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 RecordSeason:
3891:

Um...yes...

It moved with a slight southerly drift for most of yesterday, having moved somewhere between 0.1 to 0.15 degrees south in a 7 hour period. Check the storm history on WU page.


As I just said, we are very fortunate the peak in the ridge retreated. The steering map last night was indicative of a course change to ~245 degrees heading.


The question is did the ridge retreat or did the environment Igor's created around himself push it right out of the way?

Morning everyone. Wow. Igor is one of the most beautiful TCs I've seen in years.
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3945. Mikla
Here are my thoughts on the steering of Igor... please let me know where I am wrong...
1. There appears to be a small anti-cyclone ~200miles to the WNW
2. There is a large high pressure system over the US
3. There is a 1005mb low pressure system off the NE US coast

If Igor continues W it will have to dip down and under the Anti-Cyclone... unlikely.

For Igor to move W, the High over the US will have to move pretty quickly over the Atlantic to block a turn to the NW... unlikely

The path of least resistance (based on 500mb steering) it to make a turn to the NW soon and follow the Low off the NE coast.

Thoughts?
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Suggesting a trend of plateauing.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
3942. edmac
Anyone out there think Igor will follow the type track as Earl.
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Seems to me that Igor's westerly path has ceased and he's now making a slight turn to the north. I see a sharp westerly turn again tho in just a few days as that coming high blocks him in. There is a strong chance for a new england hit.
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Quoting StormW:
Just dropping in to say good morning before analysis and gettin' kids off to school.


Storm- at this time (and it is early) it is not looking great for Nova Scotia? We are still cleaning up from Earl.
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3939. Patrap
Hurricane Preparation 2010





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I wouldn't bet against the NHC recurve idea. On average they do a good job with track forecasts. Intensity forecasts still suck tho.
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Quoting LPstormspotter2:


I told my hubby last night.. We were evacuating right now!


I made a new log-on
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Quoting Patrap:
Ike roared ashore 2 Years ago this morning and last night..



I told my hubby last night.. We were evacuating right now!
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3934. Vero1
Quoting LPstormspotter2:
Good Morning! I have been coming here for a few yrs but my computer crashed and i for my password i have email WU Admin a few times but they havent sent password.. Any Idea's?

Also last night on local news 13 houston said we needed to watch 92L but only as a rain maker.


You posted here ..so whats the problem.
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Quoting beell:
Igor is a deep system. Steering should be weighted a little higher than the middle (500mb) level. 300mb may be a little too high up but you get the general idea about the southern location and persistence of this "trough".

Also note the ridging over the GOM and SE.

300mb winds (jet stream)

Off to work.

I just checked my local weather here in Tampa and rain chances are very low for the rest of the week into next week a sure sign of a strong high pressure system plus were gonna have winds out of the E to NE!
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Quoting LPstormspotter2:
Good Morning! I have been coming here for a few yrs but my computer crashed and i for my password i have email WU Admin a few times but they havent sent password.. Any Idea's?

Also last night on local news 13 houston said we needed to watch 92L but only as a rain maker.


Have you used the forgot my password page?
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Good Morning! I have been coming here for a few yrs but my computer crashed and i for my password i have email WU Admin a few times but they havent sent password.. Any Idea's?

Also last night on local news 13 houston said we needed to watch 92L but only as a rain maker.
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Quoting skincarediva:
I've got a question for Storm W- normally I'm a lurker, but I was intrigued with his comments and then a link- are you saying that you think Igor will miss his connection with the low and be blocked in with the high behind it that will squash it to the west??


Same question I have more or less...
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3928. Patrap
The NHC Official 5am EDT Track

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Quoting DestinJeff:


That is an amazing picture of an amazing part of nature.
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Quoting rmbjoe1954:
Fom what I am seeing I do not see what 'forces' will pull Igor northward anytime soon and as powerful as he is I believe he will continue his westward movement and get awfully close to the islands before turning NW IF anly if there is an 'opening' for him to do so..


Quoting StormW:


Depends...once it's more definite with this trof...I'll know.


