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 divdog:
caught up in itcz .. must separate from the itcz and with altitude maybe some spin then you may be on to something


Not for an invest. 04L is just to the left around 12N.
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Quoting weedpoet:
It's a fish.


Jeff: "The high wind shear and dry air should weaken and possibly destroy 91L late this week."

{*Sniff*}

It's a DEAD FISH!
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Already got a heat index of 115 here in Milton, Florida.
I'm really quite surprised at how small TD4 is. Back when it was still partially connected to the ITCZ I thought our future "he" would be a much larger system. Seems to me this will be its downfall, when conditions become less favorable. I think what is going to be more important than how much TD4 strengthens over the next couple of days, is how much TD4 grows, if any over the next couple of days. And to me, it seems unlikely that there will be significant expansion, given the fact that relatively dry air will continually lie just to the west of the system, as the ULL moves somewhat in tandem with TD4..
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Im in that cone
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Quoting CyclonicVoyage:
Kinda surprised we don't have 92L yet. Should be soon, IMO.
caught up in itcz .. must separate from the itcz and with altitude maybe some spin then you may be on to something
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IKE "This should quiet the Florida casters...."
153 DestinJeff "What are you? New?"

:-D Of course it would help if the NHC would quit Florida casting.
Copy&paste 9.0N35.0W, 9.1N35.4W, 9.8N36.3W-11.0N38.2W, 11.0N38.2W-30.6N81.4W, BDA, 11.0N38.2W-12.3N40.3W, 12.3N40.3W-30.6N81.4W into the GreatCircleMapper.
The leftmost short red line shows that 91L had a heading toward Jacksonville, and the
rightmost short red line shows that 91L had a previous heading toward Fernandina*Beach.

~7miles separation between the two landfalls... after traveling over 2900miles of ocean: 2909miles from the last position, and 3077miles from the previous position
Methinks someone over at NHC threw up their arms at tryin' to figure out 91L's center, and decided to place the latest center as closely inline with the previous two centers as possible.

* Airport codes of JAX and FHB ; BDA is Bermuda.
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10N 30W, Pre 92L

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Quoting yamil20:
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


Nobody is here to watch fish storms. If they all curved out to sea, this place wouldn't exist. I think "excited" is the wrong term. Many people here come for accurate information regarding these storms and the potential impact they may have on their lives. When local mets all poo-poo any system until it is on your backdoor, this place is a valuable asset.
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Just wondering..if a hurricane is cruising along at 17-20 mph, and runs into 30 knots of sheer..what happens? I mean, would it sheer apart faster because it's moving faster, or will it hold its own more because of its forward speed?
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Quoting AussieStorm:

my wife's niece lives in Bermuda.


hey... I listened to your story this morning I had to close my computer with all the thunder and lightening last night but that is an amazing survival story and thank goodness your mom knew CPR! Like I said last night you are very blessed to be here:)
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Member Since: August 11, 2008 Posts: 0 Comments: 2315
Quoting AussieStorm:

oh, can i get some of that heat over here please. It's brass monkey weather here.
You know it's cold when you see a Brass Monkey sporting a fur speedo.
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Kinda surprised we don't have 92L yet. Should be soon, IMO.
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Here we go...
The fourth tropical depression of the 2010 atlantic hurricane season has formed!!


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I have noticed that there is a weakness between the bermuda high and a new high that develops to TD-4's north later on down the road as shown on the models. This would give it that recurve up to the north and potentially out to sea. However, all it would take is for the Bermuda high to be come stronger or the high to the north to merge with the Bermuda high, thus forcing TD-4 back to the WNW and into the SE U.S. coast. I would not completely count TD-4 as fish storm just yet.
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Naples, Florida
93.7 °F
Scattered Clouds
Humidity: 67%
Dew Point: 81 °F
Wind: Calm
Wind Gust: 0.0 mph
Pressure: 30.03 in (Steady)
Heat Index: 115 °F

(Honestly, though, this is pretty typical.)
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Member Since: September 30, 2005 Posts: 0 Comments: 1606
Quoting sammywammybamy:
Jeanne the notorious loop. What caused that loop anyway?
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04L/TD/C
MARK
13.30N/42.78W
Member Since: July 15, 2006 Posts: 178 Comments: 56059
Good morning everyone. thanks Dr.M
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It's 97 and 117 heat index here in Saraland. It's so hot.
sheri
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Quoting muddertracker:
Any chance that TUTT splits?


