TD 8 forms; 97L a potential threat to the Caribbean and U.S.

By: Dr. Jeff Masters , 15:30 GMT le 19 août 2011

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Tropical Depression Eight formed last night near the coast of Honduras, and is headed westwards towards a landfall in Belize on Saturday. TD 8 is a small storm, so will impact a relatively small area of northern Honduras, northern Guatemala, all of Belize, and southern portions of Mexico's Yucatan Peninsula. TD 8 has just enough room between its center and the coast of Honduras to intensify into a moderate strength tropical storm with 50 - 60 mph winds before landfall. It is very unlikely TD8 has the time or room to intensify into a hurricane; NHC gave the storm just a 7% chance of making it to hurricane strength in their 11am EDT wind probability forecast. Should TD8 make it to tropical storm strength, it would be called Harvey.


Figure 1. Morning satellite image of TD 8.

Invest 97L likely to become a tropical storm next week, could threaten the U.S.
A tropical wave near 14°N 48°W, about 800 miles east of the Lesser Antilles Islands, is moving westward near 20 mph. This wave, designated Invest 97L by NHC yesterday, has seen a marked increase in its heavy thunderstorm activity this morning, but dry air to the north and west is slowing development. An impressive amount of large-scale spin is obvious in visible satellite loops, but the storm is at least a day away from forming a well-defined surface circulation. Ocean temperatures are about 28.5°C, about 2°C above the threshold needed to support a tropical storm, and wind shear is low, 5 - 10 knots.


Figure 2. Morning satellite image of the tropical wave 97L.

The computer models have shown an unusual amount of agreement in developing 97L over the past few days, and all the ingredients seem to be in place for a tropical storm to form by Monday or Tuesday as 97L crosses the Northeast Caribbean. The atmosphere is expected to be moister over the Caribbean, wind shear will remain a low 5 - 10 knots, and sea surface temperatures will increase to near 29°C. The main impediment for development will likely be two-fold: too much dry, stable air, and proximity to land.

As seen in Figure 3, there has been an unusual amount of dry, stable air in the Atlantic this year, due to a combination of dry air from Africa, and upper-atmosphere dynamics creating large areas of sinking air that dry as they warm and approach the surface. This stable air has been largely responsible for the fact that none of our seven tropical storms so far this year has made it to hurricane strength, despite the presence of sea surface temperatures that are the 3rd warmest on record across the tropical Atlantic. Tropical Storm Emily in early August encountered problems with dry air when it crossed the Northeast Caribbean, and 97L may have similar difficulties.


Figure 3. Vertical instability of the atmosphere during 2011 in the Caribbean (left) and tropical Atlantic between the Lesser Antilles Islands and coast of Africa (right.) The instability is plotted in °C, as a difference in temperature from near the surface to the upper atmosphere. Thunderstorms grow much more readily when vertical instability is high. Observed vertical instability (blue line) has been much lower than the climatological average from previous years (black line), due to an unusual amount of dry air in the atmosphere, inhibiting tropical storm development this year. Image credit: NOAA/CIRA.

Encounters with land will be another potential major problem for 97L. Most of the computer models take 97L near or over Puerto Rico Sunday night, then very close to or over mountainous Hispaniola Monday night through Tuesday. It is unlikely that 97L will be stronger than a 55 mph tropical storm when it encounters these islands, and passage over the islands could severely disrupt the storm. However, if 97L takes a path just south or north of Hispaniola, the potential exists for the storm to intensify into a hurricane.

There will be moderate wind shear of 10 - 20 knots to the north of the islands early next week, so a path just to the south of the Dominican Republic and Haiti would be more likely to let 97L intensify into a hurricane. A west-northwest motion is likely for 97L through Wednesday, which would bring the storm to the vicinity of Jamaica-Central Cuba-the Central Bahamas on Wednesday. On Wednesday and Thursday, the models agree that a trough of low pressure will dip down over the Eastern U.S., which is likely to turn 97L to the north. The exact timing and strength of this trough varies considerably from model to model, and will be critical in determining where and when 97L will turn to the north. The best model for predicting the timing and strength of such troughs over the past two years has been the ECMWF (European Center model), and this model currently brings 97L into the Florida Keys on Thursday night next week. You can view ECMWF forecasts on our wundermap with the model layer turned on. The European Center does not permit public display of tropical storm positions from their hurricane tracking module of their model, so we are unable to put ECMWF forecasts on our computer model forecast page that plots positions from the other major models.

