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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Quoting Levi32:
Good morning all.

Blog Update.

Tropical Tidbit for Monday, August 2nd, with Video


amen just in time!!!
Member Since: Posts: Comments:
KOTG....not at all...I just noticed your avatar
Member Since: April 26, 2006 Posts: 5 Comments: 3195
Quoting IKE:


Don't believe the models until we have a developed system. TD4 is a developed system.

Rebuttal..don't believe the models whether it's developed or not right?
some just don't want to believe it is not coming there way. Sure as heck glad to see it prob wont be coming to your and my neck of the woods.
Member Since: August 22, 2008 Posts: 0 Comments: 755
Good morning all.

Blog Update.

Tropical Tidbit for Monday, August 2nd, with Video
Member Since: Posts: Comments:
TD4 is, imho....a bit south of the forecast. It will be interesting to see if it lags far enough behind the dry air....the small size and slow development would perhaps allow it to stay west. another thing....look behind it...THAT is the storm to be...to watch.

should be a very interesting Aug. storms in August..with this kind of heat? look for explosive developments....lol
Member Since: Posts: Comments:
Reedzone Makes good since to me.
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551. StormChaser81
4:57 PM GMT on August 02, 2010
Quoting NASA101:


Missing the point - Alex did not have a good model consensus - it had a more than a few models pointing to TX/LA and few towards Brownsville!!
Operative word here is > 80% Model Consensus - TD4 has it and it will follow the NHC path which I think is the average of the models - TVCN model!


Model Caster...It's a model man, models will never be able to keep up with the fast pace of the changing earth atmosphere.

Regardless Models are not perfect and will continue to just show us best case events.
Member Since: August 11, 2008 Posts: 0 Comments: 2315
549. scott39
4:57 PM GMT on August 02, 2010
I dont understand the north track out to sea. Especially with the intensity having TD4 staying a weak tropical storm for the next 3 to 4 days. I thought with TD4 being that weak of a system it would go more W?
Member Since: June 13, 2009 Posts: 0 Comments: 6863
547. KEEPEROFTHEGATE (Mod)
4:56 PM GMT on August 02, 2010
Quoting K8eCane:
people should try a little kindness on here rather than imitating satan
i hope you are not refering to me or i should say my avatar cause its not satan but oil slick man
Member Since: July 15, 2006 Posts: 174 Comments: 54398
546. KYDan
4:56 PM GMT on August 02, 2010
I thought this was an excellent image of the area of interest from a little earlier today.

Member Since: July 6, 2010 Posts: 0 Comments: 100
545. K8eCane
4:56 PM GMT on August 02, 2010
#539


All tropical cyclones affect fish . all are fish storms
Member Since: April 26, 2006 Posts: 5 Comments: 3195
544. Chicklit
4:56 PM GMT on August 02, 2010
Member Since: July 11, 2006 Posts: 14 Comments: 11351
543. sporteguy03
4:55 PM GMT on August 02, 2010
Quoting NASA101:


Disagree Sir! IKE did not have such model consensus!
Almost all of the models are in very good agreement with TD4 - in fact as far as tropical storm go one will find it hard to find such a good agreement so early in TS!


I agree on the model agreement but models can change but the NHC track did have Ike pointed to SFL and the track did change as the models changed and the NHC track followed suit. Just because what you see today does not mean it can't change tomorrow is my point.
Member Since: July 7, 2005 Posts: 0 Comments: 5351
542. coffeecrusader
4:54 PM GMT on August 02, 2010
TD4 should moisten the environment for that beast behind it.
Member Since: August 21, 2006 Posts: 0 Comments: 254
541. nrtiwlnvragn
4:54 PM GMT on August 02, 2010
Quoting DestinJeff:


need to find one with the fish spinning around.


He may have 24hrs to do that.... admin does not like images of fish.
Member Since: September 23, 2005 Posts: 14 Comments: 11215
540. SeniorPoppy
4:54 PM GMT on August 02, 2010
Quoting KEEPEROFTHEGATE:
i will tell ya something don't cry too much but this may even end up a naked swirl and eventually an open naked wave


We have a winner!
Member Since: August 4, 2009 Posts: 0 Comments: 497
539. divdog
4:53 PM GMT on August 02, 2010
Quoting K8eCane:
to get technical, I havent yet seen a tropical cyclone that was NOT a fish storm....ever
what the heck does that mean????????????????????????????????????????
Member Since: August 22, 2008 Posts: 0 Comments: 755
538. IKE
4:53 PM GMT on August 02, 2010
Quoting MiamiHurricanes09:
Last comment before I go.

