Potentially dangerous 92L steadily developing; Igor nears hurricane strength

By: Dr. Jeff Masters , 3:04 PM GMT on September 11, 2010

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A tropical disturbance (92L) over the Eastern Caribbean, a few hundred miles south of Puerto Rico, is steadily organizing and appears likely to develop into a tropical depression by tonight or Sunday morning. Satellite loops show an impressive and expanding region of heavy thunderstorms, with good spiral banding and respectable upper-level outflow on all sides. Long range radar out of Puerto Rico shows that heavy rains are now affecting that island, but there is no rotation to the radar echoes evident. However, the rain bands are becoming more intense and more organized. San Juan, Puerto Rico reported a heavy rain squall at 8:44 am this morning, and radar estimates suggest two inches of rain fell in this squall just southeast of San Juan. Wind shear over 92L is low, 5 - 10 knots. The waters beneath are at near-record warmth, 30°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies to the north and west of 92L, and this dry air could interfere with development at times over the next few days.


Figure 1. Morning satellite image of 92L.

Track forecast for 92L
The disturbance is moving west-northwest at 11 mph, and steering currents favor a continuation of this motion for the next three days. Model support for development is scattered. The GFS and NOGAPS models do not develop 92L. The GFDL and ECMWF models predict development, with a track taking 92L into Mexico's Yucatan Peninsula on Wednesday. The HWRF model has a more northwesterly track, taking 92L over the Dominican Republic, Haiti, and Cuba, but this model has been trending too far north in its tracks. I expect 92L will follow a path south of the islands, bringing it near or just south of Jamaica on Monday, then into the Yucatan Peninsula on Wednesday. On this track, the southern Dominican Republic can expect heavy rains of 3 - 6 inches tonight through Monday morning; southern Haiti can expect similar rains Sunday through Monday, and Jamaica and the Cayman Islands can expect heavier rains of 4 - 8 inches Monday and Tuesday. Eastern Cuba will probably escape 92L's heaviest rains in this scenario (Figure 2.)

Intensity forecast for 92L
I can't find any reason to doubt this will be a tropical storm by Sunday or Monday, and potentially a Category 1 or 2 hurricane by Wednesday, if 92L avoids passage over Hispaniola and Cuba. The SHIPS model predicts wind shear will remain low, 5 - 10 knots, through the period, and makes 92L a Category 1 hurricane by Monday night. Water temperatures are certainly warm enough to support development. The main detriment to intensification is likely to be dry air, and 92L could wrap in some of the dry air to its northwest at times, slowing down development. The first Air Force Hurricane Hunter mission into 92L is scheduled for Sunday afternoon, but there will be a research mission by the National Center for Atmospheric Research G-V jet today that will give us valuable information on 92L's large scale environment and potential for development.


Figure 2. Forecast rain amounts from 92L from the 2am EDT Saturday run of the GFDL model. This model predicts most of 92L's heaviest rains will miss Haiti, but will affect Jamaica, the Cayman Islands, and the Yucatan Peninsula. Image credit: Morris Bender, NOAA/GFDL.

Igor
Tropical Storm Igor is very close to hurricane strength, and appears destined to become a large and powerful major hurricane over the Central Atlantic in the days to come. Wind shear is moderate, 15 - 20 knots, waters are warm, 28°C, and Igor has moistened its environment enough to keep the dry air of the Saharan Air Layer (SAL) at bay. Igor will track west under the influence of a strong ridge of high pressure for the next three days, then turn more to the west-northwest in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic on Tuesday and Wednesday. This should allow Igor to pass several hundred miles to the northeast of the Lesser Antilles. In the longer range, Igor may be a threat to Bermuda, and has a slight chance of making landfall on the U.S. East Coast or Canada. Climatology shows that about 10% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 10% for Bermuda and 5% for Canada. The forecast steering pattern for the coming two weeks from the GFS model shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without affecting any land areas. The odds of Igor hitting land in the U.S. or Canada are probably close to their climatological 10% and 5% probabilities, respectively.

