ZCZC HFOTCDCP3 ALL TTAA00 PHFO DDHHMM 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 NNNN
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