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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2996. mbjjm
Quoting wunderkidcayman:
umm guys I thing the HHunters have found the COC or near it atleast reporting W winds


Not true,SW winds only
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Sorry, adding link.

Link
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Quote from Wikipedia:

Annular hurricanes tend to persist, even when encountering environmental conditions which easily dissipate most other hurricanes. Forecasters have difficulty predicting the behavior of annular hurricanes; they are a recently recognized phenomenon, and as such, little is known about their tendencies. Because of this, they can be more dangerous than typical hurricanes.
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Quoting ElConando:


I would say collapsing but we shall see.
No, it's contracting. There is no outer core to cause the inner one to collapse.
Member Since: September 2, 2009 Posts: 130 Comments: 21032


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OK I have got to ask. This loop is something that StormW put up many hours ago. Does it look at all possible that the NHC and models have the correct extended path for IGOR.

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2990. pottery
Quoting GeoffreyWPB:
The wobble-casters are the most annoying. If a system was close to landfall….then wobbles would mean something. With Igor, wobbles are expected and mean nothing.

M
Hmmmm!
But accumulated wobbles will sure add up, after a few.
And these may have an impact on the 'where' and 'when' for steering.
Just a thought.
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Quoting JLPR2:
Is the eye is collapsing or turning ridiculously smaller?




I think it is contracting,
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Quoting JLPR2:
The eye is collapsing or turning ridiculously smaller.



I see the eye becoming smaller and clear on that. No sign of a EWRC.
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Quoting hurricanehunter27:
We are witnessing the most powerful hurricane of the 2010 season right now and it might make it into the top ten strongest hurricanes if it keeps this up. After a day or two Igor will start to expand and beacome a good bit larger than it is now. Man, the IR sat is shows the best looken eye iv seen sence Rita in 05. I wish the 11pm advisory was 10 pm so we can see how strong it is right now! I put Igor at 90% chance at being at cat 5 satus by 11pm the only thing that could happen to stop this is EWR. Winds right now i am guessing are in the 165-175 range.


At that surface wind speed, Igor would be making its own track and environment, wouldn't it? Not al whole lot is going to affect it.
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Quoting Vero1:
The Blob over Africa



You know, we see these tropical waves over Africa, and granted they aren't cyclones, but they must bring very heavy rains and flooding and such. But I've never seen anything in the news. Are we this self-centered in North America?
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Yeah, but 3 is the perfect number for strikes. Baseball is a game of multiples of 3.
9 players, 3 strikes, 9 innings, 3 outs per inning 3 bases.
6 is also perfect for football because 2 field goals is worth the same as 1 touchdown, which is the same as 3 safeties, this makes the extra point worth something.
Quoting PrivateIdaho:
Why are 3 strikes an out? Why 6 for a touchdown? Because these are man-mad constructs and totally artificial..as you point out, nothing magical happens between 74 and 75 mph.
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Quoting AtmosphericWrath:
Unexpected wobbles? Unforeseen changes in direction? Tracking off course?

WELL NO WONDER. Look at what is steering Igor!


It's that darn Gorton's Fisherman!


would have been funnier if you actually used a pic of Igor lol
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Quoting JLPR2:
The eye is collapsing or turning ridiculously smaller.



I would say collapsing but we shall see.
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Quoting AtmosphericWrath:
Unexpected wobbles? Unforeseen changes in direction? Tracking off course?

WELL NO WONDER. Look at what is steering Igor!


It's that darn Gorton's Fisherman!


Looks like Clooney in "The Perfect Storm".
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Quoting MZT:


Not a good sign though, when StormW has been already been stating for a day and a half that the first trough would not affect the track.


Storm already pointed out that Igor has already missed that boat... and the models/NHC obviously didn't think it would take that one.

The next train passing by is going to be the one... we hope (except perhaps if you live in Bermuda)
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'evening second shift!!!

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2977. JLPR2
Is the eye is collapsing or turning ridiculously smaller?

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Shouldn't he be busy fishing right now?

(laughs)

Quoting AtmosphericWrath:
Unexpected wobbles? Unforeseen changes in direction? Tracking off course?

WELL NO WONDER. Look at what is steering Igor!


It's that darn Gorton's Fisherman!
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Quoting CaneAddict:


Check out satellite imagery...it's CLEARLY heading southward..whether it's a wobble or not. Hopefully just a wobble..


It was just a little wobble. Heading right for the next forecast position.
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I believe the first trough has come and gone this is the second one.

I may be wrong and if I am Im sure one of you will gladly puff up your chest and point it out to all thet can read!!
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Quoting AtmosphericWrath:
Unexpected wobbles? Unforeseen changes in direction? Tracking off course?

WELL NO WONDER. Look at what is steering Igor!


