Tropical Depression Six arrives

By: Dr. Jeff Masters , 5:14 PM GMT on August 22, 2010

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Tropical Storm Tropical Depression Six is here, but it will not be a threat to land for at least the next five days. Tropical Depression Six is a classic "Cape Verdes"-type storm common during the peak part of hurricane season. Cape Verdes-type storms are so named because they form from tropical waves that come off the coast of Africa and pass near the Cape Verdes Islands just west of Africa. Cape Verdes hurricanes are the largest and most dangerous types of hurricane in the Atlantic, since they spend a long time over water have and have of opportunity to reach full maturity. Tropical Depression Six has a ways to go before it becomes a hurricane, as the storm is embedded in a strong easterly flow of wind courtesy of the African Monsoon that is generating a moderately high 15 - 20 knots of wind shear. There is also a tropical disturbance to the northeast of TD 6 that is sucking away some moisture and is interfering with the storm's circulation. Sea Surface Temperatures (SSTs) are a warm 28°C, and the storm is embedded in a moist environment, so wind shear is the primary inhibiting factor for development. The strong east winds imparting the shear are keeping any heavy thunderstorms from developing on the east side of the center of circulation, which is exposed to view in satellite imagery (Figure 1.)


Figure 1. Afternoon satellite image of Tropical Depression Six.

Forecast for Tropical Depression Six
A ridge of high pressure will force Tropical Depression Six to the west-northwest for the next five days, and the system should increase its forward speed from its current 10 mph to 15 mph by Monday night. A powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Tropical Depression Six more to the northwest late this week, and the storm should pass well to the northeast of the Lesser Antilles Islands. It remains to be seen, however, it this trough will be strong enough to fully recurve Tropical Depression Six out to sea. The GFS predicts that Tropical Depression Six may pass close to Bermuda about eight days from now, and it is also possible that Tropical Depression Six could eventually hit the U.S. East Coast 9 - 15 days from now. However, we have no skill in making these sort of ultra-long range forecasts, and the long-range fate of TD 6 is uncertain.

Elsewhere in the tropics
The ECMWF and NOGAPS models are predicting formation of a tropical depression off the coast of Africa 3 - 4 days from now.

Jeff Masters

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21Aug - 12pmGMT - 10.6n31.0w - - 25knots . . . . 1009mb
Invest95L becomes TropicalDepressionSix
- Date - - - Time - - - - - Location - - Windspeed - Pressure
21Aug - 06pmGMT - 10.8n31.8w - - 25knots . . . . 1008mb - NHC-ATCF
21Aug - 09pmGMT - 11.0n32.1w - - 30mph . . . . . 1008mb - NHC.Adv.1
22Aug - 12amGMT - 11.2n32.3w - - 25knots . . . . 1008mb - NHC-ATCF
22Aug - 03amGMT - 11.3n32.6w - - 35mph . . . . . 1008mb - NHC.Adv.2
22Aug - 06amGMT - 11.7n33.0w - - 30knots . . . . 1007mb - NHC-ATCF *was11.8n*
22Aug - 09amGMT - 12.1n33.4w - - 35mph . . . . . 1007mb - NHC.Adv.3
22Aug - 12pmGMT - 12.2n33.9w - - 30knots . . . . 1007mb - NHC-ATCF
22Aug - 03pmGMT - 12.7n34.1w - - 35mph . . . . . 1007mb - NHC.Adv.4
*before NHC reevaluated&altered TD6's path*
Copy&paste 11.3n32.6w-11.7n33.0w, 11.7n33.0w-12.1n33.4w, 12.1n33.4w-12.2n33.9w, 12.2n33.9w-12.7n34.1w, hex, bda, sid into the GreatCircleMapper for a look at the last 12hours. TD6's heading has turned northward from 11degrees west of WestNorthWest to 1.1degrees north of NorthNorthWest.
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Quoting stillwaiting:
Still no mention Of the trough Split in gom ....hmmm interesting,maybe td in central gom mid week Imo


Our local mets were talking about it last night. Their models showed an area of low pressure developing as a result of the trough split, then moving westward. They said nothing to be concerned about--it'll just increase our rain chances here in SE LA.
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Forgive me for I have sinned.

Quoting MiamiHurricanes09:
No one quote post 46. Report it that way its gone.
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Quoting TropicalAnalystwx13:


Hey!

Its you!


Yeah, the third time you said that and I'm still scratching my head wondering why. XD

If its for the avatar, yeah, it's my shadow.
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Thanks Dr. Masters...looks to me TD6 is trying to wobble abit...abit slower also...anyone else notice that?
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This erratic movement of 06L is going to mess up the models, expect a shift towards the right because of the recent latitudinal gain. The circulation (as of 16:45 UTC) appears to be near 13.0N 34.4W.

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..Can a Brother get a "Hmmm" this afternoon?"

LOL





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StormW, how would that gulp of dry air impart that NNE motion?
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Still no mention Of the trough Split in gom ....hmmm interesting,maybe td in central gom mid week Imo
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Why is it that just about every time someone has the temerity to mention--even in a very oblique and non-dramatic fashion--that it's not out of the realm of possibility that a particular system could effect a certain geographic area sometime down the road, a dozen wannabe comedians feel the need to impart their vast meteorological wisdom by posting some variation of "Oh, no, board the house! Evacuate immediately!" Guys, you're not being clever, you're not being original, and you're certainly not being funny. Just thought you might want to know that...
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Quoting JLPR2:
I guess this area approaching the coast is the real TW, right?
Looks nice...


Also hey everyone! :)


Hey!