Storm:

I can understand why it is hard for folks to see the potential turn but am not a pro. Can you outline for us how the turn is made in the current set up?

It isn't obvious and folks might learn something....
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Quoting DestinJeff:
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In response to 3922,

Good morning, Skincarediva. I am intrigued by his comments, as well.
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I've got a question for Storm W- normally I'm a lurker, but I was intrigued with his comments and then a link- are you saying that you think Igor will miss his connection with the low and be blocked in with the high behind it that will squash it to the west??
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Quoting DestinJeff:


that is 900mb level.... not surface speed.


Right but if a storm was to get to 160+ knts that would be the surface or the winds would actually be higher at the surface because the 900 mb level would be underground with a sub 900 mb storm
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3918. beell
Igor is a deep system. Steering should be weighted a little higher than the middle (500mb) level. 300mb may be a little too high up but you get the general idea about the southern location and persistence of this "trough".

Also note the ridging over the GOM and SE.

300mb winds (jet stream)

Off to work.
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3912.

thats a real good shot
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Road Trip to Game and Wunderground Headquarters maybe?

lucky s0b
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Quoting JLPR2:


That is a tricky statement as they don't specify the heading, west can have a hint of north to it and still be west.
HURRICANE IGOR FORECAST/ADVISORY NUMBER 21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL112010
0900 UTC MON SEP 13 2010

THERE ARE NO COASTAL WATCHES OR WARNINGS IN EFFECT.

HURRICANE CENTER LOCATED NEAR 17.7N 48.8W AT 13/0900Z
POSITION ACCURATE WITHIN 10 NM

PRESENT MOVEMENT TOWARD THE WEST OR 270 DEGREES AT 11 KT

Member Since: October 9, 2008 Posts: 0 Comments: 8242
Quoting Patrap:
Ike roared ashore 2 Years ago this morning and last night..



I went to sleep last night remembering Ike. Hadn't realized it was 'the' night he did come in.
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3909. IKE
Quoting whepton3:
The general tone I get is that the anticipated NW turn isn't happening... and we could see more of a walk dead west... am I in the ballpark?


There is no NW turn that was suppose to happen.

Igor is a threat to Bermuda and maybe eastern Canada.

From the latest discussion....

THE HURRICANE CONTINUES TO MOVE WESTWARD AT 11 KT...AND IS ON THE
PREVIOUS FORECAST TRACK. IGOR IS EXPECTED TO TURN WEST-
NORTHWESTWARD IN ABOUT 24 HOURS
AND THEN NORTHWESTWARD IN A
COUPLE OF DAYS
AS IT APPROACHES A BROAD TROUGH OVER THE CENTRAL AND
WESTERN ATLANTIC.
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3908. Patrap
Quoting cajunkid:
I got to throw this out there, sorry guys.

Hey Patrap....WHO DAT!



We Dat of course my friend. Saints Vs Frisco,,Sept 20 at Frisco,,Sept 20th.

Monday Night Football

Road Trip to Game and Wunderground Headquarters maybe?
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3907. Patrap
Ike roared ashore 2 Years ago this morning and last night..

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The general tone I get is that the anticipated NW turn isn't happening... and we could see more of a walk dead west... am I in the ballpark?
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Quoting DestinJeff:


Igor is.


Love the avatar with your answer.
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I got to throw this out there, sorry guys.

Hey Patrap....WHO DAT!

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With this morning's observations is everyone seeing a significant difference in Igor's projected path?
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3898. Vero1
Quoting DestinJeff:
Funny that the XTRP has the slightest bit of south of west.


Not Funny at all.. It needs to point to NYC
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Quoting DestinJeff:
Are we doing the "NEXT COUPLE OF DAYS" routine again?


Yes. :0
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3896. Mikla
I am curious as to why there is so much discussion about Igor not turning N.. The models are in pretty good agreement, though NHC has hedged a bit to the W of the models.?

Just asking this, because so far this year the models and particulary the NHC have been pretty good.
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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.