91L near tropical depression status

By: Dr. Jeff Masters , 2:08 PM GMT on August 02, 2010

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A tropical wave near 12N 41W, midway between Africa and the Lesser Antilles Islands, is very close to being a tropical depression. NHC labeled this system Invest 91L yesterday, and is giving it a 90% chance of developing into a tropical depression by 8am Wednesday. Wind shear is a low 5 - 10 knots, sea surface temperatures are at record highs, and the dust and dry air of the Saharan Air Layer (SAL) are far enough to the north of 91L to potentially allow further development. The main negative for development appears to be the storm's small size, which makes it vulnerable to modest increases in wind shear or dry air entrainment. A Windsat pass from 5am EDT this morning did not show a closed circulation. Satellite imagery shows that the intensity and areal extent of 91L's heavy thunderstorms is very limited, but that a closed surface circulation may be close to forming. Low-level spiral bands and upper-level outflow are not apparent yet.


Figure 1. Morning satellite image of Invest 91L.

Forecast for 91L
There is modest model support for 91L developing into a tropical depression. Three out of six of our reliable models for forecasting tropical cyclone genesis predict 91L will develop into a tropical depression by Tuesday or Wednesday. A west-northwest motion at 10 -15 mph is predicted, which should carry 91L a few hundred miles northeast of the northernmost Lesser Antilles Islands. However, it is possible that 91L would track over the northernmost Lesser Antilles Islands, as predicted by the Canadian model. Squalls from the outer rainbands of 91L may affect islands such as Antigua and Barbuda as early as Wednesday afternoon. As 91L makes its closest approach to the Lesser Antilles on Wednesday, the storm will begin to encounter strong upper-level westerly winds associated with the counter-clockwise flow of air around an upper-level low pressure system centered between Bermuda and Puerto Rico. The latest SHIPS model forecast predicts that these winds will cause wind shear to rise to the moderate level, 10 - 20 knots, by Tuesday night, and to the high level, 20 - 30 knots, by Wednesday. There is also a great deal of dry air associated with the upper level low that may cause problems for 91L. The high wind shear and dry air should weaken and possibly destroy 91L late this week.

A trough of low pressure is expected to move off the U.S. East Coast on Friday, and this trough may be strong enough to recurve 91L far enough to the northwest that the storm will threaten Bermuda. The HWRF and ECMWF models predict 91L could pass very near to Bermuda on Saturday. It is uncertain at this time if the trough will be strong enough to recurve 91L all the way out to sea early next week, as predicted by the GFS model, or leave 91L behind to potentially move westward again into the U.S. East Coast, as predicted by the Canadian model. The amount of wind shear that might be present early next week is also highly uncertain.

Cyprus records its hottest temperature in history yesterday
The island of Cyprus recorded its hottest temperature in its history on August 1, 2010 when the mercury hit 46.6°C (115.9°F) at Lefconica. The old record for Cyprus was 44.4°C (111.9°F) at Lefkosia in August 1956. An older record of 46.6°C from July 1888 was reported from Nicosia, but is of questionable reliability.

The year 2010 is now tied with 2007 as the year with the most national extreme heat records--fifteen. There has been one country that has recorded its coldest temperature on record in 2010; see my post last week for a list of the 2010 records. My source for extreme weather records is the excellent book Extreme Weather by Chris Burt. His new updates (not yet published) remove a number of old disputed records. Keep in mind that the matter of determining extreme records is very difficult, and it is often a judgment call as to whether an old record is reliable or not. For example, one of 2007's fifteen extreme hottest temperature records is for the U.S.--the 129°F recorded at Death Valley that year. Most weather record books list 1913 as the year the hottest temperature in the U.S. occurred, when Greenland Ranch in Death Valley hit 134°F. However, as explained in a recent Weatherwise article, that record is questionable, since it occurred during a sandstorm when hot sand may have wedged against the thermometer, artificially inflating the temperature. Mr. Burt's list of 225 countries with extreme heat records includes islands that are not independent countries, such as Puerto Rico and Greenland. Seventy four extreme hottest temperature records have been set in the past ten years (33% of all countries.) For comparison, 14 countries set extreme coldest temperature records over the past ten years (6% of all countries). I thank Mr. Burt and weather record researchers Maximiliano Herrera and Howard Rainford for their assistance identifying this year's new extreme temperature records.

Next update
I'll have an update later today if 91L develops into a TD.

Jeff Masters

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So those that believe the CMC is so correct.....i wonder why the NHC has it so dismissed.....as it does not even put it in the Southern Cone.

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1008. cg2916
Wow, first two comments of this page were ignored.
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1005. cg2916
Quoting StormChaser81:


Here look for yourself...

MODELS


Can't really tell.
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1004. pottery
Quoting Orcasystems:


We are the same... Holiday weekend :)

Nice !!
And about this weather....
This too shall pass.
Better days are coming.
All will be well.
and other inane phrases of dubious comfort and hope.
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Should they begin evacuating the Outer Banks?
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1000. KEEPEROFTHEGATE (Mod)
Quoting pottery:

BAH!!

(in case you wondered, we have a Holiday today. So I can be as obscure as I want all day long. Until a Higher Authority intervenes, that is...)
we have civic holiday today too
Member Since: July 15, 2006 Posts: 175 Comments: 54864
Quoting TexasHurricane:
when does the noaa come out with an update?


5pm EDT or 4pm CST
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Quoting pottery:

BAH!!

(in case you wondered, we have a Holiday today. So I can be as obscure as I want all day long. Until a Higher Authority intervenes, that is...)


We are the same... Holiday weekend :)
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when does the noaa come out with an update?
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Quoting cg2916:
How did the models shift?


