Leslie near hurricane strength; Son of Isaac (90L) emerges in the Gulf

By: Dr. Jeff Masters , 3:05 PM GMT on September 05, 2012

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Tropical Storm Leslie is growing more organized and is approaching hurricane strength on its slow voyage northwards at 2 mph towards the island of Bermuda. Moderately high wind shear of 15 - 20 knots due to strong upper-level winds out of the northwest continues to keep most of Leslie's heavy thunderstorms pushed to the east side of the storm, but satellite loops show that Leslie now has an impressive blow-up of heavy thunderstorms with cold cloud tops near its center. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification, but the waters underneath Leslie are warm to great depth, making this less of a factor than usual. According to the latest SHIPS model forecast, the shear is expected to fall steadily today, reaching the low category, 5 - 10 knots, by Thursday afternoon. Leslie is over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Saturday night and early Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 48% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 42-hour period of tropical storm-force winds beginning Saturday morning near 2 am AST, and lasting until 8 pm AST Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, and Leslie will be capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize. NHC is predicting that hurricane-force winds will extend outwards from the center of Leslie by 35 miles on Thursday night, and I expect this will increase to at least 60 miles by early Sunday morning, when Leslie will be making its closest pass by Bermuda.


Figure 1. Morning satellite image of Tropical Storm Leslie. Heavy thunderstorms have built near the center of the storm, and Leslie is near hurricane strength.

Leslie's impact on Canada
Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There are still significant differences among the models in the timing and speed of Leslie's track over the weekend, but we can now dismiss the threat of Leslie making a direct hit on New England. The storm is likely to make landfall in Nova Scotia or Newfoundland, though there are significant differences in the models' predictions of the timing of Leslie's arrival in Canada. The GFS model predicts an early Tuesday landfall in Newfoundland, but the ECMWF model is much faster and farther west, predicting a Monday afternoon landfall in Nova Scotia. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in strength this week. The Hurricane Hunters are scheduled to make their first flight into Leslie on Thursday afternoon.


Figure 2. Morning radar image of Invest 90L off the coast of the Florida Panhandle.

Son of Isaac: Invest 90L emerges in the Gulf of Mexico
During Tropical Depression Isaac's trek across the center of the U.S. during the Labor Day weekend, the storm was ripped in half. One portion of the storm moved over the Northeast U.S., bringing heavy rains there, and another portion sank southwards over Alabama. You can see this split by studying an animation of the vorticity at 850 mb (the amount of spin at low levels of the atmosphere, near 5,000 feet above sea level) from the University of Wisconsin. This remnant of Isaac, which still maintained some of Isaac's spin, brought heavy rains of 5 - 10 inches that caused flooding problems over portions of Alabama on Tuesday. The storm has now emerged over the Gulf of Mexico near the Florida Panhandle, and was designated Invest 90L this morning by NHC. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Friday morning. According to NHC naming rules, "if the remnant of a tropical cyclone redevelops into a tropical cyclone, it is assigned its original number or name". Since "the remnant" refers to the primary remnant, and 90L does not fit the definition of a "primary remnant", the storm will be given a new name should it develop into a tropical storm, according to information posted on the NHC Facebook page. Esau or Jacob--the names of the sons of the biblical Isaac--would be fitting names for 90L, but the next storm on the list of Atlantic storms is Nadine.

Long-range radar out of Mobile, Alabama shows a large area of heavy rainfall along the coast due to 90L. The echoes do show some spiral banding behavior, but there is only a slight evidence of rotation to the storm. Infrared satellite loops show that the thunderstorms associated with 90L are not that vigorous and do not have particularly cold cloud tops, and the area covered by the thunderstorms is relatively small. Wind shear is a high 20 - 30 knots over the northern Gulf of Mexico, but is predicted to fall to the moderate range, 10 - 20 knots, by Thursday afternoon. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28 - 28.5°C. This is still plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization on Thursday and Friday as it moves slowly south or south-southwest. 90L could become a tropical depression as early as Thursday, though Friday is more likely. A hurricane hunter aircraft is scheduled to investigate 90L on Thursday afternoon. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday.


Figure 3. Morning satellite image of Tropical Storm Michael.

Tropical Storm Michael in the Central Atlantic
Tropical Storm Michael has strengthened to 50 mph winds, and appears to have a favorable enough environment to become a hurricane later this week. Satellite loops show that this is a small tropical cyclone, far out over the open Atlantic, and none of the models show that Michael will threaten any land areas.

