runs do not have the repositioned center initialized. The 18z should.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
698. FierceWinds
7:50 PM GMT on August 24, 2006
Posted By: tornado7 at 7:45 PM GMT on August 24, 2006.
is there any chance a landfall close to rita's


Yes, but it's way too early to tell. I wouldn't worry.
697. Cavin Rawlins
7:49 PM GMT on August 24, 2006
Tropical Depresion 05
Winds:35mph
Pressure:1008mbars

Member Since: July 24, 2005 Posts: 407 Comments: 19076
696. ProgressivePulse
7:49 PM GMT on August 24, 2006
My estimate Mandy is around 13N62W.
Member Since: August 19, 2005 Posts: 5 Comments: 5458
693. AndyN
7:47 PM GMT on August 24, 2006
000
WONT41 KNHC 241912
DSAAT
SPECIAL TROPICAL DISTURBANCE STATEMENT
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
315 PM EDT WED AUG 16 2006

REPORTS FROM AN AIR FORCE RECONNAISSANCE PLANE INDICATE THAT THE TROPICAL WAVE MOVING WESTWARD THROUGH THE WINDWARD ISLANDS HAS DEVELOPED A CLOSED WIND CIRCULATION...AND ADVISORIES ON EITHER A TROPICAL DEPRESSION OR TROPICAL STORM WILL BE INITIATED AT 5 PM AST. MAXIMUM WINDS AT THIS TIME APPEAR TO BE JUST BELOW TROPICAL STORM STRENGTH...BUT IT IS POSSIBLE THAT STRONGER WINDS MAY BE OBSERVED PRIOR TO ADVISORY TIME.

$$
FORECASTER FRANKLIN
Member Since: December 29, 2005 Posts: 1 Comments: 551
692. Cavin Rawlins
7:46 PM GMT on August 24, 2006
Size does matter...If that was Debby....
Member Since: July 24, 2005 Posts: 407 Comments: 19076
691. Patrap
7:46 PM GMT on August 24, 2006
..track guidance looks close together out 96...but the low shear and warm SSts are going to become a factor..in the next 72 to come....and will probably be handled well by the SHIPS..hopefully...
Member Since: July 3, 2005 Posts: 428 Comments: 129902
689. tornado7
7:45 PM GMT on August 24, 2006
is there any chance a landfall close to rita's
688. photorescues
7:45 PM GMT on August 24, 2006
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
333 PM EDT THU AUG 24 2006

.LONG TERM...SUN THROUGH THU.
ALSO OF NOTE, TPC JUST
REPORTED IN A SPECIAL DISTURBANCE STATEMENT THAT THE RECONNAISSANCE
PLANE INVESTIGATING THE SYSTEM NEAR THE WINDWARD ISLAND FOUND A
CLOSED CIRCULATION. THE ENVIRONMENT AHEAD OF THE SYSTEM DOES NOT
LOOK CONDUCIVE FOR DEVELOPMENT, AND EVEN IF THE SYSTEM SURVIVES ALL
THE WAY TO THE YUCATAN, STRONG RIDGING N OF THE SYSTEM WOULD KEEP
THE TC WELL AWAY FROM THE NE GULF.
687. ProgressivePulse
7:45 PM GMT on August 24, 2006
NHC has it as TD5 on the floater now
Member Since: August 19, 2005 Posts: 5 Comments: 5458
686. franck
7:45 PM GMT on August 24, 2006
2006..who would hoe a road..but yes, perhaps know a road to a hoe, or like Randrewl suggests row a hoe. But yes, it is hoe a row, as in cultivating a row of veggies beginning by hoeing the row.
Member Since: August 30, 2005 Posts: 0 Comments: 1150
684. ProgressivePulse
7:45 PM GMT on August 24, 2006
Your welcome ema
Member Since: August 19, 2005 Posts: 5 Comments: 5458
683. vortextrance
7:45 PM GMT on August 24, 2006
Mandy its pretty easy to find on the visible just NW of Grenada.
Link
Member Since: October 5, 2005 Posts: 0 Comments: 700
682. ProgressivePulse
7:44 PM GMT on August 24, 2006
Estimated right now Mandy, no vortex message released yet.
Member Since: August 19, 2005 Posts: 5 Comments: 5458
681. ricderr
7:44 PM GMT on August 24, 2006
rand...td 6 just got here......sky went black...thunder.......chased the admiral back inside the house
Member Since: June 27, 2006 Posts: 676 Comments: 22373
680. Cavin Rawlins
7:44 PM GMT on August 24, 2006
Wind shear is now forecast to be at low levels...

If TD5 can move NW move through between Cuba and Haiti with out affecting them much as a TS, then move north and east out to sea that would be very good.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
679. emagirl
7:44 PM GMT on August 24, 2006
thanks ProgressivePulse i am at work so i dont get to read all the comments i miss alot
678. cajunkid
7:44 PM GMT on August 24, 2006
Link
Member Since: July 10, 2005 Posts: 3 Comments: 1281

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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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