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 CosmicEvents:
94% of the blog have never seen the commercial. 5% have seen it but forgotten it. That leaves you, me, and a handful of others. And it won't be long before you can put me in the "forgot it" pile.
"But of course"
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Hey all it's Joe. Hope everyone is well. Just getting on, are they still saying Igor is gonna recurve?
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11:00 PM AST Sun Sep 12
Location: 13.5°N 23.5°W
Max sustained: 40 mph
Moving: WNW at 12 mph
Min pressure: 1004 mb
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Igor 130kt
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...DEPRESSION BECOMES A TROPICAL STORM...TENTH OF THE ATLANTIC
HURRICANE SEASON...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...13.5N 23.5W
ABOUT 110 MI...175 KM SE OF THE SOUTHERNMOST CAPE VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/HR
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 12 MPH...19 KM/HR
MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting DestinJeff:


sans.

Pardon me, but do you have any Grey Poupon?
94% of the blog have never seen the commercial. 5% have seen it but forgotten it. That leaves you, me, and a handful of others. And it won't be long before you can put me in the "forgot it" pile.
Member Since: August 3, 2005 Posts: 10 Comments: 5684
Quoting hunkerdown:
47% of the time
Well said! :)
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Header changed.

Tropical Storm JULIA
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Quoting pottery:
I am Yawning here. Early start tomorrow.
Keep up the good work.
But please, stop feeding Igor. He is a Troll...
Just ask any BillyGoatGruff that you meet.


:)
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3132. MZT
Quoting hunkerdown:
47% of the time

Remember your 20/80 rule. 20% of the made up statistics go unchallenged 80% of the time.
Member Since: September 24, 2005 Posts: 0 Comments: 793
Quoting hunkerdown:
as I stated above, contracting diameter has no bearing on path of the center point of the eye, no matter what the size of the eye. The center point of the eye has definitely moved slightly south of due west over the last few frames.

+1 Agreed100%
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Quoting kmanhurricaneman:
i believe a few people on here dont know nautical bearings and how to determine direction or when a hurricane eye contracts mistaking for direction hmmmmmmmm. makes me wonder sometimes, and dude yes it is moving to the south !!!!!! and its not the eye that makes it looks that way, ok!!


Um, I just ran a loop of Igor, and it is definitely not moving South like you say it is. Maybe a slight SW jog but nothing more.
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3127. pottery
I am Yawning here. Early start tomorrow.
Keep up the good work.
But please, stop feeding Igor. He is a Troll...
Just ask any BillyGoatGruff that you meet.
Member Since: October 24, 2005 Posts: 0 Comments: 24871
Quoting angiest:


The earth's rotational axis also wobbles. Some planets wobble much more than Earth does.
True and since there is nothing is space to make the earth wobble it wobbles because it is not a perfect sphere...'canes only wobble on occasion, unlike the Earth so maybe they go "out of round" occasionally.
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Quoting pottery:

I would think that there are some pretty formidable wind-forces (downdrafts, updrafts etc) at work in a system as powerfull as a hurricane.
Also where intense rainfall is happening within the storm.
At the moment convection is not as pronounced on the SW quad.
These would tend to create some dynamics to cause some 'lopsidedness' and this could cause the entire structure to become imbalanced.
Hence 'wobble'.
Just my take on an interesting question.


Was thinking along those same lines. Look at a tornado. Some that are perpendicular to the ground will track quite straight. But as soon as it tilts, all bets are off. Something changes, whether ground friction, currents changes slightly, to create a slight angle, thus ruining the symmetry, effectively making it "off balance".
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3124. angiest
Some bullish intensity forecasts for 92L...

Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting extreme236:


I have extreme trouble believing that.

It's happened before, never know.
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Quoting DestinJeff:
Is Igor annular?

Do you think I can mock that question into submission, like The Chart?
Or I told someone once that they had an annular belly
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3121. xcool
JP2010: yep
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i believe a few people on here dont know nautical bearings and how to determine direction or when a hurricane eye contracts mistaking for direction hmmmmmmmm. makes me wonder sometimes, and dude yes it is moving to the south !!!!!! and its not the eye that makes it looks that way, ok!!
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Quoting PrivateIdaho:
But 100% of statistics can be verified statistically.
47% of the time
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Is Igor moving more south now of west? or just my untrained eyes playing tricks? probably just a wobble though.
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3114. xcool
shifting west come Igor
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Quoting wunderkidcayman:
I say with a little help from D-Max which start in about 2-3 hours we could see TD 13 by 5am or 11am


I have extreme trouble believing that. Not to mention 5am/11am isn't 2-3 hours away...
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Quoting sopla2o:
Anyone know if there are any bouys in the area to measure wave height...


What would you anchor a buoy to? The Mid-Atlantic Ridge? ;-)
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Quoting RecordSeason:
3085:


Yup.

Even if they want to argue that it is an illusion caused by shrinking eye, they are wrong.

You can see the SOUTH edge of the smaller eye is farther south than the south edge of the larger eye at any frame in the past 7 hour loop. This indicates a very significant "drift" south of west over time, and is definitely NOT an illusion...


Its an illusion....and no one really cares about it......LOL
Member Since: August 22, 2010 Posts: 0 Comments: 652
3107. angiest
Quoting DestinJeff:
Is Igor annular?

Do you think I can mock that question into submission, like The Chart?


While you were gone, Igor was analyzed as a 1 on the annular index, which qualifies as marginal.

Just sayin'.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting DestinJeff:


I read somewhere that 47% of all statistics are made up.
But 100% of statistics can be verified statistically.
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I say with a little help from D-Max which start in about 2-3 hours we could see TD 13 by 5am or 11am
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Quoting RecordSeason:
3032:

That's not true.

the eye has both moved south and shrank.

Know how I know?

Because the ADT center fix was at 17.6N, which is a tenth south of where it had been most of the day.

Additionally, the storm has wobbled even farther south since then, which is pretty undeniable even from the WU IR loop.


Whatever..................>!!!!!!!!!!!!!!!!!!! Tell the TPC to adjust the forecast track 1/20th of a degree south.....
Member Since: August 22, 2010 Posts: 0 Comments: 652
It looks like Igor will interact with the trough when it reaches 56 to 58W.... so the track will have to be adjusted.... to the west
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Quoting atmoaggie:
NHC advisories and 5 day track for Igor thus far. (I skipped the intermediate advisories this time to keep the valid time consistent frame to frame)



VERY cool!!!
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Quoting hunkerdown:
as I stated above, contracting diameter has no bearing on path of the center point of the eye, no matter what the size of the eye. The center point of the eye has definitely moved slightly south of due west over the last few frames.


Yes, and it will be S of the NHC forcast point also.
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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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