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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1246. scott39
Hello Everyone, What lattitude does Igor have to be at to feel the weakness and the second trough?
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Quoting stormpetrol:
I'm thinking Igor still looks to be moving at around 365 degrees or just a tad south of due west.92L was looking linear earlier but is organizing a little better now imo.
Oh crap , i just logged on without reading back Igor a cat 4 now wow! I think he will be the first Cat 5 in the Atlantic since 2007, i guess that wobble s of due west was due to RI, nhc has it moving at 270 so I'll have to go with that!
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1244. Max1023
CURSE YOU +2 Deg C SST ANOMALIES IN THE MDR!!

If this storm was where it is with normal SSTs it would barely be able to reach 115 knots under perfect conditions.
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I think we could see a 120 knot storm at 5pm

UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.1.1
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 12 SEP 2010 Time : 181500 UTC
Lat : 17:39:45 N Lon : 46:06:10 W


CI# /Pressure/ Vmax
6.4 / 939.6mb/124.6kt


Final T# Adj T# Raw T#
6.4 6.6 6.6
Member Since: June 9, 2007 Posts: 4 Comments: 15718
Quoting StormW:


I'm not sure at this point how close he "may" come to the U.S., but he will come further west than what was originally planned.


i think we need to just watch and monitor this week and if things play out then begin your action plan
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1241. Levi32
12z Japanese from today still is far southwest of the other models and puts Igor just north of the Bahamas. The future track after this (it only goes out to 144 hours on this site) is uncertain, but it is within striking distance of the SE US.

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Quoting RecordSeason:
I might be wrong, but Igor may be in the process of yet another slight southerly wobble...


Igor's being a major hurricane before previously anticipated is yet another variable to further confuse track forecasts.
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Quoting atmoaggie:
Negative. *grumble, grumble*

Loop here: http://rammb.cira.colostate.edu/ramsdis/online/loop_640.asp?product=tropical_ge_1km_c enter_relative _vis_floater


Dang. Thanks.

Hope they get it up soon. Was great to have with Earl .
Member Since: June 9, 2007 Posts: 4 Comments: 15718
1238. help4u
Point is no hit on US period!
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And the lighter color for the pimples suggests that they are higher than the eyewall clouds. Though, further west too.

Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting dolphingalrules:


WHAT ABOUT MITCH...190


Officially, Mitch peaked at 185 mph according to the NHC post-storm report on it.
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1235. Levi32
12z Canadian ensembles have Igor back to 70W in 7 days:

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WOW

Check this loop out.
Member Since: June 9, 2007 Posts: 4 Comments: 15718
Quoting Cotillion:


190mph has been seen before.

800mb would be 250-270mph or some sort, I'd imagine.


WHAT ABOUT MITCH...190
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1231. Hhunter


the big picture
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1228. pottery
Quoting wxvoyeur:


I laughed at it, when it got sheared
When NHC designated it, it was just a swirl.

Then first dry air came
and the blog pronounced it dead,
but it wouldn't die.

:-)

LOL to that..
Member Since: October 24, 2005 Posts: 0 Comments: 23080
Quoting StormW:


Well, when I ran the steering layers forecast maps early this a.m., and if you look at some of the model guidance, there is a "hint" of a bend back toward the WNW. Earlier steering forecast maps seemed to indicate a bend back...GFS in particular at 144 from the early morning run.

Here, run this:

PSU FORECAST STEERING


Yep! So, to me at least, the second trough will have a greater effect on Igor but it may not be deep enough to allow for a full recurvature. The game of wait-and-see begins.
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1225. Levi32
12z NAEFS ensembles are spread anywhere from the Bahamas to the Canadian Maritimes with Igor.

Day 9:

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1223. Max1023
Quoting flhurricane:
can someone please explane to me what an "annular" hurricane is?


Annular hurricane is a hurricane with a large 30-40nm eye surrounded by a uniform ring of eyewall convection extending at least 50 miles out from the eye. They have very few spiral rainbands and are usually resistant to shear - 20 knots would be shrugged off by most annular hurricanes.

