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 Hurricanes12:


It's already receiving dry air and it's going to be sheared quite a bit in a day or two.


I never mentioned anything about it becoming a Hurricane. I know there are factors inhibiting strengthening. I'm talking about the track, it's too early to tell if this recurves or not.
Member Since: July 1, 2008 Posts: 13 Comments: 7340
Quoting sammywammybamy:


Illegible here. Please post a link instead of the full graphic. Thanks.
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ok back later
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Quoting oracle28:


Personally, I think the hyping of "storms" like Bonnie, numb people to the real threats of major hurricanes. People were saying it's (91L) already a tropical storm, which is nuts.

1) It's not expected to reach hurricane strength.
2) The closest landmass in the 'expected' path is Bermuda.

If a recurving TS fascinates you, enjoy it. But don't get angry for being reminded it's a fish TS.


but to say that now when it just formed and is still 1350 miles from any landmass is even more nuts
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The best thing I have heard is, "I'll believe it when I see it." Ike said it believe. At least someone is keeping it real.

This season has all been about hype so far. Maybe that's all it will be. It would be nice.

Member Since: August 4, 2009 Posts: 0 Comments: 497
Quoting reedzone:
Sorry I'm holding on to a western forecast, I don't see this recurving. I called Bill right, so we'll see what happens with this one. Guys you can't just go by the models and call it a fish storm, it's only at 40W and many things can change.


It's already receiving dry air and it's going to be sheared quite a bit in a day or two.
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Here's an article from the Palm Beach Post:

Very fitting for the current situation...*goes into lurk mode*.

As height of storm season arrives, forecasters warn not to pay too much attention to 'the skinny line'

It's really the only question: Where's the storm going?

With the start of August comes the height of the hurricane season.

Traditionally, about two-thirds of hurricanes form in August or September. On average, the first forms Aug. 10; Alex, a hurricane, already showed up June 29 of this year and Tropical Storm Bonnie came and went in late July. The first "major" storm, of Category 3 or higher on the Saffir-Simpson scale, on the average, forms Sept. 4.

Now also is the time when storms are more likely to form off in the central and eastern Atlantic Ocean, giving them plenty of time to feast on bathtub-warm water as they move thousands of miles towards the North American coast.

The arrival of the high season also means that now is when people really start looking at those "cones of probability."

And human nature leads most to focus on the "skinny little line."

It doesn't show where the storm definitely will go, but where forecasters think right now it's most likely to go. The storm almost never follows that line exactly, and it can change from one advisory to another.

But people follow it religiously, and if they're not in its bull's eye, they relax.

That can be a mistake.

In 2004, virtually the entire Gulf coast, some 400 miles from Key West to Naples to the Big Bend, was in the cone of Hurricane Charley. But the "skinny line" aimed it at Tampa Bay.

Was the forecast off by more than 60 miles, the distance from there to Port Charlotte?

Not really. Forecasters say it was off by only about a dozen miles - the difference between staying at sea and making the jog that angled it ashore.

"It's not that much of a deviation," National Weather Service meteorologist Robert Molleda told a group of journalists last week . "You all the remember the stories of people in the Punta Gorda/Port Charlotte area saying they were surprised by the storm - despite the fact that they were under hurricane warnings and they were well within the cone."

And in fact, at 5 p.m. on Aug. 12 - less than 24 hours before of landfall - the chances for both Port Charlotte and Tampa Bay getting hurricane winds was 30 percent.

Even the probability cone changes constantly. On Monday, it might show the storm nearing your area by Friday. By Wednesday, it might show the storm nearing a spot on Friday that's hundreds of miles from you.

And forecasters say a third of all storms track outside it at some point.

The cone shows only the most likely places where the absolute center of the storm will strike, not the extent of wind fields, which can stretch hundreds of miles. And they're not consistent. Andrew bent fences in Boca Raton, 80 miles north of its Homestead landfall, but Key Largo, only about 25 miles south, had nearly no wind effects.

