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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Ex TD2 is starting to be affected by the ULL to the N that is digging down on top of it. From the WV loop you can see the moisture being pulled off to the NNE by the flow around the base of the ULL and there is NE wind flow in the path of the feature as a result that will also likely create some SW shear faily soon.

The combination of this and the dry air appears to be playing havoc with every comeback attempt by the system.

WV Loop
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Quoting WeatherStudent:


Not both of them, Drak. Obviously.


I'd have to agree that 90L is kinda fooling us, looks good convectively but the center is to the east. Give it till tomorrow morning and I think we'll have our TD.
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Quoting Twinkster:


there is no dry air near 90L

http://www.ssd.noaa.gov/goes/east/catl/wv-l.jpg


Dry air doesn't have to be organge to be dry air.
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Quoting Chiggy007:
NHC hasn't upgraded 90L cos it no where near TD status...some time to go...broad circulation!!


Because of the center being to the east of the convection is why, not because its broad. Also T#'s aren't high enough for em.
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Quoting Drakoen:
Both systems are unimpressive though I like 02Ls tight circulation. 90L's low is completely exposed and continues to undergo shear and dry air.


Not both of them, Drak. Obviously.
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SHIPs has 15kts of easterly shear over 90L, forecast to drop to 10 in a couple hours (CIMSS shear shows this evolving in fact) and below 5 in about 12 hours.
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Quoting jeffs713:

In that perspective, it looks like former TD2 is pulling away from 90L, and putting some distance between them, to allow for more development.


Yeah. It's certainly possible for TD2 just to split off in the faster flow completely and leave 90L behind...

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1527. Patrap
Storm Relative 16km Geostationary Water Vapor Imagery
Time of Latest Image: 200908141815



Storm Relative 1km Geostationary Visible Imagery

The current suite of geostationary satellites provides visible imagery during daylight hours at higher resolution than many of the infrared channels. Such imagery is useful, especially when animated, for position estimation and monitoring the degree of convective organization. The native visible imagery has been remapped to a one-km Mercator projection and the digital data has been stretched over its full range - allowing a more esthetically pleasing appearance. The center location is based on the last operational position estimate and the previous 12-hr motion.
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Quoting jipmg:
why hasn't the NHC upgraded 90L to TD 3?


Does not warrent it yet.
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18Z surface map, expects SW WSW motion with 90L

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NHC hasn't upgraded 90L cos it no where near TD status...some time to go...broad circulation!!
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Quoting Drakoen:
Both systems are unimpressive though I like 02Ls tight circulation. 90L's low is completely exposed and continues to undergo shear and dry air.


there is no dry air near 90L

http://www.ssd.noaa.gov/goes/east/catl/wv-l.jpg
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Quoting Patrap:
90L Multiplatform Satellite Surface Wind Analysis,1800 UTC






Looks like it is trying to consolidate its circulation, and the winds immediately to the west of the COC are stronger than they were on the last one you posted.
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Quoting Drakoen:
Both systems are unimpressive though I like 02Ls tight circulation. 90L's low is completely exposed and continues to undergo shear and dry air.


? It isn't exposed on the last shots I saw...sun just set over the storm tho, we're stuck with IR for now.
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Quoting jipmg:
why hasn't the NHC upgraded 90L to TD 3?


Read Drakes comment right above your post. It has an exposed low.
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Quoting jipmg:
why hasn't the NHC upgraded 90L to TD 3?


This:

Quoting Drakoen:
Both systems are unimpressive though I like 02Ls tight circulation. 90L's low is completely exposed and continues to undergo shear and dry air.
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1518. ackee
90L looks is the centre under all convection are is SE of the convection ?
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Quoting jeffs713:

In that perspective, it looks like former TD2 is pulling away from 90L, and putting some distance between them, to allow for more development.


Ex-TD2 is pulling away a little bit. And there is still some slight easterly shear affecting the system and really, 90L isn't really influencing TD2 anymore. They are both far enough apart.

DMAX will be important for ex-TD2 tonight.
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1516. jipmg
why hasn't the NHC upgraded 90L to TD 3?
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1515. Drakoen
Both systems are unimpressive though I like 02Ls tight circulation. 90L's low is completely exposed and continues to undergo shear and dry air.
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Still waiting for Ana. It's been several years since it has been this late in the season without a named storm. I'm thinking 90l will be Ana by Sunday. TD tomorrow. Any thoughts?
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1513. Patrap

LOL for what I highlighted in bold. I should be careful though... my g/f might hurt me for that comment (she is from NOLA)

Your pick in Women is much better than your NFL Pick,,LOL
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90L

Storm information valid as of: Friday, August 14, 2009 18:00 Z
Coordinates: 12.5N 28.8W (View Map or View Storm Centered Satellite Image)
Location: 392 miles (631 km) to the WSW (245) from Praia, Cape Verde
Distance Calculator: How far away is this storm from me?
Pressure (MSLP): 1007 mb (29.74 inHg | 1007 hPa)
Sustained wind speed (1 min. avg.): 25 knots (29 mph | 13 m/s)

We should have 03L at 8
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Quoting Drakoen:


He is telekinetic with Mother Nature. Only person that would give him a baby...



