Tropical Depression Four arrives
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
Reader Comments
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I think I might save this post for the end of the season and re-post it once it's over. For the time being, poofage!
Hey Storm, that other wave is making noise now too, might be a busy week!
Eastern.
Hmmm.. Ignorance or hurricane, ignorance or hurricane..
its TD 4
Yeah, busy couple months lol.
92L soon?
kinda how camelle developed...
Needs to gain latitude. The trof to the NW might help out that problem.
is it showing a closed low?
I know that... Danielle is my name thought you were saying hi to me lol but I know how bad that track is trust me I am on the west coast of fla we dont need oil and NOLA has had enough devestation
That's close to me.
No just a nice tropical wave axis. This isn't really a significant threat until it gets west of 75W.
ok
No model is particularly accurate more than 5 days out. We've known that the wave in the eastern Caribbean has to be watched and this is only the first model run to show development, so for now I would just watch it. And, as I tell everyone who says they're going on a cruise, I'm pretty sure they will keep you out of the way of any tropical mischief....they stay in communication with the weather offices to avoid running into a storm.
Good evening Sir:0)
GFS
the 18z was showing s strong hurricane in the gulf
Floater - Rainbow Color Infrared Loop
Perhaps, looks overdone on the 18z which it tends to do, but the wave that it develops is not without potential.
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