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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Wow.......Dr. M and NHC thinking that sheer might rip it apart in a few days......These things have a mind of their own sometimes....Just have to wait to see how much of a groove it can get in the short term before it hits the sheer.
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Quoting DestinJeff:
Here is some early modeling on Ike, that would have left a safe taste in the mouth of those on the TX coast.

huh ??????????????????????????
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For now, the prediction on TD4's life isn't especially bullish.

How it copes with the predicted shear will probably be its next challenge.
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Quoting angiest:


But the 5-day cone on that was actually pretty good...


Huh? Ike was complete outside to the left of that cone at the end of the 5 days. About the only thing they got "right" was the temporary southward dip.
Member Since: November 8, 2009 Posts: 4 Comments: 13525
Hey guys :) Look at the blob, wave...whatever you want to call it, due North of our current system TD4. Why hasn't that area been labled an invest? Because of the region it is in? It is small but with great spin. Let me know And impressive wave just behind TD4 too :)

Link
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Quoting reedzone:
The track and models will shift to the left as the days go by, Florida to the Carolinas needs to monitor the progress of TD4.


Still not going to be a strong system - regardless of the track, the shear in the later periods is going to be the big hindrance with TD 4. The best chance of this storm to flourish will be to miss the weakness altogether and stay on a more westerly course. I would be more concerned right now with the disturbance behind TD 4. That may be something to watch next week as the weakness that TD 4 feels will most likely "close up" by the time that AOI reaches the same longitude.
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Georgia keep an eye peeled
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I notice that the NHC doesn't expect this to get any stronger that a TS, does everyone here agree with this?
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According to NHC track.....NEXT
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Quoting DestinJeff:


Like I always say: Great minds think like me!



lmao
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147. IKE
IF THE CYCLONE DOES NOT INTENSIFY IN THE NEXT
DAY OR SO...IT COULD STRUGGLE TO MAINTAIN A CLOSED SURFACE
CIRCULATION WITH SUCH A FAST FORWARD SPEED...AND COULD OPEN BACK UP
INTO A TROPICAL WAVE.


Never thought I would say this about the NHC......DOWNCASTERS!
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting CaneAddict:


Personally, i'm thinking something similar to the CMC with a little more bend to the left at day's 4-5. Out till' later.
florida caster
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Expect the unexpected.
Member Since: June 29, 2009 Posts: 13 Comments: 5313
Floridawishcaster here: I don't want this thing anywhere near Florida this weekend, I have plans!!!! So I wish it away!!!
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Reedzone bite your tongue i live in Florida. All beit the west coast. Let the fish have the storms. they like it.
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probably the most reasonable model right now is the 00z CMC.

I am not buying the models until the HPC aligns with them. The reason i trust the HPC is that they are the ones that forecast the highs and troughs over the United States. Them saying the trough isn't that strong makes me believe it will go further west. The HPC 12z forecast brings TD 4 into cape canaveral 7 days from now
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Quoting truecajun:


that's bold, going with the rogue model. i can appreciate that, however.


I have to hedge against the other plots since oil is higher today.lol
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BBL
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and acceptance is the answer to all my problems today.....
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138. Relix
Seems NHC is confident it won't be near the Antilles. Glad to hear that and I trust them quite a bit. Alert Mode: -50% =P. Will just keep an eye on it. Will be off from WU and return tomorrow probably. See you guys.
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Quoting DestinJeff:
I don't post this to draw any comparisons or suggest it will happen ... but rather to simply point out the importance of staying aware, despite early advisories.

Here is one of the early Cones for Ike. Probably the folks in Galveston didn't feel too threatened by Ike based on this.



But the 5-day cone on that was actually pretty good...
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting IKE:
This should quiet the Florida casters....



For now.
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Quoting cirrocumulus:


NO! I'm going with BAMD on this one!





