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 hunkerdown:
as I stated above, contracting diameter has no bearing on path of the center point of the eye, no matter what the size of the eye. The center point of the eye has definitely moved slightly south of due west over the last few frames.


Yes, and it will be S of the NHC forcast point also.
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Quoting DestinJeff:


sans.

Pardon me, but do you have any Grey Poupon?


Yes. Yes I do.
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3093. pottery
Quoting MZT:
Probably because they are slinging around massive amounts of air and water, which are not in equal balance on all sides. Kind of like a washing machine with unbalanced clothing in it.

Heh!
That's FAR simpler than my explanation....
Member Since: October 24, 2005 Posts: 0 Comments: 24311
3092. Seastep
Quoting 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.


There is no wobble in the entire SSD loop.
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3091. JP2010
The new 0Z model LGEM, HWFR, GFDL take 92L over cancun then Brownsville TX as a Cat 2 in 120 hour.
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Quoting GeoffreyWPB:
TS Julia has formed...and our local mets...even at this hour...are still calling it a depression.
It is still on the NHC as a TD. Hasn't been changed yet.
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3088. angiest
Quoting GeoffreyWPB:
TS Julia has formed...and our local mets...even at this hour...are still calling it a depression.


Until the advisory comes out, it isn't official. That said, Julia has formed. ;)
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3086. mbjjm
The United States uses mph, some places in Europe and Asia uses m/s and the rest of the world uses km/hr to avoid the confusion the World Meteorological Organization and other international agencies uses knots to avoid the confusion. The winds measured by the Hurricane Hunters are measured in knots. The NHC discussion are in knots etc. The public discussions are in mph because the NHC caters mainly for persons in the Region who are accustomed to mph.In converted they have to round off, the saffir scale is made in knots hence the difference. It is similar to the computer models and hourly obs using Celsius, time in gmt etc.
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Quoting divdog:
eye is contracting .. still west
as I stated above, contracting diameter has no bearing on path of the center point of the eye, no matter what the size of the eye. The center point of the eye has definitely moved slightly south of due west over the last few frames.
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TS Julia has formed...and our local mets...even at this hour...are still calling it a depression.
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Quoting MZT:
Probably because they are slinging around massive amounts of air and water, which are not in equal balance on all sides. Kind of like a washing machine with unbalanced clothing in it.
Hey! There is someone using their noodle! Good theory...how would you test it?
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Quoting stormwatcherCI:
Well, it is just about at Kman's 75W so we shall see. Isn't this an area of very high TCHP ?


As high as the charts can go.
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Quoting KATRINABILOXIGIRL:
LMAO...Amen to that...LOL
And he will more than likely be there about the time he said he would. (as opposed to 25 minutes late)
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Quoting tinkahbell:


He's a man. He won't use his signal or ask for directions..... :p


hehehe :-D
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So I guess this one may or may not be a FISH now as some were saying on here last night. lol!
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92L may finally be developing an LLC at 16.5n,74.5w.

We'll see.
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Quoting CosmicEvents:
That's what he said....


;)
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do we have a center fix as of right now?
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3073. MZT
Quoting PrivateIdaho:
Which brings us back to the question...why do hurricanes wobble?
Probably because they are slinging around massive amounts of air and water, which are not in equal balance on all sides. Kind of like a washing machine with unbalanced clothing in it.
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Quoting hunkerdown:
is that your thoughts as to WNW, NW or Nerly turn ?


I suspect it will begin moving NW around, say, 67W, then N at 70W, with a turn to the NE at around 73W.