LMAO, Drak. Evening, Ike and Keeps
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i think we will have 03L when we all wake up tomorrow.
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WPB, That's why it is likely 0L2 will not become a depression until sunday.
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Quoting OSUWXGUY:
I knew old TD2 and 90L couldn't play nicely together for too long...

90L is back stealing moisture and disrupting the inflow/convergence on the southeast side of former TD2. It also appears to be stretching TD2's circulation a bit longitudinally.

There is also some dry air being pulled in towards the east just south of TD2.



In that perspective, it looks like former TD2 is pulling away from 90L, and putting some distance between them, to allow for more development.
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1506. Xandtar
I'll be battening down the hatches in Dominica, especially if that far southern track is where 90 goes. If it runs the passage between Dominica and Guadeloupe its going to be very ugly on both islands.

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1505. JLPR
Quoting jurakantaino:
JlPR The TWC just mention us, saying that the island specially Puerto Rico should be on the look for the CV Systems...


lol Im doing that xD
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90L looking impressive while 02L is not:
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1503. KEEPEROFTHEGATE (Mod)
Quoting Drakoen:
90L still looks like an overgrown beast on the latest vorticity maps.
the fact of its size may have something to do with the prize
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Quoting canesrule1:
not looking to bad, just is affecting shear.


New avatar...cool, or am I lost. The Atlantic Basin is ripe as well as the Gulf. I'm looking at some models now.
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Quoting OSUWXGUY:
I knew old TD2 and 90L couldn't play nicely together for too long...

90L is back stealing moisture and disrupting the inflow/convergence on the southeast side of former TD2. It also appears to be stretching TD2's circulation a bit longitudinally.

There is also some dry air being pulled in towards the east just south of TD2.




Explains why the NHC didn't reinstate it at 5pm.
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Cheers, y'all. :)
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JlPR The TWC just mention us, saying that the island specially Puerto Rico should be on the look for the CV Systems. next week..
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1498. KEEPEROFTHEGATE (Mod)
Quoting WeatherStudent:


I agree. God only knows what awaits us next next.
and iam afraid he's going to have nothing to do with it yer all on yer own
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Quoting IKE:


He lives in south Florida and that's where the GFS takes it...wishcaster...


I know that, I was just curious if he could back it up with anything.
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1496. Drakoen
90L still looks like an overgrown beast on the latest vorticity maps.
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I knew old TD2 and 90L couldn't play nicely together for too long...

90L is back stealing moisture and disrupting the inflow/convergence on the southeast side of former TD2. It also appears to be stretching TD2's circulation a bit longitudinally.

There is also some dry air being pulled in towards the east just south of TD2.


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Or maybe his uncle living on the Dry Tortugas knows this.
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Offshore Waters Forecast

.SYNOPSIS...TROPICAL WAVE ALONG 79W MOVING W ABOUT 20 KT WILL
MOVE W OF THE AREA SUN. A REMNANT LOW...FORMERLY TROPICAL
DEPRESSION TWO...IS FORECAST TO TRACK IN A W TO NW DIRECTION
ACROSS THE TROPICAL N ATLC LATE SUN AND MON AS A POSSIBLE
TROPICAL CYCLONE...THEN APPROACH THE FAR SE PORTION OF THE
SW N ATLC LATE MON AND TRACK THROUGH THE SOUTHERN BAHAMAS
TUE AND WED.


Link
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1492. KEEPEROFTHEGATE (Mod)
Quoting jasoniscoolman10:


wow hurricane Guillermo winds 100 mph




a beauty and a beast all in one
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Quoting extreme236:


What evidence do you have to prove that?


Easy does it, none of us have proof, just opinions.
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Thanks a lot!
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Quoting FreelanceHistorian:


I tell folks I was abused as a child - I was raised a New Orleans Saints fan.

So what did I do? I grew up and moved to Tampa in 1992!!! (The "Creamsicle"/Culverhouse days)

Weatherwise, I was extremely glad to see that HUGE blob in the Gulf this morning off Tampa moving north instead of east!


LOL for what I highlighted in bold. I should be careful though... my g/f might hurt me for that comment (she is from NOLA).

Of course, I am a Houston Texans fan, so...

Anyway, on the topic of the tropics, in one way, I am glad to see the blob moving away from FL, but at the same time, I don't want it sitting over the 30C water in the GOM.
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Quoting canesrule1:
not looking to bad, just is affected shear.
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Gallup
YouGov

All the polls you'd ever need.

Knock yourself out...
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Quoting extreme236:


What evidence do you have to prove that?


The..."It takes it over my house, therefore its right."
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Quoting StormSurgeon:
Poll this.



At. Loop
not looking to bad, just is affecting shear.
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Quoting extreme236:


What evidence do you have to prove that?


Because its JFV, come on!!! shame you didn't know already :P.
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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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