779 
 WTNT44 KNHC 142051
 TCDAT4
 
 Tropical Storm Isaac Discussion Number  29
 NWS National Hurricane Center Miami FL       AL092018
 500 PM AST Fri Sep 14 2018
 
 It has been a very interesting flight of the NOAA Hurricane Hunter
 aircraft this afternoon.  Dropsonde and SFMR data indicate that the
 maximum winds are around 35 kt again, and the pressure has fallen
 to about 1002 mb.  However, the system is tilted southward with
 vertical height due to northerly shear, and scatterometer and
 Hurricane Hunter tail-Doppler radar data indicate the system is
 elongated from northeast to southwest, albeit closed.  Note that the
 plane was unable to sample the southwestern quadrant well because of
 strong convection and intense lightning, so the flight-level winds
 showing no circulation were unrepresentative.
 
 The intensity forecast hasn't gotten any easier with Isaac.
 Vertical shear is expected to decrease a bit more, which might
 diminish the effects of dry air seen on water vapor images around
 the cyclone. However, the GFS and ECMWF continue to insist that
 Isaac will degenerate into a wave within the next 2 or 3 days, which
 is almost unanimously supported by their respective ensemble
 members.  This is the solution that the official forecast follows.
 It should be noted that none of the global models show pressures
 this low now with Isaac, except the UKMET, and that model is the one
 that holds onto the circulation the longest.  The reality of the
 situation is that the long-term future of Isaac is cloudy, and the
 best advice is just to follow NHC advisories every 6 hours to see
 if we gain any confidence.
 
 Isaac is moving westward at about 12 kt.  A ridge over the
 southwestern Atlantic should steer the cyclone westward over the
 weekend then west-northwestward early next week as Isaac reaches a
 weaker portion of the ridge.  Just like yesterday, a stronger system
 would likely turn more to the west-northwest earlier, moving
 closer to Jamaica.  Since the system is forecast to be weaker, the
 forecast lies on the westward and faster side of the guidance, and
 should also be considered low confidence since it depends on the
 intensity.  Interests in Jamaica should monitor the progress of the
 Isaac.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  14/2100Z 15.3N  68.2W   35 KT  40 MPH
  12H  15/0600Z 15.4N  70.1W   35 KT  40 MPH
  24H  15/1800Z 15.4N  72.2W   35 KT  40 MPH
  36H  16/0600Z 15.7N  74.2W   35 KT  40 MPH
  48H  16/1800Z 16.2N  76.3W   30 KT  35 MPH
  72H  17/1800Z 17.5N  80.0W   25 KT  30 MPH
  96H  18/1800Z...DISSIPATED
 
 $$
 Forecaster Blake