621 
 WTNT41 KNHC 210249
 TCDAT1
 
 TROPICAL STORM FIONA DISCUSSION NUMBER  17
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016
 1100 PM AST SAT AUG 20 2016
 
 Somewhat surprisingly, two recent ASCAT passes showed that Fiona is
 producing 45-kt winds in its northeastern quadrant.  This intensity
 is also supported by the latest ADT estimate.  Despite the increase
 in maximum winds, the next 36 hours will be critical for Fiona's
 survival as a tropical cyclone.  During this period, westerly shear
 of 30 kt will be at its strongest, and mid-level relative humidities
 will be at their lowest.  Therefore, gradual weakening is
 anticipated, and it's entirely possible that Fiona could soon
 struggle to maintain organized deep convection.  For now, the NHC
 official forecast shows Fiona becoming a remnant low by 72 hours.
 However, there is a lot of uncertainty in this forecast.  If Fiona
 can survive the next 36 hours, it might persist as a weak tropical
 cyclone through the end of the forecast period since environmental
 conditions do become a little more favorable in a couple of days. It
 should be noted that most of the global models hang onto a weak low
 for at least the next 5 days, with the exception of the ECMWF which
 shows the low opening up into a trough by 48 hours.  For now, the
 NHC forecast continues to show dissipation by day 5 as a compromise.
 
 Fiona's motion has been wavering between west-northwest and
 northwest, and the latest estimate is 305/13 kt.  Low-level ridging
 should keep Fiona on this general trajectory for the next 72 hours
 or so, followed by a northwestward turn with a decrease in speed by
 day 4 when the cyclone approaches a stalled frontal boundary off
 the east coast of the United States.  The NHC official forecast has
 been nudged south and west to be closer to the TVCN multi-model
 consensus, especially toward the end of the forecast period.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  21/0300Z 21.7N  50.1W   45 KT  50 MPH
  12H  21/1200Z 22.4N  52.0W   45 KT  50 MPH
  24H  22/0000Z 23.3N  54.6W   40 KT  45 MPH
  36H  22/1200Z 24.2N  57.3W   40 KT  45 MPH
  48H  23/0000Z 24.9N  59.5W   35 KT  40 MPH
  72H  24/0000Z 26.6N  63.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
  96H  25/0000Z 29.0N  66.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 120H  26/0000Z...DISSIPATED
 
 $$
 Forecaster Berg