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 plywoodstatenative:
the biggest question becomes are we talking eastern as around NC or around Florida?


I think the Florida east coast is to far west. I would say NC to New England if it was going to cause problems with the USA. I still think it will be a Bermuda problem.
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Quoting Cotillion:
...Bastardi's measure of a season by a maximum recorded pressure only is ridiculous. Of all the things to measure a season, that's one of the least accurate to make any informed statement.


As I said earlier: Bastardi's suggestion is completely ridiculous; if nothing else, longevity wouldn't matter under his scheme, so that, for example, a long-track storm that only reached Cat 3 pressure wouldn't be considered as powerful as a one-day wonder that RI's from a TS to a Cat 4 in, say, 48 hours, then dissipates just as quickly. His claim that it would make the measuring process more objective doesn't stand, either, as pressure readings are no more no less accurate than wind readings.

Having saidf all that, though, I fo agree with him that Hurricane Alex's Cat 2 rating seems ludicrous for a storm that maintained 947mb, a Cat 4 pressure. Post-season analysis may see that changed.
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Quoting TropicalAnalystwx13:
This is a high-end Category 3/low-end Category 4 IMOE:


Looks very frightening. Well he is Igor...
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Quoting RecordSeason:
363:

Based on laws of thermodynamics.

If I remember right, the paper I saw published on Dr. Emanuel's technique already assumes a 20% coefficient of friction, and the maps that are updated every day are based on his work.

Link to "Limits on Hurricane Intensity"

This goes into detail that I think anyone with at least a high school knowledge of physics and thermodynamics should be able to grasp the basic concepts.



THANKS. Bookmarked for later reading - not sure I can handle physics and thermodynamics at the moment! (uhhh I don't remember thermodynamics in HS - but then again that was 30 years ago!)
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I remember in one of the earlier model runs..GFS or ECWMF that Igor passed between Bermuda and the East coast and the storm was so huge that the windspan was affecting both bermuda and NC/VA..if this storm makes it past 72W, that scenario would come easily into play..the way the models have this storm setting up, it would be a big one
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for some reason the models indicate that Igor will start moving towards the weekness in the ridge and then the ridge will quickly build back and induce a west to WNW track again. my opinion
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The Cape Verdes are about to get pounded with "Julia's" squalls.
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Thanks Drak
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Here are the two models I use:

ECMWF for areas close to home (GOMEX, Caribbean, Off the Eastern Coast)

GFS for areas in the Eastern Atlantic.

These have been the two best performers this year, along with the CMC for close to home.
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Quoting BahaHurican:
Yeah, with TS warnings for the CVIs, too. Wonder if a hurricane is possible before it leaves that area....


Be the first time ever, I think.

I can't recall a hurricane hitting it. Tropical Storms, yeah.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Has to be a decent Category 3 right now.

Wish there was a way we could get more accurate intensity estimates than simply satellite estimates.

Drak can probably come up with something when he becomes a Met.

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Quoting mgreen91:
Drak, how well has the ECMWF model been doing this year?


It has been doing pretty good but it still has obvious errors in the long-range. We saw that with Earl when it tried to slam the storm into Florida and put it as a significant system in the Gulf. Right now my preference is just to follow the models out to 5 days.
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382. MZT
Quoting TropicalAnalystwx13:
This is a high-end Category 3/low-end Category 4
It's looking about as good already as Earl did off the FLA coast. And the 5 day cone doesn't even bring it there yet. We don't normally see CAT5's in the Atlantic, but this is about the best setup for one that I've seen since Floyd.
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Quoting BahaHurican:
Yeah, with TS warnings for the CVIs, too. Wonder if a hurricane is possible before it leaves that area....


I don't think so looking at the current intensity from the models. Looks like a strong TS and possibly a hurricane after it moves away from the CV islands to the north.
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Quoting plywoodstatenative:
the biggest question becomes are we talking eastern as around NC or around Florida?


Oh common, the storm is 2700 plus miles off the coast. we're talking the north side of whilmington, hows that?
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Drak, how well has the ECMWF model been doing this year?
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Quoting plywoodstatenative:
Baha, when is the last time you can think of that the Cape Verde Islands actually had tropical storm warnings from a system that just rolled off of Africa?


Yeah, Gaston.
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I'll guess Debby, 2006.

ZCZC MIATCPAT4 ALL
TTAA00 KNHC DDHHMM
BULLETIN
TROPICAL DEPRESSION FOUR ADVISORY NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042006
500 PM AST MON AUG 21 2006

...TROPICAL DEPRESSION FORMS IN THE FAR EASTERN ATLANTIC...

AT 5 PM AST...2100 UTC...THE GOVERNMENT OF THE CAPE VERDE ISLANDS
HAS ISSUED A TROPICAL STORM WARNING FOR THE CAPE VERDE ISLANDS. A
TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED WITHIN THE WARNING AREA WITHIN THE NEXT 24 HOURS.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Quoting divdog:
what r u 15 ?? grow up and lighten up frances
Hey! Nice "Stripes" reference!
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Quoting TropicalAnalystwx13:
This is a high-end Category 3/low-end Category 4 IMOE:


I agree with that statement.
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i bet we will have TS Julia and a special advisory on Igor at 2pm Eastern!!
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372. IKE
Quoting AstroHurricane001:
92L seems to be getting less organized, but some heavy rain looks possible for Haiti, especially in the southern parts this evening.




