92L still a threat to develop; Igor a hurricane; TD 12 forming near Africa

By: Dr. Jeff Masters , 2:18 PM GMT on September 12, 2010

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Tropical disturbance (92L) over the Central Caribbean, a few hundred miles south of the Dominican Republic, remains a threat to develop into a tropical depression. Satellite loops this morning show 92L may be starting to form a surface circulation, and an Air Force Hurricane Hunter aircraft will investigate 92L this afternoon to see if a tropical depression is forming.

The storm has only a modest area of heavy thunderstorm with limited low-level spiral banding and upper-level outflow, thanks to an infusion of dry air last night that disrupted the storm. Long range radar out of Puerto Rico shows that heavy rains are affecting that island, but there is no rotation to the radar echoes evident. Wind shear over 92L is low, 5 - 10 knots. The waters beneath are hot, 29.5°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 to west-northwest at 15 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 Belize or Mexico's Yucatan Peninsula on Wednesday. On this track, the southern Dominican Republic can expect heavy rains of 3 - 6 inches today through Monday morning; southern Haiti can expect similar rains tonight through Monday night, and Jamaica and the Cayman Islands can expect heavier rains of 4 - 8 inches Monday and Tuesday. Eastern Cuba can expect rains in the 2 - 4 inch range. Once 92L crosses the Yucatan, the ridge of high pressure steering it is expected to remain in place, forcing 92L to a second landfall in Mexico south of the Texas border.

Intensity forecast for 92L
NHC is putting the odds of 92L developing into a tropical depression by Tuesday at 50%; I'd put them higher, at 70%. However, time is running out for 92L to become a hurricane before hitting the Yucatan Peninsula on Wednesday. Given the current disorganized state of 92L, it would be difficult for it to intensify quickly enough to become a hurricane by then. The storm may also suffer another of its mysterious evening collapses, where it loses most of its heavy thunderstorm activity. However, the SHIPS model predicts wind shear will remain low, 5 - 10 knots, through the period, and 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. There are a number of research flights being made into 92L this afternoon that should help long-term efforts to make better predictions in the future on whether or not disturbances like this will develop or not.


Figure 2. Morning satellite image of Igor.

Igor
Hurricane Igor appears destined to become a large and powerful major hurricane over the Central Atlantic in the days to come. Wind shear is low, 5 - 10 knots, and is expected to drop below 5 knots for the next five days. Waters are warm, 28°C, and will warm to 29°C by Wednesday. Igor has moistened its environment enough to keep the dry air of the Saharan Air Layer (SAL) at bay. Igor is undergoing a period of rapid intensification today, and will probably be a Category 3 or 4 hurricane by Monday.

The track forecast for Igor remains unchanged. Igor will move west under the influence of a strong ridge of high pressure for the next 2 - 3 days, then turn more to the west-northwest then 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 does have a small chance of making landfall on the U.S. East Coast or Canada. Climatology shows that about 15% 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 10% for Canada. The forecast steering pattern for the period 5 - 12 days from now from the ECMWF and GFS models 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. Recent runs of the ECMWF model indicate that these troughs may not be as intense as previously thought, so it is possible Igor has a higher chance than usual to hit land than climatology suggests. One wild card may be the possible development of TD 12 behind Igor. If TD 12 develops into a hurricane, and moves close to Igor, as some of the models are suggesting, the two hurricanes could rotate around a common center, forcing Igor more towards the coast of the U.S. The long term fate of Igor is difficult to predict at this point.

Tropical Depression Twelve forms
Tropical Depression Twelve formed between the Cape Verdes Islands and coast of Africa this morning, and is already affecting the Cape Verdes with winds near tropical storm strength; sustained winds of 35 mph were recorded in the northwest Cape Verdes this morning. You can follow the progress of TD 12 through the Cape Verdes today using our wundermap.

Next post
I'll have a new post Monday morning, and perhaps late this afternoon if events warrant.

Jeff Masters

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Quoting cheetaking:
Igor is definitely showing the potential to continue explosive deepening if it can maintain its present structure:

Note that the latest microwave image on Igor shows a lack of any legitimate secondary bands. This means that unlike Alex, Danielle, and Earl, which had clear secondary wind maximas, nothing is dispersing the energy of the inner eyewall in Igor.



