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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Quoting MiamiHurricanes09:
If it continues to undergo rapid intensification, it will likely achieve major hurricane status by the end of the day.



Very impressive eyewall.





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

----- Current Analysis -----
Date : 12 SEP 2010 Time : 141500 UTC
Lat : 17:38:51 N Lon : 45:21:28 W


CI# /Pressure/ Vmax
5.9 / 952.4mb/112.4kt


Final T# Adj T# Raw T#
5.9 6.0 6.0

Latitude bias adjustment to MSLP : +2.0mb

Estimated radius of max. wind based on IR : 26 km

Center Temp : +7.4C Cloud Region Temp : -64.7C

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Quoting MZT:
This is "Earl" all over again. People hanging on every frame, thinking the storm has shifted direction. We even had some examples of Earl moving for two hours on a wobble, only to return to his track.




Earl had a left of track bias for days. This sure looks similar. Can't trust the wobbles! They get lots of people excited tho! If ya bet against the TPC/NHC on a regular basis, you'll lose a bunch of money!
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We have TD12, I see. But, does anyone have a better west coast of Africa satellite? I could swear that's an eye on the still.
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Quoting MZT:
This is "Earl" all over again. People hanging on every frame, thinking the storm has shifted direction. We even had some examples of Earl moving for two hours on a wobble, only to return to his track.
looks like you could drive a mack truck thru the weakness forecast to develop. igor should find that weakness and begin his treck between the us and bermuda in a few days. even he does move some southwest you cannot ignore the weakness.
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Any thoughts on 92L?
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Something in his eye

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Quoting BahaHurican:
I'm not impressed right now by the look of that second trough, which IMO will need some amplification to make itself felt for any long period of time.

What, if anything, is likely to be out there past 5 days as a potential 3rd blow to Igor? The CONUS looks pretty devoid of activity west of the Mississippi right now....

I was noticing that this morning when I woke up, and I see the models after taking Igor on a NW path bend it back to the WNW. Only the GFS for now insists on the re-curvature. Also the path that 92L takes the more further west it goes may dictate the path that Igor takes if the trough is not strong enough to pull it out to sea.
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting atmoaggie:
Alex in RSO mode:


Earl 5-minute interval:


Earl SRSO loops (both greater than 25 MB):
http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2010/08/100824_g15_vis_srso_anim.gif
http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2010/08/100824_g15_vis_srso_2_anim.gif

I love that Alex loop. Alex was a good storm to track, going through a pre-landfall RI and all. Too bad it did all of that bad stuff to Mexico.
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92L looks like it is wrapping convection around a coc at approximately 72.2W/16N.
Member Since: October 9, 2008 Posts: 0 Comments: 8324
If it continues to undergo rapid intensification, it will likely achieve major hurricane status by the end of the day.



Very impressive eyewall.

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185. MZT
Quoting divdog:
im with you i put my mouse over the eye at the beginning of the loop and at the end of the loop and it is dead on west.
This is "Earl" all over again. People hanging on every frame, thinking the storm has shifted direction. We even had some examples of Earl moving for two hours on a wobble, only to return to his track.
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Quoting ElConando:
Igor has stayed on a Westerly path. I see not realy southerly compnent.
im with you i put my mouse over the eye at the beginning of the loop and at the end of the loop and it is dead on west.
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I'm not impressed right now by the look of that second trough, which IMO will need some amplification to make itself felt for any long period of time.

What, if anything, is likely to be out there past 5 days as a potential 3rd blow to Igor? The CONUS looks pretty devoid of activity west of the Mississippi right now....
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Quoting cheaterwon:
atmoaggie I wanted to apologizes to you for the other evening if I sounded like a prick especially since I ended up being wrong about the tallest building thing. You have a great day and hopefully there is no hard feelings.
??? Is cool. (And I didn't know you were wrong about that, hadn't looked it up.)
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I bet we'll see a Cat. 3 at the next advisory. Only 10 mph away.
Member Since: July 6, 2010 Posts: 113 Comments: 31883
Quoting Stormchaser2007:
That looks eerie.



it sure is i think this could pull an Isabel,Fran track or a Frances track because the ship models shows a slight bend back west at the end of the forecast period
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Quoting ChrisDubois:


105mph, just like I guessed...woohoo. i got it right. the pressure is lower than I guessed.. so an 18 mb drop in 6 hrs.. impressive



Contrast that to Alex's 947 with 105 mph winds.
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Quoting earthlydragonfly:


I did not know that... Hmh.. you learn something everyday.. Thanks
Alex in RSO mode:


Earl 5-minute interval:


