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 reedzone:
I guess my call was right, 60% it is! 97L is ready and primed for DMAX tonight. Great structure, waning convection. May see a TD form tomorrow evening.



Quite possible. 97L is currently over 84F waters.
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2490. Grothar
Quoting ElConando:


I think he meant notch.


Oh, yeah, smarty. Now pronounce this. LOL

Donaudampfschiffahrtsgesellschaftskapitän
Member Since: July 17, 2009 Posts: 69 Comments: 25352
2489. robj144
Quoting weatherh98:


yea notche means night and its noche


Ok, I'm pretty sure you do mean notch, but why are you saying its noche? Just confused...
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Quoting Clearwater1:
Can anyone here recall a storm predicted 12 or more days out, having as much mult - model support AND consistency as 97L and NOT verify, within 100 miles either way?


We've never had such consistency so far out, that I can remember.

Not in the past 6 years or more I Believe.

May be wrong though.
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Quoting xtremeweathertracker:

Yes you are correct but remember 97L should start to turn northwestward around the periphery of the A/B High as counterclockwise winds begin to influence it!! So while the break looks farther west in reality it should move toward the eastern side of the break! (Unless of course it stays relatively weak)!!


Thanks I just dont see it getting that strong till it gets closer to florida for that to take place though
anyway i injoy your comments and videos you been putting out keep it going and thanks again

blsealevel
Member Since: August 23, 2008 Posts: 0 Comments: 1918
Quoting reedzone:
I guess my call was right, 60% it is! 97L is ready and primed for DMAX tonight. Great structure, waning convection. May see a TD form tomorrow evening.



I agree, watch out islands!
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Can anyone here recall a storm predicted 12 or more days out, having as much multi - model support AND consistency as 97L and NOT verify, within 100 miles either way?
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Quoting ElConando:


I think he meant notch.


yea notche means night and its noche
Member Since: June 17, 2011 Posts: 11 Comments: 6461
I guess my call was right, 60% it is! 97L is ready and primed for DMAX tonight. Great structure, waning convection. May see a TD form tomorrow evening.

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Quoting robj144:


Noche? Is that Spanish for night?


I think he meant notch.
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2479. gugi182
As i see 97L upgraded to 60% i will wait until tomorrow t osee if a will have to go to WAL MART to go get some batteries and some candles or some bottle waters to see if 97L becomes Tropical Storm Irene. Down here we are keeping a close eye on this system it see to be getting more organized. models still have it passing very close to the southwest of Puerto Rico so it that's true i will be experiencing tropical Storm force winds by Sunday night well wish me luck you guys
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2478. robj144
Quoting weatherh98:
its like a noche below ri


Noche? Is that Spanish for night?
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Quoting southernbell72:
i live in new orleans , do yall think we have anythng to worry about


From all current indications - NO. You folks have had enough, just keep watching to make sure & God Bless!
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2476. Grothar
Quoting CaicosRetiredSailor:





I never use this expression on the blog, but it deserves it for that post. LMAO!
Member Since: July 17, 2009 Posts: 69 Comments: 25352
its like a noche below ri
Member Since: June 17, 2011 Posts: 11 Comments: 6461
Quoting PalmBayJay:


Hello from Palm Bay! (Long time lurker) I was thinking about our potential storm named Irene and a bunch of us remembered her well back in 1999 shortly after the crazy times we had with the evacuations and the close call with Hurricane Floyd. She hit Southern Florida as a Category 1 Hurricane and came back out over water near Jupiter. Its just eerie 12 years later she may make a return trip to Florida. Obviously, we are all hoping for the best down here, but I think its going to be hard for Florida to miss some impact from potential Irene this time.


Irene... Oh, the memories.
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Quoting Grothar:


Nice animation, EYES!


Hey there, Grothar :) Those WV loops are just mesmerising.....that LSU one that you just posted is so beautiful....I know folks will think me Krazy for thinking weather visuals are beatuiful....but..I don't care :P ~~~~~
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2472. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
2471. hahaguy
Quoting CaicosRetiredSailor:




Nice lmao.
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Quoting TropicalAnalystwx13:


No, its not steadily strengthening, its intensifying pretty fast.

lol.

BLARGH! lol
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Quoting Grothar:
Come on guys. By this time there should be at least 10 posts on the correct spelling and pronunciation of the Hebert's Box. Who'll be the first?


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Quoting southernbell72:
i live in new orleans , do yall think we have anythng to worry about
I do too. I just don't know. I really don't know. The skinny weatherlady on Channel 8 looked scared.
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Quoting WeatherNerdPR:

The correct wording would be "steadily intensifying".
I think.


