Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT en Agosto 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 Relix:
Worst Case Scenario: PR gets hit by both Ana and Bill. Unlikely and has never happened before but entirely possible. Would be a disaster though.


In 1979 Hurricane David passed 79 nm southwest of PR. Five days later Frederick passed right over the island as a tropical storm. But you're right. It would be a disaster
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Hi!

I'm wondering how NHC can say that ex td2 can become a tropical hurricane in one night but did not put it back TD 2 yet?
Perhaps it's a stupid question but i usually only read you and rarely comment only if needed (tracking St Martin)
thks
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Well that's certainly interesting.. 18Z HWRF, GFDL and GFS now perfectly aligned for a hit on Guadalupe and into the Northeastern Caribbean... Hmm.. I wonder why there is now a leftward track? Is it because of the slower development?

One could think that a CAT 3 or CAT 4 would pull more rightward. I still don't think this will make it to CAT 4 before the Antilles, but stranger things have happened..
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Quoting wunderkidcayman:
GUYS SOON WE WILL HEAR THIS Link


Only if you tune into The Weather Lather. I personally do not watch them anymore...ever.
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2080. jipmg
Quoting wunderkidcayman:
GUYS SOON WE WILL HEAR THIS Link


EPIC WIN wow that music is Freaking amazing
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Quoting Weather456:
A little closer to home, an upper low just south of Cuba continues to help enhance shower activity with the aid of a frontal boundary (west) and a tropical wave (east). Something may try to develop out of the mess but it will take some time, if so. regardless of development, tropical moisture expected for the Bahamas, Cuba and the SE USA thru the weekend



Woohoo! Rain!!

Its very cloudy out in S. Florida.
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Hey guys do you guys think that TD2 could become a hurricane possibly affeting the Bahamas/Florida?
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Quoting jipmg:


I think it might be rapidly intensifying based on whats going on with the convection, its spinning wayyy faster than it was 8 hours ago when it was barely there.

Can anyone give me some model runs on TD 2


I believe so. Given that it disintegrated quickly like someone had said earlier it can easily strengthen quickly as well. Small LLC.
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A little closer to home, an upper low just south of Cuba continues to help enhance shower activity with the aid of a frontal boundary (west) and a tropical wave (east). Something may try to develop out of the mess but it will take some time, if so. regardless of development, tropical moisture expected for the Bahamas, Cuba and the SE USA thru the weekend

Member Since: Julio 24, 2005 Posts: 407 Comments: 19076
OOO thanks 456 i see!!
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GUYS SOON WE WILL HEAR THIS Link
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Fellow South Floridians and our friends in the Bahamas should still keep a close eye on (ex)TD 2:

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((( Zoo ))) Evenin! I think this'll drive you crazy whether you're home or not :P
Member Since: Septiembre 25, 2007 Posts: 53 Comments: 8533
We will probably have a TD tonight and another TD in the morning, and looks like Florida is in danger! Let's wait and see.
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Hey Taz, good to hear from you its been a while.
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2069. jipmg
Quoting TheDawnAwakening:
Wow now ex TD2 is looking the best it has in its life time. LLC is now under the convection instead of being displaced and appears it has now developed and sustained its convection for a longer period of time. Also what is encouraging for development is the fact that storm activity appears to have a spin to it instead of just blowing off to the northwest.


I think it might be rapidly intensifying based on whats going on with the convection, its spinning wayyy faster than it was 8 hours ago when it was barely there.

Can anyone give me some model runs on TD 2
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I think that 0-0-0 count's going to change very shortly
Member Since: Septiembre 25, 2007 Posts: 53 Comments: 8533
Quoting zoomiami:
Never again: (I have such a hard time with your name!)

When do they expect these storms to be a problem for so fla, if they are a problem? Based on my reading it should be about 8-10 days.

I'm going out of town for the week, this is going to make me crazy.


Nrt is fine. Your timing is about right for 90L if it would be a problem. TD2 could be an issue Thu-Fri.

Didn't you have the same issue last year, up at your daughters when a storm threatened?
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Quoting Relix:
Worst Case Scenario: PR gets hit by both Ana and Bill. Unlikely and has never happened before but entirely possible. Would be a disaster though.
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Hope to see you around ((( Ann ))) ... Look at my blog...my rescue from the shelter :)
Member Since: Septiembre 25, 2007 Posts: 53 Comments: 8533
Wow now ex TD2 is looking the best it has in its life time. LLC is now under the convection instead of being displaced and appears it has now developed and sustained its convection for a longer period of time. Also what is encouraging for development is the fact that storm activity appears to have a spin to it instead of just blowing off to the northwest.
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Quoting CandiBarr:


noob question.. what does that mean?


dvorak is a technique to estimate the intensity of a tropical cyclone using patterns seen on satellite imagery. each system is rated from "too weak" (0) to 1.0 to 8.0.

