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Tropical Depression Four arrives

By: Dr. Jeff Masters , 9:10 PM GMT on August 21, 2006

The strong tropical wave that moved off the coast of Africa Sunday has become large and well-organized enough to be classified as Tropical Depression Four. The depression is located southeast of the Cape Verde Islands off the coast of Africa, and is expected to track northwestwards just to the south of these islands over the next two days. The waters under the wave are 27-28 C, which is warm enough to allow some modest intensification. Wind shear is a low 5-10 knots. There is a large area of dry air and Saharan dust to the wave's north, but this is far enough away that it shouldn't inhibit intensification over the next day or two, and this depression should be Tropical Debby by Tuesday afternoon. The GFDL intensifies the storm up to a strong Category 1 hurricane by Sunday, and the official NHC forecast has it close to hurricane strength by Saturday.

Unless you live in the Cape Verde Islands, this storm is unlikely to affect you. As we can see from the plot of historical storm tracks of August tropical depressions that formed near the location of the current storm (Figure 1), none of these storms have affected any land areas other than the Cape Verde Islands. The GFS model has the storm recurving northwards well east of Bermuda early next week. The Cape Verde Islands, however, are under a Tropical Storm Warning, and will get some heavy rain and high winds from this system starting Tuesday morning.


Figure 1. Historical tracks of August tropical depressions that tracked near the current position of TD 4.

Sea surface temperatures cool to below the 26.5 C threshold tropical systems prefer north of the Cape Verdes Islands, so once the system moves north of about 15 N latitude, it may weaken a bit before it crosses back over warmer waters later in the week. The dry air and Saharan dust to the north of the Cape Verde Islands may cause some trouble for the storm later this week.


Figure 2. Visible satellite image of TD 4 at 1:45pm EDT Mon Aug 21 2006. Image credit: Navy Research Lab.

Elsewhere in the tropical Atlantic
An area of thunderstorms over the Bahamas is associated with an upper level low pressure system, and development is not expected. An area of thunderstorms west of Jamaica is drifting northwards towards Cuba and South Florida, and is associated with a tropical wave. Upper level winds are not favorable for development of this area, either. The long-range GFS model is predicting a series of 2 or 3 more tropical waves will emerge off the coast of Africa over the next two weeks and intensify into tropical storms. Each of these storms eventually recurves out to sea without affecting any land areas. It is possible to have a very active hurricane season and have all (or nearly all) of the storms miss land!

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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1416. reeldrlaura
1:03 PM GMT on August 22, 2006
pondscum appears to be aptly named....
Member Since: December 31, 1969 Posts: Comments:
1415. fla1963
1:01 PM GMT on August 22, 2006
PondScumEsq at 8:59 AM EDT on August 22, 2006.
I GET DRUNK WITH JEFF MASTERS. HE ALWAYS TRIES TO GET ME TO SHOOT UP CRAZY JUNK. HE TAUGHT ME HOW TO USE COLD WATER EXTRACTION TO GET PURE CODEINE OUT OF TYLONEL 3 SO WE COULD SHOOT IT.

ONE TIME HE TOLD ME HE KILLED JONBENET RAMSEY.

Somebody please tell him to get a life! NOT HERE
Member Since: December 31, 1969 Posts: Comments:
1413. MahFL
12:57 PM GMT on August 22, 2006
Looks like TD4 went WSW on the last few frames from EUMETSAT........
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1412. cajunkid
12:54 PM GMT on August 22, 2006
GulfScotsman, I tor the spec's butt up at the Cameron jetties last Wed Thurs and Fri. Green water and live finger mullet are a good combination for a STAR tourney size spec! Just wish I could catch one @ 8lbs
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1411. guygee
12:53 PM GMT on August 22, 2006
Posted By: GulfScotsman at 12:49 PM GMT on August 22, 2006.
Posted By: guygee at 7:47 AM CDT on August 22, 2006.
Posted By: GulfScotsman at 12:20 PM GMT on August 22, 2006.
...from hell's heart, I stab at thee...for hate's sake, I spit my last breath...at thee..."

Actually isn't that a quote by Gregory Peck from that movie, Moby Dick? ;)

of course..

All Star Trek great quotes are shaekespeer or Melvile

True Scotsman, LOL. Sheakespeare, Melville or "Klatoon from the Orionoids" (they alway threw in a third bard from the future).
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1410. Cavin Rawlins
12:53 PM GMT on August 22, 2006
Taz, maybe,

These EPAC storms this year are really good for studing, not one affected land.
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1409. Tazmanian
12:53 PM GMT on August 22, 2006
weather456 is that a pin hole eye
pin hole eye
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1407. thelmores
12:52 PM GMT on August 22, 2006
new blog up.....
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1406. SWLAStormFanatic
12:52 PM GMT on August 22, 2006
new blog up
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1405. jandree22
12:52 PM GMT on August 22, 2006
and thanks ricderr... I understand that fully, too.
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1404. StoryOfTheHurricane
12:52 PM GMT on August 22, 2006
somebody needs to be allowed authority to remove people like pondscum
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1402. Cavin Rawlins
12:51 PM GMT on August 22, 2006
Ioke T Number is 1.5+2+0.75=4.25

Ileana T Number is 1.5+2+0.75=4.25
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1401. Tazmanian
12:51 PM GMT on August 22, 2006
Weather456 tell me is that a pin hole eye it looks like one
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1400. StoryOfTheHurricane
12:50 PM GMT on August 22, 2006
everybody spam the SCUM SUCKING JOKE off the board please
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1398. jandree22
12:49 PM GMT on August 22, 2006
I was asking simple question about the track of the storm. Thanks for going out of your way to be rude, Randrewl... speaks highly of your character.