No, its not steadily strengthening, its intensifying pretty fast.

lol.
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2466. KEEPEROFTHEGATE (Mod)
Quoting southernbell72:
i live in new orleans , do yall think we have anythng to worry about
yes its best to stay informed with this one follow NHC/TPC guidance as event draws nearer
Member Since: July 15, 2006 Posts: 169 Comments: 53296
2465. Grothar
Member Since: July 17, 2009 Posts: 69 Comments: 25352
Quoting TropicalAnalystwx13:


No, but it is intensifying pretty fast.

The correct wording would be "steadily intensifying".
I think.
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Hello from Palm Bay! (Long time lurker) I was thinking about our potential storm named Irene and a bunch of us remembered her well back in 1999 shortly after the crazy times we had with the evacuations and the close call with Hurricane Floyd. She hit Southern Florida as a Category 1 Hurricane and came back out over water near Jupiter. Its just eerie 12 years later she may make a return trip to Florida. Obviously, we are all hoping for the best down here, but I think its going to be hard for Florida to miss some impact from potential Irene this time.
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2461. JLPR2
Quoting Hurricanes101:


actually that is probably the best thing it could have done for itself

how many systems this year have struggled due to misalignment and dueling vorticies?


92L wasn't very successful after doing that, but lets see, 97L has nicer conditions ahead than 92L.
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Quoting Grothar:
Come on guys. By this time there should be at least 10 posts on the correct spelling and pronunciation of the Hebert's Box. Who'll be the first?



An Herbert box pronounced AY-BEAR... committed that to memory from Wikipedia lol.
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Quoting Grothar:
Come on guys. By this time there should be at least 10 posts on the correct spelling and pronunciation of the Hebert's Box. Who'll be the first?


From Wiki... "An Hebert Box (pronounced AY-bear, also known as Hebert's Box)"
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Quoting hotrods:
Clearwater1- IKE posted it, 2374.



Thanks. Thought maybe I missed one specific run. But that cluster of models does pretty much point up FLA's spine. Ouch!
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Quoting tropicfreak:


Would you say Harvey is undergoing RI??


No, but it is intensifying pretty fast.
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2456. HCW
Quoting tropicfreak:


Would you say Harvey is undergoing RI??


No


RI = 26 MB drop in less than 24 hours
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Good amount of dry air in front of 97L, would likely keep it in check till AM Sunday.


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2454. KEEPEROFTHEGATE (Mod)
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting Grothar:
Come on guys. By this time there should be at least 10 posts on the correct spelling and pronunciation of the Hebert's Box. Who'll be the first?


Hebert's Box. LOL
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Quoting TropicalAnalystwx13:
I think Harvey is approaching 60 mph.


Would you say Harvey is undergoing RI??
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Quoting P451:


I think the flareup in the ITCZ could be causing this to a degree.

Surface vort must be stretched or shared by the two entities.



Dry air is still a problem as well of course. DMax should help to further isolate 97L from intrusion.



But judging by that water vapor satellite, it's doing a decent job at fending off the dry air.
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Quoting KoritheMan:


Emily's problem was not fast forward motion. Rather, it was competing areas of vorticity within the large scale cyclonic gyre.


Yea I am tired of hearing "Will be like Emily" since 'Emily" was a one time event. There was also a larger a mouth of wind shear present during emily's track. There are times when storms have been moving fast and had no time in strengthening such as Opal 1995
Member Since: July 22, 2010 Posts: 6 Comments: 752
i live in new orleans , do yall think we have anythng to worry about
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I think Harvey has at a 50-60% chance of becoming the first hurricane of the 2011 Atlantic H. Season.
Member Since: April 29, 2007 Posts: 0 Comments: 7664
2447. Grothar
Quoting EYEStoSEA:


Nice animation, EYES!
Member Since: July 17, 2009 Posts: 69 Comments: 25352
I think Harvey is approaching 60 mph.
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Video clips compiled from various 2004 & 2005 Florida hurricane landfalls for those who have never been through it:
Charley, Frances, Jeanne, Wilma


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Flight level winds..
53 knots
(~ 60.9 mph)
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Quoting JLPR2:


So 97L has become a mid-level feature, seems it left the LLC behind, now to wait and see if a new one forms under the convection.


actually that is probably the best thing it could have done for itself

how many systems this year have struggled due to misalignment and dueling vorticies?
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2442. Grothar
Come on guys. By this time there should be at least 10 posts on the correct spelling and pronunciation of the Hebert's Box. Who'll be the first?
Member Since: July 17, 2009 Posts: 69 Comments: 25352

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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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