Basically instead of a buzzsaw you get a donut.
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Quoting StormW:


He won't


Ouch, not good. If I understand all I've been reading, then that means he could come closer to the US.
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Quoting StormW:


I wouldn't be 100% sure on that. It's obvious that the first trof is a moot point now.


so what does that mean storm out to sea?
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Quoting Stormchaser2007:


Is that a RSO floater?
Negative. *grumble, grumble*

Loop here: http://rammb.cira.colostate.edu/ramsdis/online/loop_640.asp?product=tropical_ge_1km_center_relative _vis_floater
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1218. IKE
Models on Igor....Link
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1217. xcool



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Quoting StormW:


Thanks!

I wanted to point out to him though, that Igor just bust the first trof.


So igor has busted out and is on the run.lol
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1214. pottery
Quoting SouthALWX:

Just experience watching closeup visible.. they arent normally as "big" as those, but I wonder if the size of Igor is making them appear larger. They are normally overlooked in a massive spiraling storm, but given the fewer spiral bands, Im thinking they are the same phenomenon. They are much easier to see most times on mimic-tpw closeup loops of storms about to undergo an EWRC. Of course I could be wrong, as this looks a bit different from the norm, but again I think it is a perspective issue.

That's a reasonable suggestion.
Member Since: October 24, 2005 Posts: 0 Comments: 23080
Quoting reedzone:
All this talk about being confident on Igor recurving needs to stop. We don't know what is going to happen. A 50% chance Igor recurves and a 50% chance Igor threatens the USA.


i think its more like a 60% chance the us is threatened and a 40% chance it goes out to sea
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1211. Max1023
Stadium effect forming around the eyewall. Apparent on latest visible images.
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Quoting MiamiHurricanes09:
Yup, still there and a little larger. I does look like the genesis of a curved band though.





Sort of an educated guess, but I think the pimples might be the result of increased convergence from rapidly accelerating winds at the surface.

EDIT: i.e. continuing rapid deepening
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Dang. I wish/hope we had/have some RSO or SRSO on Igor. I only see it done in visible, which will be gone soon.

This morning through now on 1 minute frequency would be incredible to see. Might not have anything due to it being Sunday, which sux.
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1208. IKE
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Quoting pottery:
See the Blob
How big it's grown,
And all the while
We should have known,
It was to be.

there are some other verses, but I dont remember...


I laughed at it, when it got sheared
When NHC designated it, it was just a swirl.

Then first dry air came
and the blog pronounced it dead,
but it wouldn't die.

:-)
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can someone please explane to me what an "annular" hurricane is?
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Quoting Stormchaser2007:
Close-up of the "pimples"

First time in my 12 years of watching Tropical Cyclones have I seen this.


I think those pimples are towering storm clouds on the periphery of the circulation, that energy perhaps may get wrapped into the circulation, just my guess.
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Quoting TampaCat5:

Igor is going through puberty and has major acne. Someone airdrop some noxzema on this thing!!
Seriously though, they are an interesting feature.


Actually they kind of remind of of the satellite whorls you see in Jupiter's storm bands.
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1202. Max1023
Dean 2007 had similar pimples when it was a strong 4, he formed a curved band well outside of the CDO. This is probably caused by convergence on the edge of the convective mass. I think those pimples mark the edge of the TS wind area, as when you enter the CDO the winds increase substantially compared to the outer envelope. Also, that area is far enough from the eyewall to not be choked by the subsistence just outside it.
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When is Igor supposed to come up to the first trough?
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I'm thinking Igor still looks to be moving at around 365 degrees or just a tad south of due west.92L was looking linear earlier but is organizing a little better now imo.
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Quoting StormW:


I wouldn't be 100% sure on that. It's obvious that the first trof is a moot point now.


Agreed. Especially with the second trof lifting out and amplification favored a little further west. Depends on how much latitude it gains before reacting to the second weakness.
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Quoting atmoaggie:


Is that a RSO floater?
Member Since: June 9, 2007 Posts: 4 Comments: 15718

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About JeffMasters

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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