806 
 WTPA43 PHFO 010851
 TCDCP3
  
 Hurricane Miriam Discussion Number  25
 NWS Central Pacific Hurricane Center Honolulu HI   EP152018
 1100 PM HST Fri Aug 31 2018
  
 Miriam's satellite presentation has deteriorated significantly over 
 the past six hours, with 30 to 35 kt of vertical wind shear 
 beginning to profoundly affect the core of this tropical cyclone. 
 Deep convection lies only along the northern flank of the 
 circulation and outflow has become almost non-existent except to
 the north and northeast. Subjective Dvorak current intensity
 estimates decreased to 4.5/77 kt from JTWC and SAB, while PHFO
 remained at 5.0/90 kt. ADT from UW-CIMSS was 77 kt. Initial
 intensity for this advisory is set at 75 kt, which may be high given
 what appears to be the beginning of rapid system erosion. 
 
 Initial motion is 355/08 kt, based mainly on a 0600 UTC fix 
 influenced strongly by a 0409 UTC SSMIS pass. Miriam has likely 
 begun its turn to the north northwest this evening as it is steered 
 between an upper trough to the northwest and a deep ridge to the 
 northeast. The track that Miriam actually takes will be determined 
 by how fast the vertical wind shear decapitates it, with a weaker 
 Miriam likely forced to turn northwestward faster as system
 steering becomes influenced more by low level flow. The track
 guidance envelope shifted a bit to the left, likely in anticipation
 of more rapid Miriam weakening. The forecast track was shifted
 slightly left as well, remaining within the rather tight envelope
 between ECMWF and TVCE. 
 
 Miriam will continue to weaken in the face of increasing shear and 
 sub-26 degree C SSTs through the forecast period, with this system 
 forecast to dissipate at 96 hours. We expect Miriam will weaken to
 a tropical storm Saturday before becoming a post tropical remnant
 low Monday. While some guidance, like SHIPS, wants to dissipate
 Miriam within 48 hours, our intensity forecast follows HWRF between
 ECMWF and FSSE. 
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  01/0900Z 20.9N 141.2W   75 KT  85 MPH
  12H  01/1800Z 22.2N 141.6W   65 KT  75 MPH
  24H  02/0600Z 24.1N 143.0W   50 KT  60 MPH
  36H  02/1800Z 25.9N 144.7W   40 KT  45 MPH
  48H  03/0600Z 27.6N 146.5W   35 KT  40 MPH
  72H  04/0600Z 30.7N 150.6W   30 KT  35 MPH...POST-TROP/REMNT LOW
  96H  05/0600Z...DISSIPATED
  
 $$
 Forecaster Powell