Elsewhere in the tropics
A new tropical wave (Invest 93L) emerged from the coast of Africa yesterday, and is already showing signs of organization. Most of the models predict 93L will develop into a tropical depression 2 - 4 days from now, and NHC is giving 93L a 30% chance of developing by Monday.

Next post
This may be my only post today; I'll have a new post Sunday morning.

Jeff Masters

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Quoting JupiterFL:


Thats because you are a much better person than the rest of us.


"rest of us", are to many people to argue against them, so is better I be quiet for now, I don't want to be see like I was talking in the name of other people I don't even know.:)
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Quoting Levi32:
Good morning all.

Tropical Tidbit for Saturday, September 11th, with Video



Very nicely done.
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421. IKE
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Great shot Jonelu.... Did you re-crop that??
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Quoting Jedkins01:
I don't see why 92L will struggle with dry air. I have seen people look at water vapor satellite and see dry air on it and say that it could be a threat to a tropical system.

What people do not realize is water vapor satellite only shows upper level moisture. The lower half of the atmosphere, where most moisture is held in the tropics, does not show on water vapor satellite.

Therefore what may appear as dry air on satellite does not mean the air is overall dry. Water vapor satellite is not really designed for measuring moisture at all, rather it is used to get a better picture of what is going on in the upper levels as apposed to infrared or visible.

See almost all of moisture that a hurricane gathers does not come from the upper levels obviously, being that it is a tropical cyclone of course.

Therefore only PWATS give a great example whether dry air is actually a threat to a tropical system. Since this is the measurement for total atmospheric moisture.

Although dry air on water vapor satellite CAN indicate a very dry air mass, it certainly doesn't always. The upper levels can be dry, while the lower levels of the atmosphere can be very moist. There an atmosphere can also be very moist even if the the water vapor satellite shows dry air in the upper levels.


Dry air is a threat to a tropical cyclone IF the overall atmosphere is dry. Mainly the over low to mid level dry air.



That being said, overall the PWATS ahead of 92L look quite high in the Caribbean as they usually are, so I don't see why 92L has any dry air threat.

The air mass isn't as moist as it can be in the Caribbean, but there's plenty enough moisture to not threaten 92L.


I disagree with Dr. Masters in this case, because of my observation...



I guess that's why when we see "dry" air on these models in south Louisiana it is still muggy "gumbo" weather outside....interesting! i'm a believer!!!!
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It's so interesting that there is barely any model support for 92L...it doesn't make any sense. It will be interesting to see if the models were correct.

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Quoting clwstmchasr:


Maybe, I think Texas needs to keep a close eye on 92L.


If so, probably extreme South Texas, but who knows. These models do not even have a storm to initiate on.
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Quoting Levi32:
Out 'til later.

Tropical Tidbit for Saturday, September 11th, with Video


YAY!!!!
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Quoting Levi32:
Good morning all.

Tropical Tidbit for Saturday, September 11th, with Video


Good blog. Those last models you talk, show a more westward Igor, any danger to the antilles in your opinion or this is going to be like Earl a suffering longgg wait?
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412. Vero1
IGOR is getting his eye!

VISIBLE SATELLITE IMAGERY ALSO
INDICATES A BANDING EYE FEATURE WITH SCATTERED STRONG CONVECTION
WITHIN 60 NM OF THE CENTER.
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411. IKE
120 hour ECMWF...

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models really do not do much with 92l
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409. Vero1

Atlantic Tropical Weather Discussion
--------------------------------------------------------------------------------


000
AXNT20 KNHC 111756
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT SEP 11 2010

...SPECIAL FEATURES...

