ZCZC HFOTCDCP4 ALL TTAA00 PHFO DDHHMM Hurricane Norman Discussion Number 30 NWS Central Pacific Hurricane Center Honolulu HI EP162018 500 AM HST Tue Sep 04 2018 Norman has been holding its own during the night. The overall satellite presentation has remained generally steady during the last several hours, with some recent development of new deep convection very close to the estimated low-level circulation center. A recent 1122Z AMSR microwave pass showed a rather well-defined eye. Subjective Dvorak current intensity estimates came in at 4.5/77 kt from PHFO/SAB, and 4.0/65 kt from JTWC. We have held the initial intensity unchanged at 75 kt for this advisory. The hurricane is now tracking due west, with an initial motion estimate of 270/15 kt. Westward motion is expected to continue today and tonight, with a considerable decrease in forward speed as Norman nears the southwestern periphery of a strong subtropical ridge centered to the northeast. Thereafter, the cyclone will gradually turn to the west-northwest then to the northwest as it moves around the end of the ridge and is increasingly steered by a large deep-layered trough over the North Pacific. The reliable guidance envelope shows very good agreement with this scenario, including the location and timing of the northwest turn. The new official forecast is shifted ever so slightly to the left through the first 48 hours mainly due to the more westward initial motion, and is simply an update of the previous forecast track thereafter. This is in best agreement with the FSSE guidance, and is also very close to the consensus HCCA and TVCE guidance. The CIMSS initial vertical wind shear estimate was only 9 kt from the south-southwest, and SHIPS guidance shows light wind shear persisting for another 36 hours as Norman continues tracking around the subtropical ridge. Norman is also now moving into an area of slightly higher ocean heat content as per the current CIRA analysis. Intensity guidance generally shows little change through the next couple of days, with some of the guidance including CTCI and HWFI showing an intensity increase between the 12- and 36-hour forecast times. After 48 hours, a rapid increase in wind shear, a drier surrounding airmass, and progressively cooler sea surface temperatures should cause steady weakening. The new intensity forecast has been adjusted upward slightly from 12 to 48 hours to better match the guidance envelope, with a similar weakening trend to the previous advisory thereafter. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 19.9N 143.4W 75 KT 85 MPH 12H 05/0000Z 19.9N 145.1W 75 KT 85 MPH 24H 05/1200Z 19.9N 147.0W 80 KT 90 MPH 36H 06/0000Z 20.4N 148.6W 80 KT 90 MPH 48H 06/1200Z 21.2N 149.9W 75 KT 85 MPH 72H 07/1200Z 23.6N 151.8W 55 KT 65 MPH 96H 08/1200Z 26.5N 154.0W 40 KT 45 MPH 120H 09/1200Z 29.0N 155.5W 30 KT 35 MPH $$ Forecaster Jacobson NNNN
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