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

By: Dr. Jeff Masters , 03:30 PM GMT em 19 de Agosto de 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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Quoting smuldy:
usually dont post here much about to write up my synopsis for the other place, but being in miami it is troubling that not only have the euro and gfs come into agreement on track generally for the last few runs, but now the timing, which was a big gap, has also closed to a small one
problem with s.e. flor. its surrounded by 85-90 water right now need a fill up
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Quoting KoritheMan:


That doesn't stop them from immigrating that far northward, now does it? ;)

And that's entirely too cold for me atm. Winter can wait!


A true coonass cannot survive north of lake Pontchartrain.
Member Since: Agosto 29, 2010 Posts: 0 Comments: 5236
3440. smuldy
usually dont post here much about to write up my synopsis for the other place, but being in miami it is troubling that not only have the euro and gfs come into agreement on track generally for the last few runs, but now the timing, which was a big gap, has also closed to a small one

edit still a long way out by no means saying its a sure thing just noting its a troubling trend
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Quoting PrivateIdaho:


Monroe is too far north to be a coonass...check this out.

Fair

58°F
(14°C) Humidity: 47 %
Wind Speed: calm

Barometer: 29.98 in (1010.90 mb)
Dewpoint: 38°F (3°C)
Visibility: 10.00 Miles

January weather for you.:^)


the unwritten rule is anything north of I-10 is not a coon ass.
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Quoting 7544:


thanks how strong is that gt
995mb.
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Quoting PrivateIdaho:


Monroe is too far north to be a coonass...check this out.

Fair

58°F
(14°C) Humidity: 47 %
Wind Speed: calm

Barometer: 29.98 in (1010.90 mb)
Dewpoint: 38°F (3°C)
Visibility: 10.00 Miles

January weather for you.:^)


That doesn't stop them from immigrating that far northward, now does it? ;)

And that's entirely too cold for me atm. Winter can wait!
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Quoting DontAnnoyMe:


Hey, watch the language! Never know when we little kids are lurking ;-)


If little kids are up now we need to beat their parents....btw....isn't it about 6 hours past your bedtime?
Member Since: Agosto 29, 2010 Posts: 0 Comments: 5236
Quoting wxhatt:


There it is, the next trough. That's what the models see.
Yep, but this trough doesn't look quite as strong as the 1st one.
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Texas continues to bake.

Dome of Death may shift West a bit but only enough to allow systems tropical in nature to cause havoc to our friends out East.

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even though weak it seems emily has dug a trench
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3431. 7544
Quoting GTcooliebai:
168hrs. out makes landfall in south FLA





thanks how strong is that gt
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Quoting PrivateIdaho:


How are things in coonass land Kori?


Hey, watch the language! Never know when we little kids are lurking ;-)
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Quoting luvthetropics:
Does anyone know if it has to be a hurricane while passing through the 1st Herbert Box for the predictor to apply? Or does it generally apply to tropical systems of any strength. Thanks


I've always assumed the latter, but I dunno for sure.
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Quoting KoritheMan:


Hey, aren't you a coonass too? ;)

They're fine, though. Same as always, really.


Monroe is too far north to be a coonass...check this out.

Fair

58°F
(14°C) Humidity: 47 %
Wind Speed: calm

Barometer: 29.98 in (1010.90 mb)
Dewpoint: 38°F (3°C)
Visibility: 10.00 Miles

January weather for you.:^)
Member Since: Agosto 29, 2010 Posts: 0 Comments: 5236
168hrs. out makes landfall in south FLA



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3426. wxhatt
Quoting GTcooliebai:
144hrs. out north of the central coast of Cuba, approaching south FLA. (another trough swinging down from Canada)



There it is, the next trough. That's what the models see.
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use to watch rainfall amounts in the lesser antillias as a scale for their future intensity models its going to be a nail biter
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Quoting ChrisDcat5Storm:
some1 link the latest models on 97l plz
at your request sir Link
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Quoting PrivateIdaho:


How are things in coonass land Kori?


Hey, aren't you a coonass too? ;)

They're fine, though. Same as always, really.
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some1 link the latest models on 97l plz
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3421. 7544
thanks this run looks like fla again
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Does anyone know if it has to be a hurricane while passing through the 1st Herbert Box for the predictor to apply? Or does it generally apply to tropical systems of any strength. Thanks
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144hrs. out north of the central coast of Cuba, approaching south FLA. (another trough swinging down from Canada)

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Quoting KoritheMan:


A little over 150 mph.


How are things in coonass land Kori?
Member Since: Agosto 29, 2010 Posts: 0 Comments: 5236
Quoting Grothar:


Think it will download to my computer.



With the right adapter cables we can give you full HDMI capabilities!

