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 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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Quoting serialteg:
latest quickscat on 90l



whadya guys think, TD or TS

i see a 40 knot barb, we should have Bill.
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Quoting Drakoen:
I think 03L should go straight to Bill.


I concur.
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Quoting extreme236:
SAB says 03L is Bill, but the TAFB only came out 2.0.


Actually both came out as 2.5
T2.5/2.5
Ana came out as 2.0 from the TAFB.
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Ana still exposed... (yet again)
Member Since: July 12, 2007 Posts: 0 Comments: 5997
Quoting serialteg:
latest quickscat on 90l



whadya guys think, TD or TS


Isn't it already a Tropical Depression?
If not, it should be.
Member Since: August 9, 2009 Posts: 10 Comments: 4903
4928. Drakoen
I think 03L should go straight to Bill.
Member Since: October 28, 2006 Posts: 57 Comments: 29919
Link

This morning's Key West AFD. Interesting discussion on radar presentation of convection associated with the wave entering the GOM.
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You know, you guys can ponder over the models lots and lots...okay.

But where are the forecasters who can talk about something like this GoM blob without the benefit of model support?

Is model support that important to forecasting these days?

I'm old school. I cannot believe that.
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Will Ana open the path for "bill"?
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That keys blob is kind of freakin' me out.
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SAB says 03L is Bill, but the TAFB only came out 2.0.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
latest quickscat on 90l



whadya guys think, TD or TS

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I heard that the pressures are high in the GOM. Could that be why the mets arent too concerned about S of FL. right now?
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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.
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Quoting CycloneOz:


That's what I see...I mentioned shear to be sarcastic. I also mentioned SSTs sarcastically. The GoM is hotter-n-hell right now.

So what is it that makes this wave, that's starting to fire, that's starting to spin, that's moving into a red hot GoM...make it not develop? What?

NO MODEL SUPPORT? You've got to be kidding me!


CMC and GFS pick it up as a smaller disturbance headed toward the panhandle.
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Quoting serialteg:
for all of you model followers

ecmwf 00z
screw models all i need is a moist finger and i know where it's going, LMAO.
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Quoting ALCoastGambler:
Hey there Mobile, I believe the term "love thy neighbor" but all this talk of gulf coast storm and I may have to deport you to FL....LOL

Good moring, looks like we are going to get tropical appetizers with the wave in the gulf this weekend and no fishing.
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hey guys when is recon going out
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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.


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.
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4913. kachina
Quoting leftovers:
last night a pop up showed up on my wifes mac while on wunder weather wanting me to download something i denied it access. no telling what it was. even if you own a mac be careful surfing the net


Oh! That's been happening at work to a lot of people - and they're using PC's. It's a pop up that wants you to "update" your Microsoft virus scan....it even looks like it links to a Microsoft site - but it doesn't. It downloads a nasty little trojan that ultimately causes your computer to crash every time you turn it on. We've been using Malwarebytes to remove it. Malwarebytes has their own website - you can google it or download it from Cnet.
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Blog Update
Reflector site for those at work, which includes Weather456, daily update.


ANA

TD3

AOI

AOI
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4911. divdog
Quoting ajcamsmom2:
The 06 GFS ten Image Loop changes so fast...yesterday, we were going to suffer a direct hit here in SLA, today, it has everything going fishing?????
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Link

Large wave on the African coast is getting ready to exit. This is another one to be watched over the next few days.
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Quoting Stormchaser2007:
We may have Bill soon

15/1145 UTC 11.4N 33.5W T2.5/2.5 90L
We should have Bill.
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for all of you model followers

ecmwf 00z
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4907. Drakoen
Is this the most pages the Blog has ever had lol?
Member Since: October 28, 2006 Posts: 57 Comments: 29919
4906. tea3781
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Models are saying that TS#2 will be affecting the Islands in 42 hours, sooo i expect The Northen and central Antilles to be under a TS watch.
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We may have Bill soon

15/1145 UTC 11.4N 33.5W T2.5/2.5 90L
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Quoting stormsurge39:
MobileGirl Did you see that CMC model that Aussie posted where it maybe looks like Ana gets in the GOM and makes a beeline for central to N gulfcoast?

Yes, its either Ana or her reminants.
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mobilegirl....i'm with ya the last thing we need is a freaking storm...i'll take the surf of course but it can just stop sit and spin...
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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!!!
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4899. kachina
One of the outer bands of that blob that appears to be heading for the GOM just dropped some extremely heavy rain on Ft. Lauderdale within the past hour and then moved on.
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Quoting IpswichWeatherCenter:


Lol, he is waiting till 11 - so we can hit 6000 if we are lucky in the next hour.
LOL
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4897. Drakoen
I see there is TD3 now...
Member Since: October 28, 2006 Posts: 57 Comments: 29919
CLASSIFICATION STORM
15/1200 UTC 10.1N 140.8W T1.0/1.5 09E -- Central Pacific
15/1200 UTC 18.7N 132.5W T5.5/5.5 GUILLERMO -- East Pacific
15/1145 UTC 11.4N 33.5W T2.5/2.5 90L -- Atlantic
15/1145 UTC 14.3N 47.2W T2.0/2.5 ANA -- Atlantic
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4895. Detrina
Um, who let the dogs... err invests..err depressions out?

Sheesh.
Take a nap and the peanut butter hits the fan!
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Quoting WeatherStudent:


KMan said it, so it'll happen, OK?
Just because Kman said doesn't mean it will happen, i know he is an expert and for sure knows what he is saying, there is someone above him, Mother Nature, trust me anything can happen.
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4892. jipmg
Quoting STORMMASTERG:
From what i am seeing ts ana is the storm to watch.As of right now area behind tsana will recurve to sea,thats just based on early models/ensembles.It should feal the weakness.


according to GFS and CMC sure.. but other models say otherwise
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Thanks Dr Jeff :)
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Quoting canesrule1:
almost 5000 post, time for a new blog, jeff, lol.


Lol, he is waiting till 11 - so we can hit 6000 if we are lucky in the next hour.
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Quoting Seastep:


Yes, there is. WU updates automatically from official data feeds.

They just haven't pulled 90L yet... in the data and literally said TD, but there is no such thing as invest03


K thanks for clarifying that
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From what i am seeing ts ana is the storm to watch.As of right now area behind tsana will recurve to sea,thats just based on early models/ensembles.It should feal the weakness.
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Thanks Dr Jeff :)
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Quoting mobilegirl81:
A southerly trajectory will delay an east coast landfall and be more of a florida and gulf coast storm.
I was watching the TWC, and they said "South Florida is in great danger of another Hurricane", im like WTF? lol
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Until something comes along to change the steering flow, all storms will follow the wave entering the Gulf.
Quoting mobilegirl81:
A southerly trajectory will delay an east coast landfall and be more of a florida and gulf coast storm.
Hey there Mobile, I believe the term "love thy neighbor" but all this talk of gulf coast storm and I may have to deport you to FL....LOL

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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.