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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1146. IKE
Day 9 ECMWF...

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I guarantee that when most people turn their tv's on tonight, down here, a lot of them will be shocked at what we are seeing right now with the way that Igor is acting.
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Quoting TerraNova:


I didn't think so, especially with that feeder band on the southeast quadrant.

Just curious, does anybody know if Andrew is considered to have been annular at landfall?

Nope, far too many bands under that CDO:

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Quoting Stormchaser2007:


Puberty?

Guess he's not all grown up yet into a proud Russian hurricane.
In soviet Russia, hurricane spins you!

(well, and everywhere else, too.)
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Quoting MiamiHurricanes09:
18z SHIPS takes it to a 160mph major hurricane. A couple things to note:

1.) Upper level conditions should remain favorable.
2.) SSTs are only going to get warmer.
3.) Heat content is going to get deeper.

TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120
V (KT) NO LAND 115 124 126 126 126 129 131 138 135 130 126 123 118
V (KT) LAND 115 124 126 126 126 129 131 138 135 130 126 123 118
V (KT) LGE mod 115 128 132 130 128 124 123 124 125 122 117 114 111

SHEAR (KT) 4 1 6 6 11 6 1 7 7 6 1 5 11

SHEAR ADJ (KT) -2 0 -3 -2 -1 0 0 -3 -1 -5 5 2 0
SHEAR DIR 28 112 135 81 73 26 341 10 242 284 79 224 188
SST (C) 28.1 28.2 28.3 28.4 28.5 28.7 28.9 29.1 29.1 29.1 29.1 29.1 29.0
POT. INT. (KT) 139 140 141 142 144 147 149 152 153 153 153 152 151
ADJ. POT. INT. 132 134 135 135 135 138 138 140 140 139 137 136 134
200 MB T (C) -51.7 -51.5 -51.4 -51.3 -49.7 -50.2 -49.3 -49.7 -48.9 -49.2 -48.3 -48.7 -47.7
TH_E DEV (C) 10 11 11 11 11 12 12 12 11 10 10 10 10
700-500 MB RH 63 61 58 57 56 54 55 53 53 57 53 51 50
GFS VTEX (KT) 23 25 26 30 30 34 32 37 38 40 40 42 43
850 MB ENV VOR 72 70 65 72 72 76 100 103 120 140 167 163 177
200 MB DIV 54 67 77 73 129 20 85 72 71 3 99 19 43
LAND (KM) 1564 1513 1462 1437 1364 1236 1174 1037 922 819 759 741 767
LAT (DEG N) 17.7 17.8 17.8 18.0 18.1 18.6 19.3 20.1 21.1 22.0 23.0 23.9 24.9
LONG(DEG W) 46.3 47.5 48.7 49.8 50.8 52.8 54.5 56.0 57.4 58.9 60.4 61.8 63.2
STM SPEED (KT) 11 11 11 10 10 9 8 8 9 8 8 8 8
HEAT CONTENT 41 43 48 54 62 69 70 82 70 65 56 63 53

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



...probably rapid intensification??!
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1139. IKE
Day 8 ECMWF...

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1138. flsky
Quoting NCHurricane2009:
http://www.ssd.noaa.gov/goes/east/tatl/vis-l.jpg

With the images you guys keep posting (zoomed-in), I keep forgetting how small Igor really is (see above link, zoomed-out).

Hmmmmmm. About the size of Louisiana or S. Carolina?
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1137. Gearsts
Quoting StormW:


I wouldn't be 100% sure on that. It's obvious that the first trof is a moot point now.
StormW what do you think about Levi update and the possible west track?
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Quoting reedzone:
The two trough off the East Coast look to be too far north to fully recurve Igor, in my opinion. IF Igor recurves, I don't think it will be a sharp one.
Keep up the faith brother.
Member Since: August 3, 2005 Posts: 10 Comments: 5560
Seriously, I wonder what those "pimples" indicate. Anyone know?

Member Since: September 2, 2009 Posts: 130 Comments: 21122
Quoting NCHurricane2009:


Yeah guys, Igor is forming some pimples! Quit stressing him out! LOL!


Puberty?

