TD 2 nearly dead; African disturbance 90L gathering strength

By: Dr. Jeff Masters , 2:38 PM GMT on August 13, 2009

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Tropical Depression Two is near death, but is still worth watching. The dry, Saharan air to the north and west of the depression, combined with moderately high levels of wind shear of 15 - 20 knots, have almost completely destroyed all of TD 2's heavy thunderstorms. Satellite loops of the storm show a well-formed circulation, but almost no heavy thunderstorm activity.

Wind shear over TD 2 is expected to remain in the modereate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C three days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to to TD 2's north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that TD 2 will not be able to intensify quickly, and some of the models indicate the TD 2 may get destroyed in the next day or two. However, several models still predict TD 2 will become a tropical storm. The HWRF model predicts TD 2 will become a hurricane five days from now, but this seems unlikely given the dry air and relatively high wind shear affecting the storm.


Figure 1. Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

African tropical wave 90L
A strong tropical wave with a large circulation and plenty of heavy thunderstorm activity is a few hundred miles south of the Cape Verdes Islands, off the coast of Africa. NHC dubbed this disturbance 90L this morning. This morning's QuikSCAT pass shows that 90L has a very large circulation, and top winds of about 30 mph. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are in two major bands, to the north and to the south of the center. There is no heavy thunderstorm activity near the center yet, and this would have to happen before 90L can be named Tropical Depression Three. 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 has been. Wind shear is about 20 knots over 90L, and is forecast to remain in the moderate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days, which are high enough above the 26°C threshold for tropical cyclone formation to allow some slow development to occur. The GFS and ECMWF models continue to predict the development of this wave, though they are now less aggressive about intensifying it than they were in earlier runs. The consensus among the reliable HWRF, GFDL, GFS, and ECMWF models is to bring 90L to point near or just north of the northernmost Lesser Antilles Islands 6 - 8 days from now. The storm could be at hurricane strength by then, as forecast by the SHIPS intensity model.

I'll have an update Friday morning.

Jeff Masters

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Quoting Weather456:


My day been busy and it will get so as 90L evovles.

I'm expecting a TD between Friday and Sunday.
thanks weather i am also monitoring the situation does not look good for the northern leeward islands
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Quoting Seflhurricane:
hey weather how has your day been, around when does it look like 90L will reach TD Status ??


My day been busy and it will get so as 90L evovles.

I'm expecting a TD between Friday and Sunday.

I'm still not 100% impressed with convection.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting louisianaboy444:
downcaster just like taz said

lol you guys are unreal...


They might call you a troll next.
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Also please use the anniversary of Charley to remember how large forecast errors can be detrimental.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
well said...456...i agree
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Quoting Weather456:


true but the decisions between life and death and tropical cyclones are above all of us, both wishcasters, thrillers and downcasters. No matter how much one wishes for something, it is still up to a higher power.
hey weather how has your day been, around when does it look like 90L will reach TD Status ??
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downcaster just like taz said

lol you guys are unreal...
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1677. sky1989
Quoting DM21Altestic:

How is it downcasting to wish a storm to miss the United States and other land masses?


That's what I say.
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Wich ones? Most have it going up east coast now!!!!!!!!!!!!

yeah but i'm hoping and thinking that they are mistiming the trough
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Quoting louisianaboy444:
Well i think that is good news sorry if i upset people in here i'm not a downcaster i'm a nobodylosestheirlifecaster i guess


true but the decisions between life and death and tropical cyclones are above all of us, both wishcasters, thrillers and downcasters. No matter how much one wishes for something, it is still up to a higher power.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting CybrTeddy:


Ignore him, I've had him on my list for awhile.
cyber i have a bunch too but 2 people are particularly a pest
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WS found out that we have a potential TD in the works
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Well i think that is good news sorry if i upset people in here i'm not a downcaster i'm a nobodylosestheirlifecaster i guess
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1668. Skyepony (Mod)

Quoting FLWeatherFreak91:
That really doesn't mean much in this situation because of the terrain. That area of the DR is VERY mountainous, and mountains can easily change their area's surrounding wind vectors.


The barb its from a ship a little off shore & the whole SE side of DR doesn't have any mountains anyhow... Yeah it's only 5 knots but weak west winds shows something is trying to work to the surface. Come..join us slumming buoys, ships & surface observations.
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Quoting DM21Altestic:

TD2 never developed into Ana, n00b.