Don't tell Bastardi that.

162 hour 12Z GFS....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Considering Igor's eyesize comparative to his diameter, the time when he goes through a EWRC with a larger eye typically...

He might actually look close to a doughnut.

Member Since: August 23, 2008 Posts: 7 Comments: 5300
Baha, when is the last time you can think of that the Cape Verde Islands actually had tropical storm warnings from a system that just rolled off of Africa?
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Good morning everyone! Or afternoon, wherever you may be! Busy day in the tropics. Just two years ago today we were getting ready for Ike, and that Ike started affecting us. Time goes by pretty fast! Be safe today and have a great second half of the weekend!
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Here's Bastardi's Take


SUNDAY 9:30 AM


SUNDAY MORNING COMMENTS

First, on Igor. True to the ideas yesterday, the European has shifted west and now has Igor reaching as far west as 72 west. This is over 12 degrees from the 00z run,sep 10th. The UKMET remains west and I have not seen the 00z Japanese out that far. The GFS remains insistent on its recurve east of 65 west.

There is probably a simple rule to use here. If the storm is south

of 25 north at 70 west, the US coast will most likely have at least tropical storm impact from this. The fact is the the models are trying to get the storm to hook with the atlantic trough, and since the pattern is in a retrogressive mode, that trough keeps dipping in further west with time until by the time we are out to 168 hours, if the hurricane is south of 30 north, there really wont be anything to get it out of there. This is why you see the Ensembles, and again the Euro leads the way with predicting this, showing such a spread out area of low pressure once to day 8.. from the bahamas to south of Newfoundland. because some of its members take it westward. In many ways, the combination of Igor, what will be Julia now off the African coast, and the developing cyclone in the Caribbean supply us with a similar case to Earl, Fiona and Hermine... if one looks at Igor as the threat to the east coast, Julia having to recurve if Igor comes as far west as I think it will ( to at least 70 west) and what will be Karl the threat to Texas in the longer term via the Yucatan and then a fade northwest at the end. In fact one might as well correct the Euro north ( its track is into Tampico but at least it sees it, the GFS would have you believe nothing is there) since a) its ensembles are leaning north and b) its not like nothing has been aimed there so far.. it would make the 4th classified system to make a landfall within 75 miles of Brownsville, ALex, Hermine and the depression being the other 3.

Speaking of the system in the Caribbean, now it has a chance to go as the convection that has fired is much more co-ordinated with the low level wave. Yesterdays impressive look was all outflow but the low level wave was well behind what looked to be the mid level center and then upper outflow. Not so today as a center near 15.5 and 69 looks to be coordinated with the cloud shots and the data.


This ship report:

SHIP S 1200 16.90 -69.20 149 318 50 24.1 - 13.1


near 17 north and 69.2 west has a northeast wind at 24 kts with 13 foot seas and a pressure at 1009 mb Looking around it, I see a sharp windshift in that area with a southwest northeast trough, and its co-ordinated nicely now with the cloud shot, so this should start going now. If I had a hatch-it job, now I would have it as a high threat for development with in 48 hours. Of course, I dont have a hatch-it jobs as I am not allowed to play with sharp objects.

By the way, 13 foot seas area the give away that something is cooking. You dont get a 13 foot sea without strong concentrated winds in the tropics.

In looking at Igor we find again the US models have been too far north too quick. Its on the order of 150 miles in 3 days.. and that is not bad.. in fact its a good forecast overall but the same error continuing would mean that the model would try to recurve the system. The first challenge is tomorrow and Tuesday so lets see where it goes. Looking at the Euro hurricane forecast, there are more members south of its track than north. And as I have stated several times already this is going to be the strongest hurricane of the season thus far, hence the big threat if it comes as far west as I have it.

By the way, when you see a trough off the east coast in 192 hours, that is because the model forecasting it is recurving the hurricane. Its not because there is a trough there by then, its the hurricane that causes the

trough. If there is no hurricane, or its stalled next Sunday between Hatteras and the Bahamas, then the whole map is different. My point is that if you look at the runs that dont recurve the storm, then you get a different map. There is no trough off the east coast, without a recurved storm next week, as the pattern is shifting. In fact a look at the Euro shows it has another development trying to start up day 10 near Puerto Rico anyway,and of course the GFS day 15 is trying to scare the daylights out of the gulf with its monster. The point being this pattern is ripe for storms and rumors of storms

One more thing.. a word about my overall seasonal power index to replace the ace.. using pressures of each storm set against 1000 mb as the 0 point. If we look at the storms this year.. Alex at 947 would get 53 points, Bonnie and Colin 0 ( pressures stayed above 1000 mb) Danielle at 942 would have gotten 58 points, Earl at 929 71 points, Fiona at 989 11 points, Gaston none, Hermine 990 mb 10 points and so far Igor at 980 with 20 , you come up with a much better scale for how strong the season is. I think Igor is getting to 920-930 btw. But I am willing to bet when we get done with this season, if we total the pressures of these storms up against previous known seasons, this is a top 5 season. You watch.

