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 KoritheMan:


There are some signals that the troughing this year is not as strong as in recent years. I think another 1 - 3 US hits is a good bet.


Can't go wrong on that prediction. One thing's for sure, September is going to be big for hurricanes this year.
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Quoting Tropicsweatherpr:
To note also that the EPAC was forecast to have a very active season but so far it has not been as active as expected.


I noticed that too.
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Quoting MadinBoy:
This is the tropical storm Mickeal...... storm ????? you say storm !!!!


he will be cane
dat makes 13-7-0
no majors yet
after 90l forms...
14-7-2
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This is the tropical storm Mickeal...... storm ????? you say storm !!!!

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Quoting spathy:
After all the massive storms that could and almost did. The little Michael Just might beat them to the punch.

yep
stronger than isaac lol
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I can't wait to see what the NHC says for intensity and their forecast as Michael is intensifying pretty quickly now.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Leslie:

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To note also that the EPAC was forecast to have a very active season but so far it has not been as active as expected.
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The way Michael went from nothing to a strong Category 1 in less than 48 hours is just epic.
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Quoting wxchaser97:

ADT says 77knts and SAB/TAFB numbers are 4.5, I say more like 85-90mph.
CI# /Pressure/ Vmax
4.5 / 980.0mb/ 77.0kt

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


75 mph hurricane at 11 advisory.......We all know how the nhc is working this year
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Quoting yqt1001:


Good storms no doubt. Funso was shearly epic to track, Meteo France showed absolute doom for a few days with it. Strong category 5 epic storm bearing down on a rarely hit poor country. Would've made for the worst disaster this year. Dvorak even came back with 135kts at peak intensity so its likely to get a boost in post season.


yeah. here are season leaders
atlantic: gordon
epac: emilia
wpac: guchol, bolaven, or tembin
indian: none
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Quoting Bluestorm5:

ri?
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Quoting MAweatherboy1:

There's been some good storms out there this year though... Bolaven and Tembin like you said and Vicente and Guchol... and Guchol's pinhole eye:



Good storms no doubt. Funso was shearly epic to track, Meteo France showed absolute doom for a few days with it. Strong category 5 epic storm bearing down on a rarely hit poor country. Would've made for the worst disaster this year. Dvorak even came back with 135kts at peak intensity so its likely to get a boost in post season.

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Quoting Civicane49:
Michael looks stronger than 75 mph.


ADT says 77knts and SAB/TAFB numbers are 4.5, I say more like 85-90mph.
CI# /Pressure/ Vmax
4.5 / 980.0mb/ 77.0kt

05/2345 UTC 29.1N 42.4W T4.5/4.5 MICHAEL -- Atlantic
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Quoting yqt1001:


It's been the same globally. :( Bolaven and Tembin are nearly tied for the highest ACE so far this year. Measly 28. Igor was in the 40s. Atm Tembin is winning, but it's likely that JTWC had Bolavens winds wrong thanks to recon saying 910mb at the height of an EWRC with winds of 115kts.

There's been some good storms out there this year though... Bolaven and Tembin like you said and Vicente and Guchol... and Guchol's pinhole eye:

Member Since: February 11, 2012 Posts: 82 Comments: 7566


Virgin Islands and Caribbean region joins growing list of seismically-tense hotspots
Posted on September 5, 2012



September 5, 2012 VIRGIN ISLANDS - The VIDN say on August 30, 2012: The V.I. Territorial Emergency Management Agency said that V.I. Alert subscribers who have noticed a recent increase in earthquake notifications from the service should not be alarmed. Between 3 a.m. Monday and continuing throughout the day Wednesday, more than 50 very minor to moderate earthquakes were recorded near Latitude 19 degrees north, north of the Virgin Islands, according to a statement VITEMA issued Wednesday. Those tremors included a 5.2-, 4.6- and 4.7-magnitude earthquake between 3 and 5 p.m. Wednesday. Victor Huerfano, director of the Puerto Rico Seismic Network, confirmed that the increase in earthquake activity is a swarm of tremors, a phenomenon that occurs four or five times a year in different parts of the Caribbean region, according to VITEMA. A swarm is defined as three or more earthquakes occurring within an hour, and the Puerto Rico Seismic Network has been recording these instances since Saturday. It is normal but we cannot say what it means, Huerfano said. It is more important that we make sure we are calm and prepared, and that emergency systems are in place in case a major earthquake happens. The Virgin Islands is located in a seismically active region, which has a potential for a major earthquakes to occur at any time, according to VITEMA statement. VIDN
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Quoting KoritheMan:


I miss the BIG seasons from the Western Pacific. The 30 storms, 18 typhoons and 6 or 7 super typhoons.


It's been since August 2011 that we've had a category 5 strength TC anywhere in the tropics. It's getting stupid.
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Quoting CybrTeddy:


I'm just impressed by the fact that this was supposed to be an inactive, boring El Nino year. Everything pointed to it all through July, then August came..