Ignore him, I've had him on my list for awhile.
Member Since: July 8, 2005 Posts: 259 Comments: 23574
Quoting louisianaboy444:
It is looking more and more likely that this storm will not come near the U.S. with that trough in place....I don't want to put this storm off on Bermuda though.. :(


My check list

A. Scratch out 90L
B. Maybe watch TD2
C. Next system please
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It is looking more and more likely that this storm will not come near the U.S. with that trough in place....I don't want to put this storm off on Bermuda though.. :(
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Slowly but surely former td2 is showing signs of regeneration , looks as though shear might have lighten up a bit ahead of it.
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Quoting louisianaboy444:
Many of the major models are sending 90L out to sea which is very good news we will take breaks as long as mother nature gives them to us...Hopefully it can pass north of the islands so no one will have to feel this system...


Folks the ALL CLEAR has sounded. Lets all go back to being lax just like this season has been.
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Quoting louisianaboy444:
Many of the major models are sending 90L out to sea which is very good news we will take breaks as long as mother nature gives them to us...Hopefully it can pass north of the islands so no one will have to feel this system...



downcaster
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Quoting serialteg:




Hey, what's with that red line? >:(

If I wanted to roost the chickens back at home, I would holler at my dad so that he sees this, and then he'd call the neighbor, and the banter would begin...

"It's gonna cut us in half!"


the red line is the GFS
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting JupiterFL:


Maybe if it gets close enough it will scare your hat back straight.


LOL That's great.

I cant believe the drastic change in the blog...what a difference a few storms make.
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Quoting Vortex95:


They need to scare ppl somehow, the Tropical weather team has had nothing to say since Ike.


Failure to evacuate will cause certain death.
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Quoting Weather456:


it is rather broad but continues to organize. I'm surprise at the red code so earlier but all indications that a TD is forming. T# stands at 1.0, so still has a ways to go.

The 12Z models continue to bring it close to the islands but trending out to sea. becuz 90L circulation is broad, the models will keep changing and we will not get a sound idea until a TD forms or the circulation becomes more defined.





Hey, what's with that red line? >:(

If I wanted to roost the chickens back at home, I would holler at my dad so that he sees this, and then he'd call the neighbor, and the banter would begin...

"It's gonna cut us in half!"
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afternoon KOTG


======================================

Crown weather

Invest 90L has a good potential to eventually become a major hurricane, possibly as early as Monday. The consistency in the model guidance has been remarkable, and in addition, the low latitude track Invest 90L should take will place it in higher sea surface temperatures and not be influenced as much by the dry Saharan Air Layer.

Accuweather:


A large tropical wave just south-southeast of the Cape Verde Islands extending from 17 north and 22 west to 6 north and 19 west. This wave lost most of its convection Wednesday evening, but it still has a chance of becoming a tropical depression over the next 24 to 36 hours as upper-level conditions are favorable for development. Computer models have been picking up on this feature for several days now and strengthen it into a hurricane as it moves westward. This will have to be closely watched over the next several days as it may pass near the Lesser Antilles around the early to middle part of next week. It would likely take until the weekend of Aug. 22 to impact the United States potentially.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
1650. java162
Quoting WPBHurricane05:


that hurricane devastated the island of dominica in 1979. my mom and dad always give stories of how they survived that one.
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1649. rxse7en
Quoting java162:



you are way behind time.....
Or, I just read through the blog.
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Many of the major models are sending 90L out to sea which is very good news we will take breaks as long as mother nature gives them to us...Hopefully it can pass north of the islands so no one will have to feel this system...
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Member Since: July 24, 2005 Posts: 407 Comments: 19076
1645. KEEPEROFTHEGATE (Mod)
Quoting Weather456:
good afternoon to all
afternoon 456
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Member Since: July 31, 2006 Posts: 56 Comments: 8112
Quoting DM21Altestic:


Ouch, looks like 90L is in some trouble...


That shear is falling; an anticyclone is extending southward over 90L, which would protect it from shear and provide ventilation.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
Quoting Vortex95:
Strange that they put it in red with a 1.0. as well as a TFCA, Unless they think this thing is going to explode with convection during the overnight.


Probably been reading this blog too much and persuaded them
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Quoting DM21Altestic:


Ouch, looks like 90L is in some trouble...


Good thing 90L developed an Anti-Cyclone over it to protect from shear.
Member Since: July 8, 2005 Posts: 259 Comments: 23574

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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.