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 SeniorPoppy:
It's sad that people wish for storms to be in a certain area. The last thing anyone needs is a tropical cyclone barreling through. Ask someone in Taiwan. 80 inches of rain came down locally in some spots over 3-4 days.


Could you please point out the certain posts that say 'I hope this hits me' compared to 'I think that TD3 and Ana are a significant threat to the US IMO'.
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Quoting WPBHurricane05:
12Z GFS shows Bill hitting S. Florida in 204 hours.
can u give me the link please.
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So there may be a chance yet for my Nassau trip. What a mess it might be in Nassau as they are holding Miss Universe there for the next week. Alot of visitors etc...
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Quoting FLHurricaneChaser:
Why isn't WeatherStudent banned yet? He is clearly a troll, and his constant one letter posts and smileys clog up the blog.


he's been banned...several times...created a new handle and circumvented it...
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Any thoughts on the newly swirling area in the central Gulf? Is that a ULL?
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Quoting StormW:


I usually don't...but I promised the Commander at USCG Maintenance and Logistics Command and Atlantic Area a full update...but, not only that, I have no problem keeping all my fellow bloggers and private clients updated at times like this.
A truly good man, and we thank you.
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12Z GFS shows Bill hitting S. Florida in 204 hours.
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5626. alcomat
Quoting TexasHurricane:
yeah, that GOM water is saying come to momma.....
yeah there were a couple of spots se of matagorda bay by about 200 miles that had 90 and 91 degree water temps.. amazing! all that energy just waiting for something to come along...
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Quoting sarahjola:
there is a small spin in the gom right under ala/fla. i went on wdsu.com on their interactive radar. it looks like there may be a spin and i am wondering if that could possible form into anything or is it too close to land for that?
Link

There is support in this morning's 12Z Canadian GEM regional (15 km) model for the development of a system this weekend that travels up the west side of FLA and landfalls SW of Tallahassee tomorrow afternoon.

It doesn't have a lot of time...
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Quoting FLHurricaneChaser:
Why isn't WeatherStudent banned yet? He is clearly a troll, and his constant one letter posts and smileys clog up the blog.


I second the motion...
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Quoting FLHurricaneChaser:
Why isn't WeatherStudent banned yet? He is clearly a troll, and his constant one letter posts and smileys clog up the blog.


you put him on ignore.. that is what I have done for past 3 years even under his other handle...



I think TD3 looks darn good.. cannot believe it is not a TS Bill yet.
Member Since: August 29, 2005 Posts: 294 Comments: 40839
Quoting StormW:


I usually don't...but I promised the Commander at USCG Maintenance and Logistics Command and Atlantic Area a full update...but, not only that, I have no problem keeping all my fellow bloggers and private clients updated at times like this.

Thanks stormW. Its' getting busy.
Member Since: August 31, 2008 Posts: 0 Comments: 833
5608. atmoaggie 4:04 PM GMT on August 15, 2009

Interesting. Thanks.
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Does anyone have info and what the conditions in the gomex will be like in 7-10 days?
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Artist's impression of a black hole gobbling up a nearby star. A bit like Ana and TD3, really.

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It's sad that people wish for storms to be in a certain area. The last thing anyone needs is a tropical cyclone barreling through. Ask someone in Taiwan. 80 inches of rain came down locally in some spots over 3-4 days.
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Quoting serialteg:


ok so ana is in a 0 shear environment?... i dont get it


I have been posting about the combination of shear and dry air since yesterday. While shear is low right in the immediate area of the storm if you run the WV loop you will see a ULL to the N that has been pulling moisture away from the system since yesterday. It is also imparting light SW shear which, to a weak system like Ana, is enough to peel away the moisture in conjunction with the dry air.

There is a dry slot all the way around from the N to the SE of the circulation that is allowing dry air into the core of the system, further eroding the overall structure. This is evident also from the WV loop. The NHC has stated that the forecast for shear has not been handled well by the models.

I still think that if this trend continues a downgrade may be on the cards for later today or tonight.

Back later.
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Quoting FLHurricaneChaser:
Why isn't WeatherStudent banned yet? He is clearly a troll, and his constant one letter posts and smileys clog up the blog.


If I remember correctly he sent pretty offensive emails out to people in the beginning of the year. He should have been banned then.
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5613. JAC737
Thanks Storm W. As far as thinking a system can't develop close to land, consider Tropical Storm Allison, the only tropical storm name to ever be RETIRED. It developed right off Galveston, then slammed us with so much rain that our highways became rivers. Don't ignore anything as everything is possible. Stay calm. Be prepared.
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Quoting Vortex95:


woah!