It's that darn Gorton's Fisherman!
LMAO
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Quoting wunderkidcayman:
umm guys I thing the HHunters have found the COC or near it atleast reporting W winds


Pottery better add more ice!!
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'Miss Piggy" found a wind shift at about 15.3833N 74.2W
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Quoting 1900hurricane:
No visible outer eyewall so no EWRC at the moment. NRL has Igor at 130 knots.
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2963. angiest
Quoting HurricaneGeek:


Yeah, true. But the thing is there HAS to be a reason why. Those guys at the NHC are no dummies. I just would like to know the reasoning behind the odd number selection for those milestones.

74 makes a Hurricane. Why not 75?
111 makes a major . Why not 110? 115?
156 makes a CAT 5. Why not 155?



I figure it has something to do with the Beaufort Wind Scale, so I did a little reading in Wikipedia:

The scale was made a standard for ship's log entries on Royal Navy vessels in the late 1830s and was adapted to non-naval use from the 1850s, with scale numbers corresponding to cup anemometer rotations. In 1906, to accommodate the growth of steam power, the descriptions were changed to how the sea, not the sails, behaved and extended to land observations. Rotations to scale numbers were standardized only in 1923. George Simpson, Director of the UK Meteorological Office, was responsible for this and for the addition of the land-based descriptors.[3] The measure was slightly altered some decades later to improve its utility for meteorologists. Today, many countries have abandoned the scale and use the metric-based units m/s or km/h instead,[citation needed] but the severe weather warnings given to public are still approximately the same as when using the Beaufort scale.


If I read that right, 64kts (~74mph) is where a cup anemometer starts spinning 12 times per time unit, although I don't see the time unit.
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting wunderkidcayman:
umm guys I thing the HHunters have found the COC or near it atleast reporting W winds



Where near cuba?
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The wobble-casters are the most annoying. If a system was close to landfall….then wobbles would mean something. With Igor, wobbles are expected and mean nothing.
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2960. MZT
Quoting AtmosphericWrath:
Anyone else concerned(even slightly) that 3 of the 6 models are hinting at a bit more of a westward shift?

OK. I'll go for slightly more concerned.

It's still several hundred miles east of the islands, though. Plenty of time for the track to become more or less dangerous.

Not a good sign though, when StormW has been already been stating for a day and a half that the first trough would not affect the track.
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umm guys I thing the HHunters have found the COC or near it atleast reporting W winds
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Quoting HurricaneGeek:


Yeah, true. But the thing is there HAS to be a reason why. Those guys at the NHC are no dummies. I just would like to know the reasoning behind the odd number selection for those milestones.

74 makes a Hurricane. Why not 75?
111 makes a major . Why not 110? 115?
156 makes a CAT 5. Why not 155?
Why are 3 strikes an out? Why 6 for a touchdown? Because these are man-mad constructs and totally artificial..as you point out, nothing magical happens between 74 and 75 mph.
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2956. pottery
Quoting traumaboyy:


I do not see that....maybe just a hair but we have a massive storm....you know how the room reacts to each Wobble

True again.
But in fact, Igor is not so big as you say.
All the recent images have been close-ups. Look at the Big Picture, he is tightly wound.
He is Massive in Power though.
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SATCONN showing 130+ Knots

From CIMSS

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2954. mbjjm
92L once again beginning its mysterious evening collapse.
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Quoting HurricaneGeek:


I took a tour at the NHC one time a couple of years ago in May. It is ridiculously awesome. I would love to see what's going on there now with all the Igor, Julia, and 92L activity!
The same thing that going on in this blog.........a bunch of dissagreement and argueing lol
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Quoting HurricaneGeek:


I took a tour at the NHC one time a couple of years ago in May. It is ridiculously awesome. I would love to see what's going on there now with all the Igor, Julia, and 92L activity!


That is something I hope to do some day. They probably wouldn't offer tours during times this active, though... :(
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I think the benchmark for a US landfall will be the classic 20N/60W. If Igor passes north of it, it'll go out to sea due to the trough picking it up. If it passes south, I see a possible Hugo/Hazel-like track with the ridge building back in after the hurricane misses both troughs.
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Quoting RecordSeason:
2903:

The answer is because the scale was created in kts, but because the public doesn't understand this, they convert it to mph.

So most of the divisions are on round numbers in kts, but oddball numbers in mph.


Cool!
That makes sense! Thanks.
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Quoting CosmicEvents:
And now......For Something Completely Different..............Link


i THINK iGOR WILL LOOK LIKE THAT TOMORROW MORNING........
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Quoting nyhurricaneboy:


All I can say to that is...

The NHC works in mysterious ways...


I took a tour at the NHC one time a couple of years ago in May. It is ridiculously awesome. I would love to see what's going on there now with all the Igor, Julia, and 92L activity!
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2947. MZT
I hope we learned with Earl... a few frames, does not a change in direction make.

Looks like a third of the eyewidth wobble south. Does not mean anything when the predominat motion has been west for hours.
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Quoting will40:


Link
Thanks Link
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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.