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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946. MZT
Quoting Bordonaro:

Size matters..

Alex was spread out over an are twice the size of Igor. A more gradual pressure drop gave Alex 105MPH winds and a 947MB pressure..

Igor is half the size of Alex, the est pressure of 950MB translates into higher winds, as the pressures drop MUCH faster as you approach the eye, creating the 135MPH winds :O)


Yeah, that too. I remember Gustav and lots of people here asking the same thing - why aren't the winds higher? Well, because he's freaking HUGE and his CAT2 winds were spread over a large area.

Which reminds me... the comments here that Igor "has only a central core". Doesn't that imply that when he begins an EWRC, that his wind field will expand and he could also become freaking huge? Hmm.
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Quoting Hurricanes12:
MH09, Is there any possibility of Earl hitting Florida?


Here we go.
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Quoting MiamiHurricanes09:
A little conservative.

12/1745 UTC 17.6N 46.1W T5.5/5.5 IGOR

Extremely conservative!!
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940. IKE
Quoting Neapolitan:
92L down another mb to 1007. Winds still at 25...

AL, 92, 2010091218, , BEST, 0, 158N, 721W, 25, 1007, DB, 0, , 0, 0, 0, 0,


It was at 1007mb the 12Z coordinates...

12 GMT 09/12/10 15.7N 70.7W 25 1007 Invest
..........................................

It's moved .1N and 1.4W, in 6 hours.
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NHC has a 14% chance of Igor attaining cat 5 status in the (just posted) special advisory so how come everybody is saying that we're likely to have our first cat 5?!
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I doubt Igor will become a Category 5.

It getting close to its maximum potential intensity.
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Quoting MiamiHurricanes09:
120 hours, 92L turns into a strong tropical storm in the Gulf of Mexico. Also notice the bridging high north of Igor...not a pleasant set-up.





Yeah, I am starting to worry as a North Carolinian, because Levi was talking about such a pattern where a trough digs into the western US, with a ridge amplifying east of that trough and bringing Igor into the US. That would mean a more northward track for 92L into southern Texas on the west side of that bridging ridge, and a more west track for Igor on the south side of that bridging ridge. Yikes!
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Great Scott!!!!!

...IGOR RAPIDLY INTENSIFIES INTO A CATEGORY FOUR HURRICANE...
2:30 PM AST Sun Sep 12
Location: 17.7°N 46.1°W
Max sustained: 135 mph
Moving: W at 14 mph
Min pressure: 950 mb

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Quoting donna1960ruled:
Anyone for Cat 8? (205-227mph)?

Camille, Wilma, Allen and Mitch are the only Atlantic Hurricanes that peaked at over 175MPH to the best of my knowledge.

In 1969 as Camille approached the MS coast an advisory estimated her winds at a WHOPPING 200MPH!!!!!
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Quoting help4u:
Further west but still a fish .No hit so why the panic of it hitting.


I don't believe anyone is panicking. Just throwing around synoptic possibilities. No one is saying it is gonna make it all of the way over. But it does appear it is gonna make a closer approach given how these troughs are flattening.
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A little conservative.

12/1745 UTC 17.6N 46.1W T5.5/5.5 IGOR
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Sept 6 - 10 temps ... Lots of fuel for monster IGOR!
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Quoting TropicalAnalystwx13:
NHC has him peaking at 150 mph...

This will likely be our first Category 5 hurricane of the season.

Likely. It also could be the first cat 5 since Felix in 2007.
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Igor and friends.

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Quoting MiamiHurricanes09:
120 hours, 92L turns into a strong tropical storm in the Gulf of Mexico. Also notice the bridging high north of Igor...not a pleasant set-up.




That has Igor at 925mb!
Member Since: October 24, 2005 Posts: 0 Comments: 24055
Quoting Legion:


I found it odd as well reading Cotillion's blog of the top 100 most intense hurricanes that many Cat 4's and even a couple Cat3's had significantly lower pressures than some Cat5's on the list (they were ranked by lowest pressure, not wind speed).

For example-
#56.) Hurricane Isidore, 2002; 934mb. (125mph, Category Three.),

#90.) Hurricane Edith, 1971; 943mb. (160mph, Category Five.)
with that being said I wonder that if the storm had alot higher winds like edith?? and just was so long ago they didnt have the tech we do, hmm
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Quoting StormW:


He has a much better chance now at pumping the ridge...in fact, he's pretty much busted this first trof.


Let's hope the 2nd trough doesn't flatten too much. And keep an eye on the ridge over TX.. We do not want that ridge shifting eastward. As long as that High stays put, the U.S. is in good shape
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Quoting StormW:


He has a much better chance now at pumping the ridge...in fact, he's pretty much busted this first trof.


The second trof doesn't look any stronger. Thats what worries me.
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Quoting TropicalAnalystwx13:
NHC has him peaking at 150 mph...

This will likely be our first Category 5 hurricane of the season.

Igor will peak at between 155-165MPH!!
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920. IKE
120 hour ECMWF...Link
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Quoting MZT:

Alex did not have room to run in the bay of Campeche. His winds would have matched that pressure if he'd had one more night over water.



What came 1st the chicken or the egg?
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92L down another mb to 1007. Winds still at 25...

AL, 92, 2010091218, , BEST, 0, 158N, 721W, 25, 1007, DB, 0, , 0, 0, 0, 0,
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Further west but still a fish .No hit so why the panic of it hitting.
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NHC has him peaking at 150 mph...

This will likely be our first Category 5 hurricane of the season.
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120 hours, 92L turns into a strong tropical storm in the Gulf of Mexico. Also notice the bridging high north of Igor...not a pleasant set-up.



