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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1095. pottery
Igor has the Forecasters on Ignore???
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Might just flirt with Category 5 status. Note, though, that it's hard to predict the intensity variations that happen with a major hurricane, especially one that's rapidly intensifying.

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Quoting Stormchaser2007:
Pimples?


Tropical Acne!
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1092. Vero1
Quoting pottery:

Will create some Spectacular waves though.....


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1091. Max1023
Id be willing to bet that a recon flight into Igor would find a sub-940mb pressure and 130 knot surface winds. I would say sub-930 but Igor is small so the pressure is probably higher than normal.
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1088. angiest
Quoting DestinJeff:


as if annular wasn't enough ... you just had to.

Although, I do too. Now I don't, commercial.


Stadium effect would be much more likely. :)
Member Since: August 26, 2006 Posts: 16 Comments: 4766
18z dynamical guidance shifted towards the right. Interestingly, some show a turn towards the W/WNW at the end of the plot.

Member Since: September 2, 2009 Posts: 130 Comments: 21194
See, it was bad enough when CMC was showing something similar at 144hrs... now ECWMF too... you dastardly traitor....

[runs out to check shutters for yet the 6th time]
Member Since: October 25, 2005 Posts: 19 Comments: 22323
Quoting NCHurricane2009:


(Wiping my eyes), what are those really really white clouds around the edge of the hurricane?! Anyone else see that in post 1056?


I do see them, now that you mention them, and I have no idea either. I'm interested to see the answer myself.
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Pimples?

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Quoting tropicfreak:


Oh man, igors characteristics look so similar to isabels, hope it's not the same for the track!


dont even say that.....
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1079. Max1023
Quoting NCHurricane2009:


(Wiping my eyes), what are those really really white clouds around the edge of the hurricane?! Anyone else see that in post 1056?


Convective bursts in an outer rainband. No dry air is getting into Igor any time soon with those bursts outside the CDO.
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1075. xcool
2010 analog:
yeah is 1995


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NCEP Ensemble 12z (used to feed the GFS, NAM):

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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.

So the models, current surface features, climatology mean nothing? It will or it won't(50/50 chance) is not a percentage but simply a truism.
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I agree - the eye is large, and no where near an ewrc yet. I'd be suprised If Igor (earl LOL!!!!) doesn't hit cat 5.
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Quoting Dixiegirl:


I always heard that the wind guage at the airport in Gulfport broke at 200 mph.
Was actually at Keesler Air Force Base that the gauge measured 200mph
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1070. angiest
Quoting Stormchaser2007:


I think I see a stadium.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Perhaps a good example of what StormW describes as the "plumping" of a steering high pressure by a hurricane's exhaust or outflow?



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Quoting Stormchaser2007:


(Wiping my eyes), what are those really really white clouds around the edge of the hurricane?! Anyone else see that in post 1056?
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1067. MZT
Another thing to think about: People have long been skeptical that Andrew was a CAT5 (based on retroactive analysis). Some of the criticism being that he was such a compact storm, and an Atlantic one. Reaching CAT5 is normally a Caribbean scenario.

Observational technology is better today. If the smallish-scale Igor makes CAT5, then we may have a better documented example of how this can happen.
Member Since: September 24, 2005 Posts: 0 Comments: 793
Quoting MiamiHurricanes09:
It hasn't recurved. Moving WNW/NW so far, could still be a threat to OBX.


The pattern till now just does not favor cv threats. I see no reason for that to change.

As i mentioned yesterday in a post on wu the primary reason is the negative torque anomalies that have persisted across the last 90 days in the 20-40N band around the hemisphere. This can be seen as the blue shaded areas here. The GLAAM negative anomalies are correlated to increased meridional flow, or flows that have more south to north, or north to south components. When zonal prevails, the anomalies tend to reverse - but there is also a velocity component to the total budget. In this case, however, this has marked an increased potential for incurring trough into ambient subtropical ridges, which in turn increased(s) the background probability for earlier polarward migration of TCs due to the effect that has on the steering levels.
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1064. pottery
Quoting calder:


That's pretty irresponsible forecasting, there's no way you'd find those numbers thrown about by the NHC...

True!!
heheheheh, good one!
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Raw T# up to 6.6.

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

----- Current Analysis -----
Date : 12 SEP 2010 Time : 174500 UTC
Lat : 17:40:09 N Lon : 46:03:00 W


CI# /Pressure/ Vmax
6.3 / 942.2mb/122.2kt


Final T# Adj T# Raw T#
6.3 6.6 6.6

Member Since: September 2, 2009 Posts: 130 Comments: 21194
What do y'all think of this?

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1061. Gearsts
Quoting leo305:
The issue with igor that may hamper it's cat 5 strength is a bit of northerly shear.. which isn't lettting it's northern side ventilate much..

a CAT 5 needs to be in near perfect conditions at the minimum
True and is not in perfect conditions and alot of dry air!
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everyone remember the models have continued to trend to the left, they can easily shift right again , so i would not trust them at all i like to stick with the 2-4 days out
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What I have is the fact that local programming just went down and the Dolphin game is not on anymore :(
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1058. pottery
Quoting help4u:
That model run has igor hundreds of miles off east coast,not even close.

Will create some Spectacular waves though.....
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http://www.ssd.noaa.gov/goes/east/tatl/vis-l.jpg

With the images you guys keep posting (zoomed-in), I keep forgetting how small Igor really is (see above link, zoomed-out).
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1055. angiest
Quoting MiamiHurricanes09:
That's from 12z. The 18z text may be different.


I said most recent. :)
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1054. angiest
Quoting btwntx08:

its 384 hrs from now not likely to happen


The track is a guess, but GFS is starting to be persistent with developing this storm. Obviously we have a long time to watch the models before there is anything real to track.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
1053. Max1023
Igor has formed a pretty large eye compared to his overall CDO size. This suggests to me that an EWRC will not occur for another 24 hours at least. That eye is currently 20 miles in diameter, it needs to shrink to 15 before an outer wall could wrap up.
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Quoting angiest:
Most recent annular analysis:

## ANNULAR HURRICANE INDEX (AHI) AL112010 IGOR 09/12/10 12 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=6 NFAIL=1 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##
## ANNULAR INDEX RAN NORMALLY
That's from 12z. The 18z text may be different.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
1051. calder
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.


That's pretty irresponsible forecasting, there's no way you'd find those numbers thrown about by the NHC...
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one thing to note on Igor is that the models may not have a good handle on its current intensity and like some have mentioned on here it is creating its own environment and the second trough may not recurve it , it may induce a nw component but i see a general west to wnw movement for a while.
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1049. pottery
Heh!
That last gust had horizontal rain with it...
Getting quieter now. Nice squall.
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Quoting Chicklit:

No Zero Nada.


lmao

The only thing I can figure is that since Igor is pronouced "eee-gore" that the "eee" part is making folks think of Earl.
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1047. help4u
That model run has igor hundreds of miles off east coast,not even close.
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Quoting btwntx08:

its 384 hrs from now not likely to happen


I know it can change. That has just been the pattern so far as it seems to be with 92L as well.
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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.