Elsewhere in the Atlantic
The GFS and ECMWF models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. It's too early to tell if this system might threaten the Lesser Antilles Islands.

Jeff Masters

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Leslie:

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Michael:

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Beautiful...
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Hurricanes Leslie and Michael:

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Quoting bassis:


Sat image seems to show 90L getting ripped apart by SW shear
Northerly shear, not SW.
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free road of SAL for the waves of africa
Member Since: June 20, 2012 Posts: 0 Comments: 2159
Quoting CaicosRetiredSailor:


Leslie
Seems like she is trying to keep up with Michael. Not the best looking eye but it make shape out to be ok.

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Quoting Ameister12:
Michaels first advisory forecast 2 days ago:

INIT 03/2100Z 25.6N 42.2W 30 KT 35 MPH
12H 04/0600Z 25.8N 42.9W 35 KT 40 MPH
24H 04/1800Z 26.4N 43.7W 35 KT 40 MPH
36H 05/0600Z 27.3N 44.3W 35 KT 40 MPH
48H 05/1800Z 28.0N 44.5W 30 KT 35 MPH
72H 06/1800Z 28.5N 44.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 07/1800Z 29.5N 44.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 08/1800Z 30.5N 44.5W 20 KT 25 MPH...POST-TROP/REMNT LOW

Current Forecast:

INIT 05/2100Z 28.8N 42.7W 60 KT 70 MPH
12H 06/0600Z 29.3N 42.1W 65 KT 75 MPH
24H 06/1800Z 30.0N 41.7W 70 KT 80 MPH
36H 07/0600Z 30.6N 41.6W 75 KT 85 MPH
48H 07/1800Z 31.0N 41.8W 80 KT 90 MPH
72H 08/1800Z 32.1N 42.9W 80 KT 90 MPH
96H 09/1800Z 33.2N 44.2W 75 KT 85 MPH
120H 10/1800Z 34.8N 46.2W 65 KT 75 MPH

Quite a change.

With Michael a hurricane now the NHC may go with a 100mph peak.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Michaels first advisory forecast 2 days ago:

INIT 03/2100Z 25.6N 42.2W 30 KT 35 MPH
12H 04/0600Z 25.8N 42.9W 35 KT 40 MPH
24H 04/1800Z 26.4N 43.7W 35 KT 40 MPH
36H 05/0600Z 27.3N 44.3W 35 KT 40 MPH
48H 05/1800Z 28.0N 44.5W 30 KT 35 MPH
72H 06/1800Z 28.5N 44.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
96H 07/1800Z 29.5N 44.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 08/1800Z 30.5N 44.5W 20 KT 25 MPH...POST-TROP/REMNT LOW

Current Forecast:

INIT 05/2100Z 28.8N 42.7W 60 KT 70 MPH
12H 06/0600Z 29.3N 42.1W 65 KT 75 MPH
24H 06/1800Z 30.0N 41.7W 70 KT 80 MPH
36H 07/0600Z 30.6N 41.6W 75 KT 85 MPH
48H 07/1800Z 31.0N 41.8W 80 KT 90 MPH
72H 08/1800Z 32.1N 42.9W 80 KT 90 MPH
96H 09/1800Z 33.2N 44.2W 75 KT 85 MPH
120H 10/1800Z 34.8N 46.2W 65 KT 75 MPH

Quite a change.
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Leslie is gettin ready to take off
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Quoting yqt1001:
No one should ever trust a small storm to reliably follow intensity estimates. Michaels CDO is a grand total of 3 degrees wide, saying that it couldn't wander into decent conditions and randomly become a hurricane isn't too genius.

Although it wasn't supposed to wander into decent conditions, but here we are nonetheless. Any bets on MH status for Michael?

I'll go bet the farm, I didn't need it anyway. But once again with these high latitude storms I think there is a chance of MH status.
Member Since: March 16, 2012 Posts: 127 Comments: 7948


Leslie
Member Since: July 12, 2007 Posts: 0 Comments: 6049
Micheal you beautiful!.
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Quoting CybrTeddy:
Hurricane Michael.

People where calling this a wasted name and another Jose the other day.

