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

By: Dr. Jeff Masters , 03:30 PM GMT em 19 de Agosto de 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 wpb:
smart folks have created these models. but im not so smart but i can tell u this hispanola will chop up the toughtest hurricane. for the model to show a storm over 10k mountains and display a sub 990mb pressure is just garbade.


As we saw with Gustav, weaker systems are not as susceptible to Hispaniola's mountains, because there isn't much of an inner core to disrupt.
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2391. ackee
Quoting wpb:
agree
well said think if 97L goes over hispanola that will the end of it the ISLAND is famous for taking down tropical system
Member Since: Julho 15, 2008 Posts: 0 Comments: 1375
You know whats caught my eye is that the itcz has really litten up in the past few days
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Quoting wpb:
agree
You just agreed with yourself man.
Member Since: Setembro 2, 2009 Posts: 130 Comments: 21194
2388. KEEPEROFTHEGATE (Mod)
Member Since: Julho 15, 2006 Posts: 175 Comments: 54827
2387. P451
Quoting ackee:
invest 99L not much said on this but cant see it moving that far north out to sea


Early runs always like to have a northerly bias.

Member Since: Dezembro 16, 2007 Posts: 7 Comments: 10202
2386. wpb
Quoting wpb:
smart folks have created these models. but im not so smart but i can tell u this hispanola will chop up the toughtest hurricane. for the model to show a storm over 10k mountains and display a sub 990mb pressure is just garbade.
agree
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A bad storm named Irene would be fitting considering all the recent bad I name storms (Isidore, Isabel, Ivan, Ike, Igor,etc.)
Member Since: Agosto 7, 2010 Posts: 0 Comments: 38
Another infamous hurricane moment...LOL
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2383. hotrods
Well, model runs are starting to bring 97L straight up the spine of Florida. Not good.
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2382. P451
Quoting earthlydragonfly:
So close to being closed



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.
Member Since: Dezembro 16, 2007 Posts: 7 Comments: 10202
Member Since: Setembro 2, 2009 Posts: 130 Comments: 21194


This surface analysis at day 6 illustrates what the most of the models are seeing!! Notice the break between the Texas high over the Rockies and the A/B High in the Atlantic directly north of the central and eastern GOMEX!!! This has been consistent on the 6 to 10 day 500 MB Heights Anomalies from the GFS and EURO as well!!!
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Quoting Stormchaser2007:
18z NAM

Can't even tell how deep that is.

Might be sub-990





971 mb Link
Member Since: Setembro 23, 2005 Posts: 14 Comments: 11264
Quoting wpb:
smart folks have created these models. but im not so smart but i can tell u this hispanola will chop up the toughtest hurricane. for the model to show a storm over 10k mountains and display a sub 990mb pressure is just garbade.


lol really?

you havent tracked the tropics for that long have you?
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Quoting P451:






I don't know if they are all that far away from the center. Maybe 997 and a few tenths minimum.



Wish google earth had this pug-in for MAC
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question please, kori seems to think 97 will go no further west than the central fl panhandle and levi thinks no further than the mississippi delta, as i live in fort walton beach,fl (in the extreme western panhandle) this is quite a significant difference for me. what is the weather pattern i should be looking at to see which scenario is more likely? thanks for your help
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2374. IKE

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2373. Dennis8
Quoting IKE:



Looks like we can hope for the terrain of the islands to tear it up if it follows the models and we can all breathe a sigh of relief..NO DEATHS OR DAMAGE in the US and hopefully it will stay weak on the islands.
Member Since: Agosto 15, 2008 Posts: 0 Comments: 446
2372. ackee
Quoting Tazmanian:




99L not moveing out too see its too far S
agree think this will go west be next area on intrest why has NHC not given it colour yet on there outlook
Member Since: Julho 15, 2008 Posts: 0 Comments: 1375
Quoting StormHype:
Video of girl walking a dog in Hurricane Jeanne 2004:
Girl walking dog in hurricane


LOL What in the world...
Member Since: Julho 7, 2010 Posts: 0 Comments: 5725
2370. wpb
Quoting Stormchaser2007:
18z NAM

Can't even tell how deep that is.

Might be sub-990



smart folks have created these models. but im not so smart but i can tell u this hispanola will chop up the toughtest hurricane. for the model to show a storm over 10k mountains and display a sub 990mb pressure is just garbade.
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Quoting ackee:
invest 99L not much said on this but cant see it moving that far north out to sea
the model always go north crazy
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Quoting aislinnpaps:


LOL, no it was more like the helicoptor landing and soldiers jumping out with m16's yelling at us to get back inside and then no recess for a month followed by recess with armed soldiers spread out around the perimeter of the playground guarding us.


