92L still a threat to develop; Igor a hurricane; TD 12 forming near Africa

By: Dr. Jeff Masters , 2:18 PM GMT en Septiembre 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 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?
Member Since: Agosto 16, 2007 Posts: 6 Comments: 12461
Quoting PSLFLCaneVet:
I stand corrected. Confused by the whole Equator thingy.
Don't give up without a fight! It is the southern end of the northern half!...lol
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rectangle 4-90 degree angles square 4- 90 degree angles but also 4= equal sides.
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Quoting Levi32:


Actually not quite all. The CMC has been perfect for the last 12 hours. Its forecast point right now is right in the center of Igor's eye. The rest of the models are off to the north.


The CMC is hinting that Julia may take an interesting track. The GFS is also trying to show this...

12z CMC Ensembles..
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Quoting AussieStorm:

how is a square a rectangle??? A square is a square and will only be a square. it has exactly the same sized sides.


a rectangle is any quadrilateral with four right angles

Hiya Aussie, so when the cam going back up?
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Quoting PcolaDan:


And my parents said I didn't pay attention in school. :)
Ehh, neither did I.
Member Since: Agosto 16, 2007 Posts: 6 Comments: 12461
Quoting atmoaggie:
I was about to chime in with that...

A square does qualify as a rectangle. And not vice versa.


And my parents said I didn't pay attention in school. :)
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Is it because that these storms ramp up their intensity so quickly that they are doing all goofy things and throwing the models off?
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Quoting angiest:


That's not the southern end, it's in the middle...
I stand corrected. Confused by the whole Equator thingy.
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Quoting Levi32:


Or...they're just not perfect. They can't handle perfect data even if it was given to them.
...true...but then why would they all make the same mistake?
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Quoting DestinJeff:


Anybody remember that scene from Good Morning Vietnam, something about somebody needing something more than any man in history?
"First of all, don't make fun of the weather here, and don't say the weather is the same all the time here. Because it's not. In fact, it's two degrees colder today than yesterday.""And me without my earmuffs"
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3377. angiest
Quoting AussieStorm:

gee, someone needs to go back to school to learn there shapes.


What form of English is taught in Australia (judging by your name) that the word "there" means the same as the word "their" to the rest of the English-speaking world?

j/k
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Quoting Flyairbird:
EAST CASTERS
wow how it it merge two comments together...ugh
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Quoting PcolaDan:

Ah, but a square is a rectangle, but a rectangle is not necessarily a square.
I was about to chime in with that...

A square does qualify as a rectangle. And not vice versa.
Member Since: Agosto 16, 2007 Posts: 6 Comments: 12461
3370. Levi32
Quoting PrivateIdaho:
Makes you think they are all using the same bad data.


Or...they're just not perfect. They can't handle perfect data even if it was given to them.
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Quoting AussieStorm:

I've been back for a while, just been lurking, a lot of s*** been thrown around in here lately, just didn't want to get hit by any.
Can't fault you for that. How're things, Down Under?
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Quoting dracko19:
Take a look at the NOGAPS model. Look how it develops ridging all the way acorss the east coast. This is why it has turned IGOR back towards the US coast. If it's right, IGOR won't be able to recurve north and will head towards...um...


shhhh, don't say it, you'll bring the ???-casters out.
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Mid Level circulation is still there with 92L, but no surface circulation, or a less defined circulation is there.
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Quoting dracko19:
Take a look at the NOGAPS model. Look how it develops ridging all the way acorss the east coast. This is why it has turned IGOR back towards the US coast. If it's right, IGOR won't be able to recurve north and will head towards...um...



Exactly, look at the overall US and Atlantic WV loops to see the steering.
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Quoting PanhandleChuck:
I firmly believe that the GOM will be an area that a back yard Ninja will form within the next two weeks... It ain't gonna be pretty for whom ever gets hit with it


well, I sure hope that you keep this back yard Ninja on your side of the state line!..lol
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3363. angiest
Quoting dracko19:
Take a look at the NOGAPS model. Look how it develops ridging all the way acorss the east coast. This is why it has turned IGOR back towards the US coast. If it's right, IGOR won't be able to recurve north and will head towards...um...




... Doom.
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Quoting gordydunnot:
Wow looking at satellite Igor looks to be about 17.6 now trending south of west. Although I have notice they tend to get a little erratic when they are about to change direction. That said he is moving just like Andrew before he reached S, Fl..Which saved N. Dade County at the expense of pour S. Dade.


Bite your tongue!
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Take a look at the NOGAPS model. Look how it develops ridging all the way acorss the east coast. This is why it has turned IGOR back towards the US coast. If it's right, IGOR won't be able to recurve north and will head towards...um...

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3360. Levi32
Quoting Levi32:


Exactly....which is why although it's a small deviation it is interesting. I love it when the insanely tight-packed 6-hour model forecasts are all off by 20-30 miles.


Actually not quite all. The CMC has been perfect for the last 12 hours. Its forecast point right now is right in the center of Igor's eye. The rest of the models are off to the north.
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3359. angiest
Quoting sarahjola:
what makes you think that? thanks in advance


GFS is hinting at a Caribbean/GOM storm in 2 weeks.
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Quoting KEEPEROFTHEGATE:
''Looks like that quake was fairly close to ascension island.
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3356. angiest
Quoting PSLFLCaneVet:
Good evening Keeper. Is that a good-sized earthquake at the southern end of the Mid-Atlantic Ridge?


That's not the southern end, it's in the middle...
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Quoting KEEPEROFTHEGATE:
5.1
It's got to be Igor's fault. All that stomping about. It's like a distorted Frankenstein, with himself as the lead character..
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Quoting JLPR2:


if it were more to the SW I would be worried. XD
H-E-double hockey stick yeah, you should be if that were the case.
Member Since: Agosto 16, 2007 Posts: 6 Comments: 12461
3353. leo305
I have doubts of a north westerly movement considering there' northerly shear ahead of it, and hitting it right now too
Member Since: Abril 17, 2010 Posts: 0 Comments: 1753
Quoting Levi32:


Exactly....which is why although it's a small deviation it is interesting. I love it when the insanely tight-packed 6-hour model forecasts are all off by 20-30 miles.
Makes you think they are all using the same bad data.
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Quoting PanhandleChuck:
I firmly believe that the GOM will be an area that a back yard Ninja will form within the next two weeks... It ain't gonna be pretty for whom ever gets hit with it
what makes you think that? thanks in advance
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3350. KEEPEROFTHEGATE (Mod)
Magnitude 5.1 CENTRAL MID-ATLANTIC RIDGE
Monday, September 13, 2010 at 02:48:07 UTC
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Quoting KEEPEROFTHEGATE:
its a square

gee, someone needs to go back to school to learn there shapes.
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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.