Structure looks like a CAT 4 w/135MPH winds w/central pressure of 945MBS, my humble opinion!!
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Quoting Levi32:
Yaaaa....12z CMC is nasty.
Yeah, depicts something similar to the Japanese. Let's see what the 12z Euro comes out with.
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Honestly, this is simply splitting hairs, but:

Explosive Deepening — A decrease in the minimum sea-level pressure of a tropical cyclone of 2.5 hPa hr-1 for at least 12 hours or 5 hPa hr-1 for at least six hours.

Rapid Deepening — A decrease in the minimum sea-level pressure of a tropical cyclone of 1.75 hPa hr-1 or 42 hPa for 24 hours.

That's the difference. Anyways, I'm simply trying to share some information here. Take it or leave it, but these are official terms.
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Quoting Levi32:
Yaaaa....12z CMC is nasty.
dear god that is one monster approaching the central bahamas !!!!!!!!!!
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Quoting Bordonaro:

Igor is beginning to look like a nail-biting situation at the moment for the Eastern Seaboard!


Yeah man, time to head for the Catskills! :)
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Quoting pottery:

You are being much too harsh here.
You are obviously not reading the thing in the context it was intended.
Agreed. I think pple jumped all over the guy instead of explaining to him why 770mb is not a realistic possibility.

558. Hhunter 1:23 PM EDT on September 12, 2010
bastardi..morning update ..listen to his words onmore western threat for igor..beware s texas on 92l


Ummm.... can we not post the entire Bastardi update again and again and again? Clipping what u feel to be the relevant portion would be more enlightening and less... annoying....

Quoting MiamiHurricanes09:
12z CMC at 144 hours. Igor is moving due west here.

Ewww.... that makes my stomach hurt.
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Quoting Stormchaser2007:
I would not abbreviate Explosive Deepening.

Could lead to a FLDewey joke.
Very True Ideed...LOL. Igor is looking to be most intense this season. I'm sure maritime interests are making appropriate course and rate adjustments.
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638. MZT
Quoting CybrTeddy:
All honestly this is probably a 120 mph Category 3..

Agree. Igor doesn't have the solid ring of -80C cloud tops that Rita had. He is certainly well formed, but not yet in the superstar league. Strong 2, weak 3, is fair enough for now.

As I've pointed out, he only became a hurricane 15 hours ago! People are too anxious. Give him time to grow into his britches! LOL
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Quoting StormW:
Everything you wanted to know about Igor, but were afraid to ask:

HURRICANE IGOR / 92L / 93L SYNOPSIS SEP 12, 2010 ISSUED 9:30 A.M. EDT

Excellent write up Storm. I like it where you say "pump the ridge," because that's basically what we saw with Earl, only hardly anyone cared to explain that the outflow was contributing to the ridge.
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I wonder, if you were inside the eye of Igor, if your ears would be popping.
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Quoting doorman79:


Thanks for the video Levi!


My pleasure!
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Yaaaa....12z CMC is nasty.
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Quoting Levi32:


Hello :)


Thanks for the video Levi!
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Igor is definitely showing the potential to continue explosive deepening if it can maintain its present structure:

Note that the latest microwave image on Igor shows a lack of any legitimate secondary bands. This means that unlike Alex, Danielle, and Earl, which had clear secondary wind maximas, nothing is dispersing the energy of the inner eyewall in Igor.

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actualy i see a weak llc
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Quoting StormW:


He may eventually, but this first trof isn't going to do it.
storm looking at the current pattern in the atlantic so far it looks to me that Florida is pretty well protected so far, but october is another story
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Quoting StormW:


He may eventually, but this first trof isn't going to do it.

Igor is beginning to look like a nail-biting situation at the moment for the Eastern Seaboard!
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Quoting WeatherNerdPR:

:D Hi Levi!


Hello :)
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Quoting StormW:


Drak...not picikn...asking an opinion...did ASCAT catch the whole thing on that pass?

LINK



It didn't catch all of it but enough of of it to suggest that 92L is an open wave.
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Quoting StormW:
Hey pottery!

Greetings!
All is well?

Thanks for the good Latest Discussion.
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Quoting reedzone:
Trends are still going westward with Igor and you all are straight out calling for it to recurve, wow... Give it a few days until it actually turns north. Apparently you all haven't learned anything from Earl.