Ehh, hard to say, but my red line (official track) as of now is a mixture of the GFS and CMC runs. Could head out to sea, but I'm not convinced as others are on here. Could very well head up the East Coast, or turn west into Florida. Or it might just stall and slowly move NW to the Carolinas. Lots of uncertainty out there.
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Quoting cirrocumulus:
TD4 is a drifter.
drifting at 17mph
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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


Hey Patrap, i believe we're being cooked alive..lol.It's pretty unbearable here in BR too. I go out only for bare necess due to a heart condition. Stay ccol. Back to lurking..
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Quoting Floodman:


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

Norht texas in the summertime...yum!

oh, can i get some of that heat over here please. It's brass monkey weather here.
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Quoting CyclonicVoyage:


Forward speed is the likely culprit. 04L is making up for that stall 10 fold.
Forward speed, as we know, will slow intensification somewhat. The forward speed is also a byproduct of being caught in the due west steering. It's possible it could stay south and cross into the Carribean , thereby missing the windshear and TUTT in the vicinity of PR. Again, way too early and upper air sampling needed to get a much more accurate output from model tracks.
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RELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
855 AM EDT MON AUG 02 2010

VALID 12Z FRI AUG 06 2010 - 12Z MON AUG 09 2010

AS HAS BEEN THE STORY FOR WEEKS...TROUGHING IS EXPECTED TO REMAIN
ACROSS THE NORTHWEST AND NORTHEAST WITH A WARM CORE RIDGE
SANDWICHED IN BETWEEN ACROSS THE SOUTHERN PLAINS. THE ONLY ASPECT
OF THE FORECAST WHICH HAS CHANGED HAS BEEN THE STRENGTH OF THESE
FEATURES...WHICH HAS BEEN INCREASING AS THE SUN ANGLE SLOWLY
LOWERS WITH TIME. THE 06Z GFS/00Z UKMET PROGRESS TROUGHING OUT OF
THE NORTHWEST...WHICH WAS NOT SUPPORTED BY THE REMAINDER OF THE
DETERMINISTIC OR ENSEMBLE MEANS...SO THEIR SOLUTIONS WERE NOT
USED. THE GEFS/ECMWF ENSEMBLE MEANS...00Z CANADIAN...AND 00Z
ECMWF WERE ALL CONSIDERED USABLE WITHIN THE WESTERLIES.
CONFIDENCE IN THIS PATTERN ACROSS THE NORTHERN AND CENTRAL UNITED
STATES IS NEAR TO ABOVE AVERAGE.

