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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2892. bird72
Quoting atmoaggie:
The poll:
CACA.
lolllllllllllll!
Member Since: Posts: Comments:
2891. KEEPEROFTHEGATE (Mod)
Quoting TampaSpin:
Its very troubling to see most models are keeping 97L just off shore and south of DR and moving over the flatter part of Cuba on the Western side....HUM
if thats the way it goes gonna be a big bad day in someones backyard
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2890. 3211976
http://www.ndbc.noaa.gov/plot_supl.php?station=4104 0&meas=omws&uom=E&time_diff=0&time_label=GMT
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Quoting CaicosRetiredSailor:



Harvey is a fat rabbit.

When Harvey hits land and forward momentum kicks in, he *ought to* sling a big dirty NE quad rain band into the moisture train.


Hermine did this a year ago and brought 15" in less than a day. Of course her rainband was direct, not having to circle around before dumping on us.
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2888. pottery
I am out.
But before I go, I dont think anyone should worry too much.
This season is obviously a Bust.


heheheheh
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Quoting tennisgirl08:
Good evening! I'm on the gulf coast and my local met is very concerned about 97L...


Which met was that?
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Quoting tennisgirl08:
Good evening! I'm on the gulf coast and my local met is very concerned about 97L...
Tennisgirl my local met said that what he can see as far as the way the highs are setting up that there would be a weakness in between them and a storm follows the path of least resistance.He said that everyone from Pascagoula East needs to watch this one.And he said he is not liking what he is seeing.I am in Mobile, where are you?
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Quoting AtHomeInTX:


Evening. :) I hate when the electricity goes out and there's no Sonic Cokes! Lol. Not a big coffee drinker though. And it's really hard to get fresh donuts. ;-)


LOL.........do the DEW........LOL
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Quoting GoMMedic:
Where can I get the Buoy info at ? TIA


Knock yourself out.

If you're looking for a specific buoy, this is the one 321 posted.
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2882. KEEPEROFTHEGATE (Mod)
Quoting ShenValleyFlyFish:

No Kit complete without one of these: Link
ok give it up you
i looked at that rolled my eyes laugh a little now i think iam blind
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2881. 3211976
if it passes near Guadalupe it will hit or brush PR.

That is the Historical rule
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Quoting tennisgirl08:
Good evening! I'm on the gulf coast and my local met is very concerned about 97L...



Should be concerned, but not to concerned YET!
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Quoting aislinnpaps:
Evening AtHome

To those saying Lousiana. If it hits I'll expect you all here promptly at nine the next morning to help me clean up. I'd say I'd have some coffee ready and cinnamon rolls, but odds are I wouldn't have electric, so you'll have to bring those with you. I like my coffee sweet and light. *G*


Evening. :) I hate when the electricity goes out and there's no Sonic Cokes! Lol. Not a big coffee drinker though. And it's really hard to get fresh donuts. ;-)
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Quoting Thunderpig75:


dishwasher won't work...it's attached to a drain that will back up. Scan important documents and email them to yourself at an email address you can access from any computer.


Just put everything on an external hard drive and take it with you. Or take your laptop...
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Quoting GoMMedic:
Where can I get the Buoy info at ? TIA
http://www.ndbc.noaa.gov/

Buoy "41001" in the Station ID search box.
And "41040"...
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2875. JRRP
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Quoting zerveftexas:

Read my post again, I said "nice try, buddy".

WeatherNerdPR: You think he wasn't aware of that? Some people will never get jokes...
Umm, okay.

I knew what I was doing...and, no, I don't care how many questions were asked. I call them all the same thing, usually not in typed form, though.
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Where can I get the Buoy info at ? TIA
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Its very troubling to see most models are keeping 97L just off shore and south of DR and moving over the flatter part of Cuba on the Western side....HUM
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CBB
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97l mlc get on top of the sfc circulation I wont be surprise if we wake up with TS Irene as far of the track I see it near Guadalupe on a wnw track that should bring tge storm to the c bahamas making landfall in some point btw Tampa and NC as mayor cane.
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Quoting 3211976:
Check out!!!

just north of the convection

Station 41040
NDBC
Location: 14.477N 53.008W
Conditions as of:
Sat, 20 Aug 2011 02:50:00 UTC
Winds: E (80°) at 21.4 kt gusting to 29.1 kt
Significant Wave Height: 7.5 ft
Dominant Wave Period: 8 sec
Atmospheric Pressure: 29.83 in and rising
Air Temperature: 79.2 F
Dew Point: 75.4 F
Water Temperature: 83.3 F


Impressive winds, given the relative lack of persistent convection. Goes to show the vigorous nature of the circulation.
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Quoting zerveftexas:

Read my post again, I said "nice try, buddy".

WeatherNerdPR: You think he wasn't aware of that? Some people will never get jokes...

