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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How come storms with scary names(Walter,Igor,Bob) tend to be strong?
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The issue with igor that may hamper it's cat 5 strength is that there's a bit of northerly shear chocking off it's northern side..

a CAT 5 needs to be in near perfect conditions at the minimum
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Quoting DDR:
Pottery you getting any of the action?
I heard its raining in Freeport

LOL see my last post.
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I was so busy watching Igor I didn't catch the T Storms headed my way. A loud clap of thunder alerted me.
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We've had 3 Category 4 Hurricane so far this year...Wow
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Quoting Kristina40:


Storm likes to tease us in order to make us work harder at learning. He's a good teacher.


100% Agree! He was the first person I discovered on this blog that was so knowledgeable and so willing to help us weather-geeks and just so fricken' nice. I have learned a heckuva lot from him over the years. StormW Rocks!
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Yikes...
Torrential rain with NorthWest winds right now....
NW winds are the only ones that blow rain into this house through vent-blocks and fretwork....
It's becoming moist in here.......
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Quoting Stormchaser2007:




That thing doesn't look right.
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985. JLPR2
Quoting Bordonaro:

IF Igor is a rare annular hurricane, he will NOT have any Eyewall relacement cycles..This makes him super dangerous, as he may create his own steering currents and be very slow to weaken.

IF Igor is not an annular, his wind fields will become much, much larger during an EWRC!!


True, annular hurricanes are scary, or very large hurricanes(Tip style), they can do the same thing.
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting pottery:

And it was DEEELISHUS too.
The amount of calories packed in there, I am sure it's a sin....

We are watching an Incredible Igor, right now.


After watching Levi's synopisis (awesome) It really is not set in stone where he will go. It adds the element of suspense to the picture and I would venture to guess that more people will be watching the course of Igor than any hurricane we have seen for awhile.
Cheesecake optional.
Member Since: April 9, 2010 Posts: 5 Comments: 5001
144 hours, moving towards the WNW.

Member Since: September 2, 2009 Posts: 130 Comments: 21194
Sailingallover ,how far east you think the models will shift?
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981. IKE
144 hr. 12Z ECMWF...

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Quoting MiamiHurricanes09:
102kt (117mph).


Okay, so we have a cat. 3 on our hands then at least conserivatvely. Not surprising.
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979. DDR
Pottery you getting any of the action?
I heard its raining in Freeport
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Quoting Stormchaser2007:


If you zoom out, the maximum potential intensity increases as he progresses W/WNW.

Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting StormW:


He has a much better chance now at pumping the ridge...in fact, he's pretty much busted this first trof. Pumping the ridge would put him on a flatter course, in regards to when he turns.


I have pizza, wine, Patriots on TV and winning and tropical chatter on the weather underground. Life is good.

So a trough would guide him but a ridge would block him?
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Quoting StormW:


Aye!


Hi Storm, can't help but think that high (over TX) is going to break eventually.....just can't imagine it protecting us the whole season.
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NHC really bogged this intensity forecast, 12 hours ago they forecasted Igor to be at 75 knots at 5pm, while it is likely to be around 120 knots. It just goes to show how difficult it is to predict RI of a tropical cyclone.

PS: Igor is at about 125 knots (ADT estimates) over water that is just over 28 degrees (see WU and CIMSS SST map). He is predicted to track over water at least a full degree warmer once he reaches 55W. I can easily see this topping out as a 920mb 140 knot Category 5.
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Quoting sailingallover:

Or if the Low in the Surface analysis forms and it shifts right


Are you talking about the big Low shown in the computer model runs east of Igor? That Low would be Julia, the future of TD 12. Julia would make this situation worse if anything, because both Igor and Julia would pull a Fujiwhara interaction with each other, sending Igor's tendency further south and west and Julia's tendency further north and east.
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Hurricanes with annular eyes do have EWRCs...
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Wow

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...And TD12 still a TD:

AL, 12, 2010091218, , BEST, 0, 131N, 223W, 30, 1006, TD, 0, , 0, 0, 0, 0,
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Scary Thought
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Quoting MZT:


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 Igore "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.

IF Igor is a rare annular hurricane, he will NOT have any Eyewall relacement cycles..This makes him super dangerous, as he may create his own steering currents and be very slow to weaken.

IF Igor is not an annular, his wind fields will become much, much larger during an EWRC!!
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Quoting NCHurricane2009:


What is a T5.5 mean in terms of intensity? haven't memorized the Dvorak scale.
102kt (117mph).
Member Since: September 2, 2009 Posts: 130 Comments: 21194
I remember Igor when he was just a baby pouch in Burkano Faso....and now this!
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Quoting Neapolitan:
And to think he was a tropical storm at yesterday's 5PM TWO...


I know! If Igor pulls off cat. 4 by 5 PM, Igor would have been one of the biggest rapid intensification episodes on record, but not supreme to Wilma. Wilma went from tropical storm to cat. 5 in about 24 hours, Igor would have gone from tropical storm to cat. 4 in 24 hours if this proves true.
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Quoting StormW:
Going to be interesting to see if the models shift left.

Or if the Low in the Surface analysis forms and it shifts right
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Quoting MiamiHurricanes09:
I doubt its maxed out. Still has favorable conditions for intensification, plus, an EWRC is still a good day or two away.


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938:

If Igor was stationary you'd be correct.

However, Igor will move over cat5 max intensity predictor in like 30 minutes, and will cross +150kts and even +165kts max intensity predictors tomorrow through landfall or recurve.

It is nowhere near the max that it MIGHT have tomorrow or over night tonight...
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Quoting KanKunKid:


I am probably the farthest away from a slice of cheesecake that I have ever been in my life. Now, since you mentioned it, I have had a craving for it, bad! So, go ahead and Siestacate with a belly full of rich, delicious cheesecake, with that buttery graham-cracker crust and smooth, cool creamy filling.

Just remember, somebody, somewhere, would kill for a slice!

Which reminds me: Reason # 21,657 Why you can't have a gun in Mexico.

And it was DEEELISHUS too.
The amount of calories packed in there, I am sure it's a sin....

We are watching an Incredible Igor, right now.
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Quoting Chavalito:
How probable or possible is to get Igor near Puerto Rico? Are we already safe from IGOR?
Es posible, pero todo es posible ahora....

I still say we have to wait and see. Lots of different scenarios could play out based on minor changes in the synoptic pattern. But PR is not yet totally out of the picture.
Member Since: October 25, 2005 Posts: 19 Comments: 22563
Quoting MiamiHurricanes09:
A little conservative.

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


What is a T5.5 mean in terms of intensity? haven't memorized the Dvorak scale.
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Member Since: July 13, 2008 Posts: 6 Comments: 10796
Look at that eye...

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And to think he was a tropical storm at yesterday's 5PM TWO...
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Quoting Stormchaser2007:
I doubt Igor will become a Category 5.

It getting close to its maximum potential intensity.
I doubt its maxed out. Still has favorable conditions for intensification, plus, an EWRC is still a good day or two away.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Regardless, I am ready here in Charleston. Plans are in place. High tailing it to Atlanta if any major threatens here.
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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.


Levi agrees with that possibility, and I believe it too! This has a shot of becoming the first cat. 5 of the season since Felix 2007.
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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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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.