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 Prgal:


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


it look like 6 pm is pitch black
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Quoting winter123:
wow two more likely US misses. How are we so lucky?
Did you see the HWRF ?...Link
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370. IKE
Latest ECMWF @ 24 hours...

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wow two more likely US misses. How are we so lucky?
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Quoting galvestonhurricane:


Not very high considering 92's track and computer model support - probably more towards mexico


If this goes to MX then this season is just really weird and so far pretty predictable. Strange.....
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367. Prgal
Quoting sunlinepr:


Where is PR???


Good afternoon! We are under water lol! Its pouring here!
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Well I'm not waiting for Monday to decide to prepare for either heavy rain or something worse. Since I have help today I'm cleaning the drains and gutters and moving anything non essential that could be a hazard in a tropical storm. Checking the trusty generator too
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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...


Interesting. I'd never heard this before. Thanks. :)
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Member Since: July 11, 2006 Posts: 14 Comments: 11174
Quoting Labayourambler:
what are the chances that 92L will head towards La coast??


Not very high considering 92's track and computer model support - probably more towards mexico
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Quoting Drakoen:


I'm actually wondering why they don't just go ahead and classify 93L already.


They probably want to verify some persistence...it's barely off the African coast...come on now. We all know that anything can happen when these things roll off the coast.

In reference to 92L, last night, it was looking horrible with little convection. I wake up and there's a huge blob there. Granted no or little circulation, but still. I think many of you are being overly critical of 92L.
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NHC Late on the 2 p.m. Discussion
Member Since: July 11, 2006 Posts: 14 Comments: 11174
Kissing Hebert Box......Interesting...
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what are the chances that 92L will head towards La coast??
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Quoting AtHomeInTX:
WOW. 12Z CMC has Igor much bigger than last run and it seems more of a threat to the islands.
But that may be because of the bigger size and not track. On this it still seems to take 92L to the north but then turns it w/wsw at the end of the run.
Link


Hi AtHome....
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Quoting foggymyst:
what is 92l projected path, plz?


Yucatan
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355. ackee
I am surprise NHC still has 92L at 60 percent
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Where is PR???
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WOW. 12Z CMC has Igor much bigger than last run and it seems more of a threat to the islands.
But that may be because of the bigger size and not track. On this it still seems to take 92L to the north but then turns it w/wsw at the end of the run.
Link
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Quoting Snowlover123:
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM IGOR...LOCATED ABOUT 1030 MILES WEST OF THE CAPE VERDE
ISLANDS.

SHOWERS AND THUNDERSTORMS HAVE CHANGED LITTLE IN ASSOCIATION WITH A
BROAD AREA OF LOW PRESSURE LOCATED OVER THE EASTERN CARIBBEAN
SEA. /em>
Perhaps when they say it has change little , meaning that COC is not yet visible or define, because in banding and convection it has change a lot since this morning.
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Quoting btwntx08:

yes but 92L could be more of a threat to someone


I didn't think they use whether or not a storm is likely to impact land (in the next 48 hrs) to determine how likely an area of interest is to develop into a tropical weather system. That doesn't make any sense to me.
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Quoting weatherwatcher12:

That's exactly what I thought when I saw its position.


We have been very lucky here in Jamaica since the passage of Gustav...I wonder if our luck will hold?. If we run out of luck then Haiti could also be in trouble in a way that I don't want to imagine. 92L does not look like a fish storm at all.
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93L Prediction...
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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...
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346. JRRP
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Quoting Snowlover123:


I know right? IMO, the numbers should be switched.


I figured 92L would stay the same, but thought that 93L would be around 60%. Good call with 92L as it still needs to get to the surface and I can see their case with 93L as convection has waned.
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Quoting btwntx08:
needs a small burst more and its there


Sure as heck looks like it's "there" to me! Definitely better looking then 92L.
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Quoting MiamiHurricanes09:
I don't know why 93L is so low, and 92L is so high.