Personally, i'm thinking something similar to the CMC with a little more bend to the left at day's 4-5. Out till' later.
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11AM disco

00
WTNT44 KNHC 021452
TCDAT4
TROPICAL DEPRESSION FOUR DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042010
1100 AM EDT MON AUG 02 2010

DATA FROM AN 1148 UTC ASCAT PASS SUGGEST THAT THE DISTURBANCE IN THE
TROPICAL ATLANTIC NOW HAS A WELL-DEFINED SURFACE CIRCULATION...AND
ADVISORIES ARE INITIATED ON TROPICAL DEPRESSION FOUR. THE INITIAL
INTENSITY IS SET AT 30 KT IN AGREEMENT WITH THE ASCAT DATA AND
DVORAK DATA T-NUMBERS OF 2.0 FROM TAFB AND SAB.

THE LOW-LEVEL CENTER APPEARS TO BE LOCATED ON THE SOUTHEASTERN EDGE
OF THE DEEP CONVECTION...AND IS MOVING RATHER BRISKLY TOWARD THE
WEST-NORTHWEST AT ABOUT 15 KT. MUCH OF THE GUIDANCE SUGGESTS AN
EVEN FASTER MOTION IS LIKELY DURING THE NEXT COUPLE OF DAYS AS THE
DEPRESSION IS STEERED BY A STRONG SUBTROPICAL RIDGE TO ITS NORTH.
IN FOUR OR FIVE DAYS...THE GLOBAL MODELS SHOW A WEAKNESS DEVELOPING
IN THE RIDGE...WHICH SHOULD RESULT IN A TURN TOWARD THE NORTHWEST
WITH A DECREASE IN FORWARD SPEED. THERE IS QUITE A BIT OF SPREAD
IN THE MODELS BY THE END OF THE PERIOD...WITH THE GFS ON THE LEFT
SIDE OF THE GUIDANCE SUITE AND THE HWRF AND ECMWF FARTHER RIGHT
SHOWING MORE RECURVATURE. THE OFFICIAL FORECAST IS CLOSE TO THE
MULTI-MODEL TVCN CONSENSUS AND IN BEST AGREEMENT WITH THE GFDL. IT
IS WORTH REMINDING USERS THAT THE AVERAGE ERROR OF THE OFFICIAL
TRACK FORECAST AT DAYS 4 AND 5 IS 250 TO 300 MILES.

THE ENVIRONMENT APPEARS FAVORABLE FOR SOME STRENGTHENING OVER THE
NEXT COUPLE OF DAYS...BUT AFTER THAT TIME VERTICAL WIND SHEAR IS
EXPECTED TO INCREASE AS THE CYCLONE APPROACHES AN UPPER-LEVEL
TROUGH AROUND 65W. THE SHIPS MODEL SHOWS THE SHEAR INCREASING TO
AROUND 30 KT BY 72 HOURS...AND THE OFFICIAL FORECAST SHOWS A PEAK
IN INTENSITY AROUND THAT TIME...IN BEST AGREEMENT WITH THE ICON
INTENSITY CONSENSUS. IF THE CYCLONE DOES NOT INTENSIFY IN THE NEXT
DAY OR SO...IT COULD STRUGGLE TO MAINTAIN A CLOSED SURFACE
CIRCULATION WITH SUCH A FAST FORWARD SPEED...AND COULD OPEN BACK UP
INTO A TROPICAL WAVE.

FORECAST POSITIONS AND MAX WINDS

INITIAL 02/1500Z 12.6N 41.1W 30 KT
12HR VT 03/0000Z 13.5N 44.0W 35 KT
24HR VT 03/1200Z 14.8N 48.9W 40 KT
36HR VT 04/0000Z 16.4N 53.4W 45 KT
48HR VT 04/1200Z 18.4N 57.4W 50 KT
72HR VT 05/1200Z 22.0N 63.0W 50 KT
96HR VT 06/1200Z 26.0N 66.5W 45 KT
120HR VT 07/1200Z 29.0N 68.5W 45 KT

