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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Quoting help4u:
This season is going to be the biggest bust in history nothing out there till at least the middle of august!lol!

We haven't even hit the peak yet. I wouldn't consider this season a bust until the end...
But with so many factors lined up, I highly doubt it will be a bust. It might not be as big as they are forecasting, but I doubt it will be a bust.
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Bike ride time.....then Baseball game....not fighting kids!
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Quoting jasoncoolman2010xx:
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

wow wind shear 30 knots will destroy tropical depression four..that is way to high.
You have posted your theory about 200 times. You may be right. But there's no need to post it every few minutes.
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Quoting StSimonsIslandGAGuy:
And from the Charleston wx discussion this afternoon:

NOTE...THERE IS STILL A LOT OF UNCERTAINTY REGARDING THE TRACK AND
STRENGTH OF TROPICAL DEPRESSION FOUR IN THE EAST-CENTRAL ATLANTIC.
IT CURRENTLY APPEARS THAT VERY LITTLE...IF ANY...IMPACTS WILL BE
FELT ACROSS SE SC/GA.



WTF kind of prediction is that?
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Quoting TampaSpin:


Even METS on tv use that term......it won't go away!


As mom used to say "just because billy jumped off the bridge... does not mean you have to also"
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Quoting mynameispaul:


Fish storms are a good thing.


Not saying they aren't (as long as no places out there are affected). Just curious if we should expect that kind of track pattern again....
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Quoting LariAnn:
mcluvincane,

only as "dumb" as those who are also sure it will be a landfalling hurricane . . . If no one is allowed to express their opinion without being called "dumb", then what is this blog for?


Please ignore the ignorant...and ignorable.
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TD4 goes north of islands, and future storm behind it goes for the straight shot through the Central Carribbean. Anybody else buying into this?
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Quoting Orcasystems:
Ok.. the use of the word "Fish" is really starting to peeve me.

I understand that a lot of the tracks do not go over or near the CONUS. But, like a lot of the people on the Islands and sailors at Sea.. I like to think we are just as important as the humans on CONUS, and are basically not considered to be fish.

Find another term... Fish is wrong.


Even METS on tv use that term......it won't go away!
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Where can I get the good MODIS true color images for this storm? Navy/NRL doesn't have what I'm looking for.
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The high has been rather strong this year..If that high builds back in, we could have a betsy track... hope not...
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Quoting TexasHurricane:
I am wondering if this season isn't going to be as active as they have suggested. I'm not saying we won't have an active year (I am not a met, and I have no idea) but, it seems we are still dealing with shear and dry air. Is this suppose to be changing and will it be like last year where we will have a lot of "fish" storms? Just curious...


Fish storms are a good thing.
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This season is going to be the biggest bust in history nothing out there till at least the middle of august!lol!
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"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."
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ATLANTIC REQUIREMENTS
1. TROPICAL DEPRRESSION FOUR
FLIGHT ONE -- TEAL 70
A. 04/1200,1800Z
B. AFXXX 0104A CYCLONE
C. 04/1000Z
D. 18.4N 57.4W
E. 04/1130Z TO 04/1800Z
F. SFC TO 15,000 FT


That will get some info if they dont cancel
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Quoting BrandiQ:
Not sure if anyone saw this on the last blog...

I have a question, why is the CMC so different forecasting wise vs the GFS and the other forecasting models which call for TD4 to curve to the north much earlier and sharper then what the CMC calls for?
Each model runs a different set of assumptions and assigns different priorities to the literally thousands (millions maybe?) of variables that go into predicting track and strength.
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May be active coming up, but I think experts figured we would have more than 2 name storms by now.
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Quoting jasoncoolman2010xx:
if this tropical depression four get Wind shear is will be a wave soon. good call JeffMasters we are both right about this tropical depression four..i say the same thing this morning..i bet you in the next 48 hours it will be a tropical wave again..

You may very well be right.
But a little Humility is a good thing too.
That means you should try and put some evidence with your forecasts, and if they pan-out you should try to avoid saying "I told you so" in a way that gets people vexed.
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Fairly good conconsus i would say until the end, then doubt sets in some.
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Quoting RitaEvac:
how many names systems were in August of 05?


5 systems in August 2005.
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Ok.. the use of the word "Fish" is really starting to peeve me.

I understand that a lot of the tracks do not go over or near the CONUS. But, like a lot of the people on the Islands and sailors at Sea.. I like to think we are just as important as the humans on CONUS, and are basically not considered to be fish.

Find another term... Fish is wrong.
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12 named systems
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This storm will continue on a western route and will increase in intensity Puerto Rico is not out of the wood and this storm may not recurve North. Everybody from cuba north to the carolinas should pay attention to this system
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1041. KEEPEROFTHEGATE 7:32 PM GMT on August 02, 2010
Quoting TOMSEFLA:
bill gray update for aug due out on the 4th. will see ifthey drop the # of storms. think they will drop numbers by 30%

KOTG
we will know on wed. or thurs. i think there will be a downward turn in numbers if the euro verifies and nothing till after the 12th or 15th there could be a big drop
Action: Quote | Modify Comment
aboved carried over from last blog

thanks for update doc
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Let's see if that TUTT bustin forecast is right from Bastardi yesterday. TWave is visible to the NNW & N of TD04 approaching the weakness area.

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Quoting BrandiQ:
Not sure if anyone saw this on the last blog...

I have a question, why is the CMC so different forecasting wise vs the GFS and the other forecasting models which call for TD4 to curve to the north much earlier and sharper then what the CMC calls for?


Different data inputs produce different solutions. All the models dont use the same data like upper level conditions to compared to getting data from HH hunters. Also some are dynamic and other are statistical. Different inputs basically.
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how many names systems were in August of 05?
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mcluvincane,

only as "dumb" as those who are also sure it will be a landfalling hurricane . . . If no one is allowed to express their opinion without being called "dumb", then what is this blog for?
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Quoting sammywammybamy:




Sammy you need to use the new links with 04 in them and not 91L
Member Since: January 24, 2010 Posts: 0 Comments: 529
I am wondering if this season isn't going to be as active as they have suggested. I'm not saying we won't have an active year (I am not a met, and I have no idea) but, it seems we are still dealing with shear and dry air. Is this suppose to be changing and will it be like last year where we will have a lot of "fish" storms? Just curious...
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Shear and hot dry air are the key words for this season,9or 10 storms tops for this season.3 canes and no majors.As Dr. Masters said bye,bye td4 or Colin by thursday.
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Dr. Masters sure did not put, his prediction out there for TD4 and rightfully so i guess! Thanks Dr.
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Not sure if anyone saw this on the last blog...

I have a question, why is the CMC so different forecasting wise vs the GFS and the other forecasting models which call for TD4 to curve to the north much earlier and sharper then what the CMC calls for?
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My unprofessional forecast - a fish storm! My personal fascination with tropical storms is how often they fail to behave in the ways that the models predict. Of course, this is a good thing when the models predict the storm making landfall in a populated area.
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Thanks Jeff...
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thanx Doc.
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Thanks Dr M!
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thanks doc
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.