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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Quoting GTcooliebai:
Makes you wonder when our luck will run out? 8 years is a pretty darn long time.

It sure is. I have a feeling this isn't going to be the year, but it will happen eventually... It has to.
Member Since: February 11, 2012 Posts: 83 Comments: 7839
Quoting 954FtLCane:
at 440 hours Karen's ghostly remains are in the Carribean heading towards the Caymans..... just crazy I tell you.
I heard somewhere in here that it is still circulating the globe after all these year, quite comical if you ask me.
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Quoting GTcooliebai:
Doubt a storm would recurve into a 1028 mb. ridge and a lack of troughiness, also the GFS loses resolution this far out, so it is hard to grasp any kind of pattern.


Exactly.....168 Hours is a good forecast for the models after that everything is imprecise
Member Since: June 20, 2012 Posts: 0 Comments: 2159
at 440 hours Karen's ghostly remains are in the Carribean heading towards the Caymans..... just crazy I tell you.
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Quoting MAweatherboy1:
Wow.


Makes you wonder when our luck will run out? 8 years is a pretty darn long time.
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It will flip every time, but its still interesting to see the possibilities.
Member Since: February 11, 2012 Posts: 83 Comments: 7839
Oh my, this wouldn't be good, 372hrs.
Member Since: March 16, 2012 Posts: 127 Comments: 7951
Wow.


Member Since: February 11, 2012 Posts: 83 Comments: 7839
Quoting Grothar:


Evening Sir.
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Quoting Grothar:

I'm in the weak TS boat, I doubt 90L could become very close to a hurricane.
Member Since: March 16, 2012 Posts: 127 Comments: 7951
Quoting wxchaser97:
Now of course this is fantasy land but there are 2 storms and another wave coming off Africa.
Doubt a storm would recurve into a 1028 mb. ridge and a lack of troughiness, also the GFS loses resolution this far out, so it is hard to grasp any kind of pattern.
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Quoting MAweatherboy1:
That is a strong storm:



We're getting way out there now though.


Mid-September is prime major territory. However, way way way out there as you say.
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Now of course this is fantasy land but there is a strong recurving hurricane and a T-wave.
Member Since: March 16, 2012 Posts: 127 Comments: 7951
312:

Member Since: February 11, 2012 Posts: 83 Comments: 7839
Quoting allancalderini:
Nop But I think we will reach William this year and with the only list that most of the time fail to even reach 12 name storms.What an irony.
the other list is the one used in 2009 this two list always have an El niño but there exception was in 2003 now ours looks to be 2012.
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That is a strong storm:



We're getting way out there now though.
Member Since: February 11, 2012 Posts: 83 Comments: 7839
192 hrs. strong ridging occurring in the Atlantic and I think the intensity is a bit overdone, since we haven't seen storms develop much in the MDR.

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Starting to recurve:

Member Since: February 11, 2012 Posts: 83 Comments: 7839
Quoting MAweatherboy1:
240 hours:



Eeek, that's a big en'
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Quoting CybrTeddy:


He draws in accordance to the storms present motion in the event the storm would continue in said path. Same thing as the XTRAP. I personally find his maps very useful.


Not trying to stir a pot. Useful how? Why not just follow xtrap? I always wondered about those maps. I just can't grasp the concept.
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240 hours:

Member Since: February 11, 2012 Posts: 83 Comments: 7839
Quoting TropicalAnalystwx13:

I've already mentioned it.

I didn't hear it, tell it again.
Member Since: March 16, 2012 Posts: 127 Comments: 7951
Models are now being consistent with the development of another CV cyclone as soon as 96 hours from now.
Member Since: July 8, 2005 Posts: 259 Comments: 24193
Quoting ProgressivePulse:


Anyone taking bets on the Greek Alphabet yet?
Nop But I think we will reach William this year and with the only list that most of the time fail to even reach 12 name storms.What an irony.
Member Since: October 15, 2011 Posts: 0 Comments: 4403
216 hours- right into the northern islands:

Member Since: February 11, 2012 Posts: 83 Comments: 7839
168 Hr..........after that hour... for me everything that the models show is speculation
Member Since: June 20, 2012 Posts: 0 Comments: 2159
....Alberto
....Beryl
....Chris
....Debby
....Ernesto
....Florence
....Gordon
....Helene
....Isaac
....Joyce
....Kirk
....Leslie
....Michael
Nadine (90L?)
Oscar (GFS Storm 1?)
Patty (GFS Storm 2?)
Rafael
Sandy
Tony
Valerie
William
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Live streaming video feeding Isaac survivors in Pearlington MSLink
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In 2005, we went six names into the Greek alpha.

Early days, yet. I wouldn't be surprised if we did hit 'em.
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Quoting ProgressivePulse:


Anyone taking bets on the Greek Alphabet yet?


Well, personally I'd be dumbfounded if an El Nino year went into the greek Alphabet. Then again, I'm dumbfounded that an El Nino year is going on 13 named and 6 (soon to be 7) hurricanes by September 5th. Doesn't even matter to me that we haven't had a major hurricane yet, this season has blown my expectations out of the water.
Member Since: July 8, 2005 Posts: 259 Comments: 24193
180 hours... Pretty decent storm:

Member Since: February 11, 2012 Posts: 83 Comments: 7839
Today was Leslie's Independence Day from wind shear and has been slowly but steadily strengthening.
Member Since: March 16, 2012 Posts: 127 Comments: 7951
Out of Africa, more still to come:

Africa
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Quoting ProgressivePulse:


Anyone taking bets on the Greek Alphabet yet?