I said it could make it to a strong TS/hurricane but I didn't think this fast or if it would even survive.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
No one should ever trust a small storm to reliably follow intensity estimates. Michaels CDO is a grand total of 2 degrees wide, saying that it couldn't wander into decent conditions and randomly become a hurricane isn't too genius.

Although it wasn't supposed to wander into decent conditions, but here we are nonetheless. Any bets on MH status for Michael?
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Quoting wxchaser97:

I was always tracking tropical, winter and severe weather but not like this, thanks to all that have helped me!


The ones that don't do any damage are great, Leslie still could look pretty interesting though in a couple days.

No problem :)
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Cloud tops around the eye are fairly cold. If we want to see a major out of him though we need to see a red ring form around him. Would not be to hard seeing how most of the cloud tops are on the verge of it anyway.

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Michael's eye is warming and getting larger.
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Quoting KoritheMan:


I was one of those people, lol.
Don't worry Kori.I said 97L(which then became Kirk) would die off in the Atlantic...but he eventually became a hurricane a cat 2 at that.Lol.
Member Since: August 14, 2010 Posts: 10 Comments: 17071
Ok, the latest GFS and a few runs before that has of course Leslie and Kirk, but also a new storm approaching the Antilles. The saving grace just may be, 90L moving across FL and weakening the ridge and allowing the aforementioned new Antilles storm to curve away from the CONUS
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Quoting Stormchaser121:

Ive always Tracked tropical weather but not really in depth like i am now. This is my 2nd year tracking tropics. It is a great learning experience :)

I was always tracking tropical, winter and severe weather but not like this, thanks to all that have helped me!

Quoting washingtonian115:
Ugly as in she is headed for land and affecting people.Storms look more beautiful when they are over the open water IMO.

The ones that don't do any damage are great, Leslie still could look pretty interesting though in a couple days.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting CybrTeddy:
Hurricane Michael.

People where calling this a wasted name and another Jose the other day.


I was one of those people, lol.
Member Since: March 7, 2007 Posts: 582 Comments: 20773
Quoting stormchaser19:


This season GFS has been crowned as a best reliable model.....ECMWF second.......GFS the new king


Prince Euro.
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Hurricane Michael.

People where calling this a wasted name and another Jose the other day.
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65kts hurricane..



I'm sure...

Even AVN looks nice, which is rare.

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Quoting KoritheMan:


I have learned two things from it:

Because of Ernesto, completely ignoring the GFS and ECMWF is unwise.

Because of Isaac, trying to nail down a track 7 days in advance is nothing short of foolish. Louisiana is the last place I would have thought Isaac would come to based on the model consensus.

I won't be caught with my pants down again.


This season GFS has been crowned as a best reliable model.....ECMWF second.......GFS the new king
Member Since: June 20, 2012 Posts: 0 Comments: 2159
Lots of the ATCF's for Leslie and Michael posted, we really wanted to see what would happen.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting washingtonian115:
I love tracking storms like Kirk :).Seeing them so graceful out in the atlantic unlike Ugly Leslie that is headed for Bermuda...


Leslie will be no catastrophe. Bermuda has very strict building codes.
Member Since: March 7, 2007 Posts: 582 Comments: 20773
Quoting wxchaser97:
Leslie is not that ugly and it has been only strengthening for a day, give her time.
Ugly as in she is headed for land and affecting people.Storms look more beautiful when they are over the open water IMO.
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Quoting CosmicEvents:
What's this "TV" you speak of?


TV is to the mind what cigarettes are to the body.
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Quoting TropicalAnalystwx13:
90 mph?

05/2345 UTC 29.1N 42.4W T4.5/4.5 MICHAEL -- Atlantic
TAFB is a lot weaker with an estimate of T3.5; mainly due to the fact that it initialized the center too far west, thus not taking into account the newly developed eye feature. Personally I'd go with a 70kt intensity at 11p.m.

AL, 13, 201209052345, 10, DVTS, CI, , 2910N, 4270W, , 3, 55, 2, 994, 2, DVRK, , , , , , , , , , , , , , L, TAFB, MH, I, 5, 3535 /////, , , GOES13, CSC, T, used both GOES-E and MET-9 imagery to determine psn
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Hurricane numero siete.
AL, 13, 2012090600, , BEST, 0, 291N, 424W, 65, 990

Expect that to change.
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Quoting wxchaser97:

Its has been a great learning experience for me and this was my first year really tracking the tropics.