You're putting wayyyyyyyyy to much stock into the models. As we get more detailed information about the environment it is in from the aircraft's the investigate the system models will change. Do you remember Alex? When it was a tropical depression the models forecasted for it to hit Louisiana/Mississippi. Guess where it hit?

Too crazy on here, later everyone!


Don't believe the models until we have a developed system. TD4 is a developed system.

Rebuttal..don't believe the models whether it's developed or not right?
Member Since: June 9, 2005 Posts: 23 Comments: 37858
537. LightningCharmer
4:53 PM GMT on August 02, 2010
Often I've read on this blog that tropical systems necessarily remove or actually transfer heat from the Atlantic Basin. Since so called, "fish storms" (more accurately maritime storms or non-landfalling storms) tend to stay over water longer, do they tend to remove more heat and therefor lower the total potential energy for the season thereby lessening the number, intensity and size of possible future landfalling tropical systems?
Member Since: September 1, 2007 Posts: 0 Comments: 1344
535. StormChaser81
4:53 PM GMT on August 02, 2010
Quoting FloridaHeat:


wouldnt most ships get out of the way if a storm is coming???


Depends on the size of the storm. Wave, TD,TS if its a big ship probably not. They might stay on the edge, because no one likes to move 500 miles off course to stay away from a Wave, TD, TS.
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534. K8eCane
4:52 PM GMT on August 02, 2010
people should try a little kindness on here rather than imitating satan
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533. jeffs713
4:52 PM GMT on August 02, 2010
Quoting FloridaHeat:


wouldnt most ships get out of the way if a storm is coming???

Kinda hard to avoid it once it gets going... waves can travel quite far.
Member Since: August 3, 2008 Posts: 16 Comments: 5885
532. NASA101
4:52 PM GMT on August 02, 2010
Quoting MiamiHurricanes09:
Last comment before I go.

You're putting wayyyyyyyyy to much stock into the models. As we get more detailed information about the environment it is in models will change. Do you remember Alex? When it was a tropical depression the models forecasted for it to hit Louisiana/Mississippi. Guess where it hit?

Too crazy on here, later everyone!


Missing the point - Alex did not have a good model consensus - it had a more than a few models pointing to TX/LA and few towards Brownsville!!
Operative word here is > 80% Model Consensus - TD4 has it and it will follow the NHC path which I think is the average of the models - TVCN model!
Member Since: August 16, 2007 Posts: 0 Comments: 276
531. reedzone
4:52 PM GMT on August 02, 2010
I'm not saying a recurvature is impossible, but just not likely to me, it's too early to tell, here's my first run again with scenarios...
Notice the big ? .. I'm just not convinced right now, don't matter what the models showed, they will shift left and right the next few days.

Photobucket
Member Since: July 1, 2008 Posts: 13 Comments: 7396
529. cirrocumulus
4:50 PM GMT on August 02, 2010
34West will not stagger if it moves west of the northern Antilles later. Meanwhile, TD4 is in 28-29C waters while 34West is in 29-30C waters and heading into 30+celsius waters.
Member Since: September 30, 2005 Posts: 0 Comments: 1606
528. WeatherMSK
4:50 PM GMT on August 02, 2010
Alright back to work. Have fun arguing guys.
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527. KEEPEROFTHEGATE (Mod)
4:49 PM GMT on August 02, 2010
Quoting reedzone:


It's not set in stone that this will be a fish, models should shift left and right the next few days. Too early to determine that.
i will tell ya something don't cry too much but this may even end up a naked swirl and eventually an open naked wave
Member Since: July 15, 2006 Posts: 174 Comments: 54398
526. gordydunnot
4:49 PM GMT on August 02, 2010
What's wrong with this picture.
Member Since: August 18, 2008 Posts: 0 Comments: 3113
525. Sfloridacat5
4:48 PM GMT on August 02, 2010
But be careful. The Bermuda fans will jump in and say its not a fish storm if it affects Burmuda.
Member Since: September 16, 2007 Posts: 0 Comments: 7389
524. bajelayman2
4:48 PM GMT on August 02, 2010
Quoting oracle28:


BINGO


Only problem with that position is that models do not initialise systems properly, until they actually reach depression ststus.

Over the past few years this has become evident.

Once they do become depressions however, more often than not the NHC has got it right.

The thing is that gut feels based on other weather patterns e.g. extreme humidity and heat down here in the islands at specific times, representing a system forming (when that occasion happens), are genuine perceptions, that should have some credence.