I've already mentioned it.
Member Since: July 6, 2010 Posts: 113 Comments: 32286
Quoting FloatingCity:


Nobody on this site gives a rats ass about anything that happens above New England, unless of course you are from the Motherland (Canada). This site is used by the Yanks, and to them, nobody else exists...thats why there isn't any talk about Leslie...doesn't affect the States...they don't care. Peace Brother!!


I am not quite sure whether your comments are a display of either, bigotry or, ignorance - maybe a combination of both - with perhaps a pinch of disdain for "Yanks" thrown in.
Thankfully, for the most part, you are wrong on most counts.
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Quoting stormchaser19:
156 Hr two more names storms


Anyone taking bets on the Greek Alphabet yet?
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Quoting BDADUDE:


Looks like we are in the clear according to you.


He draws in accordance to the storms present motion in the event the storm would continue in said path. Same thing as the XTRAP. I personally find his maps very useful.
Member Since: July 8, 2005 Posts: 259 Comments: 24193
Quoting stormchaser19:

You are right in the problem Bro..

If that came true the Bermuda would get cat2-3 winds since they would be in the right front quadrant.
Member Since: March 16, 2012 Posts: 127 Comments: 7951
Quoting CybrTeddy:


yea well, StormHype doesn't exactly lean up against his screen name. Relax, he's entitled to what he thinks.

He's technically right too, as tropical cyclones are a collection of thunderstorms circulating around an area of low pressure. ;)


lol true
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Quoting BDADUDE:

Not according to you. I meen according to aspectre.


Never depend on Aspectre's maps as anything more than interesting exercise in cartography. He just draws a straight line projection based on former locations, present location, and present direction of travel. They are simple mathematical projections and have nothing to do with NHC's actual track projection. As has been said, Bermuda is in the cone of error. You may or may not suffer a direct or near direct hit, but that's what you should be planning for.
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Quoting Hurricanes101:


says the guy who said this afternoon this would be nothing more than a thunderstorm, its dmin, 90L is doing fine


yea well, StormHype doesn't exactly lean up against his screen name. Relax, he's entitled to what he thinks.

He's technically right too, as tropical cyclones are a collection of thunderstorms circulating around an area of low pressure. ;)
Member Since: July 8, 2005 Posts: 259 Comments: 24193
Quoting CybrTeddy:
I recall saying that it was possible that Michael, then TD13 could end up being like Kirk. As Grothar would say, I saw it first ;-)


Didn't think I'd be right, but clearly looks like I may be close to that guess. Worth noting though that unlike Kirk and Gordon, Michael developed completely non-tropically, and will be the strongest non-tropically developing cyclone since Hurricane Shary, and if it goes beyond 75mph as predicted, it will be the strongest non-tropically developing cyclone since Hurricane Ophelia in 2005. Interesting facts I just enjoy to share.

He is good looking, those are some interesting facts. He could get to a high-end cat1 and maybe low-end cat2 possibly imo.
Member Since: March 16, 2012 Posts: 127 Comments: 7951
Quoting StormHype:
90L looks to be evaporating at the moment. Poofage?


says the guy who said this afternoon this would be nothing more than a thunderstorm, its dmin, 90L is doing fine
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156 Hr two more names storms
Member Since: June 20, 2012 Posts: 0 Comments: 2159
505 aspectre:
4Sept.06pm: TS.Leslie had been headed for passage 86miles(139kilometres)WSWest of Bermuda
5Sept.12am: TS.Leslie had been headed for passage 238miles(383kilometres)SWest of Bermuda
5Sept.06am: TS.Leslie had been for passage 88miles(141kilometres)WSWest of Bermuda
5Sept.12pm: TS.Leslie had been headed for passage 108miles(174kilometres)East of Bermuda
5Sept.06pm: H.Leslie was heading for passage 290miles(467kilometres)ESE of Bermuda

513BDADUDE: Looks like we are in the clear according to you.

What-is-now-HurricaneLeslie's path has been pointing back&forth between both sides of Bermuda over the past 54hours. Kinda like a huntin' dog's criss-cross path while sniffing out its prey.
If I were Bermudan. I'd be very worried about Leslie's hunter-seeker behaviour.
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I recall saying that it was possible that Michael, then TD13 could end up being like Kirk. As Grothar would say, I saw it first ;-)


Didn't think I'd be right, but clearly looks like I may be close to that guess. Worth noting though that unlike Kirk and Gordon, Michael developed completely non-tropically, and will be the strongest non-tropically developing cyclone since Hurricane Shary, and if it goes beyond 75mph as predicted, it will be the strongest non-tropically developing cyclone since Hurricane Ophelia in 2005. Interesting facts I just enjoy to share.
Member Since: July 8, 2005 Posts: 259 Comments: 24193
150 Hr
Member Since: June 20, 2012 Posts: 0 Comments: 2159
Well, get home and Ch 4 (KMOV) is in my old home town of Ramsey because of wind damage, though no one saw an actual funnel cloud, so spoke too soon again. Hope it doesn't get too bad for the folks in KY, So. IN, & TN Edit: No one in town saw a funnel, did hear second hand that someone saw one in rural Ramsey.
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Quoting CosmicEvents:
Before the NHC names this spawn of Isaac, if it does get a name...maybe we can call it something else....in honor of the 5 cute but totally off-topic(as a hurricane makes landfall) puppies.
How about Isaac Part Doux-Doux?
Ha! I was thinking "Mini Me" but like yours better.
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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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