We've still got the rest of September and October to get through.


Maybe we'll get the chokehold next year? :(
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Michael looks stronger than 75 mph.

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Quoting CybrTeddy:


I'm just impressed by the fact that this was supposed to be an inactive, boring El Nino year. Everything pointed to it all through July, then August came..

We've still got the rest of September and October to get through.


Yeah, that's true.
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Quoting yqt1001:


It's been the same globally. :( Bolaven and Tembin are nearly tied for the highest ACE so far this year. Measly 28. Igor was in the 40s. Atm Tembin is winning, but it's likely that JTWC had Bolavens winds wrong thanks to recon saying 910mb at the height of an EWRC with winds of 115kts.


I miss the BIG seasons from the Western Pacific. The 30 storms, 18 typhoons and 6 or 7 super typhoons.
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Quoting K8eCane:
say what ya want, but i say leslies gonna bust loose anytime....

yep
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Quoting Bluestorm5:
CIMSS messed it up. I posted Michael's, but the link was changed to Leslie somehow.

lol
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say what ya want, but i say leslies gonna bust loose anytime....
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Quoting KoritheMan:
Two reasons this season hasn't impressed me yet: no major hurricanes and the short-lived nature of the hurricanes. I want to see more majors and more ACE before I'm impressed. Sorry guys, but that's my standard. ;)


I'm just impressed by the fact that this was supposed to be an inactive, boring El Nino year. Everything pointed to it all through July, then August came..

We've still got the rest of September and October to get through.
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I think October might produce 1 or 2 powerhouses coming out of the SW Caribbean.
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I think it is stronger than 75mph, more like 85-90mph based of SAB/TAFB and ADT.
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Quoting CybrTeddy:
Getting better organized.
For me Michael is the most beautiful storm of the season he looks beautiful I am going to say he is going to be a major.
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Quoting KoritheMan:
Two reasons this season hasn't impressed me yet: no major hurricanes and the short-lived nature of the hurricanes. I want to see more majors and more ACE before I'm impressed. Sorry guys, but that's my standard. ;)


It's been the same globally. :( Bolaven and Tembin are nearly tied for the highest ACE so far this year. Measly 28. Igor was in the 40s. Atm Tembin is winning, but it's likely that JTWC had Bolavens winds wrong thanks to recon saying 910mb at the height of an EWRC with winds of 115kts.
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Quoting snowboy:
you've got Leslie twice there Bluestorm..
CIMSS messed it up. I posted Michael's, but the link was changed to Leslie somehow.
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Quoting wxchaser97:

Gosh you got a tough standard, anyway Leslie and Michael could become majors and the ACE is raising with Leslie and Michael.


I'm definitely a very difficult person to please. But I'm pretty sure I've been here long enough so that everyone knows that by now, lol.
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JSL of Michael:
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Well this is the smallest eye I have seen.

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Personally I think Gordon & Kirk were 115mph hurricanes and might upgraded post season, just my take.
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Getting better organized.
Member Since: July 8, 2005 Posts: 259 Comments: 23494
Quoting KoritheMan:
Two reasons this season hasn't impressed me yet: no major hurricanes and the short-lived nature of the hurricanes. I want to see more majors and more ACE before I'm impressed. Sorry guys, but that's my standard. ;)

Gosh you got a tough standard, anyway Leslie and Michael could become majors and the ACE is raising with Leslie and Michael.
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Leslie has been in an Eyewall Replacement Cycle all afternoon. It'll look better in the morning as it appears the cycle is almost done.
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Quoting Bluestorm5:
I posted Michael picture, but somehow it changed to Leslie... CIMSS is messing with me again -__-

CIMSS always messes with the pictures and it gets annoying.
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Quoting KoritheMan:
Two reasons this season hasn't impressed me yet: no major hurricanes and the short-lived nature of the hurricanes. I want to see more majors and more ACE before I'm impressed. Sorry guys, but that's my standard. ;)

ACE is already above average and raising pretty quickly every 6 hours thanks to two hurricanes.
Member Since: July 6, 2010 Posts: 112 Comments: 31326
Leslie looks awful compared to Michael...





I think its very possible Michael could become a major. We've said that about a couple storms this year though and we've seen how it's worked out, lol.
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you've got Leslie twice there Bluestorm..
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Quoting wxchaser97:

Thats also Leslie, but yeah Michael is a good looking storm.
I posted Michael picture, but somehow it changed to Leslie... CIMSS is messing with me again -__-
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Two reasons this season hasn't impressed me yet: no major hurricanes and the short-lived nature of the hurricanes. I want to see more majors and more ACE before I'm impressed. Sorry guys, but that's my standard. ;)
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Quoting Bluestorm5:
Michael:


Thats also Leslie, but yeah Michael is a good looking storm.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Quoting bigeasystormcaster:
Northerly shear, not SW.


Probably got confused by the fact that it was blowing toward the southwest.
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Leslie:

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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.