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

By: Dr. Jeff Masters , 3:30 PM GMT on August 19, 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 extreme236:


Its a pretty safe bet that TD 8 will become Harvey. The recon data and satellite estimates suggest it is already.



Thats why using "Pre" anything is crazy as Fruit Punch, warm.
Member Since: July 3, 2005 Posts: 426 Comments: 129093

Houston NWS ISSUED 345 AM CDT FRI AUG 19 2011/

DISCUSSION...
UPPER RIDGE WILL REMAIN IN CONTROL INTO AT LEAST THE MID TO LATE
PARTS OF NEXT WEEK (IF NOT LONGER). SLIGHT REPOSITIONING(S) AND
STRENGTH WILL LEAD TO VERY SLIGHT VARIATIONS OF TEMPS. BUT IT`S
JUST SPLITTING HAIRS - IT`LL REMAIN HOT WITH VERY LIMITED CHANCES
OF PRECIP UFN. WILL BE WATCHING IF ENERGY CURRENTLY RIDING DOWN
THE EASTERN PERIPHERY OF THE RIDGE (NOW IN MO) WILL BE ABLE TO TRIGGER
SOME ISO STORMS LATER THIS AFTN/EVNG ACROSS ERN PARTS OF THE AREA.
ANY STORMS THAT DO MANAGE TO DEVELOP COULD PRODUCE DOWNBURST WINDS.

GFS/ECMWF/CANADIAN ARE ALL SHOWING A TROPICAL SYSTEM AROUND CUBA
ON THE 25TH...BUT HAVE WIDE RANGING SOLNS/TRACKS AFTER THAT. BOTH
GFS/ECMWF STRENGTHEN IT ENOUGH WHERE WE PROBABLY WOULDN`T COMPLAIN
IF THE RIDGE ACTUALLY HOLDS FOR JUST A WHILE LONGER...(WHICH IT
PROBABLY WILL HERE) 47
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I will be leaving for the NE coast for a mini-vacation near Cape Cod on Monday and getting back to North Florida on Friday but will be watching with great anticipation.
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choo choo all aboard!!!

Link


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Would be interesting to see another storm spin off the east coast and be named before the others..
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The GFS latest model run (animated on the wundermap)has a major storm in the northern Gulf next weekend.
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XX/AOI/XXL
MARK NEAR
33N/73W
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If it's a woman storm..it will be worse.

Camille,
Katrina,

course, who can forget
Andrew
Hugo
Georges
Frederic

I think it will be the either Irene or Jose...

Jose headed our way....

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133. P451
Quoting MississippiWx:
I know the focus is on the 12z GFS, but could it be? Lol...



If it were to fester some....sure, why not?

I was actually just getting ready to look at some loops of this to see if anything stuck out.





There is certainly something interesting going on just off of the SE NC coastline.
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Now with 588 over top, really think this will track much like Gustav in '08 between Cuba and Jamaica...beyond that central/eastern GoM (unlike Gustav which was Central/Western GoM)

Member Since: August 10, 2011 Posts: 0 Comments: 403
Quoting ncstorm:
Watching my 12:00 news right now and they are showing the ECWMF track..how dare they!



Going out that far, I'd choose the best model too. Slightly above flipping a coin.
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102 hours strong tc around haiti
Member Since: July 31, 2011 Posts: 5 Comments: 891
Spathy...see if this is better :)


Link
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Quoting violet312s:


We all keep forgetting that TD8 may or may not turn into Harvey.


Its a pretty safe bet that TD 8 will become Harvey. The recon data and satellite estimates suggest it is already.
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Quoting NoVaForecaster:
IMO I am starting to think that 97L isn't going to become anything. It is dealing with dry air and it may have a problem with land interaction on the islands when/if it travels into the Caribbean. 98L is a different matter entirely. It has a large amount of moisture and a good circulation. The entire East coast needs to watch this as it has the potential to become a major hurricane when it gets its act together


Huh???????????????????????????????????????
Member Since: June 29, 2009 Posts: 13 Comments: 5315
IMO I am starting to think that 97L isn't going to become anything. It is dealing with dry air and it may have a problem with land interaction on the islands when/if it travels into the Caribbean. 98L is a different matter entirely. It has a large amount of moisture and a good circulation. The entire East coast needs to watch this as it has the potential to become a major hurricane when it gets its act together
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Quoting TropicalAnalystwx13:


look at the trough and look at the high..high to the east..trough still there and not lifting yet
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Quoting AegirsGal:
4 of the same post with slightly different wording?


Different parts of the model run.
Member Since: July 6, 2010 Posts: 113 Comments: 32524
Quoting Skyepony:
Thank you Dr Masters!...Joe Bastardi's answer to the why has instability been so low question last night on the Barometer Bob show made no sense..he was blaming it on cold air aloft, tied to the tornadoes this spring all seemingly to mention global warming isn't happening. Your answer makes much more sense considering more dry stable air from Africa has been whisked to the Subtropical Atlantic than anywhere & that area has the least amount of instability compared to the rest.


How does the dry air in the Atlantic have anything to do with the global decrease in instability?

His explanation made a lot of sense.
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Quoting violet312s:


We all keep forgetting that TD8 may or may not turn into Harvey.


There really is not much of a question - The National Hurricane Center brings it up to 50 mph, and in their earlier advisory, they stated that it was just below tropical storm status.

