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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Based on this, I'd rate Leslie unofficially as an "10" on the HSI.



I'd rate Michael an 19 on HSI.



I ranked Isaac as a 20 at landfall.


Member Since: January 25, 2012 Posts: 33 Comments: 1520
Here in PR is we are having a fairly dry  and hot Augusts - September.
Quoting CaribBoy:
2012 is a dry year. Look at the caribbean

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Quoting ecupirate:


Insurance Adjustor


High Voltage Lineman.
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1319. sar2401
Quoting 7544:
hmm 90l trying to get it together could it become a td by latter on today ?


Wait a minute...didn't you say yesterday 90L was supposed to be a Code Red by this morning?
Member Since: October 2, 2004 Posts: 0 Comments: 14337
1318. 7544
t numbers up 1.0 might go
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1317. Grothar
Quoting GeoffreyWPB:
Before the NHC posts it...Do you think they will cancel recon for 90L?


They will mos likely cancel it.
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000
NOUS42 KNHC 051436
REPRPD
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1035 AM EDT WED 05 SEPTEMBER 2012
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 06/1100Z TO 07/1100Z SEPTEMBER 2012
TCPOD NUMBER.....12-109


I. ATLANTIC REQUIREMENTS
1. TROPICAL STORM LESLIE
FLIGHT ONE --NASA872--
A. 07/0130Z
B. NASA872 0112A LESLIE SURVEILLANCE AV-6
C. 06/1900Z
D. 26.9N 63.3W
E. 07/0130Z TO 07/1130Z
F. 55,000 TO 65,000 FT
G. IP 30.1N 81.2W OUTFLOW LAYER AXIS CYCLONIC S TO N

2. SUSPECT AREA (GULF OF MEXICO)
FLIGHT ONE --TEAL 71--
A. 06/1800Z D. 28.5N 87.8W
B. AFXXX 01DDA INVEST E. 06/1730Z TO 06/2130Z
C. 06/1700Z F. SFC TO 10,000 FT

3. SUCCEEDING DAY OUTLOOK:
A. BEGIN 12-HRLY FIXES AT 07/1200Z IF SUSPECT AREA DEVELOPS.
B. FIX OF TROPICAL STORM LESLIE AT 07/1800Z NEAR 26.6N 63.2W.
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1315. NEwxguy
Quoting TomballTXPride:

Now that I do not like. Just do not like. Period.


Safer that way my friend,avoiding the chaos in here, or should I say taking the path of least resistance.
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1314. sar2401
Quoting GeoffreyWPB:
Before the NHC posts it...Do you think they will cancel recon for 90L?


Yes, I do. They are out of gas money and the credit card is maxed out. :)
Member Since: October 2, 2004 Posts: 0 Comments: 14337
1313. Grothar
Quoting ProgressivePulse:


Good Eye Gro!

The CIMMS page support your thoughts, can 90L make it happen?


It looks like it wants to move where there is less shear. I think they might have dropped it below 50% because it is in a higher shear environment. If it does drop further South and reforms into a depression, I think it would move more to Central Florida and back into the Atlantic.
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Quoting CybrTeddy:
Mclluvin, I have been through a LOT too, so let's not bring up who's been in worse because I guatantee there people on here who had been through a lot and gotten a single dime out of it. I may be out of line yes and I apologize but saying something like we haven't seen a strong storm is ridiculous. This is why we need a new scale, people focus too much on the category which re determined by winds. We need a point based scale that takes in account the maximum sustained winds, minimum pressure, winds, storm surge and amount of rainfall it produces. A category 1 with a 14 foot storm surge doesn't get anywhere near as much as attention a Cat 3 producing the same surge. Water is the killer, and Isaac, Irene, and Ike where all strong storms because of such.


Totally agree with your statement, I was simply just stating he conus hasn't been hit with a major in 7 years and still counting. Just a stat nothing more. I wasn't downgrading the storms that have it at all.
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1309. NEwxguy
Quoting TomballTXPride:

where jus been hiding bro??



lurking
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Before the NHC posts it...Do you think they will cancel recon for 90L?
Member Since: Posts: Comments:
Mclluvin, I have been through a LOT too, so let's not bring up who's been in worse because I guatantee there people on here who had been through a lot and not gotten a single dime out of it. I may be out of line yes and I apologize but saying something like we haven't seen a strong storm is ridiculous. This is why we need a new scale, people focus too much on the category which are determined by winds. We need a point based scale that takes in account the maximum sustained winds, minimum pressure, winds, storm surge and amount of rainfall it produces. A category 1 with a 14 foot storm surge doesn't get anywhere near as much as attention a Cat 3 producing the same surge. Water is the killer, and Isaac, Irene, and Ike where all strong storms because of such.
Member Since: July 8, 2005 Posts: 259 Comments: 23880
...MICHAEL MAINTAINING CATEGORY THREE HURRICANE INTENSITY...
11:00 AM AST Thu Sep 6
Location: 30.1°N 41.3°W
Moving: NE at 7 mph
Min pressure: 964 mb
Max sustained: 115 mph


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Quoting CaribBoy:


I think he is right... models only see fishes and drough


If you consider those models beyond 5 days accurate then yes the statement is true.
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1303. NEwxguy
The trough pattern is what makes the east coast up to us in New England the most vulnerable.We get hit here in new england in September more than any other month.Those troughs dig deeper in september and cause the systems to be pulled up the east coast,but its all about timing.When the TC gets to the islands and where the deep troughs are situated that determine if the US gets hit or out to sea.
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1302. 7544
hmm 90l trying to get it together could it become a td by latter on today ?
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2012 is a dry year. Look at the caribbean
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Quoting MahFL:

How do you make $ following hurricanes ?


