Tropical Depression Four arrives

By: Dr. Jeff Masters , 7:23 PM GMT on August 02, 2010

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Tropical Depression Four has made its debut over the mid-Atlantic Ocean, about 1300 miles east of the Lesser Antilles Islands. TD 4 is a small storm with very limited heavy thunderstorm activity, and is not very impressive at present. Wind shear is a low 5 - 10 knots, sea surface temperatures are at record highs, and the dust and dry air of the Saharan Air Layer (SAL) are far enough to the north of TD 4 to allow further development, though. The main negative for development appears to be the storm's small size, which makes it vulnerable to modest increases in wind shear or dry air entrainment. Satellite imagery shows that TD 4 is gradually developing low-level spiral bands, but the intensity and areal extent of heavy thunderstorms has not increased over the past few hours. Upper-level outflow is not apparent yet.


Figure 1. Afternoon satellite image of TD 4.

Forecast for TD 4
The latest 12Z (8am EDT) models are fairly unified taking TD 4 to the west-northwest at 15 - 20 mph for the next three days. This would bring squalls from the storm's outer rainbands to the northern Lesser Antilles Islands, such as Antigua and Barbuda, by Wednesday afternoon. The center of TD 4 should pass to the northeast of the islands. A more southerly track through Puerto Rico, as predicted by the Canadian model, cannot be ruled out, though. As TD 4 makes its closest approach to the Lesser Antilles on Wednesday night, the storm will begin to encounter strong upper-level westerly winds associated with the counter-clockwise flow of air around an upper-level low pressure system centered between Bermuda and Puerto Rico. The latest SHIPS model forecast predicts that these winds will cause wind shear to rise to the moderate level, 10 - 20 knots, by Tuesday night, and to the high level, 20 - 30 knots, by Wednesday. There is a great deal of dry air associated with the upper level low that should cause problems for TD 4, as well. The high wind shear and dry air should greatly weaken and may destroy TD 4 late this week. NHC is giving TD 4 a 20% chance of attaining hurricane status by 8am EDT on Thursday. I think the storm will probably become Tropical Storm Colin tonight, and peak in strength on Wednesday as a 55 - 65 mph tropical storm. I agree that a 20% chance of it reaching hurricane strength is a reasonable forecast.

A trough of low pressure is expected to move off the U.S. East Coast on Friday, and this trough may be strong enough to recurve TD 4 far enough to the northwest that the storm will threaten Bermuda. The GFDL model predicts TD 4 could pass very near to Bermuda on Saturday. It is uncertain at this time if the trough will be strong enough to recurve TD 4 all the way out to sea early next week, or leave the storm behind to potentially move westward again into the U.S. East Coast. The amount of wind shear that might be present early next week is also highly uncertain.

Next update
I'll have an update Tuesday morning by 8:30 EDT.

Jeff Masters

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2204. PanhandleChuck
1:45 PM GMT on August 06, 2010
Member Since: May 13, 2008 Posts: 0 Comments: 1414
2203. stormpetrol
12:29 PM GMT on August 03, 2010
Good morning, TS Colin imo has been moving due west or a lil n of due west like a bat out of hell for the last 12 hours.
Member Since: April 29, 2007 Posts: 0 Comments: 8010
2202. HurricaneHunterGal
12:20 PM GMT on August 03, 2010
Wave coming off of Africa

Member Since: August 17, 2009 Posts: 0 Comments: 249
2201. cg2916
12:19 PM GMT on August 03, 2010
NEW BLOG!!!
Member Since: December 21, 2007 Posts: 13 Comments: 3046
2200. gulfbreeze
12:19 PM GMT on August 03, 2010
Is DR. Grays new forcast on August 4 ?
Member Since: June 13, 2010 Posts: 0 Comments: 925
2199. cg2916
12:18 PM GMT on August 03, 2010
Morning everyone!

We have Colin! It's now 4-3-1-0 (4 is TDs). Certainly gotten bigger than last night. You need some meat on those bones to get through the dry air.

Also, just about every model from the 6Z run is going for a recurvature. The high is already building over AL and GA (evidence being, this morning in SC, I did see a bird catch fire mid-flight). Miami, what do you think, it seems as though the models are losing it. But we have to remember, they're models.
Member Since: December 21, 2007 Posts: 13 Comments: 3046
2198. Sfloridacat5
12:18 PM GMT on August 03, 2010
Quoting smuldy:
It's been moving west by west west all night, gained less than 1d lat while pushing more than 3d west, yet still tracks are tracks and haven't budged so they see something


Yesterday at 8am the NHC forecast took TD4 to 15 degrees North Latitude, 50 degrees West Latitude.
Now here we are 24 hours later and that's pretty much right where TD4 is located.

Member Since: September 16, 2007 Posts: 0 Comments: 8197
2197. chrisdscane
12:17 PM GMT on August 03, 2010
im not bashing colin im just saying there is no evidence of a llc on satelite i dont we now were the realy center is for all u nkow it could be north of 15w
Member Since: July 21, 2010 Posts: 0 Comments: 1181
2196. BobinTampa
12:17 PM GMT on August 03, 2010
Quoting IKE:
Put it on the Wide ATL view......speed it up a little...(to the small letter "a" on Animation.) Stand back about 3 feet from the computer and you can see it's moving north of west.



