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September 2012

Leslie a Big Threat to Bermuda and Canada; Isaac May Regenerate in the Gulf

   Posted by Levi at 5:44pm on September 4, 2012

Tropical Storm Leslie continues to move extremely slowly in the west-central Atlantic north of the lesser Antilles. She remains sheared from the west by a deep-layer ridge in the central Caribbean and an upper trough to her northeast, and the low-level center is exposed to the west of the convection. This has been the story with Leslie for days now, but conditions will be improving in the near-future. As the upper trough to her northeast splits and exits, sending a cut-off low southward to the east of Leslie, it should alleviate some of the shear and provide a good ventilation pattern between that upper low to her east and another one to her west over the northern Bahamas. The farther north Leslie moves, the farther away she will be from the Caribbean ridge, which will also relax the shear over her. Cold water upwelling due to Leslie’s slow movement may also be a hindering factor right now, and the storm will continue to move slowly under weak steering currents during the next 3 days, but after that will begin to speed up, and with favorable environmental conditions, should easily become a hurricane eventually. The global models all agree on aggressive deepening. The ECMWF even makes Leslie a Cat 4 near and north of Bermuda, which may be overdone, but illustrates the conducive pattern for strengthening.

Leslie’s track has been a slow one as she has missed one trough and is now stuck south of a ridge passing by to her north, which is causing the weak steering currents. As this moves on, a new trough will dig into the eastern U.S. and allow Leslie to ride northward up the western flank of the subtropical high. This trough is forecasted to cut off into a deep upper low that will not be moving much, and should provide a clear, static steering pattern that should take Leslie around the subtropical high near Bermuda, and eventually into the Canadian Maritimes. Cut-off upper lows over the eastern U.S. can tend to bring hurricanes farther to the west towards New England than usual, but the steering pattern here looks to have the subtropical high too far south to allow a direct hit on New England. However, high surf and fringe effects from the western side of the storm may impact New England during Leslie’s passage. Leslie’s track will likely take her very close to Bermuda, and with nearly 5 whole days of slow movement ahead before she reaches the island, Bermuda should be prepared for a direct hit from a likely strengthening hurricane. The Canadian Maritimes will likely get a direct hit from Leslie afterwards, though she will be moving much quicker by then. This would be the first direct tropical impact on these two places this season.

Elsewhere….Tropical Storm Michael has formed east of Leslie from a baroclinic low turned tropical, and is not a threat to land.

The remnants of Hurricane Isaac are drifting back southward over Alabama, and will be moving back out over the Gulf of Mexico during the next 3 days. The GFS and ECMWF hint at regeneration of this low over the northeastern gulf, which would certainly be a possibility to watch for. With Leslie recurving to the east, the pattern favors this low getting pulled back out of the gulf to the northeast fairly quickly, but it would not be out of the question to see a tropical depression or weak tropical storm develop.

The models continue to show the threat for additional tropical developments from African waves coming westward during the next two weeks as we pass through the climatological peak of the hurricane season.

We shall see what happens!




  • Gary Z says:

    Lots of I told you, I saw it first! On Master’s Blog.
    Of course they never admit when they are wrong…

  • Jeff H. says:

    Matthew, Leslie, and now 91L is likely to pass up through the mid-Atlantic way offshore. Could you advise why a good number of storms this season are taking this route.

    • Levi says:

      It’s pretty common for the strongest tropical waves of an El Nino season in late August through mid-September to pass well to the north. Typical El Nino pattern.

  • derayka says:

    update the action bro’!

  • gerry says:

    Hey Levi,
    When are you planning on the next update? Than new invest has me a bit worried here in the Yucantan. Have a few things going on next weekend!!! Thanks

  • Gary Z says:

    The drama queens on Masters blog are now talking politics.
    Which makes as much sense as their weather knowledge.

  • Mike says:

    Much of this year’s ACE has been generated in the Atlantic North of say 25 degrees North Latitude. Is this common ? It suggests that more water warmth is further north compared to the MDR. I wonder what is the underlying cause and how it relates to future years ? I hope you can speculate on this at some point.

    Regards, Mike

  • Gary Z says:

    The Doom makers are just dying for 99 to hit Florida.
    They are trying to will it this way. Idiots!

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