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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3784. BenRMac
Hey all, looks like something is finally happening in the Atlantic. This place has become a lot more crowded since I left.
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3782. jipmg
why haven't we gotten satellite updates in the past hour?
3781. Drakoen
Objective Dvorak numbers are near 3.5 We could have Ana soon
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3780. 7544
man did this change in the last 5 hours

ts anyone ?

CI# /Pressure/ Vmax
3.4 / 995.2mb/ 53.0kt
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3779. Patrap
Member Since: July 3, 2005 Posts: 427 Comments: 129457
3777. Skyepony (Mod)
Keeper that Lat you posted. 02L had a pretty good wobble south.

14/2345 UTC 15.2N 44.9W T1.5/1.5 02L
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3776. Drakoen
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What are the chances that we see both storms become hurricanes? Also, what do you guys think about TD 2 moving up the east coast in between a weakness in the ridge, and an approaching trough, and then either the trough misses 90 L, and the ridge builds back in allowing 90 L to enter the gulf; or TD 2 is strong enough to make a considerable weakness in the ridge, and 90 L finds that sweet spot and does a double whammy on the east coast? Not saying this is going to happen. Just asking for your opinions.
Member Since: June 1, 2009 Posts: 0 Comments: 107
NHC didn't mention it, but it still looks to me that the eastern side of TD2 is partially exposed which was its problem a couple of days ago. There still must be some light east shear, but weaker than before. GFS model shows another wave developing off Africa behind 90L in a couple of days and then strengthening and heading into the Caribbean.
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If those Dvorak numbers are correct, TD2 should soon be Ana
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Quoting RainyEyes:
Thanks guys for answering. I am going to try to hang in there until they update...hopefully things won't get as crazy since many ppl have went to bed :-) (other than the obsessive compulsive few that hit refresh every 2 second {me}) HA!


You wait 2 seconds! JK!
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3771. Relix
I think all these systems are gonna stick to the south. Gut feeling? =P
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Thanks guys for answering. I am going to try to hang in there until they update...hopefully things won't get as crazy since many ppl have went to bed :-) (other than the obsessive compulsive few that hit refresh every 2 second {me}) HA!
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Quoting Orcasystems:


Good god.. don't use facts, that just confuses him.


Orca you don't understand facts ......
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Quoting TampaSpin:


I was just getting ready to post the same thing


Just forecast to be a TS right?
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Quoting Drakoen:
Now that 02L is in the picture 90L has a better chance of moving to the WNW taking it over the extreme northern islands or just north of there.


Yes, 90L will either absorb TD2 or follow it closely.
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3766. Drakoen
Quoting Funkadelic:


Is there a chance Florida could see a one... Two punch?? These models are beggining to concern me just a little bit


I can't say but it isn't out of the realm of possibility.
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3765. Walshy
Quoting Drakoen:
Two cyclones:



Just like the EPAC was with Felicia. Weird how tropics transition from one side to the other.
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3763. Drakoen
Two cyclones:
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Quoting FLHurricaneChaser:
Scary for South FL



I was just getting ready to post the same thing
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3760. KEEPEROFTHEGATE (Mod)
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 15 AUG 2009 Time : 034500 UTC
Lat : 14:35:39 N Lon : 45:32:41 W


CI# /Pressure/ Vmax
3.4 / 995.2mb/ 53.0kt


Final T# Adj T# Raw T#
(3hr avg)
3.4 3.4 3.4

Latitude bias adjustment to MSLP : +0.0mb

Center Temp : -57.6C Cloud Region Temp : -44.8C

Scene Type : CURVED BAND with 0.71 ARC in LT GRAY

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : OFF
Rapid Dissipation Flag : OFF

****************************************************


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3759. nash28
I'd say for TD2, FL to the Carolinas need to pay attention.
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I wouldn't expect much rain if any in Central Tx, Txrainstorm
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3757. Walshy
Quoting iceman55:
so from gom to fl need watch out ???



No. Look at the cone, its much larger than that.
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3756. Drakoen
Now that 02L is in the picture 90L has a better chance of moving to the WNW taking it over the extreme northern islands or just north of there.
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3755. Skyepony (Mod)
Thanks weathersp
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3754. JRRP
may be the track of TD2 will shift a bit south
HWRF
Link
Member Since: August 16, 2007 Posts: 0 Comments: 6213
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3751. Walshy
Whats up with these major hurricanes spinning to Hawaii? Must be some nice waves this weekend again.
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3750. Drakoen
HWRF 90L
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Quoting FLHurricaneChaser:
Scary for South FL

alt="">


Hey do you have a link for the run? Thanks :-)

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With that burst remaining consistent over 90L's center, I think its pretty much a lock for TD status by 5am if not sooner. Wind shear is not optimal in the Gulf, but water temps should give future 91L a chance.
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Ok..here we go again.. There was so much traffic on the blog that I want to ask again. Does anyone see any rain for central Texas to help with the drought. No hurricanes, thank you but just rain. It is really bad there. I will take a little weather to give them some water. So many friends are suffering.
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3745. Drakoen
The GFDL and HWRF are further north with 90L like the GFS. We need to watch both systems here in South Florida.
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Will one of these storms become a hurricane ?
A) Both
B) Ana
C) Bill
D) None
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Quoting Drakoen:
NOGAPS 00z takes 02L into south Florida


As...what? Any ideas? At this point I'm relatively cool with anything under a Category 2 (or anything that doesn't force me into a trailer for another year...not that I wasn't grateful to have that trailer from my insurance, but it's not an experience I'd enjoy repeating...saying that with full recognition we had it a lot better than so many others in 2004).
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3742. Drakoen
HWRF has 02L as a strong hurricane in the Bahamas
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3741. nash28
Um, has anyone stopped to realize that the models are still dealing w/ a shallow low pressure system right now w/90L? Until 90L deepens enough to develop a solid core, the models are going to be all over the place. The GFS has bounced around more than a six year old after a sugar rush! Yeah, the ECMWF has stayed "consistent" with its track, but IMHO it is WAAAYYY overdoing the speed (slowness) of the system as well as the strength of the shortwave anticipated to weaken the ridge to pull this system that far N.

