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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guys looking at this map it look like a anti cyclone is forming near ex-TD2

Link
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Good morning stormW! Thanks for the update. Looks like an interesting steering pattern could develop if this thing forms.
Member Since: August 31, 2008 Posts: 0 Comments: 833
I've noticed Home Depot/Lowes have batteries all over the store, I thought about buying some, but was like.....nahhhhhhh
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Good morning, all. Happy Friday. Gonna take a break from storm watching and work later today to go see District 9 with the boy.
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The small area of convection with ex-TD2 has expanded a bit further to the east, and now covers most of the circulation center.
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Given a tight model concensus and a consistent steering pattern, might be a good idea to check out any supplies one may need.
Member Since: August 31, 2008 Posts: 0 Comments: 833
Quoting HurricaneKyle:
This is the second time in 4 years that jeff has had a blog with part of the title 'TD # may rise again', take a guess what that other one was.



KATRINA!!!!!
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Quoting kanc2001:


Hugo?


Shhhh!
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Quoting mobilegirl81:
Whats interesting are that the models are almost overlapping each other.


Tight consensus
Member Since: October 28, 2006 Posts: 57 Comments: 30565
US Virgin Islands better be ready for whatever is coming down the road
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Whats interesting are that the models are almost overlapping each other.
Member Since: August 31, 2008 Posts: 0 Comments: 833
Quoting RitaEvac:


With all do respect to most on the blog the upper air pattern is set up for tropical systems to head for the Gulf


I agree the last few runs have indicated that the Azores/Bermuda high will continue to bridge together continuing 90L system on a general westward coarse. The only fly in the oitment is whether it crosses over some of the Greater Antilles Islands, and hopefully weakens some, or goes south of them into the Caribbean... A Caribbean system route has much higher degree of danger for all in the end...
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Member Since: October 28, 2006 Posts: 57 Comments: 30565
The tropical wave moving north of Cuba is heading for the Gulf and will be increasing moisture in the Gulf
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Quoting hurricanecris:
Good morning

I've been lurking and learning for the past couple of years on this blog, and I don't really post, but I do have a question about 90L. I've seen several comments regarding an anticyclone over 90L but i don't see it on this map.


Is there something that I am missing?


looking at that map no anti cyclone but I just found one forming near ex-TD2 if not on it
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Thanks Dr. Masters. We will keep an eye on it.
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Quoting hurricanecris:
Good morning

I've been lurking and learning for the past couple of years on this blog, and I don't really post, but I do have a question about 90L. I've seen several comments regarding an anticyclone over 90L but i don't see it on this map.


Is there something that I am missing?


Try the 200 mb Vorticity maps... and blue is a clockwise rotation.
Member Since: January 14, 2007 Posts: 17 Comments: 4140
Quoting hurricanecris:
Good morning

I've been lurking and learning for the past couple of years on this blog, and I don't really post, but I do have a question about 90L. I've seen several comments regarding an anticyclone over 90L but i don't see it on this map.


Is there something that I am missing?


You need to look at the "pink or peach" lines... you'll notice little triangles depicting the direction to where the winds are moving towards... so it will give you an indication if there's anticyclonic movement or cyclonic.
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I agree, the high in the western atlantic will act to steer storms into the gulf maybe even across florida into the gulf.
Member Since: August 31, 2008 Posts: 0 Comments: 833
Quoting Drakoen:
Tight consensus on going towards the northern islands or just north of there


Hugo?
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Quoting Drakoen:


ECMWF is too slow


Which may also be the reason it turns it out to sea so quickly... a slower system would allow more time for the TROF to block any USA progress.
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Quoting nfloridandr:
the ecmwf model also has the carribean disturbance and remnant td2 going into the gulf


With all do respect to most on the blog the upper air pattern is set up for tropical systems to head for the Gulf
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Thanks Dr. Masters

A special thanks for the reminder that all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength
We need to get that horse back in front of the cart.

Question for folks in the Caribbean, or Skypony, perhaps (or anyone who might know)
How are the reforestation projects going in Haiti?
What type of trees are being planted?. Something with a deep tap root, perhaps? Certainly they would need to get a good hold on the ground before a storm hit again.
I was thinking that some sort of brush (bushes) etc, would take root quickly and if they had an extensive root system, sop up some of the moisture. They also would not be as top heavy and not such a temptation to cut down for human use.

Inquiring minds want to know! ; )
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56. IKE
Quoting claimsadjuster:
Ike, What is your "gut" feeling as far as 90L? Do you think it will end up in the gulf states?


