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 atmoaggie:


Is that a RSO floater?
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Quoting atmoaggie:
Not disbelieving you, but have a resource for that?

Just experience watching closeup visible.. they arent normally as "big" as those, but I wonder if the size of Igor is making them appear larger. They are normally overlooked in a massive spiraling storm, but given the fewer spiral bands, Im thinking they are the same phenomenon. They are much easier to see most times on mimic-tpw closeup loops of storms about to undergo an EWRC. Of course I could be wrong, as this looks a bit different from the norm, but again I think it is a perspective issue.
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Quoting Cotillion:


190mph has been seen before.

800mb would be 250-270mph or some sort, I'd imagine.
A Cat "6" would imply something greater than total devastation with perhaps,wind speed of 190 mph.
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Quoting Sfloridacat5:
Currently top story on AOL.

Igor Builds to Category 4 Hurricane; 2 More Storms May Follow


OOOOOOOOOOHHHHHHHHHHH WOOOOOOOOOOOOW! AOL is right! New speical advisory, oh my gosh (catching my breath):

..IGOR RAPIDLY INTENSIFIES INTO A CATEGORY FOUR HURRICANE...


SUMMARY OF 230 PM AST...1830 UTC...INFORMATION
----------------------------------------------
LOCATION...17.7N 46.1W
ABOUT 1120 MI...1800 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...135 MPH...215 KM/HR
PRESENT MOVEMENT...W OR 270 DEGREES AT 14 MPH...22 KM/HR
MINIMUM CENTRAL PRESSURE...950 MB...28.05 INCHES


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Member Since: August 16, 2007 Posts: 6 Comments: 12461
1190. IKE
Quoting help4u:
Ike,that looks farther east than last run,i quess the trough does it's job.


It does turn it east sooner.
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1189. help4u
1176 did not post the rest,Two more storms too follow Igor out to sea.
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Quoting MiamiHurricanes09:
Seriously, I wonder what those "pimples" indicate. Anyone know?


Igor is going through puberty and has major acne. Someone airdrop some noxzema on this thing!!
Seriously though, they are an interesting feature.
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1187. Gearsts
Quoting TerraNova:


Only on Jupiter! And hopefully it'll stay that way.
There have been cyclones that have reach close to that
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I'm not saying it won't recurve, you all got me wrong there. I'm just stating we need to look at the facts that Igor may recurve too late, that way it won't be a surprise to those who had confidence in Igor recurving. We need to sort out the scenarios so that it won't be a total shock to those who actually paid attention to the possible scenarios. Gives people more time to prepare for the worst if anything happens.
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.
The pattern till now just does not favor cv threats. I see no reason for that to change.

As i mentioned yesterday in a post on wu the primary reason is the negative torque anomalies that have persisted across the last 90 days in the 20-40N band around the hemisphere. This can be seen as the blue shaded areas here. The GLAAM negative anomalies are correlated to increased meridional flow, or flows that have more south to north, or north to south components. When zonal prevails, the anomalies tend to reverse - but there is also a velocity component to the total budget. In this case, however, this has marked an increased potential for incurring trough into ambient subtropical ridges, which in turn increased(s) the background probability for earlier polarward migration of TCs due to the effect that has on the steering levels.
Quoting StormW:


?????????????????????????????????

Basically saying that statistically there is a higher than average number of alternating troughs/high pressure systems than average which increases the chance of poleward movement of an storm with a long east to west track.
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Quoting Stormchaser2007:


In soviet Russia, hurricane RIP's you!


In Soviet Russia, hurricane westcast's YOU!
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1182. pottery
Quoting MiamiHurricanes09:
Yeah, but you see how they are uniform along the NW quadrant?

Yeh. Very weird.
Do they show on Rainbow?
Member Since: October 24, 2005 Posts: 0 Comments: 24307
Quoting blsealevel:






Hot tower?
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Quoting MiamiHurricanes09:
Seriously, I wonder what those "pimples" indicate. Anyone know?



Too much vodka last night. Darn russians lol
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Yup, still there and a little larger. It does look like the genesis of a curved band though.



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Currently top story on AOL.

Igor Builds to Category 4 Hurricane; 2 More Storms May Follow
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Close-up of the "pimples"

First time in my 12 years of watching Tropical Cyclones have I seen this.
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1174. help4u
Ike,that looks farther east than last run,i quess the trough does it's job.
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Quoting MiamiHurricanes09:
Seriously, I wonder what those "pimples" indicate. Anyone know?



I always suspected it was UFO's flying real fast in circles causing these hurricanes. Kind of like superman does making a tornado. This is verification. :)
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Quoting IKE:
Day 8 ECMWF...



