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 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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2033. IKE
Quoting Weather456:


very excellent point, notice the trend

slow=pull north
fast=more westward

near 60W by wendesday


Seems to be trending toward the fast side.
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from this point on guys what all becare full on what we post and how we say thing



the baning starts when we have are 1st name storm


the Admins will be out watching the overe the blog do dont get out of line all
Member Since: May 21, 2006 Posts: 5091 Comments: 115362
2031. IKE
Quoting CycloneOz:


Unless it starts slowing down between now and then...


I think it may speed up from 15 mph.
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2029. jipmg
Quoting Tazmanian:
where would TD 2 be going???


models suggest north of islands, into bahamas, and a possible WNW or NW track after that
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(((( Ann ))) I am WONDERFUL, lady! It's soooo good to see you!!! A little activity brings us all back in *smiles*
Member Since: September 25, 2007 Posts: 53 Comments: 8533
2027. IKE
Quoting nrtiwlnvragn:


18Z HWRF

HOUR: 126.0 LONG: -63.10 LAT: 16.90 MIN PRESS (hPa): 929.00 MAX SURF WIND (KNOTS): 102.00


18Z GFDL

HOUR:126.0 LONG: -64.24 LAT: 16.98 MIN PRESS (hPa): 960.93 MAX SURF WIND (KNOTS): 99.34


Both in the Caribbean...SE of PR. 90L looks like a huge problem ahead.
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2026. Patrap
Hiya (((IMA)) Teresa says Hello too...
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Quoting Grothar:
TO: Weather456 or Tazmanian

Grothar here! You have been of assistance to me before. Do either of you know what the projection is on the building high pressure which should be over both systems? Would this not have a great effect on the path of the systems? The models which I have seen on this site, would indicate a very westerly motion. Unless I have missed it, there is not much mention of it. I would appreciate your assistance.


the high over 90L or north of 90L

If you mean upper anticyclone over 90L, it is forecast to be there but have little influence of steering of a system.

If you mean north of 90L, I can tell you a ridge remains in place to the north for atleast 5 days. beyond 5 days become problematic.
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Quoting KerryInNOLA:
Well said. This wave could even dissipate or turn to sea. I would like to see the current % odds of a strike for each city along the Gulf and East Coasts. Anybody have a link?


Link
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Quoting Patrap:


Bears watching, as anything can Happen with the SSt's and things can and do usually change fast in these situ's.Monitor the NHC and your Local NWS for anything that changes


Thanks for the input was wondering the same!
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Quoting CycloneOz:


Unless it starts slowing down between now and then...


which is precisely what strong systems usually do...
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2020. IMA
{{{{{{{{{{Baja!!!!}}}}}}}} How the heck are ya, my friend??
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2019. Patrap
Quoting Tazmanian:



now now pat i dony want to see you get ban aret you forget the Admins will be out in full fullfores and baning now that we are in a active period of hurricane season


OK Taz..I'll be careful,Thanks
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Well said, Ann
Member Since: September 25, 2007 Posts: 53 Comments: 8533
where would TD 2 be going???
Member Since: May 21, 2006 Posts: 5091 Comments: 115362
2016. ackee
2pm update by NHC will be intresting the race is on between 90L and XTD#2 who will be Ana first ?
Member Since: July 15, 2008 Posts: 0 Comments: 1376
So both 18Z GFDL and HWRF moved south than their previous runs...correct?
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I'm heading down to Punta Gorda tomorrow where Charley made landfall 5 years ago yesterday.
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2013. IMA
1916. cjswilmingtoneye Good points. I always worry that there are people who will read the "absolutely no threat"-type postings and, because they inform themselves no further, take things too lightly. Sadly, there are people (even with internet connections) who do not inform or prepare themselves properly. We saw so much of that in the days leading up to Ike's landfall that it was hard to believe they weren't trolls.

Even after my post #1922, I felt like I should've added "the 'no threat' is sarcasm". lol

Speculation is absolutely fine, that's a huge part of what this blog is all about; however, stating things in absolutes at this point or, as we learned with Ike, any point, is irresponsible & ridiculous. Ignore those who offer guarantees, they should be disregarded. Those who say, "I think", "In my opinion", "Looks like", "I believe", those people are much more likely to not cause people to panic or become complacent.
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2012. Patrap
18Z GFS


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Quoting stormpetrol:
I think the NHC will probably go straight to Ana with former TD2.


:/

seeing how fast it disintegrated it's last big convective outburst...
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With this many circles on the map, I'm getting out my troll spray :)
Member Since: September 25, 2007 Posts: 53 Comments: 8533
Quoting IKE:
TD2 is moving at 12-15 mph now.