+100.
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All honestly this is probably a 120 mph Category 3..
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Quoting sailingallover:

There is a huge difference in the Atlantic.
One Earl was supposed to follow Danille. that was the reasoning for recurve. The is no Danille this time.
There is a Trough with another behind with a Low forecast to form along the first one which will certainly pick up Igor.
There is also no extropical low north of the Azores to reinforce the ridge. The one that brushed down behind Danille flattened her for a day if you remember.

Why when the models/forcast are solid and have Igor re-curving do people insist on west casting him?


Exactly!
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The new 12Z CMC model takes IGOR much farther SW heading toward the SE US at 144HR.

http://moe.met.fsu.edu/cgi-bin/cmctc2.cgi?time=2010091212&field=Sea+Level+Pressure&hour=Animation


EARL track?
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615. Vero1
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ECMWF ensembles on Igor 192 hours out..


Also develops 92L into a TS.
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Quoting HurricaneFCast:


Two different definitions Hurricane Swirl. NWS describes Rapid Intensification as 42 mb's in 24 hours. (Loosely)
NHC describes Explosive Deepening (an even stronger rate of intensification than RI) as 2.5 mb/hr for 12 hours or 5 mb/hr for 6 hours.


1 Bergeron (the threshold of explosive deepening for baroclinic storms), is 24 mb/24h.
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Quoting reedzone:
Trends are still going westward with Igor and you all are straight out calling for it to recurve, wow... Give it a few days until it actually turns north. Apparently you all haven't learned anything from Earl.

There is a huge difference in the Atlantic.
One Earl was supposed to follow Danille. that was the reasoning for recurve. The is no Danille this time.
There is a Trough with another behind with a Low forecast to form along the first one which will certainly pick up Igor.
There is also no extropical low north of the Azores to reinforce the ridge. The one that brushed down behind Danille flattened her for a day if you remember.

Why when the models/forcast are solid and have Igor re-curving do people insist on west casting him?
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610. Vero1
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Quoting HurricaneFCast:


Oops... You mean Igor? :D


LOL!

Yup.
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moonsoonal development scott
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Quoting CybrTeddy:
Igor is angry that comrade Ivan tried to steal all the glory.


lol Scary-Looking Igor.
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Quoting Stormchaser2007:
Wow.

Pretty much guarantee that this isn't at 105mph.



Looks like a Category 4 hurricane. NHC might go with a strong Category 3 if they choose the conservative route.
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Quoting TropicalAnalystwx13:


Wilma '05 I believe.


Wasn't Wilma in the GOM when that happened? I know she hit here in her way back east and was still nasty.
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Igor, improving and expanding outflow in all quadrants, with some restriction on the western semicircle. Patriots up 10-0.
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Quoting Drakoen:
No surface circulation on 92L:



Windsat missed 92L.

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Quoting Hurricanes101:
I am not very confident that 92L will develop now


I'm still waiting. After all IIRC it was only supposed to form right before hitting the Yucatan and then hitting as a strong TS/minimal cane. So I'm willing to wait a little more but it does appear less likely now than yesterday.
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Latest CMC:

Link

Puts 92L onshore near Corpus Christi next weekend. (caution: 7 day track and intensity errors can be infinite)
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Quoting stoormfury:
tomorrow by this time. if that recurvature of Igor does not materialise then the northern islands should be on guard. remember Ivan in 2004 when most of the models hinted that the central windwards will be hit. only for Ivan to continue west and hit Grenada

Rule #1..ALWAYS be PREPARED...

Since the pattern change where the sub tropical High broke down over Central Russia on 8-20-2010, in 23 days we have had Danielle, Earl, Fiona, Gaston, Igor an the next "J" storm is brewing..that is SIX storms..wow!!
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Quoting HurricaneSwirl:


Wait, but to get 2.5mb an hour for 12 hours you only have to drop 30mb, 42mb would be 3.5mb an hour. I mean if the NWS said that then ok but they kinda contradicted themselves.


Two different definitions Hurricane Swirl. NWS describes Rapid Intensification as 42 mb's in 24 hours. (Loosely)
NHC describes Explosive Deepening (an even stronger rate of intensification than RI) as 2.5 mb/hr for 12 hours or 5 mb/hr for 6 hours.
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Wow.

Pretty much guarantee that this isn't at 105mph.

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597. xcool
Drakoen. true :)
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596. redUK
This must be well wrong?

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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.