Earl SRSO loops (both greater than 25 MB):
http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2010/08/100824_g15_vis_srso_anim.gif
http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2010/08/100824_g15_vis_srso_2_anim.gif
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btwntx....i think 92l is trouble for south tx
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Igor has a 7% chance of becoming a Cat 5 in 72hrs, let's hope not!
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171. 7544
igor likes going west if he slows down or stall that will give a chance for the high to build in and all bets are off watch for this then we will have a whole new game
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Quoting atmoaggie:
I can say that it smells a little like fall here, 40 miles N of NOLA.
(Really, though, north winds enough make the smell from the paper mill 30 miles NE of me to be detectable, a normal occurrence with a cold front.)
atmoaggie I wanted to apologizes to you for the other evening if I sounded like a prick especially since I ended up being wrong about the tallest building thing. You have a great day and hopefully there is no hard feelings.
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The NHC has both storms turning back to the west at the end of the period.
Member Since: July 6, 2010 Posts: 113 Comments: 31883
good job Igor you done well looks like its going under RI
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Igor I think will come close to the coast but if you look where he is you see he has a long way to go the reach the coast and not too much further north to miss it still watch it like a hawk, could Julia move North,west really fast and create a path through the High for Igor to take?
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Quoting Ryuujin:


The problem with that is the models are notorious for breaking ridges that are climatologically impossible to break. The have hurricanes pressing through the middle of 1025 mb Highs for example, which in my limited amount of knowledge would equate to a ant flattening a semi.

In the last 10 years of watching models I have never seen one try to break anything near a 1025 ridge. Yes that cannot happen although I have seen hurricanes put a weakness in ridges up to 1020 when trapped that they then went through. But in the ECMWF model that was posted and all the current models the trough is creating a weakness with the Igor going through the 1012MB isobar which it will easily do.
The forecast track is sound but the timing and intensity of the trof and the ridge is still to be determined.

Since there is no Extra tropical low north east of the ridge to reinforce it( although igors outflow might help it out) and the trof is getting a little extra energy from absorbing the small low in the mid-atlantic as well as the fact that North Atlantic/polar lows start to tend to become stronger this time of year I think the GFS model is more accurate and we will soon re-curve start tomorrow with Igor being no threat to land other than Bermuda
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Quoting ChrisDubois:
Im takinh a guess at the next advisories pressure reading. Currently at 988? My guess is its now at 975. A 13mb decrease since the 5am advisory. Winds of 105mph.


105mph, just like I guessed...woohoo. i got it right. the pressure is lower than I guessed.. so an 18 mb drop in 6 hrs.. impressive
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seems as if the 92 is really close to being a td good luck all islanders in its way
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Quoting flsky:

Earl?



LOL I'm tired exuse my reference to a dead and gone storm.
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160. Relix
Everyone confuses Earl and Igor XD!
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keep an i on ukmet regarding igor..thanks can happen
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.
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157. flsky
Quoting ElConando:
Earl has stayed on a Westerly path. I see not realy southerly compnent.

Earl?
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Quoting btwntx08:
92L about to head into the 2nd one here


Morning BT. I guess we'll see if 92L is going to take advantage of that hot water.
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Quoting FLdewey:
Oh no it's heading south... it's heading south!!!!



...but they don't fall down.


Better keep that one handy
Member Since: September 8, 2008 Posts: 0 Comments: 423
Quoting ElConando:
Earl has stayed on a Westerly path. I see not realy southerly compnent.



If you don't see the wobble to wsw, you're not looking very hard!
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Be Back Tommorow.....Enjoy the rest of Sunday.
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Link
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Quoting RecordSeason:
120:

Considering the shortwave is already 1:15 older than the WU visible loop, and the fact the visible takes it's most significant turn south during that 1:15, I think it's safe to say that it's more of a "turn" than a wobble...
Youngest here is only 20 minutes old. http://rammb.cira.colostate.edu/products/tc_realtime/loop.asp?product=4kmirimg&storm_identifier=AL1 12010&starting_image=2010AL11_4KMIRIMG_201009120745.GIF

Last 2 frames show a resumption of westward.
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Member Since: July 6, 2010 Posts: 113 Comments: 31883
"..CONVENTIONAL AND MICROWAVE IMAGERY SHOWS THAT IGOR IS GOING THROUGHA PERIOD OF RAPID INTENSIFICATION. VISIBLE IMAGERY DEPICTS A
CLEARING EYE AND INFRARED IMAGERY AND AN SSMIS OVERPASS REVEAL AN
INTENSE FULLY-DEVELOPED INNER RING OF DEEP CONVECTION. THE OUTFLOW
HAS BECOME QUITE IMPRESSIVE...PARTICULARLY OVER THE EASTERN PORTION
OF THE CYCLONE WHERE THE COLDEST CLOUD TOPS RESIDE..."

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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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