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 DestinJeff:


although he is in no way a Party of One.
I'm sure that the actual JFV isn't here half of the time that we think he is. I'm almost positive that people come on here, sign up for a username, and then act like they're JFV just to have a little fun.

Back to 04L.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
CMC 144hrs out, Depicts a storm right on the coast of Miami-Dade county.

Member Since: August 11, 2008 Posts: 0 Comments: 2315
Quoting StSimonsIslandGAGuy:
JFV obviously has no life outside of wunderground. The only thing he does is create new handles so he can bother people. That's all his life is, the only accomplishment to his name. Creating wunderground handles.

By the amount of time he spends here, he doesn't have any girl to care about. Neither does he have any friends. He has no life whatsoever. Except wunderground.

Even though JFV is a narcissistic stalker, I do feel sorry for him. Pity, even. Being JFV must be horrible---having a life so empty of anything but hate. Hate is the only emotion he expresses here.

Can any of you imagine how horrible it would be to wake up in the morning and be JFV?


I can't.


Nightmare.
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Quoting IKE:


Same here in Defuniak Springs....only 80.2 now. Rain just ended.
Its clouded up here in Gulf Breeze maybe we will get a little. The AC is out at my work!
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yo, I pegged it too at #511

use the minus button, takes ten clicks from ten different folks to get the comments gone
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Quoting MiamiHurricanes09:
The amount of people that visit this commentop for information and meteorological purposes is immense, also add that to the people that read Jeff Masters' blog. So in basic terms, all that JFV does is not only tarnish the reputation of Jeff Masters but also annoy each and every one of us.
Amen.
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I think the clouds Levi is showing is the fact dry air is residing to the north of TD4 in combination with cold SSTs. Although the convection is a little weak, the organization of the depression is getting better.
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700. IKE
Quoting twhcracker:
pouring here in ft walton. yay! it was so hot...


Same here in Defuniak Springs....only 80.2 now. Rain just ended.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
696-hurricane City site
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697. srada
Question? Has the CMC been right on ANY tracks this season? I thought it was the ECWMF that has been accurate so why is so many putting so much stock on the CMC taking this into FL?
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Quoting Levi32:
I had the HPC forecast pointed out to me....still showing the ridging directing this into the United States. This isn't a pot-shot recurve yet. My forecast, though not with as much confidence as yesterday, is still for this to impact the United States. We shall see what happens.
Levi, I saw a video on hurricane season last season, that 70% of waves that develope before or at 40W go out to sea. Have you ever heard of that?
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Quoting Levi32:
I had the HPC forecast pointed out to me....still showing the ridging directing this into the United States. This isn't a pot-shot recurve yet. My forecast, though not with as much confidence as yesterday, is still for this to impact the United States. We shall see what happens.
Agreed.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
Quoting DaytonaBeachWatcher:
Most times you can tell where people are located purely by what they post on here.
but most time by how they say things
Member Since: July 15, 2006 Posts: 163 Comments: 52257
pouring here in ft walton. yay! it was so hot...
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Quoting stormwatcherCI:
I figured that out with one comment from him. He can't hide.
The amount of people that visit this commentop for information and meteorological purposes is immense, also add that to the people that read Jeff Masters' blog. So in basic terms, all that JFV does is not only tarnish the reputation of Jeff Masters but also annoy each and every one of us posters and all the lurkers.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
I don't think 91L would even ramp up to a cane based solely on the computer model shenanigans of the CMC. It could get torn apart completely by the mountains of the Dominican Republic. Just guessing games for now.

The models are going to flip back and forth.

Wait 3-4 days and we may not even have 91L to track.
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Quoting cirrocumulus:
Note that big dog is behind TD4.


we get it .. you point it out every 5 minutes. we see it.
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Quoting DestinJeff:


Yeah. I like to keep my location under wraps on here.


*wink*
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Quoting Neapolitan:
wish-cast-ing: (wish-kasst-ing) noun 1 : the act of calculating some future event or condition based solely on one's hopes and fantasies rather than the study and analysis of available pertinent data 2 : meteorology: the act of ignoring any logical, climatological, and computational data that contradicts one's hopes or fantasies when predicting whether, when, and where a particular weather event will occur, while putting faith in only those data which correlate with those same hopes and fantasies.

;-)


its a verb
wishcaster is a noun.
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Quoting StSimonsIslandGAGuy:


It's not very well organized.

It will be speeding its forward motion, and could degenerate into a wave.

Strong 30 knot shear starting in 4 days.

Conditions for TD4 are far from ideal.


If TD4 stays weak (or degenerates into a wave) the possibility of the east coast trough missing it increases, leaving the system east or northeast of the Bahamas Then it would be possible for a ridge to fill in behind the trough, and if shear were favorable, we could see steady intensification for 2 or three days before landfall.

