907 
 WTNT44 KNHC 021455
 TCDAT4
 
 TROPICAL STORM HERMINE DISCUSSION NUMBER  21
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
 1100 AM EDT FRI SEP 02 2016
 
 Hermine is moving over southeastern Georgia and has weakened
 steadily since landfall.  Convective tops have warmed, but several
 land stations have shown sustained winds near tropical storm force
 near the center with some gusts close to 50 kt.  Stronger winds are
 also found over the Atlantic coastal waters, with buoy 41008
 reporting winds around 40 kt in the last hour.  Based on this, the
 initial intensity is set to 45 kt for this advisory.  The central
 pressure, based on surface data, is about 989 mb.  While the center
 of Hermine will remain over land for the next 24 hours or so, I
 don't expect the winds over water to decrease much, so the NHC
 forecast shows no change during that time.  Strengthening through a
 combination of diabatic and baroclinic processes is shown after the
 system moves offshore.  The GFS, ECMWF, and UKMET all show Hermine
 interacting with a potent upper-level shortwave trough in 2-3 days,
 and the system could re-strengthen to near hurricane force at that
 time.  Slow weakening is expected later in the period, but Hermine
 is expected to remain a dangerous cyclone through 5 days.  The NHC
 intensity forecast is based largely on global model guidance, and is
 a bit higher than the previous one.
 
 The initial motion estimate is 040/16.  Hermine should continue
 moving northeastward for the next 36 to 48 hours ahead of an
 approaching mid-latitude trough.  After that time, the cyclone
 should turn northward and nearly stall out as it interacts with the
 upper-level shortwave off the mid-Atlantic coast.  A slow
 northeastward motion is shown at days 4 and 5, but there is a fair
 bit of model spread late in the period and confidence in the details
 of the track forecast at those times remains low.
 
 Note that the NHC forecast shows Hermine as a post-tropical cyclone
 in about 48 hours, but model fields do not show it undergoing a
 full extratropical transition, as it instead appears to acquire a
 warm seclusion structure.  There is a possibility that the system
 could regain some tropical characteristics in 4-5 days, but this
 remains uncertain.
 
 Based on the latest forecast, tropical storm watches and warnings
 have been expanded northward along the U.S. mid-Atlantic coast.
 
 KEY MESSAGE:
 
 1. Hermine is expected to become a post-tropical cyclone while
 still producing hazardous winds and storm surge over land.  NWS
 policy allows NHC to write advisories on and issue tropical storm
 watches and warnings for post-tropical cyclones, when the system
 continues to pose a significant threat to life and property. NHC and
 the NWS Eastern Region have decided that this option will be invoked
 for Hermine.  After Hermine becomes a post-tropical cyclone, NHC
 will continue to issue its full suite of advisory and warning
 products for as long as the system remains a significant threat to
 land.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  02/1500Z 31.9N  82.0W   45 KT  50 MPH...INLAND
  12H  03/0000Z 33.5N  79.7W   45 KT  50 MPH...INLAND
  24H  03/1200Z 35.4N  76.3W   45 KT  50 MPH...INLAND
  36H  04/0000Z 36.7N  73.9W   55 KT  65 MPH...OVER WATER
  48H  04/1200Z 37.5N  72.6W   55 KT  65 MPH...POST-TROPICAL
  72H  05/1200Z 38.1N  72.6W   65 KT  75 MPH...POST-TROPICAL
  96H  06/1200Z 38.8N  71.9W   60 KT  70 MPH...POST-TROPICAL
 120H  07/1200Z 39.3N  71.5W   50 KT  60 MPH...POST-TROPICAL
 
 $$
 Forecaster Brennan