Remember that a 7-day forecast by even our best model will be off by an average of over 700 miles, so it is too early to tell what part of the U.S. might be most at risk from a strike by 97L. This weekend would be a good time to go over your hurricane preparedness.


Figure 4. Morning satellite image of Invest 98L off the coast of Africa.

Invest 98L near the coast of Africa
A tropical wave near the coast of Africa, a few hundred miles southeast of the Cape Verde Islands, is moving west to west-northwestward at 10 - 15 mph. This wave, designated Invest 98L by NHC yesterday, is large and well-organized, with a modest amount of spin and heavy thunderstorm activity. 98L will bring strong, gusty winds and heavy rains to the Cape Verde Islands today and Saturday as the storm skirts to the south. So far this morning, top sustained winds measured in the islands were 24 mph at Mindelo. Water temperatures are warm, near 27 - 28°C, and wind shear is low, 5 - 10 knots, so 98L should continue to organize today. NHC gave the storm a 50% chance of developing into a tropical depression in their 8am advisory. Once 98L passes to the west of the Cape Verde Islands, it has a long stretch of ocean to cross before it could affect any other land areas. Approximately 70 - 80% of all tropical cyclones that pass this close to the Cape Verde Islands end up curving out to sea and not affecting any other land areas, according to Dr. Bob Hart's excellent historical probability of landfall charts. The latest set of long-range model runs go along with this idea, but it is too early to be confident of this.

Jeff Masters

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3792. ncstorm
Quoting AussieStorm:



the track is up the east coast
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Quoting JrWeathermanFL:
For a storm so close to land Harvey is doing very well. Who says hurricane?

Waiting for recon to confirm your idea.
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97L looking very healthy!
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Quoting BahaHurican:
Also as a reminder, model runs are available by clicking on the Tropical/Hurricane link under the Severe tab at the top of the page....

Here is another link.
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For a storm so close to land Harvey is doing very well. Who says hurricane?
Member Since: 19 juillet 2011 Posts: 12 Comments: 2400
Quoting ncstorm:
Dr. Masters said in the update above that the ECWMF is the best model at predicting troughs and I think Drak said yesterday that troughs would be the deciding factor in where this storm ends up..so right now the ECWMF got an east coast scenario..the GFS has a hard time reading troughs as someone said because of the cold core aspect attach to it

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invest_DEACTIVATE_al992011.ren 20-Aug-2011 10:00 759

They never did much with 99L, only the initial analysis.
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All right... gotta make a run... TTYL all...

I wonder how early Doc will make a new blog today... lol
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Also as a reminder, model runs are available by clicking on the Tropical/Hurricane link under the Severe tab at the top of the page....
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Quoting Tropicsweatherpr:


Good evening to you down under. Do you have the link to that webcam?

Link
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Quoting MiamiHurricanes09:
Already descended. Nearing the circulation.

113430 1730N 08644W 8429 01560 0086 +178 +085 104029 030 023 000 00
would not be surprised to see a 70 MPH TS or minimal hurricane
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Quoting MiamiHurricanes09:
Already descended. Nearing the circulation.

113430 1730N 08644W 8429 01560 0086 +178 +085 104029 030 023 000 00

OK, thanks.
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Quoting smuldy:
lol not many left on the beach, the arturo sandoval club in the deuville (sp?) is the last big one
That's a pity... used to be some decent night life [or indecent, if that was ur pick lol] down there a few years back....
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looking at all the avaliable model data looks like 97L will be florida's storm, even the steering/currets favor a US coast landfall, but as many of us have said lets wait till it devlops before we begin to get worried
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Quoting WeatherNerdPR:
Wasn't recon approaching Harvey? Any info?
Already descended. Nearing the circulation.

113430 1730N 08644W 8429 01560 0086 +178 +085 104029 030 023 000 00
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3776. HCW
Fins to the right ....Fins to the left and you are the only game in town 97L
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Wasn't recon approaching Harvey? Any info?
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Quoting ManicouRiverResort:
Any updates on the track of 97L? I am in The Commonwealth of Dominica. Windward Isles.

Welcome... Somebody's been posting the tracks all morning... tracks still bring to you guys, or between you and Guadeloupe somewhere, sometime tomorrow. So far it looks like it won't be any worse than when Emily passed, i.e. a fair amount of rain and some gusty winds.

Keep safe and keep us posted!
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Very last frame of the visible loop on 97L...

Is that low level clouds trying to wrap around at 13.5N 54.5 W?