I have it going just south of east.....oh wait my monitor is upside down.....ok, that's better. Just north of west.
Member Since: August 14, 2008 Posts: 0 Comments: 544
2195. MiamiHurricanes09
12:17 PM GMT on August 03, 2010
Quoting IKE:
If he bends just a touch more right, he'll miss those northern islands.
He would need to start moving towards the NW now for him to miss the islands. Currently you can't even call his motion WNW, looks like it is is just a tad north of W.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2194. IKE
12:17 PM GMT on August 03, 2010
NEW BLOG!
Member Since: June 9, 2005 Posts: 23 Comments: 37860
2193. CybrTeddy
12:17 PM GMT on August 03, 2010
Good morning everyone!

Tropical Storm Colin


Caribbean AOI that needs to be watched. NHC gives this a 20% chance of development.
Member Since: July 8, 2005 Posts: 259 Comments: 24476
2192. aquak9
12:17 PM GMT on August 03, 2010
YO DRAGONFLY!!

No more Dental Pics!! :)
Member Since: August 13, 2005 Posts: 171 Comments: 26269
2191. AllStar17
12:17 PM GMT on August 03, 2010
NEW BLOG
Member Since: June 29, 2009 Posts: 13 Comments: 5315
2190. aquak9
12:16 PM GMT on August 03, 2010
Stand back about 3 feet from the computer and you can see it's moving north of west.


Dang, Ike...and I thought MY eyes were bad...

Good morning WU-Bloggers. I want a storm about 60 miles offa the coast of Florida, then heading OUT. Not too much to ask.

Much obliged if ya'll could take care of that for me.
Member Since: August 13, 2005 Posts: 171 Comments: 26269
2189. weathermanwannabe
12:15 PM GMT on August 03, 2010
Quoting IKE:
Put it on the Wide ATL view......speed it up a little...(to the small letter "a" on Animation.) Stand back about 3 feet from the computer and you can see it's moving north of west.



That is too complicated....I'll take your word for it Ike.......LOL
Member Since: August 8, 2006 Posts: 0 Comments: 9329
2188. earthlydragonfly
12:15 PM GMT on August 03, 2010
Morning everyone!!
Member Since: July 1, 2005 Posts: 10 Comments: 1683
2186. MiamiHurricanes09
12:14 PM GMT on August 03, 2010
I would say that Colin is moving towards 280˚-285˚ which is just slightly north of west.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2185. IKE
12:14 PM GMT on August 03, 2010
Quoting Snowlover123:


But since you have to take all of those measures, it's moving very slightly north of west, which is what the NHC has for the storm.


Well....it is important which direction he's moving and "all of those measures" took about 2 seconds.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
2183. IKE
12:13 PM GMT on August 03, 2010
If he bends just a touch more right, he'll miss those northern islands.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
2182. wayfaringstranger
12:13 PM GMT on August 03, 2010
Storm- hope all goes well today with your son.

I have a hard time seeing how Colin could move that much of a N NW movement that quickly based on the current projected path.

I am also waiting to see how much he slows down. It will be interesting to see how long he remains in the LLJ and how much more shifting in that subtropical ridge.

What are your thoughts on the sheer forecast?
Member Since: July 12, 2010 Posts: 0 Comments: 235
2181. Snowlover123
12:12 PM GMT on August 03, 2010
Quoting IKE:
Put it on the Wide ATL view......speed it up a little...(to the small letter "a" on Animation.) Stand back about 3 feet from the computer and you can see it's moving north of west.



But since you have to take all of those measures, it's moving very slightly north of west, which is what the NHC has for the storm.
Member Since: April 1, 2010 Posts: 9 Comments: 2699
2180. IKE
12:10 PM GMT on August 03, 2010
Put it on the Wide ATL view......speed it up a little...(to the small letter "a" on Animation.) Stand back about 3 feet from the computer and you can see it's moving north of west.

Member Since: June 9, 2005 Posts: 23 Comments: 37860
2179. pensacolastorm
12:10 PM GMT on August 03, 2010
Is that an ULL over the Cayman Islands or a mid level circulation?
Member Since: July 30, 2006 Posts: 0 Comments: 205
2178. GeoffreyWPB
12:09 PM GMT on August 03, 2010
Member Since: September 10, 2007 Posts: 0 Comments: 11425
2177. Snowlover123
12:08 PM GMT on August 03, 2010
Quoting IKE:
System needs a steroid shot....





It looks much better than some tropical cyclones, and its vorticy has tightened, indicating that it is still organizing.
Member Since: April 1, 2010 Posts: 9 Comments: 2699
2175. MiamiHurricanes09
12:08 PM GMT on August 03, 2010
Quoting P451:
AVN Loop. Seems to have a steady course and no re-curve as of yet. Certain to slip south of the next forecast point.

