Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. Water vapor imagery shows that since 90L is forming several hundred miles south of the dry air of the Saharan Air Layer (SAL), the storm should not be affected by dry air and dust as much as Tropical Depression Two was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


Figure 1. The remnants of Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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Quoting extreme236:
Convection trying to cover the center of Ana in the 13:45 Navy image.


13:45

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Becuz of continuity, they will likely keep Ana a TS.
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Quoting WeatherStudent:


Dying is more like it. Anyways, all of my attention is now solemnly focused on TD3.
STOP IT!!!!! Listen to me i just heard on my local news here that we could possibility have a Cat 2, on Thursday early morning.
Quoting Nolehead:
kman...morning...what is you synopsis for this blob fixing to enter the GOM?? not much clutter about it...hell i don't even think S Lions mentioned anything about it in his 30 sec of air time they give him...


Good morning. Sorry, but what blob are you referring to ?. All I see is Westward moving rain showers from a TWave.
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Quoting Drakoen:
Both these systems could be an east coast threat



Totally agree. Something has got to come to break the ridge, if nothing comes they will all follow the mean flow and the wave just entering the gulf.
Quoting Weather456:
While unlikely, forecaster Accuweather.com said, by early next week there could be as many as three active named systems in the Atlantic basin - Ana, Bill and Claudette.


Yeah, they're predicting Claudette to be the next African wave comin' off in 48 hours.

The "real" Claudette may wind up being 1st in line of the three. We'll see...Claudette...Camille....hmmmmmmmmmmmmmmm.
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Quoting BenBIogger:


Well, scratch the east coast.
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4976. Drakoen
Navy has 03L
Member Since: October 28, 2006 Posts: 57 Comments: 30562
Quoting Weather456:


very true becuz they should realise, we only need 1 more storm for it tobe right.


Exactly.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
4973. gator23
Quoting WeatherStudent:


Dying is more like it. Anyways, all of my attention is now solemnly focused on TD3.

why? development is not forecasted. And you live in S. Florida, its passing you by
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Quoting extreme236:


I dont think its that unlikely, their just covering themselves in case their wrong.


very true becuz they should realise, we only need 1 more storm for it tobe right.
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Quoting mobilegirl81:

Yea, and has alot of hot water to traverse. Hot enough that in the past things have morphed out there.


I think most people I know are out of sight out of mind on this hurricane season so far. That kind of quick development would throw them for a loop in a hurry.
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Quoting gator23:

Is Ana what used to be TD2?
Yes.
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15/1145 UTC 11.4N 33.5W T2.5/2.5 90L
15/1145 UTC 14.3N 47.2W T2.0/2.5 ANA
4967. Drakoen
Ana's center is exposed for the time being until that trough gets further away
Member Since: October 28, 2006 Posts: 57 Comments: 30562
As a resident of Mobile, the welcome mat is NOT out for Ana, Bill or anybody else this year!..lol
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Convection trying to cover the center of Ana in the 13:45 Navy image.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting cycloone:
is Ana weakening??
no it seems to be strengthening.
Quoting TaminFLA:
Would someone mind posting the navy site....THANKS!


you owe me
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Quoting mobilegirl81:

Yea, and has alot of hot water to traverse. Hot enough that in the past things have morphed out there.


wheres it supposed to go, were supposed to get alot of rain here in NOLA from it i know that
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Quoting Weather456:
While unlikely, forecaster Accuweather.com said, by early next week there could be as many as three active named systems in the Atlantic basin - Ana, Bill and Claudette.


I dont think its that unlikely, their just covering themselves in case their wrong.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
kman...morning...what is you synopsis for this blob fixing to enter the GOM?? not much clutter about it...hell i don't even think S Lions mentioned anything about it in his 30 sec of air time they give him...
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4958. Skyepony (Mod)
Quoting jpsb:
That blob about to enter the GoM was/is a tropical wave correct? It appears to have spin (link a hour or so ago) and it appears to be gaining a lot of energy (link a few minutes ago) I for one think that blob deserves a little attention from the experts here. It is after all entering the very warm, stable GoM. And there are lots of folks going to be very upset if a hurricane pops up unexpectedly in the Gulf.


I've harp on about this wave for days & been watching the surface obs since it made it to the islands.. This morning for a couple of hours the west wind that has on & off slowly moved across Cuba showed up on the west end. Low trying~ centered I'd guess around just west of La Habana, which is a little west of where most the models 00Z run have it stepping off cuba. I suspect, small & weak, if at all. Several models run it up the west side of FL, I'll say it may stay farther out in gulf after watching surface obs a few hours this morning which could allow it to be stronger. Shear has become favorable. Land seems the only inhibiter now.
Member Since: August 10, 2005 Posts: 174 Comments: 38163
Quoting cycloone:
is Ana weakening??


Too early to tell.

Right now the center is exposed. We'll see what happens.
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Quoting BiloxiGirl:
That keys blob is kind of freakin' me out.


Dont freak out.. your prps should be ready this time of year already.

Just keep an eye on it. Likely will be a heavy thunderstorm event.
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Quoting canesrule1:
I was watching the TWC, and they said "South Florida is in great danger of another Hurricane", im like WTF? lol


TWC is the awry of tropical weather information.
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Quoting gator23:

Is Ana what used to be TD2?