In a simulation based on the large, fast-moving 1938 New England "Long Island Express" hurricane, the cone for "Hurricane Shirley" showed it staying off the Carolinas and making landfall around New York.

But it also gave a 90 percent chance of tropical storm force winds along the coast from the Carolinas to New England, well out of the cone.

Such uncertainty makes it tough when forecasters post watches up to 48 hours before landfall and warnings, up to 36 hours in advance.

Storms can do all sorts of things in that time, and even a 30- or 40-mile shift is, meteorologically, a small hiccup.

That means that just because you end up not getting hit by hurricane-force winds, it doesn't mean the forecasters were way off; it just means hurricanes are big and messy and unpredictable.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
One hour and a half after TD4 is official and bloggers are ripping the storm that they declared TD 4 hours before the NHC lol. Much more entertaining to not post and sit back and watch.
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Quoting Dropsonde:
I know, this has really gotten ridiculous. <rant>I don't mind the RIP posts as much as I mind the posters who jeer at or attempt to shame people who do like watching development and want it to happen because it is amazing and beautiful. This is a blog by a meteorologist, which is frequented by meteorologists, meteorologists-in-training, and people who like watching interesting weather for its own sake, not because it is "cool" to see houses destroyed. Anyone who cannot understand that extreme weather is fascinating for its own sake and thinks that anyone who enjoys it just wants to see human dwellings get destroyed needs to find another blog, IMO! Nature will do what the laws of physics dictate it must do, and if human settlements are in the way, that's unfortunate, but it doesn't make the weather phenomena any less amazing and it certainly does not make them evil or horrible. I truly believe that attacking people for enjoying the development of a system is nothing more than trolling, and there is way too much tolerance for it. It is severely decreasing the fun of the blog.</rant>


agreed 100%
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Sorry I'm holding on to a western forecast, I don't see this recurving. I called Bill right, so we'll see what happens with this one. Guys you can't just go by the models and call it a fish storm, it's only at 40W and many things can change.
Member Since: July 1, 2008 Posts: 13 Comments: 7340
Quoting Dropsonde:
I know, this has really gotten ridiculous. <rant>I don't mind the RIP posts as much as I mind the posters who jeer at or attempt to shame people who do like watching development and want it to happen because it is amazing and beautiful. This is a blog by a meteorologist, which is frequented by meteorologists, meteorologists-in-training, and people who like watching interesting weather for its own sake, not because it is "cool" to see houses destroyed. Anyone who cannot understand that extreme weather is fascinating for its own sake and thinks that anyone who enjoys it just wants to see human dwellings get destroyed needs to find another blog, IMO! Nature will do what the laws of physics dictate it must do, and if human settlements are in the way, that's unfortunate, but it doesn't make the weather phenomena any less amazing and it certainly does not make them evil or horrible. I truly believe that attacking people for enjoying the development of a system is nothing more than trolling, and there is way too much tolerance for it. It is severely decreasing the fun of the blog.</rant>


Personally, I think the hyping of "storms" like Bonnie, numb people to the real threats of major hurricanes. People were saying it's (91L) already a tropical storm, which is nuts.

1) It's not expected to reach hurricane strength.
2) The closest landmass in the 'expected' path is Bermuda.

If a recurving TS fascinates you, enjoy it. But don't get angry for being reminded it's a fish TS.
Member Since: July 25, 2008 Posts: 0 Comments: 596
Quoting StormChaser81:


Don't ya think it could change if upper level conditions change, its still a ways out there. I guess I'm out in left field. I hope your right.