Too far in advance. I don't know. It could.
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Good morning

I've been lurking and learning for the past couple of years on this blog, and I don't really post, but I do have a question about 90L. I've seen several comments regarding an anticyclone over 90L but i don't see it on this map.


Is there something that I am missing?
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Quoting TampaSpin:
I think it will become TD2 by the end of the DAy Dr. Masters...Shear has been the main culprit the entire time with old TD2. Yes its been in dry and dust air but, Shear has caused it not to get going.

I agree with you I say TD2 by the end of the day prob when the H.H. fly into it they might find some TS wind here and there it wouldn't suprise me
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Quoting TampaSpin:
I think it will become TD2 by the end of the DAy Dr. Masters...Shear has been the main culprit the entire time with old TD2. Yes its been in dry and dust air but, Shear has caused it not to get going.
can u repost the loop from earlier of the big ouchy
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Blog Update
Reflector site for those at work, which includes Weather456, daily update.


TD2

90L

AOI
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting extreme236:


Source of this information is? And if it was illegal why would it be on a website available to the public?


Technically, any images of the Euro model that are not SLP or 500mb heights are illegal...that doesn't mean they aren't out there ;)...doesn't hurt anyone.
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Ike, What is your "gut" feeling as far as 90L? Do you think it will end up in the gulf states?
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Quoting claimsadjuster:
Drak, what is your take on 90L


It has increase it's convection significantly overnight. The upper level easterlies are 10-20knots which is keeping most of the convection on the western side of the system. As it continues to move to the WNW it should find more favorable conditions. Right now I agree witht he GFDL/HWRF track they are very tightly clustered and I still want to lend some credit to the ECMWF and the GFDL and HWRF provide the fastest solution of an ECMWF like track 5 days out. Then we'll be watching to see if the ridge can keep it moving to the WNW. The GFS and UKMET are the southern most solution provided 90L gains less latitude.
Member Since: October 28, 2006 Posts: 57 Comments: 30565
Quoting extreme236:


Source of this information is?

I'm on a really old Windows ME computer, and it uses Windows Explorer instead of Internet Explorer, and it has the description in a panel on the left, and it said it is unlawful to use it otherwise.
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the ecmwf model also has the carribean disturbance and remnant td2 going into the gulf
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46. IKE
Quoting Drakoen:


ECMWF is too slow


I edited my post. Should be between 45-50W by Monday, depending on speed.
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Quoting cg2916:
Hey guys. I know some of you use the ATCF database. I just found out something. It's illegal to use it unless you work for NOAA or the government.


Source of this information is? And if it was illegal why would it be on a website available to the public?
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Is it proper to call 02L a wave when it still has a closed LLC? I'm confused. It seems like remnant low would best describe it without convection. Anyway, I still think this will become Ana before 90L has a chance to get it's considerably more chunky self spinning.
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Thank You for your input Dr. Masters. Next week is going to be a nail biter for many people.
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Alot of things have to happen for the storm to impact the usa. I am giving it about a 60% chance but it really all depends on the strength pf the storm and how far the trough can dig
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TD 2 is definately coming back..
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Hurricane Ike was supposed to go out to sea or threaten Florida, so no experts have a clue what its gonna do.
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This is the second time in 4 years that jeff has had a blog with part of the title 'TD # may rise again', take a guess what that other one was.
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Quoting Funkadelic:
I dont know where canesrule1 is getting a catagory 4 storm coming to SFLA. Now im not down casting but it is likely that 90L will interact with land, and hopefully some tall mountains before it comes in SFLA's "General" direction.

Now keep in mind this is 10-13 days away so anything can happen. When they send a plane in there to gather data in and around 90L, we may see a major model shift. So just be prepared for anything mother nature may throw at you.


That's true. Usually after they fly in to the storm, and particuarly when they fly Gulfstreems around the atmosphere surrounding it, the models will shift.
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Hey guys. I know some of you use the ATCF database. I just found out something. It's illegal to use it unless you work for NOAA or the government.
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Quoting SQUAWK:

How can it become TD2? We already had TD2.


No he is talking about the remnant low of TD 2, he expects it to regenerate itself and become TD 2 once again
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Quoting TampaSpin:
I don't understand something why when NHC takes the Depression lable off a storm is it then not considered an Invest .....Heck its better organized than most Invest that are labeled...


It is still an "invest" just not in the traditional sense. They are still running models and stuff on it as a "LOW"
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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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