I got the joke, LOL
I posted what I was thinking XD
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Good evening! I'm on the gulf coast and my local met is very concerned about 97L...
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2866. 3211976
the winds just shifted from ENE too E and wave height increasing
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Evening all.......LOoks like 97L is now starting to get its act together.
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Member Since: July 31, 2011 Posts: 4 Comments: 753
Quoting Thunderpig75:


dishwasher won't work...it's attached to a drain that will back up. Scan important documents and email them to yourself at an email address you can access from any computer.
If you're a privacy nut, email is not secure, not even encrypted.

An online backup storage will allow you to upload them encrypted and store them (but I don't know of any free ones, nor have I looked for any recently).
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2862. pottery
Quoting ProgressivePulse:


DMAX is still about 6 hours away.

That's true.
But DMin was 5-6 hrs ago.
It looks a little Ominous right now.
The structure is excellent.
It's only lacking convection.
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Quoting Hurricanes101:


but havent you heard? 97L looks like crap lol


What has the talk been? Wherever the center decides to consolidate, big implications on track, Large area of low pressure could form anywhere within. As I said before, it's obvious where 97L wants to be.

Member Since: August 19, 2005 Posts: 5 Comments: 4863
Quoting ProgressivePulse:


DMAX is still about 6 hours away.



ouch then if it fireing up good now i cant wait for D MAX
Member Since: May 21, 2006 Posts: 5089 Comments: 114024
2858. 3211976
Check out!!!

just north of the convection

Station 41040
NDBC
Location: 14.477N 53.008W
Conditions as of:
Sat, 20 Aug 2011 02:50:00 UTC
Winds: E (80°) at 21.4 kt gusting to 29.1 kt
Significant Wave Height: 7.5 ft
Dominant Wave Period: 8 sec
Atmospheric Pressure: 29.83 in and rising
Air Temperature: 79.2 F
Dew Point: 75.4 F
Water Temperature: 83.3 F
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Quoting dfwstormwatch:
Poll Time!!!!!!!!!!!!!!!


1. how strong will harvey become?
A 65 MPH
B 70 MPH
C 75 MPH
D Higher/Lower


2. what percentage will invest 97 be at 2 am?
A 60%
B 70%
C 80%
D Higher/Lower


3. what percentage will invest 98/99 be at 2 am?
A 30%
B 40%
C 50%
D Higher/Lower
Quoting dfwstormwatch:
Poll Time!!!!!!!!!!!!!!!


1. how strong will harvey become?
A 65 MPH
B 70 MPH
C 75 MPH
D Higher/Lower


2. what percentage will invest 97 be at 2 am?
A 60%
B 70%
C 80%
D Higher/Lower


3. what percentage will invest 98/99 be at 2 am?
A 30%
B 40%
C 50%
D Higher/Lower


BCC
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2856. 3211976
the COC is passing just south of the buoy
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Harvey is a fat rabbit.
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Quoting Tazmanian:
odd am not sure if this is D MAXS or not but the t-storms with 97L is growing


DMAX is still about 6 hours away.
Member Since: August 19, 2005 Posts: 5 Comments: 4863
Quoting ProgressivePulse:
Prime set up for Dmax



but havent you heard? 97L looks like crap lol
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I think 97L is developing a surface circulation underneath that convective blowup, near 14.5n.
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2850. 3211976
Winds are increasing too

The COC is definitely trying to form near the new convection that is near the buoy

Station 41040
NDBC
Location: 14.477N 53.008W
Conditions as of:
Sat, 20 Aug 2011 02:50:00 UTC
Winds: E (80°) at 21.4 kt gusting to 29.1 kt
Significant Wave Height: 7.5 ft
Dominant Wave Period: 8 sec
Atmospheric Pressure: 29.83 in and rising
Air Temperature: 79.2 F
Dew Point: 75.4 F
Water Temperature: 83.3 F
Member Since: Posts: Comments:
Quoting zerveftexas:

nice try, there's only 3 questions buddy...
;-)
EDIT: I've been outed, I see.
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odd am not sure if this is D MAXS or not but the t-storms with 97L is growing
Member Since: May 21, 2006 Posts: 5089 Comments: 114024
Quoting atmoaggie:
The poll:
CACA.

LOL
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Quoting KEHCharleston:
RE: 2730

Regarding safe-guarding important papers, items etc. I have heard a couple of interesting solutions.
One is to use your dishwasher - Makes sense to me.
Another is to mail important papers (insurance etc) to yourself.


dishwasher won't work...it's attached to a drain that will back up. Scan important documents and email them to yourself at an email address you can access from any computer.
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2845. nigel20
Quoting atmoaggie:
Yes, some.
But the angle of approach combined with the shape of the coastline probably makes it an even wash.

Still should slow the water some...even if the hieghts attained are about the same.

OK, thanks
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Prime set up for Dmax

Member Since: August 19, 2005 Posts: 5 Comments: 4863

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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.