Yes.
Member Since: August 9, 2009 Posts: 10 Comments: 5026
Im here a lot of people asking that if Ana comes toward SFLA 03L will follow after it, is this possible???
While unlikely, forecaster Accuweather.com said, by early next week there could be as many as three active named systems in the Atlantic basin - Ana, Bill and Claudette.
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Quoting kmanislander:


You need to read my post again. The NHC will decide at 11 whether it warrants maintaining the TS classification or whether a downgrade to TD may be on the cards then or later today.

That was the point I was making.


With the track pointing towards the US, they'll be reluctant to downgrade it right after it's named.
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Quoting ALCoastGambler:
May be right but I'm a watch and see kind of guy. if not I would have to get my prozak refilled if I followed some of the people here.


WORD
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Quoting lawntonlookers:


IT LOOKS LIKE SOMETHING TO KEEP AN EYE ONThat is what my thoughts are. It lookslike it is starting to show some rotation. Quickscat didn't go over that area this morning. Also Key West doesn't have anything mentioned about this except thunder storms.
Here is the key West forecast discussion.....AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS
NATIONAL WEATHER SERVICE KEY WEST FL
948 AM EDT SAT AUG 15 2009

.DISCUSSION...
.CURRENTLY...
THE NORTHERN PORTION OF A TROPICAL WAVE EXTENDING FROM THE FLORIDA
STRAITS INTO THE CARIBBEAN IS CURRENTLY MOVING WESTWARD THROUGH THE
FLORIDA STRAITS AND IS BEGINNING TO IMPACT THE MIDDLE AND UPPER
KEYS...AND WILL IMPACT THE LOWER KEYS WITHING THE NEXT FEW HOURS. A
CONVECTIVE MASS IN THE STRAITS EAST OF THE KEYS IS EVIDENT ON KBYX
RADAR...WITH A BROAD MID LEVEL CIRCULATION DETECTABLE FROM AROUND
10KFT THROUGH 25KFT. THE APPROXIMATE MAXIMUM OF THE CIRCULATION IS
AROUND 700MB...AND THERE IS ALSO A WEAK CIRCULATION DETECTED FROM
AROUND 5KFT TO THE SURFACE.
SURFACE WINDS AT ISLAND STATIONS ALONG
THE KEYS HAVE BEEN MORE OF LESS SOUTHEAST FROM 5 TO 10 KNOTS OVER THE
PAST FEW HOURS...WITH CMAN STATIONS ALONG THE REEF A COUPLE OF KNOTS
BELOW 10 KNOTS WITH GUSTS NEAR 15 KNOTS. MOLASSES REEF...WHICH IS
NEAREST THE CONVECTION...HAS REGISTERED THE HIGHEST WINDS THUS FAR
WITH SUSTAINED WINDS OF 16 KNOTS AND GUSTS OF 18 KNOTS.
Link
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Would someone mind posting the navy site....THANKS!
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Quoting BiloxiGirl:
That keys blob is kind of freakin' me out.

Yea, and has alot of hot water to traverse. Hot enough that in the past things have morphed out there.
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Quoting HurricaneKyle:


Actually both came out as 2.5
T2.5/2.5
Ana came out as 2.0 from the TAFB.


No?

DVTS, CI, , 1170N, 3290W, , 3, 30, 2, TAFB,

Ana was 2.5 from both.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
4945. sngalla
Quoting zoomiami:
Everyone in the areas that COULD be affected needs to make sure they have their hurricane supplies and plans in effect. If even if they don't pan out coming your way, its better to be prepared.

I respect Kman's opinion, he's been right on a lot of storms, but Andrew was written off as dead and going out to sea, and Katrina was "just a tropical storm" before it came ashore. The very warm waters off the Bahamas and South Florida can cause unexpected intensifying, and needs to be watched.


You are 100% correct.
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is Ana weakening??
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4943. amd
last night, i thought that shear will keep both 02L and 90L in check.

Now, we have Ana, and Bill could possibly be here at 11 a.m. (if not, definitely TD3).

So, anyone here have any crow recipes for breakfast
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Quoting CycloneOz:
Okay then, let's examine what's in favor of the GoM wave developing:

1) Where are the eddy loops right now in the GoM? Is the wave going to pass over the top of one? Does it even need an eddy loop? Geez, the SSTs are red hot right now!

2) Track. Doesn't the track of this wave take it into the heart of the GoM? Isn't this the 40th Anniversary week of Camille...so a strong Cat storm is possible in the GoM this time of year, right?

3) Lack of inhibiting conditions. There is absolutely nothing having a negative impact on this wave! If there is, show it please!!!

Thank you for your analysis. I've been watching wave for hours with regard to its effect on south Florida which now just appears to be rain. (Just was in it) This wave appears to be organizing and drifting into the Gulf, and that's not good for quite a few folks.
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03L

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4940. Drakoen
Both these systems could be an east coast threat
Member Since: October 28, 2006 Posts: 57 Comments: 30562
Quoting mobilegirl81:

Good moring, looks like we are going to get tropical appetizers with the wave in the gulf this weekend and no fishing.
May be right but I'm a watch and see kind of guy. if not I would have to get my prozak refilled if I followed some of the people here.
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Quoting Drakoen:
I think 03L should go straight to Bill.
I agree!!!
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4935. gator23
Quoting mobilegirl81:

Good moring, looks like we are going to get tropical appetizers with the wave in the gulf this weekend and no fishing.

Is Ana what used to be TD2?
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Quoting WeatherStudent:


KMan said it, so it'll happen, OK?


You need to read my post again. The NHC will decide at 11 whether it warrants maintaining the TS classification or whether a downgrade to TD may be on the cards then or later today.

That was the point I was making.
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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.