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 stormdude77:
What if TD2 develops further, wouldn't that have an impact on 90L?


Still think 90L will ultimately win out, because it has a circulation much larger than TD2.
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Quoting extreme236:


Agreed. Usually it would be renumbered to a TD by now, so probably nothing tonight unless it changes.
but how could it get renumbered if it is already "02L"
This is not good.
Link
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Quoting Stormchaser2007:
New intensity models bring ExTD2 to a strengthening Category 1 hurricane in the very warm Bahamas.



Track.



My concern is if it can become a hurricane and develop an eye, over those warm waters and high TCHP we could see it rapidly intensify. Big IF's but, something to think about.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting Weather456:
90L isnt far from TD status, but probably not 2night
oh trust me it will be upgraded tonight everything is right! i got an unofficial report though from an "anonymous source" that we do have TD2
Quoting hurricane23:
Iam far more impressed at this hr with extd2 then the sheared large octopus behind it.


Tomorrow should be a different story for 90L.
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Quoting hurricane23:
Iam far more impressed at this hr with extd2 then the sheared large octopus behind it.


Ditto here...
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Quoting Weather456:
90L isnt far from TD status, but probably not 2night


Agreed. Usually it would be renumbered to a TD by now, so probably nothing tonight unless it changes.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting SevereHurricane:


I tell that to everyone, and most people Ive talked to think Katrina was the worst case scenario. Boy are they wrong! Not to mention the we have lost plenty of wetlands since Katrina effected the area in 2005. We are becoming more vulnerable each day, and that is the scary part.
It would have been if it were 50 to 100 miles west of where it came ashore. Correct?
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Quoting louisianaboy444:
Was Andrews projected path when it was in the CATL close to where it ended up hitting? Just curious because everyone keeps comparing it to 99L.

99l? I sure hope we don't have 99l already


LOL.. shoot sorry. You know what I mean.. Its been a long day! LOL.
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New intensity models bring ExTD2 to a strengthening Category 1 hurricane in the very warm Bahamas.



Track.

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Quoting hurricane23:
Iam far more impressed at this hr with extd2 then the sheared large octopus behind it.


90L is going to take some time to consolidate, because of its enormous size. When it does, though... o_o
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Quoting CandiBarr:


is that basically right up lake p-train?

Right up Barataria Bay and the counterclockwise winds on a bigger storm fill the lake, stack water to the west, and then slosh it back to the southeast (to the city) as the storm passes. Very much like what happened in Slidell during Kat. No 2-day fill-the-city event...2-hour-fill-the-city.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
No offense to anyone anywhere other than NO, but please please don't let it get hit again. My family literally JUST settled back in about 3 months ago. :(
Please recurve out to sea! I know, I know, too early to tell. It's just hard to see that possibility staring you in your face.
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What if Ex TD2 develops further, wouldn't that have an impact on 90L?
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90L isnt far from TD status, but probably not 2night
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2417. Patrap
Quoting duprk452:


definitely wasn't a fumble!


The Booth Officicial must be at the Bar,an that Game Ref need a Lasix procedure.

Im 4 Miles west here from the Dome and I made a better call,LOL
Member Since: July 3, 2005 Posts: 421 Comments: 127550
Quoting alaina1085:
Was Andrews projected path when it was in the CATL close to where it ended up hitting? Just curious because everyone keeps comparing it to 99L.


Andrew was initially forecast to recurve due to a split in the subtropical ridge to the north caused by an upper-level low. This did not materialize, as the upper vortex was too far north for Andrew to feel it.
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Iam far more impressed at this hr with extd2 then the sheared large octopus behind it.
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Quoting TampaSpin:
A 1 2 punch could very well be coming....DEAD SEASON RIGHT...


The 0-0-0 talk never had even a single percent of merit.
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2413. Skyepony (Mod)
Way off to the NE well away from the convection Gonzo is getting 22 & 25kt at the suface. It may already be tropical storm strength. Even though we just had a quikscat pass that doesn't comferm, it had alot of rain contamination.
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I'm not panicking or even scared yet but the thought of having a possible category 1 one day and then a Category 3+ three days later kinda scares u, and im saying thins right now, I'm not evacuating for whatever comes her to Miami!
the GFS track of invest 90L looks like George'98...here in Puerto Rico we are freaking out!
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I'm with the group who believes ex TD2 is back to TD status. In fact, I believe it's borderline TS strength. I would even go out on a limb and claim that convection-wise, this is the best it has looked. Quik-scat pass did show the circulation a little elongated from NW to SE, though. However, I don't believe it was enough to keep this from being re-classified.

02L Rainbow Loop
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Was Andrews projected path when it was in the CATL close to where it ended up hitting? Just curious because everyone keeps comparing it to 99L.