Until we get a clear TS out of 90L, anything after day 5 you can pretty much throw out.
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3740. KEEPEROFTHEGATE (Mod)
ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 AM EDT SAT AUG 15 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON RECENTLY-
REGENERATED TROPICAL DEPRESSION TWO...LOCATED ABOUT 1075 MILES EAST
OF THE LEEWARD ISLANDS.

1. SATELLITE IMAGES INDICATE THAT THE AREA OF LOW PRESSURE CENTERED
ABOUT 475 MILES WEST-SOUTHWEST OF THE WESTERNMOST CAPE VERDE
ISLANDS CONTINUES TO BECOME BETTER ORGANIZED...AND A TROPICAL
DEPRESSION MAY BE FORMING. IF CURRENT TRENDS CONTINUE...ADVISORIES
WILL LIKELY BE INITIATED LATER TODAY. THE LOW IS EXPECTED TO MOVE
WESTWARD AT ABOUT 15 MPH. THERE IS A HIGH CHANCE...GREATER THAN 50
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.

2. A TROPICAL WAVE INTERACTING WITH AN UPPER-LEVEL LOW IS PRODUCING
DISORGANIZED CLOUDINESS AND SHOWERS FROM THE WESTERN CARIBBEAN SEA
NORTHWARD ACROSS CUBA AND THE BAHAMAS. THIS ACTIVITY IS EXPECTED TO
SPREAD WEST-NORTHWESTWARD OVER SOUTH FLORIDA...THE FLORIDA KEYS...
AND THE SOUTHEASTERN GULF OF MEXICO DURING THE NEXT COUPLE OF DAYS.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

PUBLIC ADVISORIES ON TROPICAL DEPRESSION TWO ARE ISSUED UNDER WMO
HEADER WTNT32 KNHC AND UNDER AWIPS HEADER MIATCPAT2.
FORECAST/ADVISORIES ON TROPICAL DEPRESSION TWO ARE ISSUED UNDER WMO
HEADER WTNT22 KNHC AND UNDER AWIPS HEADER MIATCMAT2.

$$
FORECASTER BLAKE
NNNN


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When is DMAX for 90L?
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Scary for South FL

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000
ABNT20 KNHC 150535
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 AM EDT SAT AUG 15 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON RECENTLY-
REGENERATED TROPICAL DEPRESSION TWO...LOCATED ABOUT 1075 MILES EAST
OF THE LEEWARD ISLANDS.

SATELLITE IMAGES INDICATE THAT THE AREA OF LOW PRESSURE CENTERED
ABOUT 475 MILES WEST-SOUTHWEST OF THE WESTERNMOST CAPE VERDE
ISLANDS CONTINUES TO BECOME BETTER ORGANIZED...AND A TROPICAL
DEPRESSION MAY BE FORMING. IF CURRENT TRENDS CONTINUE...ADVISORIES
WILL LIKELY BE INITIATED LATER TODAY. THE LOW IS EXPECTED TO MOVE
WESTWARD AT ABOUT 15 MPH. THERE IS A HIGH CHANCE...GREATER THAN 50
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.

A TROPICAL WAVE INTERACTING WITH AN UPPER-LEVEL LOW IS PRODUCING
DISORGANIZED CLOUDINESS AND SHOWERS FROM THE WESTERN CARIBBEAN SEA
NORTHWARD ACROSS CUBA AND THE BAHAMAS. THIS ACTIVITY IS EXPECTED TO
SPREAD WEST-NORTHWESTWARD OVER SOUTH FLORIDA...THE FLORIDA KEYS...
AND THE SOUTHEASTERN GULF OF MEXICO DURING THE NEXT COUPLE OF DAYS.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

PUBLIC ADVISORIES ON TROPICAL DEPRESSION TWO ARE ISSUED UNDER WMO
HEADER WTNT32 KNHC AND UNDER AWIPS HEADER MIATCPAT2.
FORECAST/ADVISORIES ON TROPICAL DEPRESSION TWO ARE ISSUED UNDER WMO
HEADER WTNT22 KNHC AND UNDER AWIPS HEADER MIATCMAT2.

$$
FORECASTER BLAKE
Member Since: Posts: Comments:
SATELLITE IMAGES INDICATE THAT THE AREA OF LOW PRESSURE CENTERED
ABOUT 475 MILES WEST-SOUTHWEST OF THE WESTERNMOST CAPE VERDE
ISLANDS CONTINUES TO BECOME BETTER ORGANIZED...AND A TROPICAL
DEPRESSION MAY BE FORMING. IF CURRENT TRENDS CONTINUE...ADVISORIES
WILL LIKELY BE INITIATED LATER TODAY
. THE LOW IS EXPECTED TO MOVE
WESTWARD AT ABOUT 15 MPH. THERE IS A HIGH CHANCE...GREATER THAN 50
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.
Member Since: Posts: Comments:

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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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