ANOTHER WRINKLE IN THE FORECAST IS THE TROPICAL DISTURBANCE NEAR
12N 41W THIS MORNING...WHICH THE DETERMINISTIC GUIDANCE FLING NEAR
OR OFFSHORE THE EAST COAST OF NORTH AMERICA. NONE OF THE
DETERMINISTIC GUIDANCE HAS SHOWN MUCH CONTINUITY WITH THIS SYSTEM
FROM DAY TO DAY. THE ENSEMBLE GUIDANCE WITH THIS FEATURE HAS ALSO
BEEN QUESTIONABLE WITHIN ANY OF ITS 00Z AND 12Z RUNS OVER THE PAST
SEVERAL DAYS...THOUGH THE MULTI-DAY WAVERING IS AROUND A TRACK
WHICH MOVES JUST NORTH OF THE GREATER ANTILLES UP THE BAHAMAS AND
OFFSHORE THE FLORIDA COAST. HOWEVER...THERE ARE A FEW ENSEMBLE
MEMBERS WHICH SUPPORT THE ECMWFS ATTEMPT TO RECURVE THIS SYSTEM
OFFSHORE ATLANTIC CANADA IN A WEEK...BUT JUST AS MANY WHICH MOVE
THROUGH THE FLORIDA STRAITS AND KEYS. THE TROUGH IN THE EAST IS
NOT EXPECTED TO BE STRONG ENOUGH TO CAUSE FULL RECURVATURE...AND
THE COL IN THE FLOW PATTERN SHOULD REMAIN TO ITS NORTH...SO
FLORIDA AND THE GULF COAST ARE NOT IN THE CLEAR. THE WEAKNESS
ALOFT TO ITS NORTH SHOULD SLOW ITS FORWARD MOTION AS IT NEARS
FLORIDA AT THE END OF THE PERIOD. DUE TO THIS TRACK EXPECTATION
AND CONTINUITY FROM THE 16Z CALL ON SUNDAY...THE 00Z CANADIAN WAS
USED AS PART OF THE PREFERENCE. THE 00Z ECMWF HAD TO BE DITCHED
FOR THE 00Z ECMWF ENSEMBLE MEAN AS PART OF THE PREFERENCE LATE IN
THE PERIOD DUE TO ITS QUESTIONABLE HANDLING OF THIS TROPICAL
DISTURBANCE. NEEDLESS TO SAY...CONFIDENCE IS LOWER THAN AVERAGE
IN THIS ASPECT OF THE FORECAST...AND CHANGES MAY OCCUR DURING THE
16Z COORDINATION CALL WITH NHC TODAY.

ROTH


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What the bleep is behind 04?
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It's a fish.
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Quoting howarjo1943:
This system will almost certainly head well north of the islands with slow intensification to a min hurricane. It is embedded in the WNW flow seen on water vapor and conditions will continue to be favorable for slow to moderate intensification. Too uncertain to say after it moves north of the isles where it will go...Have to lean toward it heading out to sea as that is what most cyclones do when they move north of the islands but things can change in the 4-7 day forecast period. What is the avg human and model error on these forecasts, like 300 miles by day 5?


Isabel, Floyd, and I think Fran all moved north of the islands and made landfall on the east coast, but that is mostly because of that bermuda high.
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Quoting angiest:


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



You are exactly right. Everyone should be aware this time of year and have a plan.
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Quoting Dakster:
Flood - 'morning (or almost afternoo here).

I hope you are correct... or at least this stays a fish storm. However, I will remain ever vigilant at watching. As a "Watched Storm Never Comes".


One can only hope, Dak...you're a smart man though; keep an eye on them...
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Quoting Goaskalice:


A friendly reminder that Bermuda is out there in your fishing zones!

my wife's niece lives in Bermuda.
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Quoting reedzone:
Photobucket


Your southern track would just plain outright suck for me.
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This system will almost certainly head well north of the islands with slow intensification to a min hurricane. It is embedded in the WNW flow seen on water vapor and conditions will continue to be favorable for slow to moderate intensification. Too uncertain to say after it moves north of the isles where it will go...Have to lean toward it heading out to sea as that is what most cyclones do when they move north of the islands but things can change in the 4-7 day forecast period. What is the avg human and model error on these forecasts, like 300 miles by day 5?
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269. IKE
Large view....

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Quoting reedzone:
Photobucket
Any chance that TUTT splits?
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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.

Totally agrre with you. Mother nature is in charge and does not care for models. At the end of the day we can only try to guess the future track of these systems.
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TD4 is a drifter.
Member Since: September 30, 2005 Posts: 0 Comments: 1606


It would be nice if we were getting some of this moisture heading towards the Islands. We have not had rain for over a month, They are finally calling for a bit of rain here this week :)
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I could deal with a bit fat H sitting right over Florida. Just crank up the AC and pour some sweet tea. Watch that TD curve right on by.
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Photobucket
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Wow, that didn't take long to ramp up. LET THE SPECULATION BEGIN!
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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.
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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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