99l? I sure hope we don't have 99l already
Member Since: August 29, 2006 Posts: 22 Comments: 1342
Quoting mkmand:

Similar track as Gustav of last year. If Gustav was 20 mph stronger and 40 miles more north, it would have been the worst case scenario.

Only thing missing there is the larger radius of TS-force winds to push the water in...Ike's windfield on Gustav's track would have done it.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting extreme236:


It does, doesn't it?


I actually think I have some images from it. I was in Cancun at the time and I remember watching it on vacation.
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Quoting atmoaggie:

No, a Katrina-type passing right about in between Katrina's and Betsy's tracks would be the worstem>


is that basically right up lake p-train?
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Was Andrews projected path when it was in the CATL close to where it ended up hitting? Just curious because everyone keeps comparing it to 99L.
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A 1 2 punch could very well be coming....DEAD SEASON RIGHT...
Member Since: September 2, 2007 Posts: 178 Comments: 20439
2400. Patrap
Quoting atmoaggie:

And you know that worst-case NOLA storm that has been talked about? Katrina wasn't it. A storm making landfall and passing west of NOLA would be it. We'll see what GFS comes up with...hopefully none of that once we get closer.



Kinda funny,or not so funny as we were speaking just this day here, of a Storm they found after the Katrina core samples were taking at the 17th St. Canal..the peat from a Storm Bigger than K they figure,actually was right where the I-wall slid in During Katrina's surge.

A hurricane 400 years ago was partially the blame for the collapse that occurred there.
Uncanny,
The Piling's should have went down 13 ft deeper but a typo in Engineering was well, a bad one.




Member Since: July 3, 2005 Posts: 421 Comments: 127550
Quoting extreme236:
Looks like 90L is continuing to gradually get better organized. Should be a TD by 5am tomorrow if trends continue.


I agree, one burst of DMAX convection, TD by either 5 or 11 a.m. tomorrow.
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if you missed it they were showing model runs on the us impact. The had the GFS (New Orleans), some other model (the East Coast) and the ECMWF, south of Bermuda. Iluustrates the fact we still cant decide on us impact.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Weather456:
turn it on the weather channel

No thanks. I am in a fairly decent mood and just cleaned the food off of the TV I threw at it the last I did that.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting Weather456:
90L has an official track (black line)



Its had an official track since 06Z
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Quoting Stormchaser2007:
90L bears a striking resemblance in appearance to 90L of 2007 which later became Dean.


It does, doesn't it?
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2394. 7544
getting dark purples onsoon td2 now dry ait going south may have a better shot tonight

Link
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Quoting louisianaboy444:
Saints and Weather fan here in Destrehan. I agree about that not being a fumble. It's preseason for officials too. Saints 7 Bengles 0. Also think 90L headed for GOM.

Hey Patrap did you see the out of bounds challenge lol


definitely wasn't a fumble!
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Quoting MississippiWx:


Nope. This is though. Very similar, huh?

18z


Looks like where Gustav made landfall
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90L bears a striking resemblance in appearance to 90L of 2007 which later became Dean.
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Quoting DM21Altestic:
Haha Adrian there is one outlier model taking TD 2 deep into the Caribbean.


Thats the XTRAP...
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting FloridaTigers:


Camille, passing in the same spot Katrina did would be the worst case.

I still think New Orleans is a city people shouldn't repopulate, no offense. Its still a bowl.

No, a Katrina-type passing right about in between Katrina's and Betsy's tracks would be the worst.

Big RMW and big radius of TS-force winds has a lot more to do with the volume of surge into the lake and over levees than a Camille-small storm, regardless of peak wind speed. (Seriously, I have run surge simulations to this effect...is my job).

Should Gustav's track have been Katrina-type storm...and maybe a hair further east...NOLA nomo.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Looks like 90L is continuing to gradually get better organized. Should be a TD by 5am tomorrow if trends continue.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2387. GatorWX
Quoting hurricane23:
Early 0z runs for ex TD2



Maybe a bonnie and charley 1-2 punch???? I think one will become the dominant one and judging by 90's size, you get the point. We'll see though.
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turn it on the weather channel
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting atmoaggie:

And you know that worst-case NOLA storm that has been talked about? Katrina wasn't it. A storm making landfall and passing west of NOLA would be it. We'll see what GFS comes up with...hopefully none of that once we get closer.


I tell that to everyone, and most people Ive talked to think Katrina was the worst case scenario. Boy are they wrong! Not to mention the we have lost plenty of wetlands since Katrina effected the area in 2005. We are becoming more vulnerable each day, and that is the scary part.
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.