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Quoting PensacolaDoug:
Probably a low end CAT 4 w/135MPH winds, w/min central pressure around 945mb!!!!


And ALEX was a medium cat2 @ 947? Homey don't think so!


Alex was an exception, sometimes a hurricane has a really low pressure but the wind speeds are not high. Alex with that pressure should have been a cat. 3 or min. cat. 4 under normal circumstances, but it was embedded in a lower than normal pressure field surrounding the storm such that the pressure gradient is lower than normal leading to a lower than normal winds for that central pressure.

Igor is not in such an environment, and is more likely to follow the typical wind speed/pressure relatoinship, i.e. 947 mb would mean cat.3/cat.4 if the pressure got that low.
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Wow
FULL IMAGE
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Quoting Chicklit:
Cracks me up that every time a hurricane forms, someone asks if it's annular.
"Annular hurricanes are very rare."

Please see wiki article on them below.
annularhurricane
Agreed, though I'm not one to throw that term around. However, I think Igor actually has a chance at it. Whether it actually happens is anybody's guess...

Thanks for the MIMIC posts, all.....
Member Since: October 25, 2005 Posts: 19 Comments: 21516
Quoting MZT:

Alex did not have room to run in the bay of Campeche. His winds would have matched that pressure if he'd had one more night over water.

Size matters..

Alex was spread out over an are twice the size of Igor. A more gradual pressure drop gave Alex 105MPH winds and a 947MB pressure..

Igor is half the size of Alex, the est pressure of 950MB translates into higher winds, as the pressures drop MUCH faster as you approach the eye, creating the 135MPH+ winds :O)
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Quoting reedzone:


THE OFFICIAL FORECAST IS
BASED ON PRIMARILY ON THE TVCN MULTI-MODEL CONSENSUS BUT IS
ADJUSTED SLIGHTLY TO THE LEFT OF THE PREVIOUS ADVISORY BEYOND DAY 3
AND CLOSER TO THE UKMET...ECMWF...AND THE ECMWF ENSEMBLE MEAN.


still looks like a GFS track
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WAH!!!!
Coming down in torrents now, here..
Gutters overfloweth...
(it's Sunday. Biblical is In!)
Member Since: October 24, 2005 Posts: 0 Comments: 24055
Quoting reedzone:
Igor will probably be the first category 5 Hurricane since Wilma of 2005!


And plow into Bermuda!
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my advice dont panic yet even though it is very frighting...just cautiously watch it we will have a better idea of weather or not its going to hit the us....go over your hurricane preparedness plans check your evacuation routes and plans and hope for the best but prepare for the worst
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Quoting Ameister12:

It's Igor, IGOR!! Lol.


ROFLMAO!
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NHC has Igor peaking out at 150mph.

FORECAST VALID 13/0000Z 17.8N 47.5W
MAX WIND 125 KT...GUSTS 155 KT.
64 KT... 40NE 35SE 35SW 40NW.
50 KT...100NE 80SE 70SW 80NW.
34 KT...180NE 150SE 120SW 150NW.

FORECAST VALID 13/1200Z 18.0N 49.8W
MAX WIND 125 KT...GUSTS 155 KT.
64 KT... 40NE 35SE 35SW 40NW.
50 KT...100NE 80SE 70SW 80NW.
34 KT...180NE 150SE 120SW 150NW.

FORECAST VALID 14/0000Z 18.4N 51.8W
MAX WIND 125 KT...GUSTS 155 KT.
64 KT... 40NE 35SE 35SW 40NW.
50 KT...100NE 80SE 70SW 80NW.
34 KT...180NE 150SE 120SW 150NW.

FORECAST VALID 14/1200Z 19.0N 53.6W
MAX WIND 130 KT...GUSTS 160 KT.
50 KT...110NE 90SE 80SW 80NW.
34 KT...190NE 160SE 130SW 160NW.

FORECAST VALID 15/1200Z 20.7N 56.7W
MAX WIND 130 KT...GUSTS 160 KT.
50 KT...110NE 90SE 80SW 80NW.
34 KT...190NE 160SE 130SW 160NW.


EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 200 NM
ON DAY 4 AND 250 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY

OUTLOOK VALID 16/1200Z 22.6N 59.6W
MAX WIND 125 KT...GUSTS 155 KT.

OUTLOOK VALID 17/1200Z 24.5N 62.5W
MAX WIND 125 KT...GUSTS 155 KT.
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901. IKE
72 hour 12Z ECMWF....



96 hour....

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Quoting will40:


it all depends on what model the NHC is leaning to. The track right now has a lot of GFS bias IMO


THE OFFICIAL FORECAST IS
BASED ON PRIMARILY ON THE TVCN MULTI-MODEL CONSENSUS BUT IS
ADJUSTED SLIGHTLY TO THE LEFT OF THE PREVIOUS ADVISORY BEYOND DAY 3
AND CLOSER TO THE UKMET...ECMWF...AND THE ECMWF ENSEMBLE MEAN.
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Quoting Chicklit:

Yes and yes Igor does resemble one of them though it probably has too much banding.
They look like donuts. are supercanes and can become annular and then go back to being just hurricanes. Wiki has a good explanation and here's a pdf of one. a-canes
Look at post 811. Little banding, atm. If he loses what little he has...
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting will40:


it all depends on what model the NHC is leaning to. The track right now has a lot of GFS bias IMO


They typically lean with the GFS ensembles.. I say typically because there are times they go the other direction.
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896. MZT
Quoting PensacolaDoug:
IGOR 950 cat4 - ALEX Cat2 at 947....

Odd......

Alex did not have room to run in the bay of Campeche. His winds would have matched that pressure if he'd had one more night over water.
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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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