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 946 
 WTNT44 KNHC 040254
 TCDAT4
 
 POST-TROPICAL CYCLONE HERMINE DISCUSSION NUMBER  27
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
 1100 PM EDT SAT SEP 03 2016
 
 Hermine has changed little in structure since the last advisory,
 with most of the deep convection situated well northeast of the
 center and dry, subsiding air wrapping around the southern
 semicircle.  Earlier data from an Air Force Reserve Hurricane
 Hunter aircraft showed that the central pressure had risen to 998
 mb, and that 55-60 kt surface winds were present about 70 n mi
 northwest of the center.  Based on this, the initial intensity
 remains 60 kt.
 
 Hermine continues to move east-northeastward with the initial
 motion of 075/11.  During the next 72 hours, a mid- to upper-level
 trough currently moving through the northeastern United States will
 move close to, and then over the top of, the post-tropical cyclone.
 During this evolution, Hermine is expected to move slowly northward
 and then northwestward as it makes at least a partial cyclonic loop.
 While the track guidance is in fair agreement for the first 48-72
 hours, there remains significant spread later in the period on how
 fast the cyclone will move out to sea after it merges with the
 trough.  The UKMET is very slow to move the system out, while the
 ECMWF is much faster.  The GFS is between these extremes, and the
 current run shows a little faster motion than the previous run.
 The new forecast track is similar to the previous forecast through
 72 hours, and then is somewhat faster in moving the system to the
 east-northeast.  Overall, there remains low confidence in any
 particular model solution, and it should be noted that the GFS and
 UKMET both bring the center closer to land than the official
 forecast.
 
 Little change in strength is likely tonight.  On Sunday and Monday,
 the interaction with the upper-level trough is expected to provide
 more favorable conditions for strengthening while the system is
 over sea surface temperatures of 28C or warmer, and the dynamical
 models all show some deepening during this period. Based on this,
 the intensity forecast calls for Hermine to become a hurricane-force
 low.  The guidance is in good agreement that the system should
 slowly weaken after 48 hours, and this is indicated in the forecast
 as well.
 
 KEY MESSAGES:
 
 1. The slow motion and large wind field associated with Hermine will
 result in a long duration of hazardous conditions along much of the
 mid-Atlantic coast extending into southern New England through the
 holiday weekend and into midweek.
 
 2. Small changes in the meandering track of Hermine could result in
 large differences in the impacts along the mid-Atlantic coast during
 the next several days.  In addition, there could be multiple
 occurrences of tropical storm conditions in some locations within
 the warning area during this time.
 
 3. Although Hermine has become a post-tropical cyclone, NHC will
 continue to issue its full suite of advisory and warning products as
 long as the system remains a significant threat to land areas.
 
 4. P-surge, the model that drives the Potential Storm Surge Flooding
 Graphic, is designed for a wind field typical of a tropical cyclone.
 The wind field of Hermine is very poorly represented by the P-surge
 model and as a result, Flooding Graphics prior to today's 11 am
 EDT advisory understated the inundation risk from the Carolinas
 northward.  The NWS is using the GFS ensemble system instead of
 P-surge for ongoing issuances of the Potential Storm Surge Flooding
 Graphic to provide a more realistic depiction of the threat.
 
 5. The Prototype Storm Surge Watch/Warning Graphic accounts for
 the current wind structure of Hermine, and therefore accurately
 identifies those areas at risk for life-threatening storm surge.
 This graphic will also continue to be produced for Hermine.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  04/0300Z 36.5N  72.1W   60 KT  70 MPH...POST-TROPICAL
  12H  04/1200Z 37.1N  71.2W   60 KT  70 MPH...POST-TROPICAL
  24H  05/0000Z 37.6N  71.2W   65 KT  75 MPH...POST-TROPICAL
  36H  05/1200Z 37.9N  71.5W   65 KT  75 MPH...POST-TROPICAL
  48H  06/0000Z 38.3N  71.8W   65 KT  75 MPH...POST-TROPICAL
  72H  07/0000Z 39.0N  71.5W   60 KT  70 MPH...POST-TROPICAL
  96H  08/0000Z 40.0N  70.0W   55 KT  65 MPH...POST-TROPICAL
 120H  09/0000Z 41.0N  66.5W   50 KT  60 MPH...POST-TROPICAL
 
 $$
 Forecaster Beven
 
 
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