That would be the way for TD4 to make landfall---probably between Cape Canaveral and Cape Hatteras.

In other words, the weaker TD4 stays over the next 5 days (without dissipating), the greater the landfall threat to the USA.

And it could work---a weak sheared tropical storm can grow a lot in 60-72 hours with favorable conditions.

However, it is more likely that TD4 will stay out to sea and be a Bermuda threat only.

The wave behind TD4 may be more of a threat to us.



Thank you for your reply, very much appreciated :) I think it's easy for people to write off (or get bored with) a storm that's heading for Bermuda (not that it's early enough to make a call like that), but they took a real punch from Fabian. The radio station clocked a gust to 164, and that was from a category 3.
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Use your Ignore!!
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Quoting StSimonsIslandGAGuy:
As I recall, for hurricane Jeanne, the possibility of a loop was written in the discussions well before it occurred. It was not a total shock.


Yep. BASED ON THE RECON FIXES...THE INITIAL MOTION ESTIMATE IS 340/6. A
MID-LEVEL TROUGH OVER THE FLORIDA PENINSUAL IS FORECAST TO MOVE
EASTWARD AND TURN JEANNE NORTHWARD AND NORTH-NORTHEASTWARD DURING
THE NEXT 24-36 HOURS. HOWEVER...IN 2-3 DAYS...THIS TROUGH IS
LIKELY TO BYPASS THE TROPICAL CYCLONE AS AN UNUSUALLY STRONG
DEEP-LAYER HIGH BUILDS OVER THE EASTERN UNITED STATES. A RIDGE
EXTENDING FROM THIS HIGH IS PREDICTED...BY THE DYNAMICAL MODELS...
TO BLOCK THE NORTHEASTWARD MOTION OF JEANNE...AND CAUSE THE
TROPICAL CYCLONE TO EXECUTE A CLOCKWISE LOOP. THIS OFFICIAL
FORECAST SHOWS A LITTLE WIDER LOOP THAN THE PREVIOUS ADVISORY...BUT
HAS THE SAME GENERAL IDEA. IT SHOULD BE REPEATED THAT THIS IS A
LOWER THAN NORMAL CONFIDENCE FORECAST.
Member Since: July 25, 2008 Posts: 0 Comments: 596
I had the HPC forecast pointed out to me....still showing the ridging directing this into the United States. This isn't a pot-shot recurve yet. My forecast, though not with as much confidence as yesterday, is still for this to impact the United States. We shall see what happens.
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Quoting Jeff9641:


JFV
I figured that out with one comment from him. He can't hide.
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Quoting mydiapersarefull:
jason is ignored, man!
maybe you should change your diapers if there full
Member Since: July 15, 2006 Posts: 163 Comments: 52257
Quoting DestinJeff:


True. I can tell you are from Daytona Beach.


Wow, you smart, I cant even tell where you are from...............
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So, I take it no one knows the answer to post 656?
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wish-cast-ing: (wish-kasst-ing or wish-kass-ting) noun 1 : the act of calculating some future event or condition based solely on one's hopes and fantasies rather than the study and analysis of available pertinent data 2 : meteorology: the act of ignoring any logical, climatological, and computational data that contradicts one's hopes or fantasies when predicting whether, when, and where a particular weather event will occur, while putting faith in only those data which correlate with those same hopes and fantasies.

;-)
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Levis right---Right now TD4 is in colder water!
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Quoting sammywammybamy:


Swiming and putting on Shows at Seaworld.

Irresponsible Behaviour........
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happy happy joy joy
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Quoting jasoniscoolman2010x:
WHAT HAPPERN TO TROPICAL DRPREESSION TWO..SHE LOST LOTS OF T.STORM IN THE CENTER..SOME OF THE DRY AIR IS GETTING INTO TROPICAL DEPREESON FOUR RIGHT NOW..


You are correct. I hope this disturbance just goes poof and it won't matter about a trough, ridge, blah blah.
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671. Prgal
Quoting HurricaneColin:
cmc is a joke. oyeme, boricua, vete preparandote para lo que te viene llegando.


The CMC is probably the scenario we will have in a few days. A prepararse!
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Quoting Funkadelic:


Keeps it week, then blows up a bit in Bahamas region, hence the westward track. A trend?
Looks like it's up to the NAO. It's forecasted to turn strongly positive, if that verifies, we may see a track similar to the CMC. However, it's just one run, nothing too special, if we see other models jump aboard then we monitor it more closely.
Member Since: September 2, 2009 Posts: 130 Comments: 21032
Models---Smodules--- Back in the old days when they would move a plastic cut out of a TC on the News Weather Board and give you coordinates to track a TC was fun! Today is better fun, but those Models can sometimes make you want to cuss! Just when I think Ive learned enough, Ive got to learn more!LOL
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667. unf97
Quoting StSimonsIslandGAGuy:
As I recall, for hurricane Jeanne, the possibility of a loop was written in the discussions well before it occurred. It was not a total shock.