As do I ... I work assisting communities rebuild
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Fish it is already (nadine), fish it will stay forever

http://raleighwx.americanwx.com/models/gfsensembl e/members/06ztropf216.html
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Quoting MahFL:

How do you make $ following hurricanes ?


Insurance Adjustor
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Quoting MahFL:

How do you make $ following hurricanes ?


I work with FEMA
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1296. MahFL
Quoting mcluvincane:


Cyber I'm a female for one and definitely not a troll, i follow hurricanes for a living and been through more than you could imagine. You sir are out of line

How do you make $ following hurricanes ?
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1295. will40
1291. mcluvincane 10:30 AM EDT on September 06, 2012


give it a break while you are still behind
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1294. MahFL
Quoting TomballTXPride:
We can't forget about mikey!! we have our strong storm right here!!!



But Michael did not destroy NO, so it does not count, lol.
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The forgotten community of Pearlington, MS...



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Quoting ProgressivePulse:


Trough patterns that help in August & September can turn around and bite you in the arse in October. Still most of September left ahead so a little premature IMO to declare the US safe for the rest of the month considering accurate forecasts go out 5 days...



I think he is right... models only see fishes and drough
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Maybe I should have said major hurricanes hitting the conus. That should help with some of you novice bloggers
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Quoting Tropicsweatherpr:
Things starting to take shape in the West Africa area.



More south than what the GFS/EURO are showing. I guess
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Quoting mcluvincane:


Didn't say a bust there Sherlock. I said a strong storm, storms that have hit were not strong by no means


Oh, I'm sorry. I forgot we had someone here with a crystal ball. I will keep this comment in mind for the remainder of the season.
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Quoting mcluvincane:



The overall pattern, first of all, the east coast is pretty much out of the equation with the trough pattern which is normal this time of the year. The gulf might be open to a storm but like i said is very slim,


Trough patterns that help in August & September can turn around and bite you in the arse in October. Still most of September left ahead so a little premature IMO to declare the US safe for the rest of the month considering accurate forecasts go out 5 days...

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Quoting CybrTeddy:


Just ignore that guy, he is convinced still even after Isaac and Ike they have to be category 3 or higher to cause damage. Tell that to the people of Louisiana. Guy is either a troll, or seriously misinformed.


Cyber I'm a female for one and definitely not a troll, i follow hurricanes for a living and been through more than you could imagine. You sir are out of line
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NO MAJOR OR
SIGNIFICANT WEATHER PRODUCER IS IN SIGHT APPROACHING THE REGION AT
LEAST FOR ANOTHER WEEK OR SO.


Considering this, 2012 is way different compared to 2010 and 2011. They have been saying the same for weeks. Looks like april here.
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Quoting mcluvincane:
Well, looks like the conus has escaped another season without a strong storm impacting them. Just a couple of months left but highly doubt there is anything that could impact the U.S. the remainder of the season, the Atlantic is nothing but fish storms from here on out, the only place that could possibly get a storm would be the gulf states which is very slim.


You are pretty insensitive to say that with what just happened in Louisiana.
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Quoting NOLALawyer:


We are not even to the peak of the season and you are making bold predictions.

Anyway, it does not matter. Three storms have already impacted the US, and there are damages in the billions. This season has been far from a bust.


Just ignore that guy, he is convinced still even after Isaac and Ike they have to be category 3 or higher to cause damage. Tell that to the people of Louisiana. Guy is either a troll, or seriously misinformed.
Member Since: July 8, 2005 Posts: 259 Comments: 23880
Quoting mcluvincane:


I was there for Isaac, i don't think you are understanding me, I'm talking winds in strength Cat 3 or higher.


Ok. :)
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Quoting MNhockeymama:


Tell that to the people who were hit by Isaac.


I was there for Isaac, i don't think you are understanding me, I'm talking winds in strength Cat 3 or higher.
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Quoting Grothar:
Looks like a new low wants to form closer to the convection. This would move the center quite a bit South before it starts its trek towards Florida.



Good Eye Gro!

The CIMMS page support your thoughts, can 90L make it happen?
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Quoting GetReal:




I agree with your analysis about the east coast, with the current trough pattern in the clear. However, IMO, there is a better chance for a "home-grown" system in the GOM, or NW Caribbean that may cause concern in September and early October.


I would normally agree with you on the gulf as did leave that door open, but if something did form i don't think it would be all that strong. Shear and dry air have been active to this point and i dont really see any let up in those 2 factors
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Quoting mcluvincane:


Didn't say a bust there Sherlock. I said a strong storm, storms that have hit were not strong by no means


Tell that to the people who were hit by Isaac.
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1276. GetReal
Quoting mcluvincane:



The overall pattern, first of all, the east coast is pretty much out of the equation with the trough pattern which is normal this time of the year. The gulf might be open to a storm but like i said is very slim,




I agree with your analysis about the east coast, with the current trough pattern in the clear. However, IMO, there is a better chance for a "home-grown" system in the GOM, or NW Caribbean that may cause concern in September and early October.
Member Since: July 4, 2005 Posts: 204 Comments: 8806

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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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