274 
 WTNT44 KNHC 120834
 TCDAT4
 
 Tropical Storm Isaac Discussion Number  19
 NWS National Hurricane Center Miami FL       AL092018
 500 AM AST Wed Sep 12 2018
 
 Isaac is a poorly organized tropical storm. Geostationary satellite
 and microwave images indicate that the center of the cyclone is
 located near the western edge of the main area of deep convection.
 This asymmetric cloud pattern is due to about 20 kt of
 west-northwesterly shear.  The satellite intensity estimates have
 been decreasing, and an average of the Dvorak CI-numbers supports
 lowering the initial wind speed slightly to 50 kt.  The NOAA
 Hurricane Hunters are scheduled to investigate Isaac later this
 morning, and that data should provide a better assessment of the
 storm's intensity and structure.
 
 Isaac continues to move due westward at about 13 kt.  The track
 forecast reasoning remains unchanged.  A fairly strong mid-level
 ridge to the north of Isaac should steer the system westward at
 about the same forward speed during the next several days.  The
 models are now in fairly good agreement, and the NHC track forecast
 is just a little north of the previous one to come in line with the
 latest guidance.  Based on this forecast, Isaac is expected to cross
 portions of the Leeward and Windward Islands in about 36 hours.
 
 Isaac is feeling the effects of wind shear, and the global models
 suggest that the shear will likely remain moderate to strong during
 the next couple of days.  These hostile winds combined with nearby
 dry air will likely cause Isaac to gradually weaken during the next
 several days.  The intensity models are in fair agreement, and this
 forecast is close to the model consensus, except a little lower than
 that aid at 96 hours.  The latest runs of the GFS and ECMWF models
 show Isaac opening up into a trough by day 5, and the NHC forecast
 follows those models.
 
 Key Message:
 
 1. Isaac is expected to remain at tropical storm intensity when it
 moves across the Lesser Antilles on Thursday, and tropical storm
 warnings are in effect for Martinique, Dominica, and Guadeloupe.
 Tropical storm watches are in effect for Montserrat, St. Kitts and
 Nevis, Antigua, and Saba and St. Eustatius.  Interests on those
 islands should follow any advice given by their local officials.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  12/0900Z 14.5N  53.5W   50 KT  60 MPH
  12H  12/1800Z 14.8N  55.7W   50 KT  60 MPH
  24H  13/0600Z 15.0N  58.6W   45 KT  50 MPH
  36H  13/1800Z 15.2N  61.5W   45 KT  50 MPH
  48H  14/0600Z 15.4N  64.8W   40 KT  45 MPH
  72H  15/0600Z 15.3N  70.6W   40 KT  45 MPH
  96H  16/0600Z 15.2N  75.0W   35 KT  40 MPH
 120H  17/0600Z...DISSIPATED
 
 $$
 Forecaster Cangialosi