Jeanne's loop indeed was not a total shock SSI Guy. NHC had that forecast definitely in the long range discussion after it moved away from Hispaniola on 9/18/04. I keep an archive of advisories and discussions from NHC on major hurricanes that affect the CONUS, and I found this for everyone:

TTAA00 KNHC DDHHMM
TROPICAL STORM JEANNE DISCUSSION NUMBER 21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SAT SEP 18 2004


THE TRACK FORECAST REASONING HAS NOT CHANGED. IT IS ONLY BEING
SHIFTED EASTWARD DUE TO THE REFORMATION. JEANNE IS FORECAST TO MOVE
TOWARD THE NORTH-NORTHWEST AND NORTH ABOUT 6 KNOTS FOR THE NEXT 3
DAYS. THEREAFTER...A RATHER STRONG HIGH IS EXPECTED TO REPLACE THE
TROUGH AND DEPENDING HOW FAR NORTH JEANNE MOVES...THE CYCLONE COULD
BE BLOCKED AND MOVE WESTWARD OR COULD TURN NORTHEASTWARD FOLLOWING
THE TROUGH. SINCE THERE IS MUCH UNCERTAINTY IN GLOBAL MODELS BEYOND
3 DAYS...THE BEST OPTION AT THIS TIME IS TO KEEP JEANNE NEARLY
STATIONARY BETWEEN BERMUDA AND THE BAHAMAS AT DAYS THREE THROUGH
FIVE. IN FACT...NOW ALL THE RELIABLE GLOBAL MODELS...THE GFS...THE
UKMET AND NOGAPS KEEP THE CYCLONE LOOPING WITHIN THIS REGION
THROUGH THE PERIOD OR LONGER.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 18/2100Z 22.0N 72.3W 40 KT
12HR VT 19/0600Z 22.9N 72.5W 40 KT
24HR VT 19/1800Z 24.1N 72.6W 40 KT
36HR VT 20/0600Z 25.7N 72.5W 50 KT
48HR VT 20/1800Z 27.0N 72.5W 60 KT
72HR VT 21/1800Z 28.5N 71.5W 65 KT
96HR VT 22/1800Z 28.5N 71.5W 65 KT
120HR VT 23/1800Z 28.5N 71.5W 65 KT
Member Since: September 25, 2007 Posts: 0 Comments: 1193
Quoting cirrocumulus:


Actually it's in 28-29 degree water according to NOAA SST loops on the central Atlantic. Meanwhile, big dog, on it's tail, is approaching 30 degree Centigrade boiling water.


A look at the visible loop will tell you that it's over colder water and near even colder water.
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Quoting MiamiHurricanes09:
Levi,

Superb job on the video, I really enjoyed it. Let's hope that the ridge doesn't develop too strong after the shortwave trough lifts out.


Thanks :) Yes let's hope.
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Quoting StSimonsIslandGAGuy:


It's not very well organized.

It will be speeding its forward motion, and could degenerate into a wave.

Strong 30 knot shear starting in 4 days.

Conditions for TD4 are far from ideal.


If TD4 stays weak (or degenerates into a wave) the possibility of the east coast trough missing it increases, leaving the system east or northeast of the Bahamas Then it would be possible for a ridge to fill in behind the trough, and if shear were favorable, we could see steady intensification for 2 or three days before landfall.

That would be the way for TD4 to make landfall---probably between Cape Canaveral and Cape Hatteras.

In other words, the weaker TD4 stays over the next 5 days (without dissipating), the greater the landfall threat to the USA.

And it could work---a weak sheared tropical storm can grow a lot in 60-72 hours with favorable conditions.

However, it is more likely that TD4 will stay out to sea and be a Bermuda threat only.

The wave behind TD4 may be more of a threat to us.



Seems plausible.
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Not to venture too far off topic...but we've broken 100 degrees for at least the third day in a row here in Pensacola. It's 102 right now, and the heat index is approaching 130. I couldn't breathe when I got in my car.
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Most times you can tell where people are located purely by what they post on here.
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659. Lizpr
Quoting serialteg:


lizzzzzzzzzzzz! :D


Heya! I'm so gonna miss this hurricane season cus I not longer live in PR I move to Oregon! very different! But always come back to this blog never stop to amaze me lol.
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.