Ike,

Fujiwara? They are sharing isobars...
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Quoting MiamiHurricanes09:
Seriously, I wonder what those "pimples" indicate. Anyone know?


Maybe the start of a expansion in size? That's my guess. It's either that or puberty lol.
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Quoting Gearsts:
cat 6 would be 190mph winds 800mb...lol


190mph has been seen before.

800mb would be 250-270mph or some sort, I'd imagine.
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Quoting Stormchaser2007:


In soviet Russia, hurricane RIP's you!


Hey thats tru.. Hey wait a minute! Hurricanes R.I.P people in America too!
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Quoting 1900hurricane:

Nope, far too many bands under that CDO:



Thanks!
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Quoting RecordSeason:
1126:

Incredible.

The heat content is exactly double along the forecast track compared to the current location...Can you say "Wilmafication"?


LOL, I love that word. I'll keep that word in mind for my arsenal of tropical discussions!
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1166. IKE
Day 10 ECMWF...no lower 48 hits again on this run...gets it through Sept. 22nd.

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Igor will definetly reach Cat 5 status. The eyewall just became very symetrical and the winds are 135mph. Once the inner eyewall builds in and creates that white inner ring we will have cat 5 storm. My predictions is cat 5 by the 10pm update with winds of 160mph.. Then an Eye wall replacement within 24-36hrs.
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Quoting Gearsts:
cat 6 would be 190mph winds 800mb...lol


Only on Jupiter! And hopefully it'll stay that way.
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Quoting SouthALWX:
The "pimples" sometimes precede EWRCs.
Not disbelieving you, but have a resource for that?

Or just a personal observation. which isn't a bad thing...
Member Since: August 16, 2007 Posts: 6 Comments: 12461
Quoting MiamiHurricanes09:
Seriously, I wonder what those "pimples" indicate. Anyone know?


My guess would be the overshooting tops from developing bands, but like I said, that is just a guess. I don't recall observing anything like that since I began tracking storms in 1998.
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1160. Max1023
Quoting NCHurricane2009:


Saw that too, but wobbles are common in big intensification episodes. Danielle and Earl wobbled a lot, but that didn't equate to any real changes in the forecast track.


Igor wobbled a lot this morning when the pressure bombed, the pressure likely dropped slightly ahead of the satellite appearance, that explains why the eye cleared out during the wobbling phase. Igor has likely come close to leveling off, it should begin to track more steadily to between 270 and 280 degrees.

My intensity forecast for Igor:

5pm: 125 knots
5am Monday: 130 knots
5pm Monday: 135 knots
5am Tuesday to 5am Wednesday: 140 knots - Minimal Category 5.

After that a slow weakening.
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sry - double post
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Quoting CybrTeddy:
Our 3rd Category 4 of the season..


He's soooo good lookin' too! ;)
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Quoting atmoaggie:
In soviet Russia, hurricane spins you!

(well, and everywhere else, too.)


In soviet Russia, hurricane RIP's you!
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Quoting pottery:

Not tall cloud tops??
Yeah, but you see how they are uniform along the NW quadrant? Never seen that before.
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Quoting StormW:


I wouldn't be 100% sure on that. It's obvious that the first trof is a moot point now.


Hey Storm! I noticed that a lot of the models are trending towards a close approach to Bermuda, save the CMC which builds a ~1024 mb ridge in to keep Igor further west. I think the NCEP ensembles which fuel the GFS take this too far to the right. Do you think the ridge could build back in to force Igor further west than forecast?
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1153. flsky
Quoting MiamiHurricanes09:
Seriously, I wonder what those "pimples" indicate. Anyone know?


Has anyone ever seen this happen before?
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Quoting MiamiHurricanes09:
Seriously, I wonder what those "pimples" indicate. Anyone know?

I dunno. Outside of more convective banding in the near future? Maybe?
Member Since: August 16, 2007 Posts: 6 Comments: 12461
1151. Gearsts
Quoting MZT:
I suppose if a CAT6 classification needs to exist, it would be like for situations like the Mount Saint Helens eruption... "Nearly all trees blown over, and man made structures blasted down to their foundations". Whew.
cat 6 would be 190mph winds 800mb...lol
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Quoting Max1023:


Could one of the trough's miss recurving Igor but pass close enough to form an outflow channel?? Right now Igor's is mostly radial.


Yes, that large trough just NW of Igor is supposed to pass just north of the storm, which would allow for such an outflow channel.
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The "pimples" sometimes precede EWRCs.
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1147. pottery
Quoting MiamiHurricanes09:
Seriously, I wonder what those "pimples" indicate. Anyone know?


Not tall cloud tops??
Member Since: October 24, 2005 Posts: 0 Comments: 24307
1146. IKE
Day 9 ECMWF...

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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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