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

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

Share this Blog
53
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 774 - 724

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28Blog Index

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: 16775
Quoting KoritheMan:


Pretty sure it was predicated on El Nino being here, which it isn't.

I'm not going to make seasonal forecasts again. I don't think we've come far enough.

We have learned a lot this season
Member Since: Posts: Comments:
Leslie remains at 4.0 for SAB/TAFB but Michael is most likely stronger that Leslie with SAB/TAFB numbers of 4.5 and ADT of 4.4/75knots. Who would've guessed that tiny Michael would be stronger than Leslie a few days ago.
05/2345 UTC 25.8N 62.3W T4.0/4.0 LESLIE -- Atlantic
05/2345 UTC 29.1N 42.4W T4.5/4.5 MICHAEL -- Atlantic
Member Since: March 16, 2012 Posts: 127 Comments: 7940
Almost certainly a hurricane, probably about 80mph right now:

Member Since: Posts: Comments:
Quoting TropicalAnalystwx13:
90 mph?

05/2345 UTC 29.1N 42.4W T4.5/4.5 MICHAEL -- Atlantic


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.
Member Since: July 8, 2005 Posts: 259 Comments: 23882
Member Since: Posts: Comments:
Quoting Stormchaser121:

I meant the areas circled for landfall/development. It looks soooo unlikely for the western gulf to be above normal, and the open Atlantic where they had it yellow, has had many many storms this year. So im really beginning to doubt that forecast.


Pretty sure it was predicated on El Nino being here, which it isn't.

I'm not going to make seasonal forecasts again. I don't think we've come far enough.
Member Since: March 7, 2007 Posts: 573 Comments: 20371
Quoting LargoFl:


Sat image seems to show 90L getting ripped apart by SW shear
Member Since: Posts: Comments:
Quoting Stormchaser121:

I meant the areas circled for landfall/development. It looks soooo unlikely for the western gulf to be above normal, and the open Atlantic where they had it yellow, has had many many storms this year. So im really beginning to doubt that forecast.


Good points.
Member Since: Posts: Comments:
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???
What's this "TV" you speak of?
Member Since: Posts: Comments:
Quoting TropicalAnalystwx13:
90 mph?

05/2345 UTC 29.1N 42.4W T4.5/4.5 MICHAEL -- Atlantic

Its a possibility , he looks good, and ADT shows 75knts.
CI# /Pressure/ Vmax
4.4 / 981.7mb/ 74.6kt
Member Since: March 16, 2012 Posts: 127 Comments: 7940
Quoting sporteguy03:

9-12 storms

I meant the areas circled for landfall/development. It looks soooo unlikely for the western gulf to be above normal, and the open Atlantic where they had it yellow, has had many many storms this year. So im really beginning to doubt that forecast.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting washingtonian115:
The 2012 season has proven many times why man is not perfect when it comes to forecasting future weather patterns and cyclones.This season is all ready looking for a total of anywhere from 17-20 name storms.The storms have also been tricky to track this year.2012 will go down as a huge lesson in the meteorology world.


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.
Member Since: March 7, 2007 Posts: 573 Comments: 20371
Quoting indianrivguy:


Your Dad is Ed Asner!!! wow!!! :)

Ya know, south Florida was magic back then... another paradise lost.
Oh so very true about paradise lost!!Trying to explain it to the younger generation so they can understand is impossible.Even the storms were an experience of a lifetime.
Member Since: Posts: Comments:
90 mph?

05/2345 UTC 29.1N 42.4W T4.5/4.5 MICHAEL -- Atlantic
Member Since: July 6, 2010 Posts: 113 Comments: 31883
Quoting washingtonian115:
The 2012 season has proven many times why man is not perfect when it comes to forecasting future weather patterns and cyclones.This season is all ready looking for a total of anywhere from 17-20 name storms.The storms have also been tricky to track this year.2012 will go down as a huge lesson in the meteorology world.


No steering.

Stall...wait for it...coffee break...next day..stall...


*repeat above at least twice for at least half the storms.*
Member Since: Posts: Comments:
Quoting Stormchaser121:
\what do you mean?

9-12 storms
Member Since: Posts: Comments:
...................here is the long term forecast,unless they change it again
Member Since: August 6, 2011 Posts: 4 Comments: 37995
The 2012 season has proven many times why man is not perfect when it comes to forecasting future weather patterns and cyclones.This season is all ready looking for a total of anywhere from 17-20 name storms.The storms have also been tricky to track this year.2012 will go down as a huge lesson in the meteorology world.
Member Since: August 14, 2010 Posts: 10 Comments: 16775
..............................well not a drop of rain by me today,well this weekend I should be getting some unless things change once again
Member Since: August 6, 2011 Posts: 4 Comments: 37995
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???
LOL..good one
Member Since: August 6, 2011 Posts: 4 Comments: 37995
Quoting LargoFl:
gee gro..if it does go Back into the gulf..would that make weather history?


