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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3142. Levi32
Quoting xtremeweathertracker:

Levi what do you think about the GFS's solution of 98L and 99L moving it directly northeast toward the Bermuda High!! I just don't buy that and feel a more westward track would be probable!! Is there something im missing here? I see no ULL in the GFS solution to tug it northward!!!


Yeah there is an ULL. Look 12 hours out northwest of the system. It's way up at 300mb, but apparently may take enough air out of a day to create a dent in the high that the wave will move towards.

Member Since: November 24, 2005 Posts: 635 Comments: 26686
Quoting redwagon:

Are FL mets talking about 97 enough? Now's the time to start awareness, not three days from now.
I dunno what FL mets are saying.
Anyone?

~7 days from now would the earliest approach to FL from 97L. Serious talk about monitoring the system should begin soon. But without a developed system, it would take more faith in the models than usual.

Also, the models have been about as consistent as I think I've ever seen them at developing a system...
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204 hours out no way this is going to happen
Member Since: July 31, 2011 Posts: 5 Comments: 891
3139. Gorty
It is hard to tell which direction Harvey is moving right now.
Member Since: November 8, 2008 Posts: 12 Comments: 1058
Quoting Levi32:


The concern is that the model does actually see those mountains, to a certain extent, and to see it strengthen the storm regardless (the even higher resolution ECMWF does also), may speak to how favorable the environment may be for intensification at that point, which means that even a short time over water after dealing with Hispaniola and/or Cuba could result in a still potent storm. We will see. Step 1 is to get it named.


Well if you believe it then I will. If it wasn't for you I would say it would hit Florida as a tropical storm maybe even depression looking at that model.
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Quoting dfwstormwatch:

189 hours out system is hitting lost of major cities...


And going toward Richmond, DC, Baltimore....

but this is 189hrs out tho, so....

Kinda reminds me of a Donna track almost
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Quoting atmoaggie:
No, the other way around. A well-developed, closed TC stops bringing in mid-level air, only low-level.

In-up-out.

And, yes, right now Harvey still vulnerable to mid-level dry air.

I would tend to argue that anything ingested in the lower levels will work its way to all levels eventually as the TC ventilates to the atmosphere!! Like you said In-up-out!!! Even with your solution of in-up-out dry air is still affecting the basic structure of the storm!!
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Quoting redwagon:

Are FL mets talking about 97 enough? Now's the time to start awareness, not three days from now.


I have heard them bring 97 up in every broadcast for the last 36 hours. We have pretty good mets here. IMO
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189 hours out system is hitting lost of major cities...
Member Since: July 31, 2011 Posts: 5 Comments: 891
3133. Levi32
Quoting atmoaggie:
No, the other way around. A well-developed, closed TC stops bringing in mid-level air, only low-level.

In-up-out.

And, yes, right now Harvey still vulnerable to mid-level dry air.


...At least support your own theory with correct terminology :P

I think you're thinking about the eye...which does trap air inside itself above a certain level. However, the storm very much does ingest air from the mid-level environment all the time. Why do you think the winds even exist at 700-500mb?
Member Since: November 24, 2005 Posts: 635 Comments: 26686
And, I might add again, the "psychic twins", predicted this very scenario, over 6 months ago, on the View, not that I watch the View. RE gfs 00z run.
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Quoting ProgressivePulse:
100 bucks that as soon as 97L develops, the models drop it?
better yet, recurving east of the CONUS, possibly threatening Bermuda
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Quoting atmoaggie:
lol.
Read Shakespeare much?

Are FL mets talking about 97 enough? Now's the time to start awareness, not three days from now.
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Quoting dfwstormwatch:

177 hours out Savannah hit and run this storm is a criminal!!!!!!!!!!!!
What I'm noticing is this is not going to be a sharp right hand turn, almost looks due North with an eastward component.
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3128. gugi182
I'm out have a great night see what surprises 97L brings when i wake up?
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Quoting KoritheMan:


JFV will be happy.
while the majority run to Home Depot, Lowes, Wal-Mart, Target, Publix and any other grocery store, JFV can and will be found traversing to and from every Bed Bath & Beyond stocking up on his needed supplies...SHOWER CURTAINS of all kinds !
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Quoting Levi32:


The concern is that the model does actually see those mountains, to a certain extent, and to see it strengthen the storm regardless (the even higher resolution ECMWF does also), may speak to how favorable the environment may be for intensification at that point, which means that even a short time over water after dealing with Hispaniola and/or Cuba could result in a still potent storm. We will see. Step 1 is to get it named.