Its you!
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From the 11AM NHC Discussion:

BUT THE CIRCULATION IS A LITTLE STRETCHED FROM NORTHEAST
TO SOUTHWEST DUE TO ANOTHER DISTURBANCE LOCATED ABOUT 350 N MI TO
THE NORTHEAST. THIS HAS ALSO CAUSED THE CENTER TO MOVE ALMOST DUE
NORTH OVER THE PAST FEW HOURS...PULLING IT FARTHER AWAY FROM THE
DEEP CONVECTION.
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Still exposed, and idk if some experts want to look at this loop, but is the LLC weakening, it looks like it to me. Maybe a new one will form, under the convection?

weakening llc?
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I guess this area approaching the coast is the real TW, right?
Looks nice...


Also hey everyone! :)
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Quoting LongIslandXpress38:


I would begin evacuating NYC tomorrow...
It would take that long if it really happened!
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Quoting StormW:
Forecast for Tropical Depression Six
A ridge of high pressure will force Tropical Depression Six to the west-northwest for the next five days, and the system should increase its forward speed from its current 10 mph to 15 mph by Monday night. A powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Tropical Depression Six more to the northwest late this week, and the storm should pass well to the northeast of the Lesser Antilles Islands. It remains to be seen, however, it this trough will be strong enough to fully recurve Tropical Depression Six out to sea. The GFS predicts that Tropical Depression Six may pass close to Bermuda about eight days from now, and it is also possible that Tropical Depression Six could eventually hit the U.S. East Coast 9 - 15 days from now

Doc keeps reading my forecasts.


Why not, I don't think you've been wrong yet. :)
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Quoting StormW:


That's possible...just a "qucik punch" so to speak...cause this says...are ya ready for it? WEST!

OOooooo, and that A/B high has moved even further west, as you predicted it would last night on your blog. Cool!
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jkrocket
comment tagged and flagged for comm. standards violation
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Sorry Grothar, missed the hyper-jump to the new blog.

Pottery, sorry to hear about your "problem". :)

Quoting Grothar:


Yo, Snake! Doing a little recon on the blog?


Always here reading and learning, more so in the last week after someone mentioned Georgia as a "possible" cane strike target. :)

Macon is 167 miles NW of Savannah so I don't think storm surge will be a problem.
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Quoting MiamiHurricanes09:
The 12z CMC keeps it moving NW (which doesn't make sense considering the mid-level steering flow) then it starts heading west as it meets the subtropical ridge. Then, at around 50W it begins NW movement. After that a banana ridge build north of the system and shoots it WNW-ward very close to Bermuda. To give you an idea of the intensity that the CMC is forecasting, the closed isobars aren't even discernible from each other. This is going to be a very interesting scenario after 50W.


I gotta say, as a resident of New Jersey I really don't like where this latest CMC run is going. Granted, it wouldn't take much of a trof to recurve a system that large, but still, not a very pretty ridging pattern.
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However, we have no skill in making these sort of ultra-long range forecasts, and the long-range fate of TD 6 is uncertain. Most important statement I have seen yet..Thanks Doc!
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Quoting StormW:


That's possible...just a "qucik punch" so to speak...cause this says...are ya ready for it? WEST!


Is the rotation/coriolis effect enough to bend the system north, on it's own impetus? Regardless of the MidLevel steering trends?
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Quoting jlp09550:


*poof*
Or that, lol.
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HWRF at the end brings it back more WNW.
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Quoting StormW:


Yeah...it has come back to that, but the very first frames show a distinct NNE.


BTW.. I have not been around or said hi for awhile. I am one of the was fortunate to sit with you through one of your analysis runs a few years back. Brought you the cruzian rum in gratitude for your time. Hope all is well!
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Thanks Dr. Masters!
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No one quote post 46. Report it that way its gone.

Ok, mission complete, good job everyone. LOL!
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Oh, it's very distinct NNE, StormW. first time today That I got a chance to get online since last night, and I was expecting to see a well developed TD, almost TS, not this! Very odd!
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Quoting StormW:


Yeah...it has come back to that, but the very first frames show a distinct NNE.


I see that too, weird..
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Quoting StormW:
What I want someone to explain to me is...how is the exposed LLC moving NNE, when there's NOTHING to indicate a flow that would send it that way?

First time I've seen this.

LINK


That is STRANGE storm!! Good Observation as usual.
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The 12z CMC keeps it moving NW (which doesn't make sense considering the mid-level steering flow) then it starts heading west as it meets the subtropical ridge. Then, at around 50W it begins NW movement. After that a banana ridge build north of the system and shoots it WNW-ward very close to Bermuda. To give you an idea of the intensity that the CMC is forecasting, the closed isobars aren't even discernible from each other. This is going to be a very interesting scenario after 50W.
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this year has been acting like a EL Nino so far
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Fantastic Update by you, StormW.
Thanks so much, as usual.
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Quoting breald:
I still think this is a Bermuda bound storm. But the east coast from NC to New England is at risk. Just my opinion.


I would begin evacuating NYC tomorrow...
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Quoting Patrap:
O,lordy...


???
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I think what we're going to see happen in the next 12 hours is the COC starts going WNW towards the deeper convection as shear starts to abate as it moves away from the 20 knot shear.
Member Since: July 8, 2005 Posts: 259 Comments: 24015





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Quoting StormW:


Yeah...me either!


Storm,

The only thing I can think of is that the disturbance to the north and east had some sort of tug on the circulation.
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Quoting StormW:
What I want someone to explain to me is...how is the exposed LLC moving NNE, when there's NOTHING to indicate a flow that would send it that way?

First time I've seen this.

LINK


Hey Storm.. with the L/L grid up the llc motion looks more NNW. The convection moving faster to west of the llc makes it movment look more easterly.
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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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