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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This is from the NWS MIAMI From Early this morning.
THE LATEST LONG RANGE MODELS ARE ALSO SHOWING A STRONG TROPICAL
WAVE EAST OF THE LESSER ANTILLES TO MOVE WEST NORTHWEST OR NORTHWEST
THIS WEEK AND BE EAST OF BAHAMAS THIS WEEKEND. WE WILL CONTINUE TO
MONITOR THIS STRONG TROPICAL WAVE TO SEE IF WE SEE ANY AFFECTS
ON SOUTH FLORIDA THIS WEEKEND.
Member Since: July 14, 2009 Posts: 0 Comments: 3022
TD 4 is smaller than I would've expected
Member Since: April 1, 2010 Posts: 9 Comments: 2699
Quoting markinthedark:
models schmodels its gonna be a fish storm you just gotta let things pan out


A friendly reminder that Bermuda is out there in your fishing zones!
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If the high shifts back over as some forecast, we'll be right back in the high 90s with heat indices in the low to mid 100's just as we were a week ago.
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Quoting HouGalv08:
A lot of people on here jumping the gun. The storm just got upgraded to a TD. IMO, the NHC is way too early on sending this thing out to sea as a "fish storm". Take a look at the steering currents--almost due WEST at this time. Besides, the models need upper air sampeling from a high altitude flight before they get a real handle on this storm, and then give a really accurate track.


Forward speed is the likely culprit. 04L is making up for that stall 10 fold.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
253. XLR8
Quoting Patrap:
I think I saw a Pigeon burst spontaneously into Flame Mid Flight.




LOL me too :)
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The models are sure taking their time to reset on TD4 :(



AOI

AOI

AOI

AOI

AOI

TS BUSTED FORECAST ALIBI
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Maybe the gulf will ignite from the heat with oil on it and burn off the rest of it
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Quoting IKE:
TD4....

.......***scratches head***.....looks more like colin to me;)
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Quoting reedzone:
My first run on Tropical Depression 4, which is reasonable as well as the NHCs track because of the uncertainty, you can clearly see it on the last few days of the run. I'm very confident though that we will see a general WNW movement for the next few days, after it reaches the islands, the uncertainty really kicks in.

Photobucket


TD4- "The Riddler"?
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Roastin' in Austin as well. Forecast to be in the 100's this week. Good times.
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Quoting Patrap:
I think I saw a Pigeon burst spontaneously into Flame Mid Flight.



ROFL. The sad part is, I think that's pretty likely. If we weren't have overcast conditions here, I would be frying crow on the hood of my car, just in case.
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Doesn't seem to be a lot shear associated with the ULL north of Puerto Rico..

http://www.ssd.noaa.gov/goes/east/tatl/loop-wv.html
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Quoting Patrap:
I think I saw a Pigeon burst spontaneously into Flame Mid Flight.



Pigeon Pilau? :D
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Quoting PanhandleChuck:
94 with a heat index of 108 right now... think I'll work on my tan...Walter says he's staying the box today
silence!
Member Since: July 15, 2006 Posts: 171 Comments: 53825
Quoting Patrap:
I think I saw a Pigeon burst spontaneously into Flame Mid Flight.



LOL

Was it at a Kings of Leon concert?
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Quoting CoopsWife:
Don't hate me - but since the high retreated and we hd that big storm roll through it's been quite pleasant here. Supposed to be in the 80s today and 90s by wednesday as the wind backs around to the south....


Norfolk, Virginia (Airport)
Updated: 15 min 50 sec ago

72 °F
Light Rain Mist
Humidity: 94%
Dew Point: 70 °F
Wind: 12 mph from the East


We also have a few light showers in our area in Richmond as well.
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My first run on Tropical Depression 4, which is reasonable as well as the NHCs track because of the uncertainty, you can clearly see it on the last few days of the run. I'm very confident though that we will see a general WNW movement for the next few days, after it reaches the islands, the uncertainty really kicks in.

Photobucket
Member Since: July 1, 2008 Posts: 13 Comments: 7387
240. XLR8
Quoting bohonkweatherman:
Sorry for you, Hot here in Texas also but No humidity so I will take it.


The humidity is at 56% it is just bad. We are looking for around 103 temp today. Just yuck all the way around. And going to be like this all week.
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Gulf is now being cooked with very hot air temps along the entire gulf coast region
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Quoting Patrap:
Itsa Hotsui


Current Conditions

Uptown, New Orleans,


Louisiana (PWS)
Updated: 1 min 5 sec ago
Partly Cloudy

94.1 F

Partly Cloudy
Humidity: 60%
Dew Point: 78 F
Wind: Calm
Wind Gust: 3.1 mph
Pressure: 30.03 in (Steady)

Heat Index: 110 F


I hate it. I just tried to walk and had to come back to the house.
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Looks like I won't even have to fire up the burner on the grill to boil some peanuts, I'll just set the pot on the sidewalk.... LOL
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Don't hate me - but since the high retreated and we had that big storm roll through it's been quite pleasant here. Supposed to be in the 80s today and 90s by wednesday as the wind backs around to the south....


