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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That would put the center to the north of the convection now...
Ok fess up how did you get an hour old ASCAT?? I can never get ones less than about 6-8 usually 10 hours old
On another note..ANITA last year..same scenario and forcast to go north of us on about the same track..ended up dying to our south...
Bill behind it suddenly develops from a robust wave and goes North of us..kind of Deja vue like..
I suspect the COC has moved to the deep convection looking at ASCAT. Thinks we might have Colin by 5 am.
With the vort as stacked as it is, I doubt it opened up. More than likely, it is just a partial ASCAT pass.
Jason....... give it a rest! LOL
Lets hope so!! Just depends what we have as it moves just North of the Islands. I have a large sharks teeth collection as well:-)
Now you're talking.
Well if Anita passed by you you must live somewhere in the South Atlantic LOL! XD
The A 2009 North Atlantic storm was Ana and here you go: Link it only shows the ascending pass but it updates quicker than the other one.
We also have a new GFS...lets see what happens in the morning..
JMO
I would put more curve in your cone.
Your cone starts off with o4 heading WNW.
still don't think it will curve like that miami. I just don't see a strong enough trough. If i were to make a track which I won't. It would be identical to cmc
We need quickscat, half of a system just isn't good enough, quickscat almost always got the entire system -.-
I miss that satellite!
Twas a Quint,Jaws Google un.
I know what they are picking up on, I think the models are being a little aggressive as far as the northward pull.
what do you do with all the sharks teeth you collect?
No.
he could be a military clock tho
it is definitely not an open circulation. ASCAT hints that center is under big burst of convection
I agree.
they sit in brandy snifters, spaghetti jars, you name it. Got thousands.
wow thats really cool
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