TD 8 forms; 97L a potential threat to the Caribbean and U.S.
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
Reader Comments
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AL, 08, 2011082000, , BEST, 0, 161N, 847W, 45, 998, TS, 34, NEQ, 35, 0, 0, 35, 1008, 120, 15, 0, 0, L, 0, , 0, 0, HARVEY, M,
What do you mean "stays over water"? It's never been away from it.
Look at how much farther south 97L is on the run for Harvey, which puts it in the outer nest instead of the inner nest. Why is it farther south on this HWRF run? Because the outer nest means that the HWRF doesn't bomb it out unrealistically as it does in the inner nest, and thus it does not track poleward as much.
seems like a lot less trouble to just go ahead and die of thirst....
That is true. I missed that.
99L is ~10N 29W. 98L is ~16N 22W.
Hey Baha , know what you mean, BTW How's my old stomping ground, Nassau, used to love to go out west to the Cable beach casino & PI , never been there in 21 years, was supposed to go this year, but due to unforeseen circumstances couldn't make it!
oh boy
It should stay over water.
Hi all,
Long time lurker, just wondering what is my chances of 97L giving me some rain in the Upstate of SC (Greer). The worst part of the storm minus the damage it will do, is that its gonna hit on my days off :( Oh well, back to lurking.
Lee
(So need to get a new handle)
I wonder if they had it about ready to send or was sending it, saw the the new max & tacked it on the end.
Skypony! You add alot to this blog. I always learn something from your posts. Thankyou and keep it up.
wife insisted on joining me...kinda ruined it...
Oh come on , it could well go onshore, why would u make such a statement, " do you realize how u sound"?
.
.
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Kindly remove that last line about Code Red.
In the future, when posting an official NWS statement, do not change, move, alter, delete, or add any word.
.
Thank you.
The time has come to perform Feats of Strength...
2175. stormpetrol 12:21 AM GMT on August 20, 2011 +0
Quoting TropicalAnalystwx13:
What do you mean "stays over water"? It's never been away from it.
Oh come on , it could well go onshore, why would u make such a statement, " do you realize how u sound"?
Oh well, I guess it could be taken either way, not looking an argument thats for sure!
Shall I air my grievences now or later:)
The inner-nest grid has the most complex algorithms and dynamics thrown in. I'd hazard a guess that the outer-nest is rather simple compared to it.
Rising Tide 6 is next Friday, well the Party the night before.
I want to Video the Feats of Strength at the Bar
Then Next Saturday we have the Conference at Xaiver University here, this will be my 3rd year attending for portlight.
Rising Tide 6 is at Xavier University on Aug. 27
Check RisingTideNola.com, the Rising Tide Blog & this page for details, y'all.
Friday Night Party Aug. 26: Tracey's, 2604 Magazine Street
Amazing Speakers and Panels all day Saturday, Aug. 27.
Registration includes morning pastries & beverages and lunch by J'Anita's
Everyone is welcome (not just for geeks)!
Huh? I just posted the TWO...
BTW
Not kidding.
The ants are on the move in my yard.
Yep, but the best advise is to follow patrap lead and evac. to a safer place no need to put your self and faimly through something like that if you dont need to
no power you get the heat, bugs, drinking water from a milk jug a very tiresome ordel to say the least
just be sure to leave eirly if you can most will stay just so they wont go through the traffic jams again
hope we can get the message out.
Thanks
you should have locked her in the garage with the dog.
The first vortex message had it at 51 kt, they sent a second vortex message correcting it to 44 kt.
Re: 97L
THIS SYSTEM HAS A HIGH CHANCE...60 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES GENERALLY WESTWARD AT 20 MPH.
INTERESTS IN THE LEEWARD ISLANDS SHOULD MONITOR THE PROGRESS OF THIS DISTURBANCE. LOCALLY HEAVY RAIN AND
GUSTY WINDS ARE LIKELY OVER THE LEEWARD ISLANDS LATE SATURDAY INTO SUNDAY.
Wasn't this weekend your anniversary for 40 years of married bliss? *G*
Uh oh watch out the critters are moving.
hes this trolling dont went it get too you this move on
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