After Jeanne, I don't let my guard down. Actually I think there is enough out here to play a game of pepper?
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Quoting Dropsonde:
I know, this has really gotten ridiculous. <rant>I don't mind the RIP posts as much as I mind the posters who jeer at or attempt to shame people who do like watching development and want it to happen because it is amazing and beautiful. This is a blog by a meteorologist, which is frequented by meteorologists, meteorologists-in-training, and people who like watching interesting weather for its own sake, not because it is "cool" to see houses destroyed. Anyone who cannot understand that extreme weather is fascinating for its own sake and thinks that anyone who enjoys it just wants to see human dwellings get destroyed needs to find another blog, IMO! Nature will do what the laws of physics dictate it must do, and if human settlements are in the way, that's unfortunate, but it doesn't make the weather phenomena any less amazing and it certainly does not make them evil or horrible. I truly believe that attacking people for enjoying the development of a system is nothing more than trolling, and there is way too much tolerance for it. It is severely decreasing the fun of the blog.</rant>

Well said!!
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Quoting sammywammybamy:


92L will miss the weakness that TD4 is going to feel.


I think you are correct! 34West is much more likely to have conducive conditions now.
Member Since: September 30, 2005 Posts: 0 Comments: 1606
Quoting KEEPEROFTHEGATE:


Something smells fishy... :)
Member Since: August 4, 2009 Posts: 0 Comments: 497
What does Storm see that NHC doesnt. Storm has been good w/steering so far. Drak has been good and Levi has been good...all three have had awesome discussion with I think Levi coming out and saying 92L will be a threater...meanwhile JVF is casting bones and rubbing a chicken foot on his door...maybe NHC is too...
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Quoting TampaSpin:
ANYONE AND I DO MEAN ANYONE, that does not Currently have this as a Storm for the fishes is truly out in left field with nobody else to throw too....a lot of non-sense being posted now.

Hey Tampa...I usually listen to what you got to say but your off the wall today!!! NOBODY knows where this one is going...on topic now...Pensacol Naval Air Station
95°F
Feels Like: 108°
Wind Chill: 95° Ceiling: Unl
Heat Index: 108° Visibility: 10mi
Dew Point: 76° Wind: 6mph
Humidity: 54% Direction: 290° (WNW)
Pressure: 29.97" Gusts: NA
Report Text: KPNS 021553Z 29005KT 10SM CLR 35/24 A2998 RMK AO2 SLP152 T03500244
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Quoting Drakoen:


Yep right next to a big upper level low


thats probably closer to the truth of this storm than the earlier thinking, because i dont think it will be as strong as earlier thought and therefore not as far north and might even miss the trough
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Quoting TampaSpin:
ANYONE AND I DO MEAN ANYONE, that does not Currently have this as a Storm for the fishes is truly out in left field with nobody else to throw too....a lot of non-sense being posted now.


Don't ya think it could change if upper level conditions change, its still a ways out there. I guess I'm out in left field. I hope your right.
Member Since: August 11, 2008 Posts: 0 Comments: 2315
Member Since: July 15, 2006 Posts: 169 Comments: 53296
Quoting CyclonicVoyage:
Sit back and let some things come together.

000
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

IT
IS WORTH REMINDING USERS THAT THE AVERAGE ERROR OF THE OFFICIAL
TRACK FORECAST AT DAYS 4 AND 5 IS 250 TO 300 MILES.


not possible on here at all lol
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Sit back and let some things come together.

000
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

IT
IS WORTH REMINDING USERS THAT THE AVERAGE ERROR OF THE OFFICIAL
TRACK FORECAST AT DAYS 4 AND 5 IS 250 TO 300 MILES.
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TO ME it looks like its getting ripped ...wait, can i say that? I hope Im not in trouble....
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TD4 may serve as leverage for 33West by moistening up some of the dry air it is moving into. Also, it is rapidly advancing, allowing 33West to gain more energy from the ITCZ.
Member Since: September 30, 2005 Posts: 0 Comments: 1606
*Note to Self*

Avoid this blog when there is a storm out in the Atlantic

See ya later folks lol
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Quoting Floodman:


Isn't that a recipe for squab?

Actually, it is...more or less...mmmmm, lunchtime!
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Quoting nrtiwlnvragn:


By 138 hours barely discernable off the Florida east coast.


Yep right next to a big upper level low
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Quoting sammywammybamy:


92L will miss the weakness that TD4 is going to feel.


