ZCZC HFOTCDCP3 ALL TTAA00 PHFO DDHHMM Hurricane Miriam Discussion Number 24 NWS Central Pacific Hurricane Center Honolulu HI EP152018 500 PM HST Fri Aug 31 2018 Vertical wind shear has begun to take its toll on Miriam. The eye is no longer present in geostationary satellite imagery, and a decreasing amount of deep convection has become confined to the northern semicircle. Subjective Dvorak current intensity estimates remained at 5.0/90 kt from all fix agencies. However, the final T numbers were down to 4.0 or 4.5, and given the degradation of the satellite presentation, the initial intensity will be lowered to 80 kt. Also, a minor adjustment was made to the wind radii based on partial ASCAT passes from this morning. The initial motion estimate is slightly east of due north (010 degrees) at 10 kt. Timely microwave passes (SSMI at 0014Z and SSMIS at 0106Z) were helpful in placing the center and determining the short-term motion. Through tonight, Miriam will continue to be steered northward by a mid to upper level trough to the northwest and a deep ridge to the northeast. On Saturday, Miriam will begin a turn toward the northwest. This will occur as the steering flow of the weakening system becomes increasingly influenced by the low level ridge that will shift to the north of Miriam. The general northwestward motion is expected to persist until dissipation. The track is essentially an update to the prior forecast and is close to the middle of the guidance envelope near CTCI and HCCA. Rapid weakening will occur during the next couple of days. The already vigorous, southwesterly vertical wind shear of 30 to 35 kt will increase through the next 36 to 48 hours to about 50 kt. In addition, SSTs, which are currently running around 26.5 C, will steadily decrease along the forecast track. This will cause Miriam to weaken to a tropical storm on Saturday and become a remnant low late Sunday or Monday. The intensity forecast remains in the middle of the guidance envelope and is close to LGEM through 36 hours, then remains closer to HWRF. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 20.1N 141.0W 80 KT 90 MPH 12H 01/1200Z 21.7N 141.1W 65 KT 75 MPH 24H 02/0000Z 23.6N 142.1W 50 KT 60 MPH 36H 02/1200Z 25.6N 143.7W 40 KT 45 MPH 48H 03/0000Z 27.4N 145.6W 35 KT 40 MPH 72H 04/0000Z 30.7N 149.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 05/0000Z...DISSIPATED $$ Forecaster Wroe NNNN
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