Member Since: July 6, 2010 Posts: 113 Comments: 32524
Watching my 12:00 news right now and they are showing the ECWMF track..how dare they!
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Quoting violet312s:


We all keep forgetting that TD8 may or may not turn into Harvey.

True.
Member Since: August 17, 2010 Posts: 21 Comments: 6939
Quoting TropicalAnalystwx13:
Is this Hurricane Jose, Tropical Storm Irene, and Tropical Depression 11?

4 of the same post with slightly different wording?
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Member Since: July 6, 2010 Posts: 113 Comments: 32524
Quoting TropicalAnalystwx13:
Irene, Jose, Katia???



We all keep forgetting that TD8 may or may not turn into Harvey.
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a course between Cuba, Jamaica, and Haiti I think may be likely this run ... ultimately south of Cuba

Member Since: August 10, 2011 Posts: 0 Comments: 403
Quoting reedzone:


Noooo that's extratropical :P


Yeah, but so have the other ones before they became tropical.
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112. Skyepony (Mod)
Thank you Dr Masters!...Joe Bastardi's answer to the why has instability been so low question last night on the Barometer Bob show made no sense..he was blaming it on cold air aloft, tied to the tornadoes this spring all seemingly to mention global warming isn't happening. Your answer makes much more sense considering more dry stable air from Africa has been whisked to the Subtropical Atlantic than anywhere & that area has the least amount of instability compared to the rest.
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XX/INV/98L
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Is this Hurricane Jose, Tropical Storm Irene, and Tropical Depression 11?

Member Since: July 6, 2010 Posts: 113 Comments: 32524
*REPOST*






Member Since: June 29, 2009 Posts: 13 Comments: 5315
90 hours out south of d.r
Member Since: July 31, 2011 Posts: 5 Comments: 891
Quoting reedzone:


Yeah.. I think the GFS initialized the low a bit further south then where it really is. I'm really thinking this is more of an East Coast storm. It was soo consistent for days with bringing it over FL.


The GFS is initializing at almost the exact spot you are referring to...

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Quoting P451:


Have you found any place with pressure readings on the coast close to TD8?

TIA!!!
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Quoting TropicalAnalystwx13:
A tale of three tropical storms?

till sept 20th one right after another comes
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Quoting MississippiWx:
I know the focus is on the 12z GFS, but could it be? Lol...



Noooo that's extratropical :P
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Quoting MississippiWx:
I know the focus is on the 12z GFS, but could it be? Lol...



I think we both know the answer to that, :\
Member Since: July 6, 2010 Posts: 113 Comments: 32524
Quoting kmanislander:


If you run the RGB loop and check the lat/lon then zoom it looks like the center is rotating right near 13.7 N and 50.6 W

There is a larger gyre around this feature but I believe 97L has been trucking to the West faster than last indicated.



Yeah.. I think the GFS initialized the low a bit further south then where it really is. I'm really thinking this is more of an East Coast storm. It was soo consistent for days with bringing it over FL.
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101. P451
Quoting Minnemike:
i wonder what factors propel the instability anomaly? would be good to know how climatology extremes function in the bigger picture of systems dynamics, to answer some of those ambiguities in the climate, eruh, conversations...


Temperature differential in atmospheric heights.
The larger the temperature difference from surface to high altitude the easier it is for a rising motion to occur.

Dry versus moist air.
The more moist the air the better chance at convective development.


Now, what drives those features?

Well, the MJO upward pulse is favorable for vertical instability to rise. We have been in a prolonged downward pulse.

Since we are entering an upward pulse you can see the dry air giving way to a moist atmosphere. You will see the vertical instability anomalies come more in line with climatology and perhaps even go positive quite soon.

Temperature differential. This one is a bit trickier. SAL (dust in the atmosphere) helps to heat the upper layers thus lowering the differential and lowering instability. On the other hand a lack of convection should serve to warm the surface more which could create a larger differential leading towards higher instability. There are certainly other factors involved which I am not very knowledgeable about.
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Thanks Dr. Once again, the fate of the US may be determined by the Puerto Rico/Hispanola terrain buffer but it may be a dangerous threat to Florida or the Gulf coast if it misses those islands unscathed......Looks like a potential nail bitter next week.
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A tale of three tropical storms?

Member Since: July 6, 2010 Posts: 113 Comments: 32524
Quoting spathy:
Not to add to the ADDHD here.
But does anyone have a good loop of the very strong wave over Africa?


Hi Spathy....try this one...click on movie for animation :)

Link
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I know the focus is on the 12z GFS, but could it be? Lol...

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08L/TD/XX
NEARING LANDFALL
mark
16.63N/83.63W
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Irene, Jose, Katia???

Member Since: July 6, 2010 Posts: 113 Comments: 32524
INV/XX/97L
MARK
13.51N/48.68W
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Hey there Mr. Levi. nice job on the show by the way. You know you are our main man on this blog right?! :)

quick question. based on your excellent tropical tidbit analysis, looking currently at the forward speed of 97L and the projected timing of the trough into the SE USA, would you still say logically that Florida is the state with the most at risk

I guess the odds are lowered for the central and western gulf correct?
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Irene, Jose, and the monster wave that is currently over Central Africa.

Member Since: July 6, 2010 Posts: 113 Comments: 32524

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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.