Basically, I'd expect another Earl type track, sans the hit on the islands.
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Quoting JupiterFL:

Finally...
That's what he said....
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Quoting tinkahbell:


He's a man. He won't use his signal or ask for directions..... :p
LMAO...Amen to that...LOL
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Quoting MiamiHurricanes09:
No, it has been jogging towards the SW for a few hours now. The recent contraction of the eye didn't fool you, it really has been moving towards the WSW.
agreed, the contraction of the diameter of the eye would have no bearing on the path of the center of said eye if the movement was a consistent, unchanged westerly direction.
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Quoting atmoaggie:
NHC advisories and 5 day track for Igor thus far. (I skipped the intermediate advisories this time to keep the valid time consistent frame to frame)



You watch that and it looks like a snake slivering ever so slyly toward the west-N-west. Creeeepy
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Quoting MiamiHurricanes09:
No, it has been jogging towards the SW for a few hours now. The recent contraction of the eye didn't fool you, it really has been moving towards the WSW.


Run the loop.....and align the south edge of the eyewall. It has not dropped AT ALL. The northern portion has contracted. Thats why at the same time the appearance of a wobble took place...the eye just happened to contract.......
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3064. angiest
Quoting BahaHurican:
Every top I have ever watched has wobbled. Not all the time, but at least some part of the spin had a wobble to it. I'd bet ur average TC wobbles for the reason u mentioned... hitting an "imperfection"....


The earth's rotational axis also wobbles. Some planets wobble much more than Earth does.
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Quoting KoritheMan:


I'd say if current trends continue, late tomorrow morning. But if this system fails to develop tomorrow, I think its chances are nil.
Well, it is just about at Kman's 75W so we shall see. Isn't this an area of very high TCHP ?
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Quoting DestinJeff:


When I designate it a DOOMICANE, then you can be worried.

Right now it doesn't meet the DOOMICANE criteria, as made up by me.


I am waiting for all the doomcasters to arrive now how about you? LOL!
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Quoting atmoaggie:
NHC advisories and 5 day track for Igor thus far. (I skipped the intermediate advisories this time to keep the valid time consistent frame to frame)



Cool Post!
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Quoting BahaHurican:
Every top I have ever watched has wobbled. Not all the time, but at least some part of the spin had a wobble to it. I'd bet ur average TC wobbles for the reason u mentioned... hitting an "imperfection"....
Which brings us back to the question...why do hurricanes wobble?
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3058. divdog
Quoting kmanhurricaneman:
am i seeing things or is Igor going wsw
eye is contracting .. still west
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Quoting KoritheMan:


Agreed.
is that your thoughts as to WNW, NW or Nerly turn ?
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Quoting EnergyMoron:


RLOL -> actually one must have humility when faced with possibly birufications (like is happening now) hence moron
Glad to have you pumping up the collective raw t#, relative to IQ here.
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Quoting DestinJeff:


When I designate it a DOOMICANE, then you can be worried.

Right now it doesn't meet the DOOMICANE criteria, as made up by me.
You didn't use enough CAPS, bold, or statistics to mesmerize the blog.
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Quoting stormwatcherCI:
I think at this rate MAYBE by the AM we have a TD. So far convection is holding pretty good and consolidating much better.


I'd say if current trends continue, late tomorrow morning. But if this system fails to develop tomorrow, I think its chances are nil.
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Quoting PrivateIdaho:
Gyroscopes don't wobble, tops only wobble when disturbed or when they hit an imperfection....so Yes!
Every top I have ever watched has wobbled. Not all the time, but at least some part of the spin had a wobble to it. I'd bet ur average TC wobbles for the reason u mentioned... hitting an "imperfection"....
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Quoting BahaHurican:
Closer 2 70W, IMO


Could be. It's all going to depend where the highs and that trough is. I hope it's not another needle threader like Earl. I hope the high makes it all the way off the coast or we'll be in serious trouble.
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3049. MZT
92L may have a center of circ, but it looks to be mostly going POOF again.
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Quoting rareaire:
wobbles for 3 consecutive frames is a movment not really a wobble. And it has moved S of w some but not enough to be overly concerned with. Its if he keeps going west after the appointed go north signal we need to be watching for!!


Its the northern eye wall contracting (the eye is getting smaller. The southern portion of eyewall is at the same latitude - the northern has dropped (smaller eye).
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Quoting bluenosedave:


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?


i believe most of those rainstorms are very beneficial, they produce the water for the african plains that sustains them for the dry season.
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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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