Guess he's not done yet becoming a proud Russian hurricane.
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WOW! Gone for a day and Igor is a massive cat 4 with an impressive eye forming!!! Small storm, though.
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1132. Max1023
Quoting StormW:


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


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.
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Quoting palmasdelrio:
I'm not totally sure, but it seems to my untrained eyes that Igor is traveling right now a little south of due west. What is your opinion and what if this is true, does that mean that the track will shift to the left?


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.
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1130. 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.
Member Since: September 24, 2005 Posts: 0 Comments: 793
Quoting TerraNova:


Hey angiest! Should gradually grow larger, especially if/when Igor undergoes eyewall replacement cycles. That acne could get worse (/bad pun) and spread out Igor's convective deck.
And larger should help the poleward a bit. Possibly leading to a "right-of-track" forecast adjustment.

EWRC might be a good thing for eastern seaboard to cheer for and soonest.
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Quoting Stormchaser2007:
Pimples?


Igor must be hitting puberty...
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18z SHIPS takes it to a 160mph major hurricane. A couple things to note:

1.) Upper level conditions should remain favorable.
2.) SSTs are only going to get warmer.
3.) Heat content is going to get deeper.

TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120
V (KT) NO LAND 115 124 126 126 126 129 131 138 135 130 126 123 118
V (KT) LAND 115 124 126 126 126 129 131 138 135 130 126 123 118
V (KT) LGE mod 115 128 132 130 128 124 123 124 125 122 117 114 111

SHEAR (KT) 4 1 6 6 11 6 1 7 7 6 1 5 11

SHEAR ADJ (KT) -2 0 -3 -2 -1 0 0 -3 -1 -5 5 2 0
SHEAR DIR 28 112 135 81 73 26 341 10 242 284 79 224 188
SST (C) 28.1 28.2 28.3 28.4 28.5 28.7 28.9 29.1 29.1 29.1 29.1 29.1 29.0
POT. INT. (KT) 139 140 141 142 144 147 149 152 153 153 153 152 151
ADJ. POT. INT. 132 134 135 135 135 138 138 140 140 139 137 136 134
200 MB T (C) -51.7 -51.5 -51.4 -51.3 -49.7 -50.2 -49.3 -49.7 -48.9 -49.2 -48.3 -48.7 -47.7
TH_E DEV (C) 10 11 11 11 11 12 12 12 11 10 10 10 10
700-500 MB RH 63 61 58 57 56 54 55 53 53 57 53 51 50
GFS VTEX (KT) 23 25 26 30 30 34 32 37 38 40 40 42 43
850 MB ENV VOR 72 70 65 72 72 76 100 103 120 140 167 163 177
200 MB DIV 54 67 77 73 129 20 85 72 71 3 99 19 43
LAND (KM) 1564 1513 1462 1437 1364 1236 1174 1037 922 819 759 741 767
LAT (DEG N) 17.7 17.8 17.8 18.0 18.1 18.6 19.3 20.1 21.1 22.0 23.0 23.9 24.9
LONG(DEG W) 46.3 47.5 48.7 49.8 50.8 52.8 54.5 56.0 57.4 58.9 60.4 61.8 63.2
STM SPEED (KT) 11 11 11 10 10 9 8 8 9 8 8 8 8
HEAT CONTENT 41 43 48 54 62 69 70 82 70 65 56 63 53
Member Since: September 2, 2009 Posts: 130 Comments: 21122
1124. pottery
See the Blob
How big it's grown,
And all the while
We should have known,
It was to be.

there are some other verses, but I dont remember...
Member Since: October 24, 2005 Posts: 0 Comments: 24245
Quoting MiamiHurricanes09:
SHIPS says Igor is not annular.

## ANNULAR HURRICANE INDEX (AHI) AL112010 IGOR 09/12/10 18 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=6 NFAIL=1 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##
## ANNULAR INDEX RAN NORMALLY


I didn't think so, especially with that feeder band on the southeast quadrant.

Just curious, does anybody know if Andrew is considered to have been annular at landfall?
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I dont buy the annular idea .. too much outflow over a wide area.
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Quoting angiest:


What about growing in size?


Hey angiest! Should gradually grow larger, especially if/when Igor undergoes eyewall replacement cycles. That acne could get worse (/bad pun) and spread out Igor's convective deck.
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!?! Seems someone is behind...

