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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Good night Everyone, going to lurk for the 2 AM two, and Intermediate advisory for Harvey... then off to bed
Member Since: Posts: Comments:
Quoting emguy:
Everyone mentions Charley (2004) and Wilma (2005) and Donna (1960) over the last few days with this. Honestly, this pattern seems to have more of a Hurricane Georges feel to it. (Not saying Mississippi as an end result, just saying it merits inclusion in the discussion).


Or a hurricane Frederic
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Quoting dfwstormwatch:

ok ill stay up for umm... 3 more hours what models do you guys want me to post?

>?
Member Since: July 31, 2011 Posts: 5 Comments: 891
Quoting Levi32:


See it's just like them to report what the computer is forecasting. Whatever happened to Steve Lyons giving his own opinion on things.

What I just said doesn't imply that Florida isn't a big target though, because it is.


What is your idea on the track? Has it really changed any from this morning? Models like Florida/SE Coast tonight it seems.
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so when should 97L be named, according to the models?
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Lets consider one at a time, please...

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3286. KEEPEROFTHEGATE (Mod)
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Quoting scottsvb:


Do you have the 55,426hr BS Run to see if there is snow in florida by then?


I agree with you it may very well not develop, but what if it does? It has been showing this for almost 12 days now. Very close to the same scenerio. How shocked would we all be if it actually ended up happening
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3284. Grothar
Quoting IFuSAYso:


Katrina survived crossing FL when 90% said she was doom. Some blame the everglades.


Happened with Wilma in reverse. Storm got stronger as it moved from East to West. It hit as a Cat 3, down to Cat 1 and by the time it reached us on the East Coast, it was back to a Cat 2. Although those of us between North Broward and South Palm Beach still argue it was higher. Andrew maintained its strenghth going across the Everglades quite a bit. Very warm water to feed off in the Everglades.
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Quoting Levi32:


See it's just like them to report what the computer is forecasting. Whatever happened to Steve Lyons giving HIS opinion on things.

What I just said doesn't imply that Florida isn't a big target though, because it is.


I really liked Steve Lyons when he was on TWC. I thought he did a very thorough tropical update. Rick Knabb....not so much - but its not his fault, TWC is more worried about Social Media or some other entertainment thing.
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ok ill stay up for umm... 3 more hours what models do you guys want me to post?
Member Since: July 31, 2011 Posts: 5 Comments: 891
Quoting P451:


98L is not on the site because it is beyond the GOES satellite reaches. SSD only puts out GOES floaters.

Rammb is what you need to see 98L - it's under Meteosat jurisdiction (for lack of a better term lol)


Thanks for the link and the info...
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3280. Levi32
Quoting ChrisDcat5Storm:


hey levi i dont know if uve noticed but the weather channel is convinced that this is a florida storm im a have to agree have u see the dynamical models


See it's just like them to report what the computer is forecasting. Whatever happened to Steve Lyons giving his own opinion on things.

What I just said doesn't imply that Florida isn't a big target though, because it is.
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Quoting Levi32:


That model hour falls in June...


hey levi i dont know if uve noticed but the weather channel is convinced that this is a florida storm im a have to agree have u see the dynamical models
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Quoting dfwstormwatch:
yep it says 98 inches of snow will cover floriday and africa will be covered in oceans also that the poles would melt and the equator would freeze lolz


Lol
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Noaa is updating 99L, 98L has been dropped... 99L is the one in the S

Link
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Night All.

Going to tidy up some supplies this weekend, long work week ahead.

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Quoting KoritheMan:




and ty
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3272. Levi32
Quoting scottsvb:


Do you have the 55,426hr BS Run to see if there is snow in florida by then?


That model hour falls in June...
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Quoting Grothar:


ty
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Quoting IFuSAYso:
would someone post the 1928 Okeechobee track plz?


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Quoting IFuSAYso:
would someone post the 1928 Okeechobee track plz?
1928 Okeechobee track
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Quoting GTcooliebai:
Hey dfw, staying up for the ECMWF run?...btw good job posting the GFS run :)
umm what time does it come out?
Member Since: July 31, 2011 Posts: 5 Comments: 891
3266. emguy
Everyone mentions Charley (2004) and Wilma (2005) and Donna (1960) over the last few days with this. Honestly, this pattern seems to have more of a Hurricane Georges feel to it. (Not saying Mississippi as an end result, just saying it merits inclusion in the discussion).
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3265. Grothar
Quoting IFuSAYso:
would someone post the 1928 Okeechobee track plz?


