764 
 WTNT44 KNHC 131441
 TCDAT4
 
 Tropical Storm Isaac Discussion Number  24
 NWS National Hurricane Center Miami FL       AL092018
 1100 AM AST Thu Sep 13 2018
 
 Satellite imagery indicate that Isaac remains a poorly organized
 tropical cyclone, with the low-level center mostly exposed during
 the past several hours.  The center of Isaac passed between Dominica
 and Martinique around 1300 UTC, with westerly winds reported on both
 St. Lucia and Martinique, indicating that Isaac is still a tropical
 storm. Data from a NOAA P-3 Hurricane Hunter aircraft indicate that
 maximum winds remain near 40 kt, although the area of tropical-
 storm-force winds has shrunk since yesterday.
 
 1200 UTC radiosonde data from the eastern Caribbean and Hurricane
 Hunter aircraft data indicate that the circulation of Isaac is
 fairly shallow and small.  It is entirely possible that Isaac will
 degenerate into a tropical wave during the next day or two due to
 the continued effects of strong shear.  However, the environment
 becomes much more conducive for increased organization in a few days
 when the cyclone, or its remnants, moves across the west-central
 Caribbean Sea.  Model guidance is not consistent at all on whether
 Isaac will survive as a tropical cyclone, which frankly might not be
 a very predictable event given the initial uncertainties.  The best
 course of action is to let the full 1200 UTC guidance suite ingest
 all of the latest radiosonde and other data before making any
 changes, so this advisory holds the status quo for now.
 
 Isaac is moving a little south-of-west and a bit faster, since it
 was devoid of convection most of night, at about 265/17. A mid-level
 ridge is forecast to persist over the southwestern Atlantic,
 steering Isaac westward for the next few days.  The track forecast
 is fairly dependent on the intensity forecast, since a deeper
 tropical cyclone will move slower due to slightly weaker winds in
 the middle part of the atmosphere.  The forecast has been too slow
 so far, and with the current forecast showing little strengthening,
 the official track prediction is shifted west of the previous one,
 close to the NOAA corrected consensus aid.  At the end of the
 forecast, if Isaac remains a tropical cyclone, it could start moving
 more toward the west-northwest, but I would place little emphasis on
 the 96-hour point until we get a better handle on the future
 structure of Isaac.
 
 Key Messages:
 
 1. Isaac is expected to produce tropical-storm-force winds across
 portions of the Lesser Antilles into this afternoon, and tropical
 storm warnings are in effect for Martinique, Dominica, and
 Guadeloupe.
 
 2. Tropical storm watches are in effect for Montserrat, St. Kitts
 and Nevis, Antigua, Barbuda, Saba and St. Eustatius, St. Maarten,
 and St. Martin.  Tropical storm conditions are possible on these
 islands today and interests on those islands should follow any
 advice given by their local officials.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  13/1500Z 14.9N  61.8W   40 KT  45 MPH
  12H  14/0000Z 14.9N  64.2W   35 KT  40 MPH
  24H  14/1200Z 14.9N  67.0W   35 KT  40 MPH
  36H  15/0000Z 14.9N  69.8W   35 KT  40 MPH
  48H  15/1200Z 15.0N  72.3W   35 KT  40 MPH
  72H  16/1200Z 15.5N  76.5W   35 KT  40 MPH
  96H  17/1200Z 17.0N  80.5W   30 KT  35 MPH
 120H  18/1200Z...DISSIPATED
 
 $$
 Forecaster Blake