912 
 WTNT43 KNHC 082102
 TCDAT3
 
 Tropical Storm Helene Discussion Number   6
 NWS National Hurricane Center Miami FL       AL082018
 500 PM AST Sat Sep 08 2018
 
 During the past few hours, Helene has developed a convective band
 that wraps about three-quarters of the way around the storm, and
 the intensity of the inner core convection has increased.  In
 addition, microwave imagery shows an elliptical inner ring feature.
 Satellite intensity estimates at 18Z were in the 35-50 kt range, and
 given the recent increase in organization the initial intensity is
 increased to 50 kt.
 
 Helene should continue to strengthen through at least 72 h in a
 light vertical shear environment over sea surface temperatures near
 27C.  This part of the intensity forecast has been increased over
 the previous forecast and lies near the intensity consensus.
 However, there remain a couple of alternate forecast scenarios.  The
 first is that Helene could rapidly intensify and become stronger
 than currently forecast, and the rapid intensification index of the
 SHIPS model has about a 35 percent chance of 25 kt of strengthening
 in the next 24 h.  The second is that a large plume of African dust
 and associated dry air that has spread over the Cabo Verde Islands
 starts entraining into the cyclone and inhibits intensification.
 The former alternative is more likely than the latter at this time.
 After 72 h, Helene is expected to encounter increasing southwesterly
 shear associated with a mid- to upper-level trough over the central
 Atlantic, which should cause the system to weaken significantly.
 
 The initial motion is 275/11.  There again is little change in the
 forecast guidance or the forecast track, with Helene expected to
 move westward to west-northwestward for the next 3 days or so on the
 south side of the subtropical ridge, then turn northwestward in
 response to the aforementioned trough.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  08/2100Z 13.6N  21.7W   50 KT  60 MPH
  12H  09/0600Z 13.7N  23.5W   55 KT  65 MPH
  24H  09/1800Z 14.1N  26.2W   65 KT  75 MPH
  36H  10/0600Z 14.7N  29.1W   75 KT  85 MPH
  48H  10/1800Z 15.5N  32.0W   85 KT 100 MPH
  72H  11/1800Z 17.5N  37.0W   85 KT 100 MPH
  96H  12/1800Z 19.5N  40.5W   65 KT  75 MPH
 120H  13/1800Z 23.0N  42.5W   55 KT  65 MPH
 
 $$
 Forecaster Beven