Of course, notice the rapid dissipation flag is on.
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Quoting CybrTeddy:
Well.. WS is certainly making his rounds today even though as usual he doesn't have any evidence.
A few days ago he was on his knees praying to the gods and now..

that's why I finally added him to my ignore list
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Scheduled to go to Nassau this Tuesday to Saturday with the family. Seems that will not be happening.
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Quoting P451:
GFS 6Z - 168HR


In line with what wx man and I were talking about last night, seems that the GFS ingests obs and makes troughs (and ridges for that matter) weaker at night and stronger during the day, following diurnal pressure cycles. Might be that the 06, and especially the 12 UTC, GFS runs have a weaker trough and the 18 and 00 have a stronger trough. The effect seems amplified over land...for obvious reasons.
This has also obvious implications on track forecasts days into the future.

For example, the pressure cycles at Lake Murray, SC (inland lake) shows rather broad swings day to day.
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Quoting Orcasystems:


Its a 50/50 split in the groups.

Florida/NOLA
Orca, you forgot TX
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5606. Michfan


And a west they both go.
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5605. Drakoen
Latest TD3 models from 06z:
Member Since: October 28, 2006 Posts: 57 Comments: 29714
Tropical Storm 02L

UW-CIMSS Automated Satellite-Based
Advanced Dvorak Technique (ADT)
Version 7.2
Tropical Cyclone Intensity Estimation Algorithm


Current Intensity Analysis




UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 15 AUG 2009 Time : 144500 UTC
Lat : 14:17:53 N Lon : 48:14:18 W


CI# /Pressure/ Vmax
3.0 /1000.0mb/ 45.0kt


Final T# Adj T# Raw T#
(3hr avg)
2.5 2.1 1.0

Latitude bias adjustment to MSLP : +0.0mb

Center Temp : +11.4C Cloud Region Temp : -13.6C

Scene Type : SHEAR (>1.25^ TO DG)

Positioning Method : FORECAST INTERPOLATION

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

Tno/CI Rules : Constraint Limits : 0.5T/hour
Weakening Flag : ON
Rapid Dissipation Flag : ON
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Why isn't WeatherStudent banned yet? He is clearly a troll, and his constant one letter posts and smileys clog up the blog.
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ANA

TD3
Member Since: October 1, 2007 Posts: 81 Comments: 26493
5601. sfla82
Quoting BiloxiIsle:
I feel better today with the GFS turning TD3 more to the north. Hopefully, it will continue and it turns before anyone can be affected. Didn't like how it kept slapping the central GOM yesterday!


Yeah...TD3 will be a known issue!
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Again the main culprit for ana troubles are dry air.
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Well.. WS is certainly making his rounds today even though as usual he doesn't have any evidence.
A few days ago he was on his knees praying to the gods and now..
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Quoting alcomat:
dont you know that the bloggers on here are always wishing a storm into florida?they do it every season...


Its a 50/50 split in the groups.

Florida/NOLA
Member Since: October 1, 2007 Posts: 81 Comments: 26493
Quoting StormW:


I have about an hour errand to run, then I'll be back to start my analysis, then issue an update. If I'm not disturbed here at home, I should have an update out around 3:00 p.m.

Oh hey StormW, Thought u didnt post or do analysis on weekends, family time.
Thanks for taking time out from your family to do what you do best.
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5596. Drakoen
There are models that predicted WSW movement of TD3 and still take it north of the islands
Member Since: October 28, 2006 Posts: 57 Comments: 29714
5595. Seastep
Quoting ftpiercecane:
Any sign of stormw this morning?


He popped in and then out with a be back in the evening, i think. could have been afternoon.
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Quoting WeatherStudent:
Adrian is just being realistic, unlike the yest of y'all. I give him kudos for that.


It has nothing to do with being realistic,learn how to analyze water vapor loops, shear charts,UL charts etc...
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thanks storm w
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5592. alcomat
Quoting weatherfan92:


I agree. If Ana hits S. FL, it should still move into the Gulf to reorganize.
dont you know that the bloggers on here are always wishing a storm into florida?they do it every season...
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Quoting extreme236:


Hmm can't believe I've waited this long to say this, but time to put ya on ignore. Too much flip flopping around.


TropicalAmanda??????
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ok so ana is in a 0 shear environment?... i dont get it
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.
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Thanks atmoaggie. I would not have thought that the MJO would be effective with a el nino going on. I'm a rookie at this weather stuff. Just trying to put the pieces of the puzzle together.
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there is a small spin in the gom right under ala/fla. i went on wdsu.com on their interactive radar. it looks like there may be a spin and i am wondering if that could possible form into anything or is it too close to land for that? and what about that big area spining and moving s/w in the n. atlantic. won't that prevent the 2 systems from moving north? it looks as though that is making everything else move west and south. thats what it looks like on the water vapor. what do you all think?
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Quoting farhaonhebrew:
is true they will adjust to the left..but tha hurricane will be hit here in Puerto Rico then move to the Carolina's like Hugo'89
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.