Levi what do you think about the GFS's solution of 98L and 99L moving it directly northeast toward the Bermuda High!! I just don't buy that and feel a more westward track would be probable!! Is there something im missing here? I see no ULL in the GFS solution to tug it northward!!!
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Quoting Levi32:


How does that work? The stronger the storm, the more air it ingests from the environment.

Harvey's momentary jump for joy also leaves him open to suck in a quick burst of dry air that chokes him up for a while, a problem that small systems often have when they try to intensify.
No, the other way around. A well-developed, closed TC stops bringing in mid-level air, only low-level. (However, exceptions always exist in this subject, it seems.)

In-up-out.

And, yes, right now Harvey still vulnerable to mid-level dry air.
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177 hours out Savannah hit and run this storm is a criminal!!!!!!!!!!!!
Member Since: July 31, 2011 Posts: 5 Comments: 891
Skirts GA and SC by 177 hours.

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I'll ask then late night crew. Does anyone recall a storm predicted 12 or more days out, by a group of models, to remain so consistent, run after run, and then not verify withing 100 miles or so of predicted landfall? Anyone?
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on the GFS pressure is falling as it crosses FL. How is that? This isnt a TS like Fay
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3119. gugi182
Last week we where attending the funeral of 93L wishing it a special resting place as it went from 40% to 0% to puff out he goes now look at him, look at the comeback now at 60MPH and giving it all he's got trying to at least bring one for the home team as the first hurricane of the season. Speaking of hurricanes we haven't seen one for the past 10 months.
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3118. Thrawst
Key West, according to www.windfinder.com ... has the system as a 996 mb storm near the area.

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3117. aquak9
Quoting dfwstormwatch:

168 hours out Jacksonville hit and run!


EEEEKK!! ok there I said it, EEEEK!!! you just HAD to bring Jax into the picture, didn't you?? EEEEKKK!!

(falls out into dead faint)
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Quoting FrankZapper:
Does anyone have solid thoughts on where 97 is going?



I did a couple hours ago.
Member Since: August 19, 2005 Posts: 5 Comments: 5452
Quoting FrankZapper:
Does anyone have solid thoughts on where 97 is going?


The United States.
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DON'T LOOK AQUA!!!!..lol
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Quoting ProgressivePulse:
100 bucks that as soon as 97L develops, the models drop it?
Well, GFDL already doing that, so, nah.
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3111. Levi32
Quoting atmoaggie:
I dunno. The proximity to land could aid it in the way of force convergence. And it's small enough to quickly intensify. And the OHC is supportive.

Only saying that it *could* cross that cat 1 threshold.

But:


The biggest hindrance might be dry air, but if it ceases ingesting mid-level dry air (as any mature TC should), that will not stop it either.


How does that work? The stronger the storm, the more air it ingests from the environment. If the environment is dry, then a mature hurricane ingests more than ever (remember Typhoon Muifa recently?)

Harvey's momentary jump for joy also leaves him open to suck in a quick burst of dry air that chokes him up for a while, a problem that small systems often have when they try to intensify.
Member Since: November 24, 2005 Posts: 635 Comments: 26686
Quoting AtHomeInTX:


Yes. It is. I've got a bunch of links about her somewhere I'll try to find them and send them your way. :)


Thanks, I'd appreciate it.
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Quoting redwagon:

I have them out of nowhere, too. We call them ground hornets.. ours that look like that build underground.

Cicada larvae/pupae have a 17-yr life cycle. Must be a big outbreak of them coming.

