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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1982. pottery
Quoting truecajun:
hello everyone. i'm just checkin' in real quick. so td6 is most likely for east cost, bermuda, or the fish, right??

Well, um, yeah!
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COC 13.7N/36.7W moving WNW or just N of due west probably 60mph TS jmo.
Member Since: April 29, 2007 Posts: 0 Comments: 8134
Quoting FLdewey:
Mark it on the calendar... Hurricanes101 loosened up 8/22/10

Welcome to the blog. :-)
Lol. I got it.
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hello everyone. i'm just checkin' in real quick. so td6 is most likely for east cost, bermuda, or the fish, right??
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Quoting ShenValleyFlyFish:
So is the red east of Delaware the trough that is supposed to be coming out of US?


Its new jersey; that is how the water actually looks up there
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Quoting StormW:


Will, looking at how she's "grown" this will be the next layer.

Even though the flow is pretty straight forward, the storm still "sees" the "out" from the tropics. The storm will naturally try to go in between the ridges, and where the "weakness" (most predominate) over eastern CONUS. These motions have to be combined to give a close approximation of actual steering.



Hi StormW, I realize we are a ways out still and we can't be certain of the path. That said, based on where things are now, are there mainly 2 scenarios at this point --> either it impacts the E coast of US or goes out to sea?
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Quoting Hurricanes101:


his dogs name is climatology? hmmmm must be a very obedient dog lol


Only if there is a lot of continuity.
Member Since: July 29, 2005 Posts: 21 Comments: 794
Quoting StormW:


Will, looking at how she's "grown" this will be the next layer.

Even though the flow is pretty straight forward, the storm still "sees" the "out" from the tropics. The storm will naturally try to go in between the ridges, and where the "weakness" (most predominate) over eastern CONUS. These motions have to be combined to give a close approximation of actual steering.

So is the red east of Delaware the trough that is supposed to be coming out of US?
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1968. bappit
Quoting StormW:


They're updated every 3 hours

I think pipelines has a point with the first statement: "The steering maps are plenty accurate, the issue lies with the the interpretation of the data." If the beta effect is real--I do think it is--then a storm would not travel in the same direction as the surrounding air flow. That is what the beta effect is. Part of the BAM model name I believe.

Beta and Advection Model (BAM)

The Beta and Advection Model (BAM) refers to a class of simple trajectory models that utilize vertically averaged horizontal winds from the GFS to compute TC trajectories. These trajectories include a correction term to account for the impact of the earth.s rotation. The BAM is based upon the concept of a simple relationship between storm intensity/depth and steering levels. Strong cyclones typically extend through the entire depth of the troposphere and are steered by deeper layer-average winds, while weaker cyclones are steered by shallower layer-average winds. The BAM is run in three versions corresponding to the different depths used in the trajectory calculation: BAM shallow (850-700 mb), BAM medium (850-400 mb), and BAM deep (850-200 mb), known as BAMS, BAMM and BAMD, respectively. The performance of the BAM is strongly dependent on the dynamical input from the GFS. A divergence of the three versions of the BAM indicates varying steering flow within the parent GFS model. Hence, spread among the three versions of the BAM also serves as a rough estimate of the vertical shear as well as the complexity and uncertainty in the track forecast.
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Quoting StormW:


Will, looking at how she's "grown" this will be the next layer.

Even though the flow is pretty straight forward, the storm still "sees" the "out" from the tropics. The storm will naturally try to go in between the ridges, and where the "weakness" (most predominate) over eastern CONUS. These motions have to be combined to give a close approximation of actual steering.

Thanks, that helped me too!
Member Since: August 11, 2010 Posts: 0 Comments: 895
No cats were harmed in the making of Fldeweys joke.
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Quoting Hurricanes101:


Is there a carpenter there too?

and do you like oysters?
No, Oysters are the seas mucus in a shell. Sorry oysters, I just don't like you.
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Link

Not really liking the looks of ECMWF. Showing a more westward track from Danielle. Moving south of Bermuda.

Also, GFS is showing a potential of 3 storms (2 cape verde systems, and a system in the gulf hitting FL)
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1959. tkeith
Quoting P451:


Hey hey now, Jersey here.

We got plenty of attractions. Probably quite a few that I wouldn't mind seeing a hurricane wipe out... but, well, we have 'em.

Snookie :)
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Quoting aquak9:
cat cat cashew (i am the walrus)


bord you're killin' me here


Is there a carpenter there too?

and do you like oysters?
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1957. Dakster
Quoting aquak9:
high-fives to bord and h-101

clearly this place is tipping the sanity line


Which direction? I thought we were already far away from sanity...
Member Since: March 10, 2006 Posts: 0 Comments: 10646
1955. will45
Quoting StormW:


Will, looking at how she's "grown" this will be the next layer.

Even though the flow is pretty straight forward, the storm still "sees" the "out" from the tropics. The storm will naturally try to go in between the ridges, and where the "weakness" (most predominate) over eastern CONUS. These motions have to be combined to give a close approximation of actual steering.



ok got it now thanks a bunch StormW
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Quoting CosmicEvents:
The same person who would name a dog Deogee?
Nah, it's climatology...that's his dog.
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Quoting Bordonaro:


A remonstration of the computer models, up and down, west to east!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
1948. JRRP
Member Since: Posts: Comments:
CI# /Pressure/ Vmax
3.4 / 995.2mb/ 53.0kt

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1946. DVG
blsealevel-#1843

Hmmm is it even possible the CMC gets one right while the rest don't see this?
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Quoting blsealevel:
Every time u post the radar, the rain gets worse!! Please stop! lol
Member Since: August 11, 2010 Posts: 0 Comments: 895
1940. HadesGodWyvern (Mod)
I see it's comedy hour until the next advisory.
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Quoting aquak9:
Who would name a cat "Cashew?"
The same person who would name a dog Deogee?
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1937. bappit
Quoting KEEPEROFTHEGATE:
06L/TS/D/CX
MARK
14.36N/36.23W


Gosh! That does look like an explosion.
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All you need is troughs
All you need is troughs
All you need is troughs, troughs. Troughs is all you need...troughs is all you need
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Quoting FLdewey:
Bordonaro FTW!

Excuse my Smiley, he's having heat stroke! It was 105F today, in the shade!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785

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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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