1.5 is 29 mph

You can see the full chart here
and here is realtime dvorak info.
Member Since: Julio 24, 2005 Posts: 407 Comments: 19076
2061. Grothar
TO: SavannahStorm

Saw your post on the intensity of the two models. Are these models reliable? One would hope they are just worst case scenarios. Thank you again for your responses.
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Watching the ensembles and both days the 12z and 18z kept switching back and forth. I expect the 00z to once again so a bunch of solutions pushing 90L south of FL. Seems the 18Z runs are the ones that point east coast.
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Blog Update
Reflector site for those at work, which includes Weather456, daily update.


TD2

90L

AOI

AOI
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Never again: (I have such a hard time with your name!)

When do they expect these storms to be a problem for so fla, if they are a problem? Based on my reading it should be about 8-10 days.

I'm going out of town for the week, this is going to make me crazy.
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2057. JRRP
well.... the carnival continue
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2056. IMA
{{{Pat & Teresa}}} Still hopin' to see y'all again in October!

Baja, it's like "old home week", huh? The closer it gets, the more trolls we'll have but the more "oldies but goodies", too. lol

Have to run for a bit to pick up a crate for a doggy transport I'm driving Sunday.
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Thanks, nrt!! And good to see you, btw
Member Since: Septiembre 25, 2007 Posts: 53 Comments: 8533
One of our local mets in Lafayette led me to believe the GOM situation would just be a lot of rain for the Gulf Coast later this weekend into next week. But, with the temps high and SST's low, isn't it fairly easy for an ULL to become a low level circulation?
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Quoting Tazmanian:



thats old info waiting on the new info wish sould be out soon


yea its a bit old
Member Since: Julio 24, 2005 Posts: 407 Comments: 19076
Quoting BajaALemt:
Is the dropsonde data input in the 18z? Or not until the 0z? Anyone know?


00Z run. You can check it at http://www.nco.ncep.noaa.gov/pmb/nwprod/realtime/gfs/t00z/index.shtml. It will be under dropw.
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2050. 7544
some one will be in the bulls eye for these two
Member Since: Mayo 6, 2007 Posts: 0 Comments: 6872
2049. Patrap
Me too Ike,The NFL calls...!!!!!!!!!!!!!!!!!!
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Quoting Weather456:
90L has a dvorak of 1.5



noob question.. what does that mean?
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Lord Have mercy, I live right at the center

Member Since: Julio 24, 2005 Posts: 407 Comments: 19076
2045. IKE
I'll be back after supper.

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Was the dropsonde data input in the 18z? Or not until the 0z? Anyone know?
Member Since: Septiembre 25, 2007 Posts: 53 Comments: 8533
Quoting Weather456:
90L has a dvorak of 1.5




thats old info waiting on the new info wish sould be out soon
Member Since: Mayo 21, 2006 Posts: 5091 Comments: 115359
What's worrying is that 18Z HWRF with a CAT 4 shifted a little south and now south of PR moving WNW!
I DO NOT think this will hit CAt 4 before the islands - think it will be lot weaker and henve may even be futher south - through the Lesser Antilles perhaps!!?
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2040. Grothar
TO: SavannahStorm

I must have missed your comment. Thank you for the information. You made it very clear and concise. It is most helpful. I do not want to repeat this all the time but English is not my first language. It is quite disconcerting not be able to always pose a question in the manner in which it is intended. I hope you understand my English and please feel free to correct me, especially in the field of weather with which I am not familiar with the terminology.
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90L has a dvorak of 1.5

Member Since: Julio 24, 2005 Posts: 407 Comments: 19076
2038. Patrap
Quoting IKE:


Both in the Caribbean...SE of PR. 90L looks like a huge problem ahead.


Sure dont like to see that trend flattening out Ike,the Nose of that High is going to be someone's friend,and someone's worst enemy as usual downstream.
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Can I have the link to the GFDL 18Z run?

TIA
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I'll check back later. I'm going to go down and see what our local mets have to say about it on the tropical update.
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Quoting IKE:


I think it may speed up from 15 mph.


Oh...did I leave that out! :)
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Quoting IKE:


Both in the Caribbean...SE of PR. 90L looks like a huge problem ahead.


4-8 more model runs, much better idea for the Carribean.
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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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