Simple. 92L is a lot closer to land areas and has the potential to ramp up to a strong hurricane if it can ever develop closed a low level circulation. Also, 93L just emerged from Africa and the NHC loves to have their 12 or more hours of "such and such."
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Quoting MississippiWx:


It stayed the same? You don't say? LOL


I know right? IMO, the numbers should be switched.
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Quoting Snowlover123:


Miami: Post 327. ;)

92L has a 60% chance, and 93L has a 50% chance...
I don't know why 93L is so low, and 92L is so high.
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Quoting Snowlover123:
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM IGOR...LOCATED ABOUT 1030 MILES WEST OF THE CAPE VERDE
ISLANDS.

SHOWERS AND THUNDERSTORMS HAVE CHANGED LITTLE IN ASSOCIATION WITH A
BROAD AREA OF LOW PRESSURE LOCATED OVER THE EASTERN CARIBBEAN SEA.
ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR DEVELOPMENT...AND A
TROPICAL DEPRESSION COULD FORM AS THE SYSTEM MOVES WESTWARD INTO
THE CENTRAL AND WESTERN CARIBBEAN SEA. THERE IS A HIGH CHANCE...60
PERCENT
...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS. REGARDLESS OF DEVELOPMENT...LOCALLY HEAVY RAINFALL
IS POSSIBLE IN THE NORTHERN LEEWARD ISLANDS...PUERTO RICO...THE
VIRGIN ISLANDS...AND HISPANIOLA DURING THE NEXT DAY OR SO. THESE
RAINS COULD CAUSE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES...
ESPECIALLY IN MOUNTAINOUS TERRAIN.


It stayed the same? You don't say? LOL
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Dvorak numbers at 2:30 or so will be interesting.
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It should have read, No much DRY AIR aroung 93L, so it's going to be a healthy one...
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Quoting MiamiHurricanes09:
I expect 93L to go red at 2pm EDT. IMO, it should be up near 90% right now.


Miami: Post 327. ;)

92L has a 60% chance, and 93L has a 50% chance...
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what is 92l projected path, plz?
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No much water vapor over 93L, so it's going to keep healthy....
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Quoting moonlightcowboy:


That's a disturbing arrow in the Caribbean. The other is too but still hoping for a recurve there.
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I expect 93L to go red at 2pm EDT. IMO, it should be up near 90% right now.
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FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM IGOR...LOCATED ABOUT 1030 MILES WEST OF THE CAPE VERDE
ISLANDS.

SHOWERS AND THUNDERSTORMS HAVE CHANGED LITTLE IN ASSOCIATION WITH A
BROAD AREA OF LOW PRESSURE LOCATED OVER THE EASTERN CARIBBEAN SEA.
ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR DEVELOPMENT...AND A
TROPICAL DEPRESSION COULD FORM AS THE SYSTEM MOVES WESTWARD INTO
THE CENTRAL AND WESTERN CARIBBEAN SEA. THERE IS A HIGH CHANCE...60
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS. REGARDLESS OF DEVELOPMENT...LOCALLY HEAVY RAINFALL
IS POSSIBLE IN THE NORTHERN LEEWARD ISLANDS...PUERTO RICO...THE
VIRGIN ISLANDS...AND HISPANIOLA DURING THE NEXT DAY OR SO. THESE
RAINS COULD CAUSE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES...
ESPECIALLY IN MOUNTAINOUS TERRAIN.

SATELLITE IMAGERY AND UPPER-AIR OBSERVATIONS INDICATE THAT THE
VIGOROUS TROPICAL WAVE AND ASSOCIATED LOW PRESSURE AREA NEAR THE
WEST COAST OF AFRICA HAVE BECOME BETTER ORGANIZED DURING THE PAST
SEVERAL HOURS. SURFACE PRESSURES ARE QUITE LOW...AND A TROPICAL
DEPRESSION COULD FORM OVER THE NEXT COUPLE OF DAYS AS THIS SYSTEM
MOVES TOWARD THE WEST OR WEST-NORTHWEST AT 10 TO 15 MPH. THERE IS
A MEDIUM CHANCE...50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS.
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Quoting sunlinepr:
Link

What's her name, 93L???


Mama Grizzly
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Link

What's her name, 93L???
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Super 93L....
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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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