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 bluenosedave:


You know, we see these tropical waves over Africa, and granted they aren't cyclones, but they must bring very heavy rains and flooding and such. But I've never seen anything in the news. Are we this self-centered in North America?


i believe most of those rainstorms are very beneficial, they produce the water for the african plains that sustains them for the dry season.
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am i seeing things or is Igor going wsw
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3044. pottery
Quoting PrivateIdaho:

And what makes a storm wobble? You would think a large system, spinning like a top, would be more stable...just a thought.

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.
Member Since: October 24, 2005 Posts: 0 Comments: 24909
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)

Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting KoritheMan:


Correct.
I think at this rate MAYBE by the AM we have a TD. So far convection is holding pretty good and consolidating much better.
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Quoting barotropic:


The eye has gotten smaller. As a matter of fact the southward wobble that some have mentioned wasn't a wobble at all. It was the northern part of the eyewall closing in (contracting) giving the appearance of a southward jog.
No, it has been jogging towards the SW for a few hours now. The recent contraction of the eye didn't fool you, it really has been moving towards the WSW.
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Quoting BahaHurican:
Like a top. Tops wobble. Ever actually watched one?
I have missed that humor!!
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Quoting RufusBaker:
If one percent of the energy in one hurricane could be captured, all the power, fuel, and heating requirements of the United States could be met for an entire year. It takes 500 trillion horsepower to whirl the great core of winds at such tremendous speeds. It is the equivalent of exploding an atomic bomb every 10 seconds.


Not that I don't believe you but, source?
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Quoting BahaHurican:
Closer 2 70W, IMO


Agreed.
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Quoting BahaHurican:
Like a top. Tops wobble. Ever actually watched one?
Gyroscopes don't wobble, tops only wobble when disturbed or when they hit an imperfection....so Yes!
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Quoting JLPR2:
Is the eye is collapsing or turning ridiculously smaller?



The eye has gotten smaller. As a matter of fact the southward wobble that some have mentioned wasn't a wobble at all. It was the northern part of the eyewall closing in (contracting) giving the appearance of a southward jog.
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Quoting DestinJeff:
How can I be of assistance?
Maybe you can wrangle a ride on a HH mission. Spread the scythe far and wide.
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Quoting weatherwart:


Not before 60W, maybe 65W.
Closer 2 70W, IMO
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Quoting PSLFLCaneVet:


RLOL -> actually one must have humility when faced with possibly birufications (like is happening now) hence moron
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WV reveals no EWRC

Member Since: June 9, 2007 Posts: 4 Comments: 15950
3023. ssmate
Quoting DestinJeff:
How can I be of assistance?
Where's it gonna hit?
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Quoting stormwatcherCI:
And at the estimated COC.


Correct.
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3021. h0db
Quoting DestinJeff:
How can I be of assistance?


Prepare the doom graphic for when Igor becomes an annular hurricane with a stadium pinhole eye with spokes. Headed for Florida AND Texas.
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Quoting Flyairbird:
OK ...so where do you think Igor will be putting on his right turn signal?


Not before 60W, maybe 65W.
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If one percent of the energy in one hurricane could be captured, all the power, fuel, and heating requirements of the United States could be met for an entire year. It takes 500 trillion horsepower to whirl the great core of winds at such tremendous speeds. It is the equivalent of exploding an atomic bomb every 10 seconds.
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Quoting pottery:

No room in the glass...
(oh, you mean THAT ice. OK, coming up in a few...)
LOL! better get Kcubed ready with his hair drier just in case.
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Quoting KoritheMan:


To be fair, it has waned a bit over the last two hours. The convection it does have though, is fairly deep.
And at the estimated COC.
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Quoting PrivateIdaho:

And what makes a storm wobble? You would think a large system, spinning like a top, would be more stable...just a thought.
Like a top. Tops wobble. Ever actually watched one?
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Quoting MelbourneTom:
OK I have got to ask. This loop is something that StormW put up many hours ago. Does it look at all possible that the NHC and models have the correct extended path for IGOR.



If the nose that is at Bermuda catches Igor, yes, the NHC and models are correct.

Somebody else already pointed it out (once again morons like myself we don't see it until the train is almost there)
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OK ...so where do you think Igor will be putting on his right turn signal?
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3013. Seastep
Alright, too fast.

Just a hey to pottery.

Back to catching up... at least I'm keeping one page behind.
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Quoting angiest:
39mph, tropical storm strength, is Beaufort Number 8. Rotations per second of a cup anemometer I suppose?


I read your other post too, that sounds like an interesting point! Thanks.
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3010. will40
Quoting pottery:

M
Hmmmm!
But accumulated wobbles will sure add up, after a few.
And these may have an impact on the 'where' and 'when' for steering.
Just a thought.


Yes pott a few wobbles with Earl would have made tremendous difference.
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3009. Relix
I am all against the WSW WOBBLE FORCE! but that was a nasty wobble there. For models to verify it needs to move WNW in the next 6 hours.
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3007. angiest
Quoting hercj:

They are going by knots. that is the mph conversion numbers.


No, because hurricane strength is 64kts, but they round to 65. Tropical Storm is 34kts, but they round to 35.
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wobbles for 3 consecutive frames is a movment not really a wobble. And it has moved S of w some but not enough to be overly concerned with. Its if he keeps going west after the appointed go north signal we need to be watching for!!
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3005. pottery
Quoting PrivateIdaho:


Pottery better add more ice!!

No room in the glass...
(oh, you mean THAT ice. OK, coming up in a few...)
Member Since: October 24, 2005 Posts: 0 Comments: 24909
Quoting pottery:

M
Hmmmm!
But accumulated wobbles will sure add up, after a few.
And these may have an impact on the 'where' and 'when' for steering.
Just a thought.

And what makes a storm wobble? You would think a large system, spinning like a top, would be more stable...just a thought.
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Quoting btwntx08:

???i see strong convection still what the hell ur looking at


To be fair, it has waned a bit over the last two hours. The convection it does have though, is fairly deep.
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3002. sopla2o
Anyone know if there are any bouys in the area to measure wave height...
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3001. angiest
39mph, tropical storm strength, is Beaufort Number 8. Rotations per second of a cup anemometer I suppose?
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Quoting EnergyMoron:


LOL. Moron + "computational fluid dynamics" = solution not found. Does not compute.
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2999. hercj
Quoting PrivateIdaho:
Why are 3 strikes an out? Why 6 for a touchdown? Because these are man-mad constructs and totally artificial..as you point out, nothing magical happens between 74 and 75 mph.

They are going by knots. that is the mph conversion numbers.
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2998. JLPR2
Quoting Hurricanes101:



I think it is contracting,


That's the word!

If it contracts it could mean Igor is thinking big, the most intense hurricanes tend to have small eyes or what (Taz loves to say) pinhole eyes. XD
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Quoting MiamiHurricanes09:
No, it's contracting. There is no outer core to cause the inner one to collapse.


Sorry i meant EWRC but yes you are right with your statement. We shall see what is really going on soon enough. BBL.
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2996. mbjjm
Quoting wunderkidcayman:
umm guys I thing the HHunters have found the COC or near it atleast reporting W winds


Not true,SW winds only
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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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