Anything is possible with adapter cables...and duct tape...even pink duct tape. ;)
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Quoting wxhatt:


ok, but how do you get the panhandle out of all the runs shifting east continually?


I wouldn't say the shift is a continual one. The trick is to average them, which to me leads to the central or eastern panhandle (after the peninsular crossing) -- most likely the latter.
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Quoting 7544:


132kts how strong is that tia

It's low-end cat5,exactly 158mph
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3414. wxhatt
Quoting jonelu:
that could be good news for SE FL


Yes, I think it will be a surprise to all to see this jump north.
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Quoting 7544:


132kts how strong is that tia


just type out "convert 132 knots to miles per hour" in google and it will give the answer. Google will do most any conversion if you type it out.
Member Since: Agosto 29, 2010 Posts: 0 Comments: 5236
Quoting 7544:


132kts how strong is that tia


A little over 150 mph.
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Quoting wxhatt:


ok, but how do you get the panhandle out of all the runs shifting east continually?


They are flipflopping back and forth no track is nailed down this early...Alot of things will occur over the next few days...Center repositioning...land interaction...certain longwave patterns not coming to pass...lots of uncertainly
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unlike the past systems 97 never lost its spin watching 99 it could break off the trough and follow 97 footprints just like the old timers postulated sometimes they follow each other in fact they felt it you got hit your chances increase of getting hit again
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3408. wxhatt
Quoting KoritheMan:


No, the GFS has a poleward bias, in that it tends do overdo the strength and amplification of large scale troughing.

In this case it's probably correct, though, in that the greatest threat is to the Florida peninsula and the central panhandle.


ok, but how do you get the panhandle out of all the runs shifting east continually?
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3407. 7544
Quoting Grothar:
Just remember that many storms have crossed over Cuba and Hispaniola and reformed into formidable Hurricanes. Yes, they do disrupt systems, but I have been here off and on long enough to see many of them become quite strong.




132kts how strong is that tia
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3406. jonelu
Quoting GTcooliebai:
120hrs. out making landfall on eastern Cuba (High still building in, notice the Heights over Canada going zonal)

that could be good news for SE FL
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Quoting louisianaboy444:



Excatly nobody is out of the woods yet


I'm feeling pretty safe.
Member Since: Agosto 29, 2010 Posts: 0 Comments: 5236
3404. Grothar
Just remember that many storms have crossed over Cuba and Hispaniola and reformed into formidable Hurricanes. Yes, they do disrupt systems, but I have been here off and on long enough to see many of them become quite strong.


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Quoting ProgressivePulse:



I'll have to dust off my vintage bottle of Boons Farm for the occasion.


The 7.21.2011 vintage/
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Quoting wxhatt:


Right; but doesn't the GFS normaly have a large westward bias?

I have noticed this over every hurricane season.


No, the GFS has a poleward bias, in that it tends do overdo the strength and amplification of large scale troughing.

In this case it's probably correct, though, in that the greatest threat is to the Florida peninsula and the central panhandle.
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120hrs. out making landfall on eastern Cuba (High still building in, notice the Heights over Canada going zonal)

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Leaving for home later this afternoon (morning back west)

If convection continues to increase over the LLC/MLC, 97L should be rather close to tropical depression status when recon arrives at 2pm.

Member Since: Junho 9, 2007 Posts: 4 Comments: 15889
3398. wxhatt
Quoting KoritheMan:


Just because the 0z suites are shifting east, doesn't necessarily reflect the start of a trend.


Right; but doesn't the GFS normaly have a large westward bias?

I have noticed this over every hurricane season.
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Anyway ya'll... I gone... I gotta stop getting up at 1 a.m. to see the next edition of the TWO.... lol

'nite!
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3396. Grothar
Quoting cycleranger:


Somebody get friend Gro a smartphone.

Your wits will be needed in the days ahead.


Think it will download to my computer.

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Quoting nofailsafe:


I really wish we had a way of comparing previous runs without having to eyeball everything.
Idk, maybe right click & save as.
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Quoting sunlinepr:


And it is really S of the projected path they are plotting... So it could get closer to the islands instead of going into the ATL...
It clearly has broken away from 98L tonight, and I agree, it's headed southwest, and should move under the ridge that builds in above it. 98L has opened the door for 99L to sneak under.

If it stays small, it might make the crossing. Demonstrating an early mind of its own is helping me believe in it.
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Quoting KoritheMan:


Just because the 0z suites are shifting east, doesn't necessarily reflect the start of a trend.



Excatly nobody is out of the woods yet
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Quoting GTcooliebai:
96hrs. out west of Haiti, south of the Eastern Tip of Cuba (Trough lifting out, High building in)



I really wish we had a way of comparing previous runs without having to eyeball everything.
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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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