TROPICAL STORM IGOR IS CENTERED NEAR 17.4N 39.5W AT 11/1500 UTC
OR ABOUT 895 NM W OF THE CAPE VERDE ISLANDS AND ABOUT 1275 NM E
OF THE LEEWARD ISLANDS MOVING W AT 17 KT. ESTIMATED MINIMUM
CENTRAL PRESSURE IS 995 MB. MAXIMUM SUSTAINED WIND SPEED IS 60
KT WITH GUSTS TO 75 KT
. GRADUAL INTENSIFICATION OF IGOR IS
FORECAST OVER THE NEXT FEW DAYS AS IT TRACKS ON THE SOUTHERN
PERIPHERY OF A CENTRAL ATLANTIC UPPER LEVEL ANTICYCLONIC
CIRCULATION CENTERED NEAR 23N46W. VISIBLE SATELLITE IMAGERY ALSO
INDICATES A BANDING EYE FEATURE WITH SCATTERED STRONG CONVECTION
WITHIN 60 NM OF THE CENTER.
ELSEWHERE SCATTERED MODERATE
CONVECTION IS FROM 14N-18N BETWEEN 38W-44W...LOCATED MAINLY
WITHIN THE SW QUADRANT. SEE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS.

A 1009 MB SURFACE LOW PRESSURE IS CENTERED IN THE EASTERN
CARIBBEAN SEA NEAR 14N64W
MOVING W AT 10 TO 15 KT. BROAD
LOW-LEVEL CYCLONIC FLOW IS LOCATED IN THE CARIBBEAN BETWEEN
60W-70W ALONG WITH A FAVORABLE UPPER LEVEL DIFFLUENT ENVIRONMENT
DUE TO AN UPPER LEVEL ANTICYCLONE NEAR 18N67W. SCATTERED
MODERATE AND ISOLATED STRONG CONVECTION COVERS A LARGE AREA FROM
11N-18N BETWEEN 62W-70W...INCLUDING PORTIONS OF THE US/UK VIRGIN
ISLANDS AND PUERTO RICO. IT IS POSSIBLE THAT A TROPICAL
DEPRESSION MAY FORM DURING THE NEXT FEW DAYS AS THE SYSTEM MOVES
TOWARD THE CENTRAL AND WESTERN CARIBBEAN SEA.

A TROPICAL WAVE IS FROM 08N TO 19N ALONG 15W MOVING W AT 10 TO
15 KT. A 1008 MB LOW IS ANALYZED ALONG THE WAVE AXIS NEAR 13N15W

WITH METEOSAT-9 VISIBLE SATELLITE IMAGERY INDICATING BROAD
CYCLONIC FLOW IN THE LOW-LEVEL CLOUD FIELD EXTENDING FROM
INTERIOR W AFRICA ALONG 08W WESTWARD INTO THE EASTERN ATLC ALONG
27W. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS FROM
09N-16N BETWEEN 13W-22W. AS THE WAVE MOVES OUT OVER THE OPEN
WATERS OF THE EASTERN TROPICAL ATLC AND INTERACTS WITH W-SW
MONSOONAL FLOW ALREADY IN PLACE FROM 06N-11N BETWEEN 15W-27W...
FURTHER ORGANIZATION OF CONVECTION IS ANTICIPATED WITH THE
POSSIBILITY OF TROPICAL CYCLONE DEVELOPMENT OVER THE NEXT COUPLE
OF DAYS.



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Quoting IKE:
Day 4 ECMWF...Link


A bit farther south on this run, looks like a Bermuda hit. Thanks for the continued updates.
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407. IKE
Day 4 ECMWF...Link
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kind of eery how there seems to be a shield around the US this year
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Quoting Levi32:


I think we will have our turn, unfortunately. Very few Cape Verde hurricanes ever hit the United States in any year, but once the activity shifts west we will be right in the target zone.