After all, if this were an exact science, the experts would not have to alter predictions regularly during the season, based on models.
Member Since: August 13, 2007 Posts: 0 Comments: 488
523. MiamiHurricanes09
4:48 PM GMT on August 02, 2010
Quoting NASA101:


You don't think that all these sophisticated models take these things into consideration!? - I mean come-on!! Every storm will behave given the pattern it will see NOW and NOT how other storms behaved last week, month, year etc!
However, i am of course not stopping anyone voicing their opinion, it's just that this blog would be better served if bloggers are a little more learned about tropical weather!!
Last comment before I go.

You're putting wayyyyyyyyy to much stock into the models. As we get more detailed information about the environment it is in from the aircraft's the investigate the system models will change. Do you remember Alex? When it was a tropical depression the models forecasted for it to hit Louisiana/Mississippi. Guess where it hit?

Too crazy on here, later everyone!
Member Since: September 2, 2009 Posts: 130 Comments: 21194
521. NASA101
4:47 PM GMT on August 02, 2010
Quoting sporteguy03:


And you do realize models can change in 24 hours and so can the NHC track, if that was the case as you say Ike should of hit South Florida and not Tx. Today's outlook on TD4 is bleak and the track yes can take it out to sea away from land lets hope it does, but things can and do change and the conditions could improve for TD4 or worsen. This has alot of real estate to go lets be realistic that conditions can change and not limit ourselves to one NHC official track and one day of model runs.


Disagree Sir! IKE did not have such model consensus!
Almost all of the models are in very good agreement with TD4 - in fact as far as tropical storm go one will find it hard to find such a good agreement so early in TS!
Member Since: August 16, 2007 Posts: 0 Comments: 276
520. FloridaHeat
4:47 PM GMT on August 02, 2010
Quoting DestinJeff:


yes, but be careful using it because some will jump all over you about how there are ships at sea, etc....


wouldnt most ships get out of the way if a storm is coming???
Member Since: July 31, 2010 Posts: 0 Comments: 357
519. WeatherMSK
4:47 PM GMT on August 02, 2010
Quoting reedzone:


It's not set in stone that this will be a fish, models should shift left and right the next few days. Too early to determine that.


I wish people on this blog could grasp that concept.
Member Since: February 12, 2007 Posts: 0 Comments: 479
518. K8eCane
4:47 PM GMT on August 02, 2010
to get technical, I havent yet seen a tropical cyclone that was NOT a fish storm....ever
Member Since: April 26, 2006 Posts: 5 Comments: 3195
517. Sfloridacat5
4:47 PM GMT on August 02, 2010
If TD4 crosses the intersection of 15 north lat and 50 west long its on track.
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516. reedzone
4:46 PM GMT on August 02, 2010
Quoting KEEPEROFTHEGATE:
Quoting MiamiHurricanes09:
I'll be updating it in the evening

your blog header should say

"FISH TALES OF THE ATLANTIC"

that sounds about right for now


It's not set in stone that this will be a fish, models should shift left and right the next few days. Too early to determine that.
Member Since: July 1, 2008 Posts: 13 Comments: 7396
515. divdog
4:45 PM GMT on August 02, 2010
Quoting cirrocumulus:
34West just increased areal coverage and intensity in the last 30 minutes. They need to place a floater on it also since it is in a better environment than TD4.
its not even close to be anything yet but a blob in the itcz. like mh09 said, it barely has any 850mb support yet.
Member Since: August 22, 2008 Posts: 0 Comments: 755
514. sebastianflorida
4:45 PM GMT on August 02, 2010
I think it is a storm that sucks up fish from the ocean, and then dumps those fish on land, especially Florida, just my thought, not sure though.
Member Since: August 5, 2007 Posts: 0 Comments: 713
513. WeatherMSK
4:45 PM GMT on August 02, 2010
Quoting FloridaHeat:
is a fish storm just a storm that stays over water???


u got it
Member Since: February 12, 2007 Posts: 0 Comments: 479
509. sebastianflorida
4:44 PM GMT on August 02, 2010
Quoting Hurricanes101:


but to say that now when it just formed and is still 1350 miles from any landmass is even more nuts
At least half on here will Poof you, Ignore you, yell about your comment, call you a Troll, call you a Downcaster, but whatever, as long as you are making educated guesses or following the most reliable tools we have, which are not perfect, then you have the right to post comments. The real loosers here, are those that state ridiculous predictions that use no common sense and defy logic. Those people should go poof themselves, afind a psychic site to visit.
Member Since: August 5, 2007 Posts: 0 Comments: 713

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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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