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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Member Since: Posts: Comments:
Quoting Progster:


Oh< i though you were joking with your earlier extrapolation. Sub 800 storms could not likely be reached let alone maintained. The presure gradient force and internal shear would make likely them unstable and disrupt their structure well before to 800 mb mslp was reached. I don't know if this kind of superstorm has been modeled, but it would be interesting.


A bit too interesting.

Unnecessarily interesting...
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Quoting LongIslandXpress38:


Best of luck Igor!


Interesting feature just east of the Antilles.
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For you that may be in the line for a tropical storm/hurricane I'd like to offer a suggestiion that I consider very important.
Since we live on the coast of La. we have been through many storms. To me the worse part is after the storm with no electricity for days or even weeks. We have always kept a battery operated small TV for comfort and information. They have served us well through many years and storms. When everything went digital we had to go out and buy a new one.
You never think about checking to see if they really work until you need them. Right? Right! CAUTION! Please check yours before you need it. Even if you can get just 1 or 2 channels I consider that working.
We have tried everything,bought a better Antenna,moved it all over the house and went outside with it, called the help line, etc. Bottom line,they only have working distance of 20 miles from a tower. We're back to buying a good weather radio.
Yeah for new technology.
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1500 UTC = 11 a.m EST

0300 UTC = 11 p.m. EST

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Quoting sailingallover:

We definitely don't want Igor anywhere near us..
Earl became a Cat 4 just north of us so did not have as solid and expansive wind field as Igor will when he gets to 60-65W.

For some reason on her everyone seems to want to westcast/not recurvecast storms..
True... but as I said earlier, I'd be more than happy to be dead wrong.... lol.... I thought the Bahamas got dead lucky with Earl because of the limitations on wind/rain in the SW quadrant at that time. Even on a similar track to Earl, Igor could at least potentially do much greater damage. I'd be happy to see a pre-70W turn.... just not currently convinced about it happening right now.

But we shall see.
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Quoting Bordonaro:

A tropical wave being attacked by dry air. IF 92L moistens its environment, it will be a BIG problem!

Oh. Looks like eggs frying in a sidewalk.
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Quoting nyhurricaneboy:


Thank you for not completely blasting the calculation.

We could see sub-900. I'm not completely confident in the sub-800 calculation. If I was so sure of it, I'd get myself some professional help; trust me. ;-)


Oh< i thought you were joking with your earlier extrapolation. Sub 800 storms could not likely be reached let alone maintained. The presure gradient force and internal shear would likely make them unstable and disrupt their structure well before to 800 mb mslp was reached. I don't know if this kind of superstorm has been modeled, but it would be interesting.
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Quoting IKE:
92L...

lol
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Best of luck Igor!
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Quoting WeatherNerdPR:

What the hell is that supposed to be?


That's interesting.
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Quoting CosmicEvents:
Don't worry atmo....I won't poof you.
.
.
.
Though I did have beans for dinner last night.....
*clothes pin - engaged*
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Quoting nyhurricaneboy:


Thank you for not completely blasting the calculation.

We could see sub-900. I'm not completely confident in the sub-800 calculation. If I was so sure of it, I'd get myself some professional help; trust me. ;-)
one last remark to your senseless thinking (unless you don;t know what the prefix "sub" means)...a sub-800 would be pressures in the 700s which is purely ridiculous. sub-900, possible, yes. the lowest Atlantic cane ever was Wilma at 882 mb and the lowest recorded anywhere was Tip at 870mb.
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Quoting btwntx08:
465 ???

What I meant to say is that I can barely recognize it as the same, well organized system it was 24 hours ago.
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Quoting IKE:
92L...



A lot like fay.
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Quoting atmoaggie:
A linear, in time, intensification of Igor to 730mb is not a reasonable expectation. Extrapolation of the most recent behavior to that point is a folly.


Quoting nyhurricaneboy:


Thank you for not completely blasting the calculation.

We could see sub-900. I'm not completely confident in the sub-800 calculation. If I was so sure of it, I'd get myself some professional help; trust me. ;-)
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Quoting WeatherNerdPR:

What the hell is that supposed to be?

A tropical wave being attacked by dry air. IF 92L moistens its environment, it will be a BIG problem!
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Quoting Stormchaser2007:
Very disorganized.



Looked like trouble yesterday but today is death by DR
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Quoting nyhurricaneboy:


If you guys have a dispute with my calculation, please explain it in a dignified and reasonable manner. The purpose of this blog was so that some intelligent banter regarding the tropics could be created. That can be achieved without plain rudeness.
A linear, in time, intensification of Igor to 730mb is not a reasonable expectation. Extrapolation of the most recent behavior to that point is a folly.