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00z runs of ECMWF model have shifted a bit west. Now showing 97l splitting up the middle of Florida.
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3771. smuldy
anyway last beer is now dry so i'm off to bed, may be on here late night if the storm seems headed my way this week; if not and you want my take i will be on the other place offering my take when possible, hope everyone stays safe
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This is the jma run show the trof moveing faster then expected will have to see how this plays out never whatched this one before




Link
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3767. smuldy
Quoting BahaHurican:
I'd love to be a writer, but need a steadier income than most writers can claim... I used to spend a lot of time in the latin music clubs down there... even that I don't have as much time for these days.... maybe too much time in the WX blog.... lol

lol not many left on the beach, the arturo sandoval club in the deuville (sp?) is the last big one
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Quoting USAFwxguy:


HWRF doing a number on that thing.... as per usual.


Yep, they still have some work to do on the vortex initialization ramping intensity up too fast.
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Quoting AussieStorm:
Currently at Santa Maria, CV Islands.



Good evening to you down under. Do you have the link to that webcam?
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UKMET this morning is interesting as well.

Link
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While I may be wrong, I think there is a very high probability that this storm will ultimately end up somewhere between New Orleans and Miami.
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3762. HCW
No way this gets west of Mobile bay and is still most likely to take a Charley like track
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Quoting smuldy:
ya it sounds cool lol but non scripted ratings have driven down writers' wages and hence why I'm back in grad school lol and I live here and even I only make it to SOBE once a week so i feel you its not what it used to be, but I do love mid beach where I'm at
I'd love to be a writer, but need a steadier income than most writers can claim... I used to spend a lot of time in the latin music clubs down there... even that I don't have as much time for these days.... maybe too much time in the WX blog.... lol

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3760. jfm1975
Hi everyone. I know that this blog and the amount of activity usually is a good reflection on something brewing ( I especially seek the opinion of the FSU Meteorology students..GO NOLES.. ) Is this soon to be Irene something to worry about for Ft Lauderdale next week ? Thanks
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Quoting MiamiHurricanes09:

LOL XD
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3758. zparkie
I am glad the model runs show 97L heading to south florida now, that means in a few days the model runs will have it going some where else, always happens. I wouldnt look at model runs till a storm becomes tropical.
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3757. ncstorm
Quoting nrtiwlnvragn:
97L 06Z HWRF 126 hours




Wow..942mb??
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3754. smuldy
Quoting stormhank:
Morning...the GOM seems to be getting in the clear according to latest model runs,,of course they could all shift again n again before its all said n done.
No actual surface low, so until there is, take the globals for what they are, the likliest possibilities, would not say the eastern GOMEX(non panhandle) is out of the woods by any stretch, its just not the likliest outcome right now
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Any updates on the track of 97L? I am in The Commonwealth of Dominica. Windward Isles.

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3750. wpb
looked at the ridge. you can see{100 hours out) that 98l moves into the ridge may cause some weakness to the strentch causing 97l to f track to the right starting at 77 west?. models may hinting at that since a right shirt to gfs last runs.
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97L 06Z HWRF 126 hours







HOUR: 126.0 LONG: -76.90 LAT: 22.40 MIN PRESS (hPa): 945.00 MAX SURF WIND (KNOTS): 93.00
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Morning...the GOM seems to be getting in the clear according to latest model runs,,of course they could all shift again n again before its all said n done.
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Quoting ncstorm:
Dr. Masters said in the update above that the ECWMF is the best model at predicting troughs and I think Drak said yesterday that troughs would be the deciding factor in where this storm ends up..so right now the ECWMF got an east coast scenario..the GFS has a hard time reading troughs as someone said because of the cold core aspect attach to it


There ya go...
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3745. ncstorm
Dr. Masters said in the update above that the ECWMF is the best model at predicting troughs and I think Drak said yesterday that troughs would be the deciding factor in where this storm ends up..so right now the ECWMF got an east coast scenario..the GFS has a hard time reading troughs as someone said because of the cold core aspect attach to it
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Quoting aquak9:
Ya'll are gonna make me lose my mind....

Thanks for getting THAT stuck in my head.

Good morning, ya'll. Go easy on the coffee...looks like it's gonna hafta last a LONG time.
Morning aqua, and blame nc for the track... lol

I've got the small pot and the big one both going for quick turnover.... lol surely going to need it today...

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3743. aquak9
And good morning back to all the others. Baha- I've got some homemade granola bars, with dried apple and cranberries. Simple, munchable breakfast that will be east to just blow the crumbs off the keyboard.

Enjoying the discussion from last night. We got some good folks in here this time. hope it stays that way.
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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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