831 
 WTNT44 KNHC 032057
 TCDAT4
 
 POST-TROPICAL CYCLONE HERMINE DISCUSSION NUMBER  26
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
 500 PM EDT SAT SEP 03 2016
 
 Hermine has the look of an extratropical cyclone this afternoon,
 with most of the deep convection situated well northeast of the
 center and dry, subsiding air wrapping around the southern
 semicircle.  This descending air resulted in a band of very strong
 winds over portions of the Outer Banks of North Carolina today, and
 those winds along with SFMR data from the aircraft support an
 initial intensity of 60 kt for this advisory.  Hermine has an
 expansive wind field, with 34-kt winds extending about 200 miles
 from the center.  Hermine is still expected to interact with a
 shortwave trough in the next couple of days over warm SSTs, which
 should result in some intensification, although the global models
 are a little less bullish this cycle.  The NHC forecast continues to
 show Hermine at or near hurricane intensity for the next 72 hours,
 with slow weakening expected thereafter.
 
 After moving due eastward earlier today, the initial motion is now
 back toward the east-northeast at around 10 kt.  Hermine should turn
 northward and slow to a crawl as it merges with the upper-level
 trough, and the NHC track shows only 2-3 kt of forward speed from 24
 through 96 hours.  The spread in the track model guidance has
 increased this cycle, with the UKMET and GFS now showing more of a
 westward motion and are slower to begin moving Hermine
 northeastward.  The ECMWF has trended eastward and is much faster,
 taking Hermine south of Cape Cod in about 4 days, while the GFS and
 UKMET are still centered offshore of New Jersey at that time. Given
 the spread, and the possibility of looping motions during the
 interaction with the upper trough, confidence in the details of the
 track forecast remains quite low.  The new NHC track tries to
 maintain some continuity with the last one, but lies to the right of
 the previous one in the first 12-24 hours due to the more easterly
 motion of Hermine today.  The NHC forecast is close to the
 multi-model consensus through 72 hours.  After that time, the NHC
 track is faster than the new consensus but slower than the previous
 forecast, reflecting the increasing spread at those times and low
 confidence in any particular solution.
 
 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  03/2100Z 36.2N  73.3W   60 KT  70 MPH...POST-TROPICAL
  12H  04/0600Z 36.8N  72.0W   60 KT  70 MPH...POST-TROPICAL
  24H  04/1800Z 37.2N  71.3W   65 KT  75 MPH...POST-TROPICAL
  36H  05/0600Z 37.7N  71.6W   65 KT  75 MPH...POST-TROPICAL
  48H  05/1800Z 38.0N  72.0W   65 KT  75 MPH...POST-TROPICAL
  72H  06/1800Z 38.8N  71.9W   60 KT  70 MPH...POST-TROPICAL
  96H  07/1800Z 40.0N  71.0W   55 KT  65 MPH...POST-TROPICAL
 120H  08/1800Z 41.0N  68.5W   50 KT  60 MPH...POST-TROPICAL
 
 $$
 Forecaster Brennan