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Quoting scottsvb:


Do you have the 55,426hr BS Run to see if there is snow in florida by then?
yep it says 98 inches of snow will cover floriday and africa will be covered in oceans also that the poles would melt and the equator would freeze lolz
Member Since: July 31, 2011 Posts: 5 Comments: 891
Hurricanes101,
Think about it, there's only one more potent wave shown by the models and that's when the "Irene" is supposed to have already done her damage, and dying off, which would be around August 28th to August 30th, and so that would gives just a few days to put out another storm, just don't think it will happen... though im willing to Eat crow if we do get Jose before August ends, just think its not likely at this time.
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Quoting dfwstormwatch:
by the way 99l's no longer being updated so it might not be here anymore...
Hey dfw, staying up for the ECMWF run?...btw good job posting the GFS run :)
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99L COC is around 9N, has been moving WSW




Seems like The proyected path, should be adjusted...

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3260. Patrap
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3259. Grothar
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would someone post the 1928 Okeechobee track plz?
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Quoting dfwstormwatch:

384 hours out looks like this could be a system to watch...


Do you have the 55,426hr BS Run to see if there is snow in florida by then?
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Out for the night. cya!
Member Since: September 2, 2006 Posts: 110 Comments: 6878
3254. Patrap
Gulf Of Mexico - Rainbow Loop
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3253. KEEPEROFTHEGATE (Mod)
XX/INV/98L
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Quoting IFuSAYso:


Allot of warm water in the glades, Lake Okeechobee, and may skirt the west side. I just hope the levy's in Okeechobee are intact if a direct hit (use to live in Clewiston).


Someone else last night made a good point talking about swimming pools and how warm they are. It sounds silly, but if you think about how many people have pools especially in south Florida maybe they have a point. That's not even mentioning all the land made lakes.I live in the Naples area and there are tons of lakes everywhere, and they are very warm.
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3251. emguy
I gotta admit, recalling when I was tracking the wave that is now Harvey (many days ago), when it was in the central atlantic and people started getting excited now 97L, I thought the conversation was crazy. Another crystal ball discussion of a phantom system 2 week out or so.

Now, it just disturbing how the 2 weeks of models flip flopping back and fourth east and west with Florida somewhere in the middle and have slowly come together over time into what is becoming a remarkably tight consensus in days 5-7 all things considered. Dislike...
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3250. Grothar
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3249. Patrap
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3248. Patrap






TS Harvey Floater - Rainbow Color Infrared Loop
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Quoting dfwstormwatch:
by the way 99l's no longer being updated so it might not be here anymore...

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Member Since: July 31, 2011 Posts: 5 Comments: 891
Quoting HurricaneDean07:
This year is been a weird and entertaining one for sure: History ; Present ; Forecasted~ for the Season
June~ 1-0-0
Arlene: 65 Mph, 993 MB, 25 Deaths

July~ 3-0-0
Bret: 65 Mph, 996 MB, 0 Deaths
Cindy: 60 Mph, 1000 MB, 0 Deaths
Don: 50 Mph, 998 MB, 0 Deaths

August~ So Far: 4-0-0
Emily: 50 Mph, 1003 MB, 5 Deaths
Franklin: 45 Mph, 1004 MB, 0 Deaths
Gert: 60 Mph, 1000 MB, 0 Deaths
Harvey(So far): 60 Mph, 994 MB, 0 Deaths

August~ Forecast for the rest of the month
Irene

September~
Jose
Katia
Lee
Maria
Nate

October~
Ophelia
Phillipe
Rina

November~
Sean


I like your breakdown save for one thing....

I have a hard time believing that we will only have 1 more named storm the rest of August
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Quoting P451:
Good early morning.

Taking a look at all that is out there one last time.

Put center fixes within the loops - all corresponding with the 0Z center fixes according to ATCF - all placed on the 0Z image frames. Each loop temporarily pauses at that frame.


Harvey




97L (look where the convection fires, over the surface center!)





98L and 99L (Yep, those are the fixes according to ATCF)

A system below 10N would have a hard time developing because it wouldn't be able to take advantage of the Coriolis effect of the Earth right P451?
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3243. Thrawst
I'm off for the night. P'ce out everyone.
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by the way 99l's no longer being updated so it might not be here anymore...
Member Since: July 31, 2011 Posts: 5 Comments: 891

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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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