LOL; Poor tiger was probley long gone by then toppling garbage cans, still I dont think i would venture to far out never know
Member Since: Agosto 23, 2008 Posts: 0 Comments: 1918
2366. ackee
invest 99L not much said on this but cant see it moving that far north out to sea
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2365. IKE

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Quoting Stormchaser2007:
984


Reminds me of...
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Quoting stormpetrol:
WoW!! What a nice little squall we're having here now on SW side of Grand Cayman, probably some outer bands of Harvey, no rain just some good old fashion storm breeze!
Member Since: Abril 29, 2007 Posts: 0 Comments: 8001
2362. P451
Quoting Stormchaser2007:
I doubt that...

MAX SFC WND OUTBOUND 61 KTS, 345/03 FM FL CNTR, NW QUAD, 00:41:10Z
GOOD BANDING WEST SIDE APPROX 30 NM FM FL CNTR


I agree with all who say... contaminated.


I wouldn't be surprised if such readings turned out legitimate come tomorrow morning.

We'll see if hitting the perpendicular coastline of Belize tightens up the core in the hours before landfall.

Wouldn't be the first system that it happened to.
Member Since: Dezembro 16, 2007 Posts: 7 Comments: 10202
984

Member Since: Junho 9, 2007 Posts: 4 Comments: 15946
Quoting Stormchaser2007:
18z NAM

Can't even tell how deep that is.

Might be sub-990





It's certainly sub-990.
Member Since: Agosto 10, 2010 Posts: 2 Comments: 1971
Video of girl walking a dog in Hurricane Jeanne 2004:
Girl walking dog in hurricane

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Quoting Stormchaser2007:
18z NAM

Can't even tell how deep that is.

Might be sub-990




O_O
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WoW!! What a nice little squall we're having here now on SW side of Grand Cayman, probably some outer bands of Harvey
Member Since: Abril 29, 2007 Posts: 0 Comments: 8001
Lowering pressures, growing convection, increasing winds...Harvey is doing OK for a system barely offshore rugged terrain.
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18z NAM

Can't even tell how deep that is.

Might be sub-990



Member Since: Junho 9, 2007 Posts: 4 Comments: 15946
2353. P451
Quoting Levi32:
Dropsonde northeast of the center found a 998mb pressure with a 22kt surface wind. The real central pressure could be a millibar or so lower than that.






I don't know if they are all that far away from the center. Maybe 997 and a few tenths minimum.
Member Since: Dezembro 16, 2007 Posts: 7 Comments: 10202
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Wow.
Member Since: Julho 6, 2010 Posts: 113 Comments: 32512
Quoting MiamiHurricanes09:
Thanks for the feedback on the DGEX.

As for the 61kt SFC winds...I find that hard to believe. But hey, I'm not the one on the plane.


Lol, this is kind of my feeling too. 70mph doesn't seem likely to me, but if that's what they are measuring and reporting, then I guess they know better than me.
Member Since: Agosto 10, 2010 Posts: 2 Comments: 1971
2349. Dennis8
Quoting KeyWestwx:
Wow It sounds like somebody has a sandal shopping addiction :0)


This pretty lady ships them to Houston. I discovered my first pair last Spring while in your beautiful city.
Member Since: Agosto 15, 2008 Posts: 0 Comments: 446
Thanks for the feedback on the DGEX.

As for the 61kt SFC winds...I find that hard to believe. But hey, I'm not the one on the plane.
Member Since: Setembro 2, 2009 Posts: 130 Comments: 21194
Quoting Levi32:


In the morning. I don't do more than one a day, though chances are I would do multiple updates if a major storm was threatening land.


Okay Ill be lookin for it, you help understanding so muucch thanks for it
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2346. scott39
My local met put 97Ls track into very simple layman terms! There is going to be a high pressure system and a weakness. Picture a high symbol stopping at LA. down into the GOM. Next picture a high symbol over to the E. The break in between those 2 areas is where the hurricane will follow. The big question is now, how far to the E will it break? Hopefully we will know soon!
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2345. Skyepony (Mod)
Quoting NICycloneChaser:


Maximum Surface (likely estimated by SFMR) Wind Outbound: 61kts (~ 70.2mph) in the quadrant at 3:45

Might have something to do with it. 70mph seems fairly unlikely to me, I have to say.



That's what it looked like. As soon as they hit that they climbed. Also noticed the turbulence looks to be overall rough for a TS.
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2344. emcf30
Quoting Grothar:
18Z gfs ensemble models


Good evening Gro..
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2343. emcf30
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Quoting weatherh98:
That will be marked as contaminated or suspect or whatever... they would have to find a lot more of thosse for me to believe it


The HDOD messages can be marked as suspect, but that was in the 'REMARKS' section of the Vortex message, which they themselves write, which makes me wonder.
Member Since: Agosto 10, 2010 Posts: 2 Comments: 1971

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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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