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???
Member Since: July 17, 2009 Posts: 71 Comments: 25996
Quoting stormchaser19:
156 Hr two more names storms
You continue to post incorrectly. Look at the time stamp. That shows Sept,2 2012!
Member Since: Posts: Comments:
Member Since: August 6, 2011 Posts: 4 Comments: 37995
Member Since: August 6, 2011 Posts: 4 Comments: 37995
Quoting sporteguy03:

already wrong..
\what do you mean?
Member Since: Posts: Comments:
Quoting Pirate999:


Our house was on the icw in boca back then.. My dad was retired nypd.. Fort apache. So he had time on his hands. My sister and I thought it was all great fun..


Your Dad is Ed Asner!!! wow!!! :)

Ya know, south Florida was magic back then... another paradise lost.
Member Since: Posts: Comments:
Member Since: August 6, 2011 Posts: 4 Comments: 37995
Quoting MahFL:
Our local met had an 81 F on the chart for next week, that's pretty cool for September.


Supposed to get down to the mid 80s and mid 60s here near Baton Rouge on Sunday after the frontal passage. A wee bit below average, I must say, but welcome. However, if my forecast is correct, then return flow should begin shortly afterward.
Member Since: March 7, 2007 Posts: 573 Comments: 20371
Quoting Stormchaser121:

I'm beginning to doubt this...

already wrong..
Member Since: Posts: Comments:
Quoting Grothar:


I wouldn't pay much attention to the SHIPS. Although if it does move across and back over the Bahamas or back into the Gulf????
gee gro..if it does go Back into the gulf..would that make weather history?
Member Since: August 6, 2011 Posts: 4 Comments: 37995
18z GFS 192 hours:
Member Since: Posts: Comments:
Quoting Thing342:
I think '03 - '05 bests it. 2012 would have to have 21 storms to match.

2003: 16
2004: 15
2005: 28

Total: 59

2010: 19
2011: 19
2012: 19?

Total: 57

So close!
If 2012 Exhausts the naming list, then we will be tied ;)
Member Since: Posts: Comments:
Quoting CaicosRetiredSailor:


Michael

I see the eye, he is getting stronger.
Member Since: March 16, 2012 Posts: 127 Comments: 7940
737. MahFL
Our local met had an 81 F on the chart for next week, that's pretty cool for September.
Member Since: Posts: Comments:
Quoting windshear1993:
lmao didnt know the dolphins was that good back in the day never heard of back to back superbowl champs wow
Patriots just did it a few years ago. Plus I think the Cowboys and a couple other teams have done it.
Member Since: Posts: Comments:


Michael
Member Since: Posts: Comments:
734. JLPR2
Quoting washingtonian115:
This is the CMC we're talking about...


Well yes, that is true. XD
Member Since: Posts: Comments:
Quoting LargoFl:
yes im expecting alot of rain, cool front and 90L together..would be nice if it cooled us down some for a few days..cant wait til fall comes..if we get fall this year lol
Should have a few cool days. Definitely colder than 2010-2011 though, purely based on the much warmer equatorial Pacific.
Member Since: Posts: Comments:

I'm beginning to doubt this...
Member Since: Posts: Comments:
Mike seems close to hurricane status.
Member Since: Posts: Comments:
Quoting JLPR2:
Jeez, the CMC likes 90L.

This is the CMC we're talking about...
Member Since: August 14, 2010 Posts: 10 Comments: 16775
Quoting LargoFl:
wow ships really wants to bring it up close to cat-1 huh


I wouldn't pay much attention to the SHIPS. Although if it does move across and back over the Bahamas or back into the Gulf????
Member Since: July 17, 2009 Posts: 71 Comments: 25996
Member Since: August 6, 2011 Posts: 4 Comments: 37995
Quoting MiamiHurricanes09:
LOL, truth.

I'm surprised they raised the percentage on 90L despite the waning convection.


They didnt raise the percentage because of the system's organization. Is the fact that conditions are improving and will continue to improve tomorrow as shear is dropping.


Member Since: Posts: Comments:
Quoting Thing342:


2003: 16
2004: 15
2005: 28

Total: 59

2010: 19
2011: 19
2012: 19?

Total: 57

if we get william...
Member Since: Posts: Comments:
Quoting HurricaneDean07:

Redemption at last!
Can't believe it... It appears we will pull off with at least 16 Named storms, and possibly reach 19 Named storms...

My forecast for 2012:
19 Named Storms
9 Hurricanes
4 Major Hurricanes

3 seasons in a row with 19 Named Storms...


...(adding my predictions onto the 2010-11 numbers)
3 season totals:
57 Named Storms
28 Hurricanes
13 Major Hurricanes


Average 3 season totals:
45 Named Storms
21 Hurricanes
9 Major Hurricanes


My conclusion is that 2010-2012 will go down as the most active 3 year run of Hurricane activity in Hurricane Tracking History.
Something tells me we have reached our peak of high activity in the active era occuring here in the Atlantic...JMO...
Member Since: August 14, 2010 Posts: 10 Comments: 16775
Quoting LargoFl:
yes im expecting alot of rain, cool front and 90L together..would be nice if it cooled us down some for a few days..cant wait til fall comes..if we get fall this year lol

with the way things are going, fall will be winter, winter spring, etc.
if we get past winter
2012 doomcanes lolololol
Member Since: Posts: Comments:

Viewing: 774 - 724

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Mostly Cloudy
77 °F
Mostly Cloudy