Oh Lord...here in Middle Tennessee, they came out in full force during May and June of this year. They were every freaking where, and you had to be careful where you'd step or you'd get them all over your shoes. And they were so LOUD too! Thank goodness they're all gone now, and we won't have to see their big ugly red eyes again for another 13 years (we have one of the 13-year broods).
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168 hours out Jacksonville hit and run!
Member Since: July 31, 2011 Posts: 5 Comments: 891
Does anyone have solid thoughts on where 97 is going?
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100 bucks that as soon as 97L develops, the models drop it?
Member Since: August 19, 2005 Posts: 5 Comments: 5452
Quoting Clearwater1:


Who doth dare to dispute the word of he who did appoint the designated poster, Sir (or Madam) dfwstormwatch. Let it be known to all men and women, that at all times, time shall be presented in Greenwich Mean time. So state this day .. . blah blah and so on.

I for one am glad we have Sir (or Madam) dfwstormwatch at the watch, because I really have to get some sleep.


NEVER MIND THAT @?#!, HERE COMES MONGO HOUR 144
lol.
Read Shakespeare much?
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Quoting dfwstormwatch:

156 hours out and ahead of the competitors


Your the only one who is officially notarized so keep em coming.
Member Since: August 19, 2005 Posts: 5 Comments: 5452
Very close to the ECMWF's solution...and basically right over my house. Time to get da plywood out! Lol. 6 days out...

Member Since: September 2, 2009 Posts: 130 Comments: 21194
3102. Levi32
Quoting TropicalWeatherGrl88:
I find it amazing how this system hit east cuba which is suppose to have mountains? No? And continues to strengthen it. I honestly think this thing will torn pretty badly if that were to materialize.


The concern is that the model does actually see those mountains, to a certain extent, and to see it strengthen the storm regardless (the even higher resolution ECMWF does also), may speak to how favorable the environment may be for intensification at that point, which means that even a short time over water after dealing with Hispaniola and/or Cuba could result in a still potent storm. We will see. Step 1 is to get it named.
Member Since: November 24, 2005 Posts: 635 Comments: 26686
Quoting KoritheMan:


JFV will be happy.


LOL!
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Quoting TropicalWeatherGrl88:
I find it amazing how this system hit east cuba which is suppose to have mountains? No? And continues to strengthen it. I honestly think this thing will torn pretty badly if that were to materialize.


loks to me like it goes over central cuba, does not have very many high mountains I think
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Quoting Levi32:
Harvey's convective burst is dying off. I didn't stoke up the fire when I saw it because it is typical for such a system to jump in the air for jubilation, and then not have enough energy for another jump for a little while . This is why I don't think this makes hurricane status, but a moderate-strong tropical storm is still likely.

I dunno. The proximity to land could aid it in the way of forced convergence. And it's small enough to quickly intensify. And the OHC is supportive.

Only saying that it *could* cross that cat 1 threshold.

But:


The biggest hindrance might be dry air, but if it ceases ingesting mid-level dry air (as any mature TC should), that will not stop it either.
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156 hours out and ahead of the competitors
Member Since: July 31, 2011 Posts: 5 Comments: 891
3097. Levi32
Quoting xtremeweathertracker:

If 97L can stay on the GFS's current track for 0Z the interaction with the mountainous terrain of Hispaniola will be limited!! Although it could be close enough to limit convection, especially on the northern side of circulation!!JMO


On such a track, convection would be abundant along the north-facing slopes of Hispaniola's mountains, providing them with heavy rains that they don't need. Dried-out inflow due to downsloping on the other side of the mountains would then try to choke the northern side of the core of the cyclone.
Member Since: November 24, 2005 Posts: 635 Comments: 26686
3096. aquak9
Quoting dfwstormwatch:
why do i feel like im competing with people


you're not! we are all enjoying the play-by-play. Please, proceed.

ok, not "enjoying", so to speak...actually my poor tummy is hurting.
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3095. gugi182
will 97L be a tropical Storm today Saturday.August.20.2011?
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I find it amazing how this system hit east cuba which is suppose to have mountains? No? And continues to strengthen it. I honestly think this thing will torn pretty badly if that were to materialize.
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Quoting chevycanes:
135 hrs just north of cuban coast.

You know something the 00z GFS is in line with the 12z ECMWF, up to this point.
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Quoting redwagon:

I have them out of nowhere, too. We call them ground hornets.. ours that look like that build underground.

Cicada larvae/pupae have a 17-yr life cycle. Must be a big outbreak of them coming.


Floods,droughts, tornadoes,tropical storms, now locusts?
Houston, we got a problem.
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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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