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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3446. xcool
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dE ja vu, poor 92L is going again through the "poof" night syndrome,ex-Gaston's Spirit left behind.
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3443. Levi32
Now that Igor is no longer even remotely annular, an EWRC is far more likely, especially with the eye contracting the way it is.
Member Since: November 24, 2005 Posts: 635 Comments: 26647
3442. xcool
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3441. Drakoen
Igor looks like he's developing his spiral banding.
Member Since: October 28, 2006 Posts: 57 Comments: 30489
The wishcasting that goes on here is hysterical..
Member Since: August 4, 2010 Posts: 0 Comments: 166
Quoting PSLFLCaneVet:
He, like Atmoaggie and others, is given to wanton and unannounced bits of sarcasm. Not to worry.
Yeah, I figure that if K cubed posts something serious it will be because a cat 5 is steam rolling his abode. :)
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...could igor be making it's own enviroment...by pressing west ...
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3435. KEEPEROFTHEGATE (Mod)
011L/MH/I/C4
MARK
17.69N/47.90W

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Quoting AtHomeInTX:


From the Rita log September 23, 2005 six hours before landfall.

8:35 PM - The U.S. Geological Survey is reporting an earthquake, magnitude 5.0, in the
Gulf of Mexico, 530 miles south of Brownsville
Wow.
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Quoting PSLFLCaneVet:
It's got to be Igor's fault. All that stomping about. It's like a distorted Frankenstein, with himself as the lead character..


From the Rita log September 23, 2005 six hours before landfall.

8:35 PM - The U.S. Geological Survey is reporting an earthquake, magnitude 5.0, in the
Gulf of Mexico, 530 miles south of Brownsville
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Quoting PrivateIdaho:
huh?!?
He, like Atmoaggie and others, is given to wanton and unannounced bits of sarcasm. Not to worry.
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The warming of Igor's cloud tops is do to the natural processes of diurnal convective cycles and/or an eyewall replacement cycle that is a normal occurrence for a matured hurricane which Igor is right now.
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Quoting sunlinepr:
Hey, something strange going on.... You see that cloud region in the right area of this image, it is loc. around 20N 58 W, and it is STILL moving West. That means that the trough is not affecting it.... So that means that it won't affect IGOR.... if that's correct, We have a problem here.....

the move west northwest is forecast to start by 8am ... then the really strong move more northwest ... we could wakeup to a new picture..i don't see the move coming...
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3421. xcool
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Hurricane Igor reminds me of Hurricane Luis back in 1995.
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Quoting angiest:


In 1988, Galveston famously ordered an evacuation for Gilbert based on Accuweather's forecast of Gilbert turning north towards a trough.

The question is, can you really fault them for doing that?


With Galveston's history, I think not.
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Quoting PcolaDan:


Who me?

Busted!
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Small cloud area around 58W 20N moving west ahead of Igor.... No trough effect on it????

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Quoting jurakantaino:
George followed a pretty straight line towards us, just guessing having check, history tracks...
By statistical analysis of historical storms, Igor's present location leads to a ~30% chance of hitting any land as a tropical system. (Far less for PR)


(Big version...click)
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Quoting PcolaDan:


a rectangle is any quadrilateral with four right angles

Hiya Aussie, so when the cam going back up?

going back up soon my friend. just gotta get things sorted a bit.
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Question: assuming a slow retreat in intensification, what are the chances that Igor, assuming again it follows a path similar to Earl, re-intensifies? Just like Earl did going over the loop current
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3408. JRRP
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Quoting PSLFLCaneVet:
Can't fault you for that. How're things, Down Under?

Things are warming up nicely, can feel a hot summer coming.
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what is the weakening of the convection on Igor contributed to? dry air?
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Hey, something strange going on.... You see that cloud region in the right area of this image, it is loc. around 20N 58 W, and it is STILL moving West. That means that the trough is not affecting it.... So that means that it won't affect IGOR.... if that's correct, We have a problem here.....

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Quoting DestinJeff:


VINDICATED!

After further review, the lame joke stands.
Round hole...square peg..
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Igor will recurve and hit Bermuda while he does..
Member Since: August 4, 2010 Posts: 0 Comments: 166
3399. xcool
cowboyz lol ha
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Quoting JLPR2:


if it were more to the SW I would be worried. XD
George followed a pretty straight line towards us, just guessing having check, history tracks...
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Quoting PrivateIdaho:
Don't give up without a fight! It is the southern end of the northern half!...lol
Ah, feels so good to be back to the splitting hairs thingy. LOL
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Quoting PcolaDan:


a rectangle is any quadrilateral with four right angles

Hiya Aussie, so when the cam going back up?
Confess, now. Did you have look that up?
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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.