Member Since: January 24, 2010 Posts: 0 Comments: 529
133. IKE
This should quiet the Florida casters....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting angiest:


Jeff you and I had the same thought. ;)


good point. from no GOM allllll the way to texas, that's a biiiig window of error
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128 - lmao
Member Since: August 26, 2006 Posts: 16 Comments: 4766
The models are rather tightly clustered considering the system just developed.
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Quoting truecajun:
So, is GOM out of the questions at this point??
the crystal ball says no one knows where a storm is going this many days out. i'll say yes if it makes you feel better.
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Quoting cirrocumulus:


NO! I'm going with BAMD on this one!





that's bold, going with the rogue model. i can appreciate that, however.
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Quoting DestinJeff:
I don't post this to draw any comparisons or suggest it will happen ... but rather to simply point out the importance of staying aware, despite early advisories.

Here is one of the early Cones for Ike. Probably the folks in Galveston didn't feel too threatened by Ike based on this.



Jeff you and I had the same thought. ;)
Member Since: August 26, 2006 Posts: 16 Comments: 4766
125. PR51
For Puerto Rico, we are not in the cone of possibilities...we, as has been for the last 12 years, are blessed and no hurricanes to our Island...Let's see what happens with Colin Fish...
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Quoting oracle28:
Fish storm, err Fish Depression.


We will see where the Bermuda High is when it gets "closer" to the US. Any slight shift will make a big impact on the track of future Colin.
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Quoting FloridaHeat:
i am getting frustrated by the blog because i type out a post and hit post comment and my comment never shows up is this normal???


you have to refresh before your comment will show up.
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Quoting DestinJeff:
Not sure what is worse for the blog, a GW discussion or that track from the NHC.


Why does either one have to be "worse"? I find them both to be very interesting...and, IMO, far less tedious than page after page discussing the viability of the various models.
Member Since: November 8, 2009 Posts: 4 Comments: 13525
Quoting truecajun:
So, is GOM out of the questions at this point??


NO! I'm going with BAMD on this one!



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Quoting truecajun:
So, is GOM out of the questions at this point??


Lot's of people here said GOM was out the question for this guy. Never let your guard down.

Member Since: August 26, 2006 Posts: 16 Comments: 4766
The track and models will shift to the left as the days go by, Florida to the Carolinas needs to monitor the progress of TD4.
Member Since: July 1, 2008 Posts: 13 Comments: 7387
Thanks post 101, I submitted a ticket, not sure who to tell or contact. I was wondering if I was the only one with this issue.
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Quoting frecklespugsley:
I live in MD. Any chance this thing may affect me? It looks more likely that it will go out to sea.


It does look like it may go out to sea. Who knows. BBL
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Quoting CaneAddict:
The NHC's track is WAY to far north in my opinion. The models don't have a very good handle on the system yet so I expect that track to shift quite significantly to the left. I'll have an blog update w/my graphics around 5PM today when the system should be a moderate tropical storm in my opinion and the models have a change of heart once they grip on. I'll be back in a few.
if i had a nickel for every time that has been said this morning i coulds quit my day job
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We need this one to make our swell window before any recurvature.

North of the Antilles, west of Bermuda, a slow down in forward speed motion, cat 3 status, and finally a 24-36 hour 'loop-de-loop' before exiting stage right into the north atlantic.

Is that too much to ask for?
Member Since: August 16, 2007 Posts: 0 Comments: 73
i am getting frustrated by the blog because i type out a post and hit post comment and my comment never shows up is this normal???
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NHC advisory indicates that the current movement is towards the WNW, or 290 degrees... That is, IMO, a generous WNW estimate, because currently it looks to be no better than 280 degrees...
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i suppose i shouldn't say "at this point", but you know what i mean. GOM not likely?
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I live in MD. Any chance this thing may affect me? It looks more likely that it will go out to sea.
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Quoting largeeyes:
NHC has it splittin the uprights. Guess we here in NC will keep an eye on him.


And in VA.
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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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