BTW some wild weather coming the next two weeks as heat refires and tries to come northeast into a stubborn boundary, but summer is not done yet for some of you that are a bit on the chilly side now. Interestingly enough, the same old GFS nonsense with temps has been going on from when I was in college the US models overcooling the east. For all the cold air that was coming, the days of 6-9 below normal over the east coast, where the heck is it. PHL last 5 days plus 1.4 Bos plus 2.4..even Chicago, where it was supposed to have gotten quite chilly is only 2-6 below normal the past 5 days. Heck this surge coming this weekend or next week gets up into there, it will wipe out 10 days of cool with 2 days of warm

But there is no question that cooler air has gotten into the pattern since Aug 22, when we named Danielle. And since by Sept 22 we may be all the way to the letter L or M, I think I have made my point to you about what sets seasons off. In fact the only thing I need now ( besides running the total numbers up a bit more) is to get the end game to give me the impact scores I need to verify. Again faced with the problem of having to balance the desire to be right.. and by doing so, performing a valuable service, against the implications of such things. It is a problem I wrestle with constantly

Member Since: September 7, 2008 Posts: 0 Comments: 703
the biggest question becomes are we talking eastern as around NC or around Florida?
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This is a high-end Category 3/low-end Category 4 IMOE:

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Quoting TropicalAnalystwx13:
I predict at 2PM, we will have TS Julia.

At 5PM, I expect Igor to be a Category 4.

for IGOR is very quite possible
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Quoting Drakoen:
I see TD12 formed this morning from that powerful tropical wave we were watching over the West African coast:

Yeah, with TS warnings for the CVIs, too. Wonder if a hurricane is possible before it leaves that area....
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Thanks for all the responses. It is very interesting. But one more question..

How is the theoretical maximum potential measured?
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Quoting plywoodstatenative:
Drak whats your forecast with Igor, you were just about dead on with Earl, the question I also have: whats this about Bastardi, what is he saying that has people agreeing with him?



The models have been coming in with a weaker trough run to run which has resulted in pushing Igor closer to the eastern seaboard with the ECMWF being the western most and the GFS being the eastern most and the GGEM splitting the difference. I think the storm will come further west than what the NHC has right now so that the long-range track is between Bermuda and the U.S. eastern seaboard.

I don't follow Bastardi.
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Quoting BahaHurican:
I wouldn't be surprised to see another Earl-like track, at least up to about 70W. After that, I'm still trying to figure. One thing I'm fairly sure about is that we're unlikely to see less than a major at 70W, regardless of how far north it is at that point. And I seriously doubt we'll see a recurve to Nward track before that point [though I would love to be wrong about that...]

Why do you think it will not get picked up into the current trough that it will intersect with at 55W.
Note I should have said start re-curving and moving on a more NW NNW track.

This shows the trough
http://www.goes.noaa.gov/GIFS/ATIR.JPG
This shows the trough making good progess eastward and a little southward still
http://www.ssd.noaa.gov/goes/east/tatl/loop-avn.html

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357. MZT
Quoting MiamiHurricanes09:
Igor will likely become the first category 5 hurricane of the season.
Earl came pretty close... If Igor does not, then any CAT5's this season would probably need to be Caribbean events. Gilbert/Wilma style.
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Quoting tornadolarkin:

He's going nuts!!!!!!!


He looks like an early cat 3 to me and not quite annular yet....
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I predict at 2PM, we will have TS Julia.

At 5PM, I expect Igor to be a Category 4.
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Quoting MZT:
StormWatcherCI: Truce. I learned something today - people on here will call bullshit when they see it.
No problem. We're good. LOL
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Quoting AstroHurricane001:
92L seems to be getting less organized, but some heavy rain looks possible for Haiti, especially in the southern parts this evening.

Rain will be the issue for now.
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Quoting cheaterwon:
What effect would that have on the track of a hurricane?
I don't know that becoming annular has a track effect per se. It has more to do with the strength and structure of the storm. AFAIK, annular storms are still subject to the same forces that direct non-annular 'canes.
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Link

As usual, ADT goes through the roof as soon as it sees an eye. You can see the figures - particularly raw T# - go up in a shot as soon as the eye is seen.

That said, this is probably a Category 3 at the moment.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
Quoting MiamiHurricanes09:
Igor will likely become the first category 5 hurricane of the season.

O_O
*Starts to hyperventilate*
Not very surprising though.
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92L seems to be getting less organized, but some heavy rain looks possible for Haiti, especially in the southern parts this evening.

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Miami I won't be surprised if afterwards there are more than just this system that are reclassified as category 5 storms.
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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.