StoryOfTheHurricane, thanks for your answer, that's all I was looking for.
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1397. ricderr
12:49 PM GMT on August 22, 2006
jandree....if someone gave you a direct answer that far out....it would be a pure guess....best answer..is it's not projected to affect key west at this time...note the key words..."at this time".....as far as the keys evacuation plan...they want tourists out 72 hours before landfall...remember..only one lane in and out..and i believe...it's ts or above.....
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1395. nash28
12:49 PM GMT on August 22, 2006
That sucks. Station policy should be to give all possibilities regarding the Bermuda High and not what the Allmighty models spit out every six hours.

All people have to do is use their own eyes and they will see that TD4 track is not quite playing out as the early model runs indicated.
Member Since: December 31, 1969 Posts: Comments:
1392. Cavin Rawlins
12:48 PM GMT on August 22, 2006
Ileana Intensity at 8:00amEDT

Curved Band Pattern/Cloud Pattern
0.3 Spiral - DT 1.5

Shear Pattern
None - 0.00

CDO
-CDO Central Feature

1 degrees latitude- DT 2

-CDO Banding Features

1 degree - DT 0.75

Eye Feature/Pattern
Eye appearing - DT 0.00

Further Considerations (environmental factors)
None

Ioke T Number is 1.5+2+0.75=4.25

4.25 is 76mph, 988mbar MCP/Category One Hurricane (Not official)

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1390. cajunkid
12:48 PM GMT on August 22, 2006
I've been critical of TWC and NHC for being so conservative with past storms, but if they weren't as conservative no one would listen. I still love when I hear someone talk about a storm and what its going to do according to TWC. The piece of mind I have from the knowledge we all gain from this site is priceless thats written in stone.
Member Since: December 31, 1969 Posts: Comments:
1388. vortextrance
12:47 PM GMT on August 22, 2006
It will be interesting to see what the high does. So far the NHC track has been pretty good with the WNW motion. I do think that TD4 might be developing a little slower than anticipated. Evertime it gains some deep convection it goes away pretty quickly. Now there is only moderate convection around the center, so if anything it is weakening some. Would be surprised to see it named before tonight, if the daytime heating can help it build some deeper convection.
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1386. guygee
12:47 PM GMT on August 22, 2006
Posted By: GulfScotsman at 12:20 PM GMT on August 22, 2006.
...from hell's heart, I stab at thee...for hate's sake, I spit my last breath...at thee..."

Actually isn't that a quote by Gregory Peck from that movie, Moby Dick? ;)
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1384. nash28
12:46 PM GMT on August 22, 2006
Stormtoe? That's funny:-)
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1383. StoryOfTheHurricane
12:46 PM GMT on August 22, 2006
it has taken a considerable turn north over the past 6hrs, but is still heading dominantly west
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1382. ricderr
12:45 PM GMT on August 22, 2006
nash...i heard the the local nbc "severe weather expert" out of WPB called td4 "just something to take up time" because of its track and showed it projected course because it was "station policy"
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1381. Tazmanian
12:45 PM GMT on August 22, 2006
so TD for as of now is not a fish storm any more right?
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1377. StoryOfTheHurricane
12:43 PM GMT on August 22, 2006
theres no way it will go south of the south carolina
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1375. ProgressivePulse
12:42 PM GMT on August 22, 2006
Good Read Gulf, thanks!

Morning all!
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1373. jandree22
12:41 PM GMT on August 22, 2006
I'm a noob when tracking these storms and I don't fully understand all the elements in play with how a storm moves. The general consensus here seems to be that the models are wrong and TD-4/Debby will take a more westerly path.

Enter my selfish interests... I'm vacationing in Key West next week. While thankfully it appears that regardless I'll get a few days in before it hits, does anyone think it'll track as far South long enough to have a direct impact on the latter half of my trip? Supposing it'd be a direct shot, anyone know how far in advance of the storm they require visitors to evacuate? Do they generally evacuate if it's still under TS status?

I was initially comfy hearing the forcasts that it'll wrap up back by Bermuda, but now I'm getting a little concerned... thanks.
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1372. Rlennon
12:40 PM GMT on August 22, 2006
Thanks for the answer
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1371. PascMississippi
12:40 PM GMT on August 22, 2006
Is the UKMET a very reliable model? It is the shows a little different track for the TD4.
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1370. reeldrlaura
12:40 PM GMT on August 22, 2006
Mornin gentlemen......how's our fish storm doing this morning?
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1369. StoryOfTheHurricane
12:40 PM GMT on August 22, 2006
let me tell ya how i get my path, i just follow past 12hrs movement until i reach land, its not necessarily what i believe
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1368. nash28
12:38 PM GMT on August 22, 2006
This from Bay News 9 in Tampa. It is so far the ONLY meteorologist locally and nationally that I have seen be objective regarding the high pressure....

According to Bay News 9 Meteorologist Josh Linker, a lot of uncertainty remains with the system. If high pressure builds more in the Atlantic, the system could take a more left turn. If high pressure weakens, the storm could take a right turn. So, obviously this track is not set in stone.
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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