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1118. Max1023
Hopefully Igor stays a little south of track and hits Earl's wake. It is still a half degree cooler there than to the north/south.
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The two trough off the East Coast look to be too far north to fully recurve Igor, in my opinion. IF Igor recurves, I don't think it will be a sharp one.
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I'm not totally sure, but it seems to my untrained eyes that Igor is traveling right now a little south of due west. What is your opinion and what if this is true, does that mean that the track will shift to the left?
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1115. Max1023
If we have a storm like Igor at 17.7 N 46.1 W...

What will we get at 19N 80W?? TCHP there is easily 4 times what it is under Igor, the air has more moisture and the water is 2 degrees warmer. October in the NW Caribbean might be interesting/crazy.
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Quoting angiest:
Most recent annular analysis:

## ANNULAR HURRICANE INDEX (AHI) AL112010 IGOR 09/12/10 12 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=6 NFAIL=1 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##
## ANNULAR INDEX RAN NORMALLY
Huh. Displaying *some* of the characteristics. I thought a "1" was possible...guess not.

(and, I see, no change from 12 to 18 UTC)
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CI# /Pressure/ Vmax
6.3 / 942.2mb/122.2kt
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Quoting Stormchaser2007:
Pimples?



Yeah guys, Igor is forming some pimples! Quit stressing him out! LOL!
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1110. MZT
Quoting NCHurricane2009:


You don't need a cat. 6 classification. Here's why. Because the cat. of a hurricane determines the destructive potential of its max.

Exactly. Quoting Saffir-Simpson for CAT5:

"Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Major damage to lower floors of all structures located less than 15 feet above sea level and within 500 yards of the shoreline. "
Member Since: September 24, 2005 Posts: 0 Comments: 793
1109. angiest
Not annular:


## ANNULAR HURRICANE INDEX (AHI) AL112010 IGOR 09/12/10 18 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=6 NFAIL=1 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##
## ANNULAR INDEX RAN NORMALLY
Member Since: August 26, 2006 Posts: 16 Comments: 4766
Quoting reedzone:
All this talk about being confident on Igor recurving needs to stop. We don't know what is going to happen. A 50% chance Igor recurves and a 50% chance Igor threatens the USA.


You are just kidding, right?
Member Since: August 22, 2010 Posts: 0 Comments: 652
If the first trof does not do the job the next one will. Could see another track similar to that of earl.
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Our 3rd Category 4 of the season..
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SHIPS says Igor is not annular.

## ANNULAR HURRICANE INDEX (AHI) AL112010 IGOR 09/12/10 18 UTC ##
## STORM NOT ANNULAR, SCREENING STEP FAILED, NPASS=6 NFAIL=1 ##
## AHI= 0 (AHI OF 100 IS BEST FIT TO ANN. STRUC., 1 IS MARGINAL, 0 IS NOT ANNULAR) ##
## ANNULAR INDEX RAN NORMALLY
Member Since: September 2, 2009 Posts: 130 Comments: 21122
Quoting KATRINABILOXIGIRL:
Was actually at Keesler Air Force Base that the gauge measured 200mph


You are right. I remember that now.
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Quoting hurricane23:


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.

Ummm what? wow those be big words to me... wow... can you show me a map.
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1101. angiest
Quoting TerraNova:


lol! A sign that Igor's not done intensifying.


What about growing in size?
Member Since: August 26, 2006 Posts: 16 Comments: 4766
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Quoting WeatherNerdPR:

Tropical Acne!


lol! A sign that Igor's not done intensifying.
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Quoting KanKunKid:


At the 2, NHC didn't change their track guidance, so I believe they are still holding that Igor will hang a right and ease up WNW. I think with Earl, there was more agreement with what would happen afterward, if he took the bait. It looks like with Igor, he could still turn, but not recurve. This will be a pain in the kiester for emergency management on the east coast.


Yeah. If we really wanted to be proactive, it would be funny right now to hold a conference with emergenecy management officials on Igor right now, showing them a cone of uncertanity the size of the North American conteninent, LOL! That would be hard for me to walk in with such huge uncertainty. No one likes forecasting beyond 5 days.
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Quoting hurricane23:


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.
Thanks for the information. 'Need to throw-on my high-brow hat now.
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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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