As is my temperature example of 172 F.
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470. IKE
92L...

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Quoting atmoaggie:
Oh, it's cool. Everyone can poof me if they want.
Don't worry atmo....I won't poof you.
.
.
.
Though I did have beans for dinner last night.....
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Quoting nyhurricaneboy:


Oh yeah. "Hope for the best, prepare for the worst."



Looks like the Caribbean is trying to fry an egg on the sidewalk! ;-)

When the MJO pulse hits the Caribbean, WATCH OUT!!
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Quoting philliesrock:

Because it's almost inevitable that a trough will pick Igor up by the end of this week, unless it somehow trends much flatter. Storms can go through areas of surface high pressure if the upper-level pattern says recurve.

I agree with the picked up and thinking about the back to back troughs we have now Irenes track makes sense if the first trough just lifts Igor north but the second actually re-curves it.
I didn't think of that..

My feeling is the first trough will do the job especially since it looks like a low is going to form along the stalled front in a day or two which will pick up Igor for sure
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Quoting Stormchaser2007:
Very disorganized.



What the hell is that supposed to be?
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Looks pretty tranquil around the U.S.....For now...
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Quoting Bordonaro:

Under perfect conditions the SST's & atmosphere would support an 880MB storm. Lets hope that does NOT happen!!!


Oh yeah. "Hope for the best, prepare for the worst."

Quoting Stormchaser2007:
Very disorganized.




Looks like the Caribbean is trying to fry an egg on the sidewalk! ;-)
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Quoting IKE:


This may have something to do with it....


Looks like an MJO pulse around 9-17 through 9-24-2010. That is SCARY!!
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Quoting TropicalAnalystwx13:


Poof, Poof?

lol


Pass???

LOL!
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Very disorganized.


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Quoting nyhurricaneboy:


Thank you for not completely blasting the calculation.

We could see sub-900. I'm not completely confident in the sub-800 calculation. If I was so sure of it, I'd get myself some professional help; trust me. ;-)

Under perfect conditions the SST's & atmosphere would support an 880MB storm. Lets hope that does NOT happen!!!
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Quoting atmoaggie:
Oh, it's cool. Everyone can poof me if they want.


Poof, Poof?

lol
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Quoting plywoodstatenative:
Baha, when is the last time you can think of that the Cape Verde Islands actually had tropical storm warnings from a system that just rolled off of Africa?
Earlier this week? LOL.... just kidding.... but it was close. Prolly the last time was Big Bertha back in 06???

Quoting TropicalAnalystwx13:


Yeah, Gaston.
U mean I wasn't jokin'??? lol

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Quoting Bordonaro:

Nah, maybe down to about oh, 900MB at the worst case scenario!!!


Thank you for not completely blasting the calculation.

We could see sub-900. I'm not completely confident in the sub-800 calculation. If I was so sure of it, I'd get myself some professional help; trust me. ;-)
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Oh, it's cool. Everyone can poof me if they want.
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Quoting MiamiHurricanes09:
Thanks!

Those satellite estimates are from 12z (8am EDT)...the ADT estimates are much more recent. Yes, ADT tends to overdo it once the eye appears, but, the intensity of Igor right now is likely around category 4 strength.


Precisely my point, yet people throw it about like it is gospel.

ADT's great for analysing trends, but it is a very raw instrument. I'll say it's likely to be around the 120-125mph mark. Could well be wrong, of course.

Nonetheless, Igor has put on an impressive spurt today.
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First recon to 92L is scheduled at 1800Z.
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448. IKE
Quoting Bordonaro:
Well well well..TD 12 was born :o)!! Igor is going to ramp up to a CAT 4 or even CAT 5..Up to almost 10 TC's, TD 12 should be the next TS later today.

Poor 92L is having a hard time with dry air, hopefully that does not develop into a TS/Hurricane.


This may have something to do with it....

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Quoting Cotillion:
Let's recap, folks:

' THE INITIAL
INTENSITY OF 90 KT IS BASED ON A COMPROMISE OF SATELLITE INTENSITY
ESTIMATES OF 77 AND 90 KT FROM SAB AND TAFB...RESPECTIVELY...A
UW-CIMSS ADT OF 107 KT...AND A SATELLITE CONSENSUS OF 86 KT...THAT
INCLUDES A BLEND OF AMSU MICROWAVE ESTIMATES.'

Now, what does this tell us?


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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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