That, and it is way ahead of timing, that forecast point is for 2PM EDT.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2174. Snowlover123
12:07 PM GMT on August 03, 2010
Quoting P451:
AVN Loop. Seems to have a steady course and no re-curve as of yet. Certain to slip south of the next forecast point.



If this trend continues, then it will impact the US Leeward Islands.
Member Since: April 1, 2010 Posts: 9 Comments: 2699
2173. IKE
12:06 PM GMT on August 03, 2010
System needs a steroid shot....



Member Since: June 9, 2005 Posts: 23 Comments: 37860
2171. stormhank
12:05 PM GMT on August 03, 2010
Quoting StormW:


If it keeps ahead of the forecast, about 5-7 days. If it slows, 7-10 days.







thanks storm, so by Aug 10th onward things should pick up..are you still going with 15 plus named?? Im sticking with 16 named. I also wanted to ask your opinion on if you feel the ridg/ trough setup for this summer, could we have more recurving storms or 2004 tracks?? Thanks
Member Since: September 8, 2005 Posts: 0 Comments: 1386
2170. MiamiHurricanes09
12:04 PM GMT on August 03, 2010
Satellite imagery shows that Colin is evidently better organized than it was last night. Steering layers from CIMSS suggest that Colin should be moving towards the W, however the large weakness to the north may make him move just north of west.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
2169. WarEagle8
12:04 PM GMT on August 03, 2010
Good morning all! The 8A Atl Trop Discussion still shows the 5AM position of TS Colin. Does anyone have the 8AM position? Yes, it appears the storm is moving west, west, west.
Member Since: August 19, 2008 Posts: 0 Comments: 126
2168. psuweathernewbie
12:03 PM GMT on August 03, 2010
Quoting IKE:
SHIPS shear forecastSHEAR (KT) 7 10 11 7 12 13 23 22 27 19 26 18 27
....Colin.

Ending coordinates....31.8N and 69.7W....SHIPS.



It looks like SHIPS is decreasing the forecasted shear for Colin. For those of us in SNE, we need to watch this carefully. Colin could be a hurricane off the US East Coast sometime late this weekend. Again everything needs to go right for a New England landfall, but it needs to be monitored.
2167. WxLogic
12:03 PM GMT on August 03, 2010
Good Morning...

So we have Colin now...
Member Since: August 14, 2008 Posts: 4 Comments: 5029
2166. IKE
12:03 PM GMT on August 03, 2010
Dr. Masters should be updating within a half-hour.

6Z GFDL at 126 hours....

Member Since: June 9, 2005 Posts: 23 Comments: 37860
2164. WeatherMSK
12:02 PM GMT on August 03, 2010
Good Morning Storm. Well it appears our storm is still not on track for an out to sea scenario. The fact that Colin is not rapidly developing represents his westward movement. Just not strong enough to feel the weakness from that upper level low.
Member Since: February 12, 2007 Posts: 0 Comments: 479
2162. Hardcoreweather2010
11:59 AM GMT on August 03, 2010
Quoting gulfbreeze:
Is the wave in the Carb. the one the models had as a hurricane in the Gulf?


Yes it is... Stay Classy WU bloggers :)
Member Since: January 24, 2010 Posts: 0 Comments: 529
2161. gulfbreeze
11:58 AM GMT on August 03, 2010
Is the wave in the Carb. the one the models had as a hurricane in the Gulf?
Member Since: June 13, 2010 Posts: 0 Comments: 925
2160. gulfbreeze
11:56 AM GMT on August 03, 2010
Quoting stormwatcherCI:
8 am TWO

CLOUDINESS...SHOWERS...AND THUNDERSTORMS OVER THE SOUTHEASTERN
CARIBBEAN SEA AND THE ADJACENT LAND AREAS ARE ASSOCIATED WITH A
WESTWARD-MOVING TROPICAL WAVE. THERE ARE CURRENTLY NO SIGNS OF
ORGANIZATION...AND DEVELOPMENT...IF ANY...IS LIKELY TO BE SLOW DUE
TO THE PROXIMITY TO LAND. THERE IS A LOW CHANCE...20 PERCENT...OF
THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

Member Since: June 13, 2010 Posts: 0 Comments: 925
2158. smuldy
11:55 AM GMT on August 03, 2010
Quoting wunderkidcayman:
new steering map is out and even more so west what in the word is going on with the models

by the looks of it TS Colin is the caribbean storm and watching for the past several hours TS Colin has been moving WEST-WEST-WESTWARD

It's been moving west by west west all night, gained less than 1d lat while pushing more than 3d west, yet still tracks are tracks and haven't budged so they see something
Member Since: July 23, 2010 Posts: 0 Comments: 527
2156. IKE
11:55 AM GMT on August 03, 2010
84 hr. 6Z GFDL.....interesting track on the eastern Caribbean wave....

Member Since: June 9, 2005 Posts: 23 Comments: 37860
2154. stormhank
11:54 AM GMT on August 03, 2010
Quoting StormW:
How's everyone this morning?
Morning Storm!! I noticed the MJO is turning back to octant 2 Link when would you predict it to be over our region and start causing atlantic avtivity to start picking up??
Member Since: September 8, 2005 Posts: 0 Comments: 1386

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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.