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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3846. scott39
StormW If,and I hope its a big if! At what longitude and lattitude will we know IF Igor has missed the trough? Is there another one behind that one to turn it in time?
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Pretty neat ridge over the northern Gulf of Mexico.

24-Hours WV LOOP
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3844. surfmom
MorningALL - quick peeks b/4 work... will be interesting to see what I come home to..
Cot. I trust you had a lovely Sunday : )?
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Quoting IKE:
GFS has trended east on the track for Igor. Now going east of Bermuda...



I guess it is possible but I just don't see it happening.....
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Referring to the models, Storm.

I already made a mention of NHC in that comment.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
3839. IKE
GFS has trended east on the track for Igor. Now going east of Bermuda...

Member Since: June 9, 2005 Posts: 23 Comments: 37858
3838. scott39
Quoting StormW:


No...the first trof became a moot point yesterday.
Ok, Did I get anything right in your Question you posted?
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Quoting StormW:


Very possible. Not definite, but the more he doesn't gain any north component, the more he comes closer to missing the influence of the trof.


Holy Turnip Greens....that could change the forecast a bit!!!
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3835. WxLogic
Quoting StormW:
Igor's current steering layer


Based on the current steering currents you have posted Igor will have 2 choices.... 1) Slow down further to turn NW to get out to sea or 2) Go further W underneath that High as it could potentially build N of it given that there's hardly a noticeable weakness to feel and continue further W... there might be another scenario but can't think of one just yet.
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Quoting StormW:


Correct!

What would that kinda indicate?

Oh...he will slow as that trof gets a little closer, but other than that.


WEST!!??
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Quoting Cotillion:


I see the NHC expect a Cat 5 as well. I still stand firm with my prediction until it happens.

I see the intensity guidance doesn't bring him up to it. They seem to think he's reached his MPI. Be interesting to see if that is indeed the case.


Everything this monster does will be interesting!!!
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3829. scott39
It looks like the first trough is farther S than the one coming off the eastern Seaboard. will this influence Igor?
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Last post before I go....

Member Since: October 25, 2005 Posts: 19 Comments: 20733
3827. stormy3
If Igor stays far enough south it won't catch that northward steering pattern right?
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Quoting TXCaneCrasher:


good morning Storm....will be anxious to see what you think 92L will do today and where it may head....have a great day


Ditto!!!
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3825. IKE
SYNOPSIS FOR THE GULF OF MEXICO
430 AM CDT MON SEP 13 2010

.SYNOPSIS...COLD FRONT WILL CLIP THE FAR NE GULF TODAY. LOW PRES
IN THE CENTRAL CARIBBEAN JUST SOUTH OF HAITI WILL MOVE INTO THE
NW CARIBBEAN WED...POSSIBLY AS A TROPICAL CYCLONE...INCREASING
WINDS AND SEAS IN THE FAR SOUTHERN GULF. THE LOW WILL MOVE INTO
THE SW GULF THU AND FRI...POSSIBLY AS A TROPICAL CYCLONE. THE
LOW WILL BE NEAR 21N93W THU AND NEAR 21N96W FRI.
...........................................

SYNOPSIS FOR CARIBBEAN SEA AND TROPICAL N ATLC FROM 07N TO 22N
BETWEEN 55W AND 65W
530 AM EDT MON SEP 13 2010

.SYNOPSIS...LOW PRESSURE NEAR 16N73W WILL MOVE TO NEAR 17N78W
TONIGHT AND NEAR 18N84W TUE NIGHT. THE LOW COULD POSSIBLY
DEVELOP INTO A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
HURRICANE IGOR E OF THE AREA CENTERED NEAR 17.7N48.8W AT 0900
UTC. WILL MOVE TO 20.4N 54.9W TUE NIGHT AND NEAR 22.5N 57.7W WED
NIGHT THEN CONTINUE TO MOVE N OF THE AREA THU.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting StormW:
Just dropping in to say good morning before analysis and gettin' kids off to school.


good morning Storm....will be anxious to see what you think 92L will do today and where it may head....have a great day
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BTW, I'm not saying we won't eventually see that NW turn.... just not at 50W.....

Out for now. Will check in later this a.m. if time permits...
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3820. scott39
Quoting StormW:
Go to the link, put it in motion, with LAT/LONG., and zoom in as much as you need.

Look at the trof coming off the east coast...what do you notice about the flow to the south of it?

Look at the flow of the clouds west of Igor...especially that flare up of convection...which way is it going?

Look just north of that convection...see the little ridge above it?

Just subtle hints

LINK

Hmm, I will take a guess. It looks like the trof off the east Coast in weakning and going N. It looks like Igor has jogged to the WSW.
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Quoting traumaboyy:


Good Morning Cotillion!!

I could not have said it better!!