Norfolk, Virginia (Airport)
Updated: 15 min 50 sec ago

72 F
Light Rain Mist
Humidity: 94%
Dew Point: 70 F
Wind: 12 mph from the East
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Member Since: September 30, 2005 Posts: 0 Comments: 1606
I don't mind High Pressure systems during the Winter but to have one over you in the Summer and not have it move much can be very depressing.
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A lot of people on here jumping the gun. The storm just got upgraded to a TD. IMO, the NHC is way too early on sending this thing out to sea as a "fish storm". Take a look at the steering currents--almost due WEST at this time. Besides, the models need upper air sampeling from a high altitude flight before they get a real handle on this storm, and then give a really accurate track.
Member Since: Posts: Comments:
Itsa Hotsui


Current Conditions

Uptown, New Orleans,


Louisiana (PWS)
Updated: 1 min 5 sec ago
Partly Cloudy

94.1 F

Partly Cloudy
Humidity: 60%
Dew Point: 78 F
Wind: Calm
Wind Gust: 3.1 mph
Pressure: 30.03 in (Steady)

Heat Index: 110 F
Member Since: Posts: Comments:
Member Since: September 30, 2005 Posts: 0 Comments: 1606
Quoting TampaSpin:
Morning all. I'm sure there will be alot of peeps that will be calling for the High to build back in......You know its coming.


yep, rather be roasting than running, LOL!
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In Levi's tropical tidbit yesterday, he was saying that the TUTT could possibly split thus allowing for intensification later on...based on the sheer outlook, a more westerly track would be marginally better for development...who knows? It's time to sit back and watch mother nature do her thang.
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Good morning everyone,I really wish all storms this year would follow this NHC track. We just had enough with the oil disaster, it is sad that you see people come here and get excited when a track is pointing at a landmass, I just dond get it. Have a nice day everyone
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Member Since: September 30, 2005 Posts: 0 Comments: 1606
Quoting TampaSpin:
Morning all. I'm sure there will be alot of peeps that will be calling for the High to build back in......You know its coming.
they are out in full force already
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it is very hot here also
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Yeah that forward speed of the system right now certainly doesn't help things for strengthening down the road.
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Quoting JupiterFL:


Too bad the lightning didn't fry the chickens.


Yeah, that would have been better. lol

Since we're getting into August, I'm spending today getting my hurricane stuff together -- lantern & batteries, propane cookstove, ice chests, tarps, run-from-it evac stuff, etc.. 'Tis the season...
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Very well organized:



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models schmodels its gonna be a fish storm you just gotta let things pan out
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Quoting bohonkweatherman:
Sorry for you, Hot here in Texas also but No humidity so I will take it.


88.6 with 46% humidity here in DFW...looking for 106 later today

Norht texas in the summertime...yum!
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Morning all. I'm sure there will be alot of peeps that will be calling for the High to build back in......You know its coming.
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94 with a heat index of 108 right now... think I'll work on my tan...Walter says he's staying the box today
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After watching Ike, anything is possible now to me. There was no way in hell that storm should of came here. it was way up in lattitude and for it to of kept going west like it did due to the ridges was just ridicoulous
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Well; at least it's safe to have lunch today....... :)
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Quoting WINDSMURF:
It is still a waiting game. Conditions will change each day. Just yesterday all the experts on this blog were saying that shear would be low for the next seven days and that there was nothing out there to stop the development. Today we are hearing the opposite. I have the feeling that NHC is just playing it safe and declaring TD4 at this time even if they are not sure of what is going to happen.


Actually, we expected this. Shear is low over the system now, but once it passes north of the Antilles, it will hit a TUTT, which will cause weakening.
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Good morning everyone. If you notice, my posts have suggested this trend we are seeing today for more than a while. I don't want to get into the abusive arguments that I read on this page. Hey, we only know what we have all said and done.
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211. srada
Good Morning Everyone,

So we now have TD4..I will be watching this one closely..there is no telling with these systems and if it makes it into the gulf stream near the east coast, all bets are off..the SSTs are really high right now
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Quoting RitaEvac:
Fantastic news, track takes it away from gulf and Florida


yep, and points it up the East Coast - maybe.....
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IDK, I won't be calling anyone a anything "caster" so long as they aren't totally off the rocker...like saying that TD4 is going to strengthen to a 5 and hit NOLA (that would FOR SURE be a "wish" caster.) I think that saying that the front won't be strong enough, etc. etc. opens up the blog for healthy debate. Since weather isn't an exact science, it takes all view points to eventually learn from or prove/disprove a thesis with data. Even the outlier ones :)
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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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