How do you see the pattern shaping up next month, in terms of track?
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It looks like Igor and 93L will miss CONUS and hopefully spare Bermuda, but have you seen the wave train over Africa? Like StormW had indicated the weaknesses that allow northerly turns will not be there for all these waves. The question remains how many storms will it take to lower the SST's in the CATL.
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Out 'til later.

Tropical Tidbit for Saturday, September 11th, with Video
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Quoting Neapolitan:
Ah, well, soon enough it'll get a new color...if not a new symbol:

CLICK FOR LARGER IMAGE

Tropical weather-related image


itcz comin down folks. looks like stormw will not eat crow this time. they are deftly coming lower
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Quoting bird72:

I'm always more concern about peoples life in a hurricane strike, than a bottle of liquor, but is a matter of priorities.


Thats because you are a much better person than the rest of us.
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399. IKE
72 hour ECMWF...Link
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Quoting TexasHurricane:



hmmmmmm, so MX again huh? This season is just so strange....MX and out to Sea...


I think we will have our turn, unfortunately. Very few Cape Verde hurricanes ever hit the United States in any year, but once the activity shifts west we will be right in the target zone.
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Quoting Levi32:
Good morning all.

Tropical Tidbit for Saturday, September 11th

great information Levi.Thank you for taking the time to show that.
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Southern portions of the convection have pretty much dissipated.

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Quoting GTcooliebai:

Hey Levi what's your thoughts on 93L?


I want to see it come fully off Africa first, and when there's multiple storms I don't usually have the time to analyze the steering for each of them, so I stick to the ones that are closest to land. 93L will be worried about later.
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Ah, well, soon enough it'll get a new color...if not a new symbol:

CLICK FOR LARGER IMAGE

Tropical weather-related image
Member Since: November 8, 2009 Posts: 4 Comments: 13465
Quoting Levi32:
Good morning all.

Tropical Tidbit for Saturday, September 11th, with Video


Hey Levi what's your thoughts on 93L?
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Im concerned for Bermuda now with Igor. I know its early...but the models are showing a VERY strong large hurricane. Even a near miss could be bad news.
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Quoting Levi32:
Good morning all.

Tropical Tidbit for Saturday, September 11th, with Video




hmmmmmm, so MX again huh? This season is just so strange....MX and out to Sea...
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388. JRRP
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Quoting serialteg:


rain and wind, my friend. welcome cool. had to stop doing the yard

Oh man that's hurt.....
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Quoting Labayourambler:
what are the chances that 92L will head towards La coast??


Too soon to tell, but chances are still good. I predict La will get the left (West) side of the storm. The eye will pass over me in Biloxi.
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Quoting bird72:

Now you feel the rain....


rain and wind, my friend. welcome cool. had to stop doing the yard
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Good morning all.

Tropical Tidbit for Saturday, September 11th, with Video

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Looks impressive.
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Quoting serialteg:
pr's south gettin hit by the first bands

Now you feel the rain....
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Quoting AtHomeInTX:


Hey Tex. :)


wumail
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378. IKE
48 hour ECMWF...Link
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Quoting Prgal:


Good afternoon! We are under water lol! Its pouring here!

Toa Alta, below a strong rain.
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pr's south gettin hit by the first bands
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I dont know but 92L looks like its working it, I believe in the 60%
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2pmNHCDiscussion

IGOR: GRADUAL INTENSIFICATION OF IGOR IS FORECAST OVER THE NEXT FEW DAYS AS IT TRACKS ON THE SOUTHERN PERIPHERY OF A CENTRAL ATLANTIC UPPER LEVEL ANTICYCLONIC CIRCULATION CENTERED NEAR 23N46W.

92L: IT IS POSSIBLE THAT A TROPICAL DEPRESSION MAY FORM DURING THE NEXT FEW DAYS AS THE SYSTEM MOVES TOWARD THE CENTRAL AND WESTERN CARIBBEAN SEA.
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Quoting Prgal:


Good afternoon! We are under water lol! Its pouring here!


it look like 6 pm is pitch black
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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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