I see the NHC expect a Cat 5 as well. I still stand firm with my prediction until it happens.

I see the intensity guidance doesn't bring him up to it. They seem to think he's reached his MPI. Be interesting to see if that is indeed the case.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Quoting GetReal:



IMO the clouds to the west of Igor are moving generally towards the west. The two troughs to the north and northeast of Igor appear to be lifting towards the north...
They've been doing that since yesterday. In the NW Bahamas we have seen little / none of their energy, which is kinda surprising when u consider Nassau is at 25N.... and they've been lifting N for a while now, slowly but steadily....

I'm doubting any serious impact from these troughs right now...
Member Since: October 25, 2005 Posts: 19 Comments: 20733
HurricaneIgor's heading had turned northward to (6.1degrees north of) dueWest
from its previous heading of (6.5degrees south of) dueWest
H.Igor's average speed moving between its last 2 reported positions was ~11mph(~17.7km/h)

12Sep . 09amGMT - - 17.7n44.4w - - - 80mph - - 988mb - - NHC.Adv.#16
12Sep . 03pmGMT - - 17.7n45.7w - - 105mph - - 970mb - - #17
7:30pmGMT H.Igor becomes 140mph-Cat.4
12Sep . 09pmGMT - - 17.7n46.9w - - 140mph - - 942mb - - #19
13Sep . 03amGMT - - 17.6n47.8w - - 150mph - - 935mb - - #20
13Sep . 09amGMT - - 17.7n48.8w - - 150mph - - 935mb - - #21

Copy&paste 17.7n44.4w-17.7n45.7w, 17.7n45.7w-17.7n46.9w, 17.7n46.9w-17.6n47.8w, 17.6n47.8w-17.7n48.8w, puj, pos, 17.7n48.8w-18.66n64.27w into the GreatCircleMapper for a look at the last 24*hours.

Using straightline projection upon the speed&heading averaged
over the 6hours spanning the last two reported positions:
~3days&19hours from now to Anegada

* The westernmost line-segment is the straightline projection.
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3814. WxLogic
Good Morning...

I sure sure hope Igor does not go to Bermuda.
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3812. GetReal
Quoting StormW:
Go to the link, put it in motion, with LAT/LONG., and zoom in as much as you need.

Look at the trof coming off the east coast...what do you notice about the flow to the south of it?

Look at the flow of the clouds west of Igor...especially that flare up of convection...which way is it going?

Look just north of that convection...see the little ridge above it?

Just subtle hints

LINK




IMO the clouds to the west of Igor are moving generally towards the west. The two troughs to the north and northeast of Igor appear to be lifting towards the north...
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Quoting Cotillion:
Igor is very, very impressive.


Good Morning Cotillion!!

I could not have said it better!!
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Igor is very, very impressive.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
3808. scott39
Quoting traumaboyy:


Mornin Scott....He is quite a monster!!
Yes he is, I hope that trough and wind shear tames him and sends him packing out to sea! This one has the potential to cause alot of havoc in people lives!
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Morning all.

Just a quick look in before I head to work...

I looked at the graphics archive, and I have to give NHC credit, as so far Igor has been on track, albeit a little faster than their forecast. At 8 a.m. this morning Igor was expected to have reached the point he passed around 11 a.m. yesterday [approximately 17N, 47W].



I'm still not buying an abrupt NW turn at 50W, which is what's been forecast pretty much since day 1, but I can understand why they'd be reluctant to change. I also am realizing that NHC has consistently been well LEFT of model consensus on this turn, so the tiny shifts to right have, I suppose, accommodated what they are likely seeing as strong model consistency. I'm watching today to see how much latitude Igor gains. IMO that'll be today's news, since by 11 a.m. we will see 50W crossed.....
Member Since: October 25, 2005 Posts: 19 Comments: 20733
3805. stormy3
Storm, a minute? Boy you must be well organized.All my daughter gets is " where's my bookbag, wheres my lunch, you need to sign this, i need money for that, can i go to so and so's after school, can you pick me up after school and so on and so on?'
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I wish the NHC would call Igor a five. It will happen when I'm in school.
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moening
that turn by Igor might be delayed because the upper and mid level steering from CIMMS is still showing a strong ridge and a movement to west to continue, the weakness in the ridge seems to have levelled out and should delay that model turn. it is really dicey at the moment and the northern islands should monitor Igor very closely
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Quoting StormW:


Give me a second, and I'll leave something for everyone to look at


I can't wait for your take on 92 now :)
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Quoting scott39:
Goodmorning, Igor is a sight to behold.


Mornin Scott....He is quite a monster!!
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3800. scott39
I hope Igor timing beats the new pattern change in high pressure!
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Quoting StormW:
Morning Ron!

You ever sleep?


LOL...not at work sir!!
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3796. scott39
Goodmorning, Igor is a sight to behold.
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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.