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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Link to Cuban Radar?
Member Since: Posts: Comments:
1233. fmbill
Quoting chevycanes:

guess you guys missed this from the blog discussion.

The ECMWF was by far the most reliable model for forecasting hurricane tracks last year


Commonly...it is rather hard to believe the "outlier". Not that it should be totally disregarded, just somewhat skeptical.
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NOUS42 KNHC 141400
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1000 AM EDT FRI 14 AUGUST 2009
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 15/1100Z TO 16/1100Z AUGUST 2009
TCPOD NUMBER.....09-078

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY: PSBL LOW LEVEL INVEST
FOR 16/1800Z NEAR 17.0N AND 55.0W ON THE REMNANTS
OF TD-02.
3. NOTE: 1- THE G-IV WILL FLY A RESEARCH MISSION AROUND
THE REMNANTS OF TD-02 TODAY DEPARTING TBPB 14/2000Z.
2- BOTH NOAA43 AND G-IV WILL FLY RESEARCH MISSIONS
IN AND AROUND THE REMNANTS OT TD-02 DEPARTING TBPB
15/2000Z.

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.
WVW
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1231. Fshhead
Quoting chevycanes:

guess you guys missed this from the blog discussion.

The ECMWF was by far the most reliable model for forecasting hurricane tracks last year


Whiiiich means absolutely nuthin'!!! LOL
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22N, 79W
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Quoting canesrule1:
agreed.

guess you guys missed this from the blog discussion.

The ECMWF was by far the most reliable model for forecasting hurricane tracks last year
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1228. Patrap
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1227. slavp
Quoting Patrap:
Of more immediate concern,the wave continues wnw towards S Fla and the Keys,then is forecasted to enter the Central Gom this Weekend.



Very much agree
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N49RF Gulfstream IV-SP (Gonzo)

Built for long range, high altitude and a special 30" radar antena.

More Specs can be found here
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Quoting canesrule1:
I hear that a Hurricane Hunter plane is going to investigate 02L at 4PM EST, true or false?


True from what I read about 5 minutes ago here on the blog...never confirmed though. lol
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Quoting WeatherStudent:


Thank you.
your welcome, lol.
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1221. Prgal
We are keeping a close eye here in PR on the systems that are on the way. People are not in panic mode...yet lol. Today I saw people buying things for the storm but I guess most will wait until Sunday or Monday. We will see.
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1220. Drakoen
Quoting nrtiwlnvragn:


Ya, we got 20 more model runs untill it gets in the vicinity of the Leewards.


Exactly.
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Quoting canesrule1:
agreed.


You all do realize just how reliable the Euro is historically, correct? Just cause it's not predicting CAT 5 IN MIAMI!!!!! doesn't mean it's a joke.
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I hear that a Hurricane Hunter plane is going to investigate 02L at 4PM EST, true or false?
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Appearantly 90L sucked up that missing Russian freighter.......

Link
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Quoting Patrap:
Of more immediate concern,the wave continues wnw towards S Fla and the Keys,then is forecasted to enter the Central Gom this Weekend.





Def something to watch. o.o
Member Since: August 2, 2006 Posts: 0 Comments: 1240
1214. Patrap
The G-4 dosent Flu INTO the storm/invest per se,the G-4 High G-4 flyer flys around the Periphery of the System to sample the upper air Pattern to Input into the runs,

The C-130's penetrate at 10k when they can as it gets into range
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Quoting WeatherStudent:


The model is a joke, FM.
agreed.
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Hmm, I thought the ensemble models were more for tracking larger systems like fronts and highs, not necessarily tropical systems.

Have they become more reliable now with tropical systems or something?
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Quoting hahaguy:


They could find clouds LOL.
J/K

sustained winds of 35 mph some 40 there and there
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1209. Fshhead
Quoting Dakster:


I keep thinking that way too... The last place this thing will hit is where the long range models show it...


Afternoon Everyone,
Being in Miami I Know I am rather happy we are in the cross-hairs this far out. I said it many times last year in similar situations that those models will change alot over the coming days.. ;)
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1208. fmbill
Quoting Patrap:


this is the longest I've seen TD2 have continous precipitation
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1207. cg2916
If they find a closed LLC and organized convection during this flight, will they regenerate it, or do research missions do that? Because I'm not sure if research missions regenerate it or if they need an actual mission.
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Quoting Wariac:
Looks like I may need to start checking my hurricane check list. I hope people in PR start paying attention to this.


Yes, I hope so too. I asked a friend that works at Costco and he says there's people already buying flashlights, batteries and the sort. Guess it's gonna be hell to go to any of those stores this weekend.
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1204. Patrap
Of more immediate concern,the wave continues wnw towards S Fla and the Keys,then is forecasted to enter the Central Gom this Weekend.



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What type of system does GFS show in GOM?
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1201. hahaguy
Quoting louisianaboy444:
Do you think anything surprising can happen when they fly into ex-td2


They could find clouds LOL.
J/K
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I hope NHC is right about the area in the gulf having a low threat for developement.
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1198. Prgal
Quoting Wariac:
Looks like I may need to start checking my hurricane check list. I hope people in PR start paying attention to this.

We are!
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Do you think anything surprising can happen when they fly into ex-td2
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Quoting Patrap:
Getting plenty of Pings with my Firewall and Blocker protection last 5

Nothing is hitting here, but the corporate firewall and my no-ad subscription may be helping with that.
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12Z ECMWF shows 02L over Florida

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1193. Wariac
Looks like I may need to start checking my hurricane check list. I hope people in PR start paying attention to this.
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1192. Patrap
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gfs is still showing gom
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1189. cg2916
I'm back. Was scanning with Webroot, Windows Defender, and installing AVG just in case.
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1188. Patrap
Getting plenty of Pings with my Firewall and Blocker protection last 5
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By the way, it's 1930z now, so they'd leave in half an hour.
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Quoting BobinTampa:


amen. in Tampa, the safest place to be is in the center of the Cone of Uncertainty 5 days out.
Thats why I am not to worried about 90l
1185. WxLogic
Quoting weathersp:


We got the G-IV jet going out in about an hour and half.. Hopefulle we get some good sondes..


Sure thing... it will help these models get more accurate on the track to the Leeward Islands.
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(ex) TD 2 is looking much better and is wrapping around nicely, we may have a regeneration on hand.
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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.

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