90L is moving at 15 mph now. With a movement of 15 mph, you can throw out the 12Z ECMWF run. It shows it just beyond 40W on Monday at 12z...way too slow.

It'll be near 50W by Monday afternoon.


very excellent point, notice the trend

slow=pull north
fast=more westward

near 60W by wendesday
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Quoting RyanFSU:
HWRF 18Z, same as GFDL 12Z






925 mb?? That's a Cat. 4 / borderline Cat. 5!
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2007. jipmg
Quoting serialteg:


just like it got very un-impressive at an extremely high rate... lol


yea, wind shear can destroy a small system easily (look at tropical storm chris in 06)
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Quoting IKE:
TD2 is moving at 12-15 mph now.

90L is moving at 15 mph now. With a movement of 15 mph, you can throw out the 12Z ECMWF run. It shows it just beyond 40W on Monday at 12z...way too slow.

It'll be near 50W by Monday afternoon.


Unless it starts slowing down between now and then...
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Quoting Patrap:
"Hebert in a Box"





now now pat i dony want to see you get ban aret you forget the Admins will be out in full fullfores and baning now that we are in a active period of hurricane season
Member Since: May 21, 2006 Posts: 5091 Comments: 115362
Quoting KerryInNOLA:
Well said. This wave could even dissipate or turn to sea. I would like to see the current % odds of a strike for each city along the Gulf and East Coasts. Anybody have a link?


I don't think that number is issued yet this early in the game.
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Quoting IKE:
TD2 is moving at 12-15 mph now.

90L is moving at 15 mph now. With a movement of 15 mph, you can throw out the 12Z ECMWF run. It shows it just beyond 40W on Monday at 12z...way too slow.

It'll be near 50W by Monday afternoon.


It's a race against time.
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90L now expected to become a TD later 2night or satruday
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Quoting ackee:
who will ba ANA first


I vote for the one that becomes a tropical depression first.
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1998. IKE
TD2 is moving at 12-15 mph now.

90L is moving at 15 mph now. With a movement of 15 mph, you can throw out the 12Z ECMWF run. It shows it just beyond 40W on Monday at 12z...way too slow.

It'll be near 50W by Monday afternoon.
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Just looking at the nhc update - I think this falls under the category of watch what you wish for!
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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.


fail

dont do that >:|
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1995. RyanFSU
HWRF 18Z, same as GFDL 12Z


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1994. Grothar
TO: Weather456 or Tazmanian

Grothar here! You have been of assistance to me before. Do either of you know what the projection is on the building high pressure which should be over both systems? Would this not have a great effect on the path of the systems? The models which I have seen on this site, would indicate a very westerly motion. Unless I have missed it, there is not much mention of it. I would appreciate your assistance.
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I noticed the NHC said 02L could become a "tropical cyclone" tonight, rather than a "tropical depression"...maybe just a preference thing or maybe it could become either a TD or a TS.
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I must compliment the blog tonight. Things are much more civil around here. The purge of viruses from the site has settled us down.
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Quoting Tazmanian:


wish storm???


Sorry, 90L
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I think the NHC will probably go straight to Ana with former TD2.
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Our local tv mets are loving this...stay tuned!
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1988. Patrap
Hurricane Preparation Entry
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In my opinion, through the language the NHc decided to use and through the latest satellite imagery and data, it would not be surprising to see the former tropical depression regain tropical depression status and to see Invest 90L become Tropical Depression 3 at 11pm tonight. They both have a well-defined low level structure and have adequate convection to gain such classification.
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1986. ackee
Quoting wunderkidcayman:

TWO REDS
who will ba ANA first
Member Since: July 15, 2008 Posts: 0 Comments: 1376
Quoting nrtiwlnvragn:


18Z HWRF

HOUR: 126.0 LONG: -63.10 LAT: 16.90 MIN PRESS (hPa): 929.00 MAX SURF WIND (KNOTS): 102.00


18Z GFDL

HOUR:126.0 LONG: -64.24 LAT: 16.98 MIN PRESS (hPa): 960.93 MAX SURF WIND (KNOTS): 99.34


wish storm???
Member Since: May 21, 2006 Posts: 5091 Comments: 115362
Ex-TD2 had some really well stacked vorticity from 850-500mb early this morning that was barely visible at 200mb....I'm not surprised by the new reports at all *shrugs*
Member Since: September 25, 2007 Posts: 53 Comments: 8533

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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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