Please don't call it 92L. It is not 92L yet, and it causes lots of confusion on the blog.
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Quoting oracle28:


I don't "know". For that matter, does anyone here "know"??
I'm just guessing from the models.
We'll see the models flip flop a lot. Let's see what the models show tomorrow that they have been able to lock on to a well-defined surface circulation.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting MiamiHurricanes09:
I'm in agreement with the 00z run of the CMC. The NAO will likely stay positive for another 5-7 days keeping the subtropical ridge strong.


Maybe the CMC is out to lunch. I'm just saying :).
Member Since: August 4, 2009 Posts: 0 Comments: 497
Quoting IKE:
12Z GFS @ 108 hours....



By 138 hours barely discernable off the Florida east coast.
Member Since: September 23, 2005 Posts: 14 Comments: 10870
About two hours until we see if there is an invest at 33W. TD4 is pulling away and weakening slightly in the last frame. The original CMC of a few days ago had 33West as the bigger storm.
Member Since: September 30, 2005 Posts: 0 Comments: 1606
well guys this is what I think

I think that the models are very crap and will continue to be crap until the noaa's G-IV
flys and maybe after that the models might even go west bound straight into CA or GOM so as I say I wiil not bother with the models till the G-IV flys
Member Since: June 13, 2009 Posts: 2 Comments: 10903
Quoting SeniorPoppy:
Glad most of the Florida wish-casting crowd is gone. It would have to be one hell of a bridging effect of both areas of high pressure to have this disturbance (if it does not get sheared apart first)to make a bee-line to Florida or the Gulf.


Now all we have to do is get rid of the "fish" crowd
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Joe Bastardi from AccuWeather stated yesterday that he did not expect shear to affect TD4 in the long run due to some effect of a nearby trough on the TUTT.
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Quoting MiamiHurricanes09:
How do you know? Models are now beginning to lock on to the system since it is a tropical depression.


I don't "know". For that matter, does anyone here "know"??
I'm just guessing from the models.
Member Since: July 25, 2008 Posts: 0 Comments: 596
People were yelling at the Jasoniscoolman guy, but he is right about the dry air.
Member Since: August 4, 2009 Posts: 0 Comments: 497
Quoting sarahjola:
hi mh09- do you see any evidence that the high will build back in? the nhc has been doing pretty good on projection and i was just wondering what the steering pattern holds for the next 3-5 days? what is making the nhc think that it will go north or be a fish storm? thanks in advance:)
I'm in agreement with the 00z run of the CMC. The NAO will likely stay positive for another 5-7 days keeping the subtropical ridge strong.
Member Since: September 2, 2009 Posts: 130 Comments: 21091
Quoting WeatherNerdPR:

People wanted it to be classified and now that it is they're RIPing it. People are weird!
I know, this has really gotten ridiculous. <rant>I don't mind the RIP posts as much as I mind the posters who jeer at or attempt to shame people who do like watching development and want it to happen because it is amazing and beautiful. This is a blog by a meteorologist, which is frequented by meteorologists, meteorologists-in-training, and people who like watching interesting weather for its own sake, not because it is "cool" to see houses destroyed. Anyone who cannot understand that extreme weather is fascinating for its own sake and thinks that anyone who enjoys it just wants to see human dwellings get destroyed needs to find another blog, IMO! Nature will do what the laws of physics dictate it must do, and if human settlements are in the way, that's unfortunate, but it doesn't make the weather phenomena any less amazing and it certainly does not make them evil or horrible. I truly believe that attacking people for enjoying the development of a system is nothing more than trolling, and there is way too much tolerance for it. It is severely decreasing the fun of the blog.</rant>
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I don't care how warm the water is. The dry air is doing a number on these disturbances in the Atlantic so far.
Member Since: August 4, 2009 Posts: 0 Comments: 497
It WONT track westward it WILL die or go out to sea sad to say
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Quoting ho77yw00d:
IMO not that mine matters but it's only August 2nd and we have a td4 I feel it is a big reminder of what is to come and people should get prepared and enjoy mother nature as she does her work...


Heart of season is well underway, it's already showing by what's coming off Africa
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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.