ZCZC HFOTCDCP4 ALL TTAA00 PHFO DDHHMM Tropical Storm Norman Discussion Number 43 NWS Central Pacific Hurricane Center Honolulu HI EP162018 1100 AM HST Fri Sep 07 2018 Strong southwesterly shear ripped thunderstorms from the center of Norman overnight, and the partially exposed low-level circulation center (LLCC) is now evident in visible satellite imagery. With thunderstorms limited to the northern semicircle, subjective Dvorak intensity estimates ranged from 3.0/55 kt from PGTW/SAB to 4.0/65 kt from PHFO. A blend of these data supports lowering the initial intensity to 60 kt for this advisory. Norman is moving toward the north-northwest between a deep-layer ridge centered to the east, and a longwave trough to the northwest, and the initial motion estimate for this advisory is 340/8 kt. A general motion toward the north-northwest and then north is expected to continue as the steering flow changes little through day 3. The updated forecast track again is shifted to the right of the previous due to significant shifts in the guidance envelope, and the updated forecast lies close to the HCCA and TVCE. Toward the end of the forecast period, a severely weakened and shallow Norman is expected to briefly move toward the northwest before dissipating on day 5. Norman will continue to weaken as it will remain embedded in an environment characterized by 40-50 kt of vertical wind shear. The updated intensity forecast closely mimics the previous forecast and ICON. Continued rapid weakening in the short term should taper off somewhat on days 2 and 3 as the low-level remnant slowly spins down over gradually decreasing SSTs. A more rapid decrease in SSTs on days 4 and 5 should ensure decay, then dissipation. The official forecast delays dissipation as compared to the statistical guidance, with preference given to dynamical model guidance that indicates that Norman will weaken more slowly. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 24.0N 152.8W 60 KT 70 MPH 12H 08/0600Z 25.0N 153.6W 50 KT 60 MPH 24H 08/1800Z 26.4N 154.6W 45 KT 50 MPH 36H 09/0600Z 27.8N 155.0W 40 KT 45 MPH 48H 09/1800Z 29.4N 154.7W 35 KT 40 MPH 72H 10/1800Z 32.0N 154.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 11/1800Z 34.5N 156.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 12/1800Z...DISSIPATED $$ Forecaster Birchard NNNN
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