615 
 WTNT43 KNHC 132048
 TCDAT3
 
 Tropical Storm Helene Discussion Number  26
 NWS National Hurricane Center Miami FL       AL082018
 500 PM AST Thu Sep 13 2018
 
 Helene has maintained deep convection this afternoon though only
 in the northern semicircle.  Dvorak estimates from TAFB and SAB are
 continuing to drop, and a blend of these with the CIMSS SATCON
 supports lowering the intensity to 55 kt.
 
 Strong tropospheric vertical shear along with only lukewarm waters
 are likely contributing toward Helene's weakening.  The shear
 should further increase during the next two days, though the sea
 surface temperatures will rebound up to 27C along with an increase
 in low-level moisture.  Helene is expected to be either slowly
 weakening or steady state during this time.  Beginning in about
 three days, Helene will commence baroclinic transition, and it is
 expected to become an extratropical cyclone by 96 hours.  The
 baroclinic forcing should preclude any additional weakening through
 the remainder of the forecast period, and the official intensity
 forecast is nearly the same as the last advisory.  This prediction
 is based on a blend of the stronger HWRF/COAMPS dynamical models and
 the weaker SHIPS/LGEM statistical schemes for the next couple of
 days, and is based on a blend of the GFS/ECMWF/UKMET global models
 at the extended lead times.
 
 Helene is moving northward at about 12 kt between the subtropical
 ridge to its east and a deep-layer trough to its west.  The system
 should accelerate and turn toward the northeast over the next few
 days as it rounds the subtropical ridge and starts getting picked
 up by the mid-latitude westerlies.  The official track forecast is
 based upon the tightly clustered variable consensus technique (TVCN)
 and is nearly the same as the previous forecast.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  13/2100Z 26.3N  37.0W   55 KT  65 MPH
  12H  14/0600Z 28.8N  36.7W   50 KT  60 MPH
  24H  14/1800Z 32.3N  35.8W   50 KT  60 MPH
  36H  15/0600Z 35.5N  34.2W   50 KT  60 MPH
  48H  15/1800Z 37.9N  31.7W   50 KT  60 MPH
  72H  16/1800Z 40.6N  24.4W   50 KT  60 MPH
  96H  17/1800Z 44.0N  17.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
 120H  18/1800Z 51.0N   7.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
 
 $$
 Forecaster Landsea