Here look for yourself...

MODELS
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Quoting hurricanejunky:


Uh, no...Rubio stickers are akin to nails on a chalkboard...afternoon to you too...haven't seen you on lately...


Ive been around... I saw some Rubio advertisement on your Extreme site....
Member Since: July 1, 2005 Posts: 10 Comments: 1683
How did the models shift?
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Quoting Neapolitan:


Very nicely done! Thanks; bookmarked.


Thanks, Neapolitan! I appreciate it!
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Quoting Orcasystems:


Oh man, that shows Pottery's little shower is just starting... then its going to rain like it means it.

BAH!!

(in case you wondered, we have a Holiday today. So I can be as obscure as I want all day long. Until a Higher Authority intervenes, that is...)
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hey jasoncoolmanx and xx,your circumventing by creating multiple handles is against the rules and you should be perminantly banned imo,plus its just plain wierd....
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Quoting jasoncoolman2010xx:
its still going to be a fish storm.


And your still going to be on my ignore list. =)
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Quoting earthlydragonfly:


R u a Rubio supporter?? I got his sticker on my car!! Go junkie... I mean Junky LOL

Afternoon everyone!!!


Uh, no...Rubio stickers are akin to nails on a chalkboard...afternoon to you too...haven't seen you on lately...
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Quoting WildWillyFL:
Is 95L starting to feed off of the wave behind it? I don't understand the dynamics, but it visually looks like the front edge of the other storm is supplying moister.


Not yet, but there is some interaction happening between them.
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Quoting KEEPEROFTHEGATE:


latest as of 9 minutes ago


Man the Eastern Carib is lighting up like a christmas tree!!!
Member Since: July 1, 2005 Posts: 10 Comments: 1683
Is 95L starting to feed off of the wave behind it? I don't understand the dynamics, but it visually looks like the front edge of the other storm is supplying moister.
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Quoting KEEPEROFTHEGATE:


latest as of 9 minutes ago


Oh man, that shows Pottery's little shower is just starting... then its going to rain like it means it.
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Blend the CMC and the BAMS

SE coast on guard!
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Quoting KEEPEROFTHEGATE:
don't worry he's going to get his in about 3 months and its called winter

Yeah, he gets to dent his Halo on the ice when he tries to come up for air.
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latest as of 9 minutes ago
Member Since: July 15, 2006 Posts: 175 Comments: 54864
Quoting jasoncoolman2010xx:
its still going to be a fish storm.


You speak with a lot of absolutes and have no evidence to back up your claims.
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So, how did the models shift?
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I dont see this as a fish spinner right now, but the intensity gains in the next 48hrs will be critical. A stronger storm will stay further south because it will further split the trough. A weak system tends to get sucked north (I know this is counter to what you would normally think with strong storms moving more poleward). Dry air could be a problem but there is an upper high giving outflow support if it can generate some convection. Key West to the Outer Banks are all fair game at this point so stay tuned and stay informed. I still think the 2pm later model runs will move a lot to the left.

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has anyone thought that the reason for the lack of deep convection is that it is Dmin right now.... just wait till 6-7 PM Eastern time and then the storm will be in the dark and convection may begin to increase
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Quoting pottery:

1.75" so far today.
And still falling.........
I hope you get yours soon.
don't worry he's going to get his in about 3 months and its called winter
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974. JLPR2
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Quoting reedzone:
This is why the CMC made sense this afternoon, and models starting to trend that way.


Please tell us all why you think the CMC make sense since yesterday. Since that is the only model coming into Florida.....you sound like premier Wishcaster if you don't have a good reason!
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972. IKE
12Z ECMWF...eastern ATL view.




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Quoting Drakoen:


I get the feeling they don't sound too happy about the NHC taking the eastern route.


Ya and I can see their point. I think there is only 2-3 long range forecasters at HPC, at least from names I recognize in their discussions. There are about 10 NHC hurricane forecasters, so while HPC and NHC may agree for a few shifts, you get another forecaster come on board at NHC that may have a different forecast and now no longer coordinated between the two agencies.
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Quoting StormChaser81:


Let's not through gas on that fire.

hahahaha!
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Unless TAFB goes with T3.0 it is likely that 04L will stay a tropical depression at 5PM. Reason I say this is because SAB is already at T2.0, if TAFB gives it a T3.0 I would assume that the NHC go down the middle with a "T2.5" which equals to a 35 knot cyclone.
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Quoting Orcasystems:


You said you got 3/4" yesterday... how about today? We are in desperate need of a monsoon here.

1.75" so far today.
And still falling.........
I hope you get yours soon.
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Quoting MississippiWx:
If you look at the low level flow out in front of TD4, it's moving almost due west. Until TD4 strengthens any, don't expect it to gain too much latitude.


I'll be watching. I've been watching TD4 since 8am this morning. Its been on a pretty steady WNW path. I told myself to keep watching TD4 and see if it goes north of the 15 degree north and 50 degree west intersection. That was the forecasted path early this morning (which shows its on a WNW path).
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Naples, Florida
97.5 °F
Scattered Clouds
Humidity: 54%
Dew Point: 78 °F
Wind: Calm
Wind Gust: 0.0 mph
Pressure: 30.00 in (Falling)
Heat Index: 115 °F

At least we have a nice cooling breeze. :-\
Member Since: November 8, 2009 Posts: 4 Comments: 13626
The rest of the 18Z models from the NHC

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how will this storm be able to deal with all that dry air in front of it. don't know alot just curious.
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Quoting neonlazer:
There is no vorticity with that area..so its just a bunch of storms


Seems to me that there is some organization to it but lets see what it's like tomorrow. That was just a quick observation on my part that something is developing there.
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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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