Ive always Tracked tropical weather but not really in depth like i am now. This is my 2nd year tracking tropics. It is a great learning experience :)
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ATCF say 75mph, that should change though, anyway its the 7th hurricane of the season.
AL, 13, 2012090600, , BEST, 0, 291N, 424W, 65, 990, HU, 64, NEQ, 10, 10, 0, 10, 1016, 140, 10, 0, 0, L, 0, , 0, 0, MICHAEL, D,
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Micheal has achieved hurricane status officially.
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MICHAEL be comes the 7th hurricane of the season
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According to ATCF Michael is a hurricane with 75mph winds.
Member Since: February 11, 2012 Posts: 83 Comments: 7833
AL, 13, 2012090600, , BEST, 0, 291N, 424W, 65, 990, HU
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AL, 13, 2012090600, , BEST, 0, 291N, 424W, 65, 990, HU, 64, NEQ, 10, 10, 0, 10, 1016, 140, 10, 0, 0, L, 0, , 0, 0, MICHAEL, D,

Seems to be a bit low to me, considering ADT suggests a 75kt cyclone with 981mb.
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Quoting Grothar:


I don't recall one ever doing that many loops, but who ever thought "Dancing with the Stars" would be the number show on TV???
Good point! If something that inane can happen, who's to say this storm couldn't just wear a groove across Florida for a couple weeks?
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This season has really shocked me.
I never thought we'd have such a hyperactive like season with the storngest landfalling U.S. storm in may(Beryl), record number of storms before July(4), and tied record number of storms in August(8).
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Quoting CybrTeddy:


Defiantly have a Hurricane now, ADT is at 4.4, combined with the 4.5 from the SAB/TAFB would give an average intensity of 88mph, so 90mph isn't out of the question. I'm going to guess 85mph.
Michael sure has been quite the renegade.
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Pressure dropped and winds stayed the same for Leslie.
AL, 12, 2012090600, , BEST, 0, 261N, 625W, 65, 985, HU, 64, NEQ, 20, 20, 15, 15, 1013, 250, 15, 0, 0, L, 0, , 0, 0, LESLIE, D,
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Leslie holding at 75mph.
AL, 12, 2012090600, , BEST, 0, 261N, 625W, 65, 985
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Pressure fell 2 millibars with Leslie.

AL, 12, 2012090600, , BEST, 0, 261N, 625W, 65, 985, HU, 64, NEQ, 20, 20, 15, 15, 1013, 250, 15, 0, 0, L, 0, , 0, 0, LESLIE, D,
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No change in Leslie's winds at the ATCF update, pressure down to 985mb from 987.
Member Since: February 11, 2012 Posts: 83 Comments: 7833
Hello Floridians send some of your rain to Texas Please, LOL. Saw 3 grass fires in my area today driving around. THE COLD FRONT COULD CREATE
A POSSIBLE CRITICAL FIRE WEATHER CONDITIONS FOR THE AREA
SATURDAY...BUT WILL KEEP WORDING AS NEAR CRITICAL FOR NOW. IT
APPEARS NO SIGNIFICANT OR WIDESPREAD WETTING RAINS WILL OCCUR
WITH THE COLD FRONT SATURDAY. ELEVATED FIRE WEATHER CONDITIONS SUNDAY
INTO EARLY NEXT WEEK CONTINUING DUE TO A VERY LOW AFTERNOON
HUMIDITIES..
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Invest 90L's pressure is down one millibar.

AL, 90, 2012090600, , BEST, 0, 296N, 878W, 25, 1009, LO, 34, NEQ, 0, 0, 0, 0, 1013, 100, 60, 0, 0, L, 0, , 0, 0, INVEST, M,
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Quoting washingtonian115:
I love tracking storms like Kirk :).Seeing them so graceful out in the atlantic unlike Ugly Leslie that is headed for Bermuda...
Leslie is not that ugly and it has been only strengthening for a day, give her time.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
Quoting Stormchaser121:

We have learned a lot this season

Its has been a great learning experience for me and this was my first year really tracking the tropics.
Member Since: March 16, 2012 Posts: 127 Comments: 7948
I love tracking storms like Kirk :).Seeing them so graceful out in the atlantic unlike Ugly Leslie that is headed for Bermuda...
Member Since: August 14, 2010 Posts: 10 Comments: 17071

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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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