ZCZC HFOTCDCP4 ALL TTAA00 PHFO DDHHMM Tropical Storm Norman Discussion Number 46 NWS Central Pacific Hurricane Center Honolulu HI EP162018 500 AM HST Sat Sep 08 2018 Deep convection near the exposed low-level circulation center (LLCC) of Norman dissipated around 07Z last evening, and has not returned as of advisory time, with only a small area of convection present about 90 nm north of the center. The LLCC has remained clearly visible in infrared and fog product satellite imagery during the night. The subjective Dvorak current intensity estimate came in at 3.0/45 kt from PHFO, while JTWC estimated 3.0 or 45-50 kt using the subtropical method. The latest objective estimates remain lower, with CIMSS SATCON showing 43 kt, and CIMSS ADT 2.3/32 kt. The overnight ASCAT pass missed Norman, but a 0648Z ScatSat pass found winds of 40 kt in the northeast quadrant. The initial intensity is lowered to 50 kt for this advisory, reflecting an assumed gradual spindown from the stronger winds measured by the 53rd Weather Reconnaissance Squadron aircraft on Friday, and this may be generous. Norman appears to have turned more to the northwest during the night, likely in response to the loss of deep convection, and the initial motion estimate for this advisory is 320/8 kt. All of the reliable guidance insists that the current northwest motion is temporary, and that Norman will quickly resume a north-northwest motion today, becoming almost due north thereafter, as it moves between a deep-layer ridge centered to the east and a cutoff low to the west. The guidance envelope did not shift much from the previous advisory. The new track forecast is on the left side of the reliable guidance for the first 24 hours due to the current motion, then near the previous forecast and the consensus HCCA and TVCE aids thereafter. The CIMSS vertical wind shear estimate for this advisory is 235/52 kt, and very strong southwest vertical wind shear of 45 to 55 kt is expected to persist over Norman for the next 36 hours or so, with some decrease possible thereafter. However, the system is forecast to be moving over cool SSTs below 25C by that time. Also, the SHIPS and experimental ECMWF-based SHIPS guidance now both categorize Norman as extratropical in 24 hours. This seems plausible given the asymmetric wind field observed by the ScatSat pass, the fact that the system already is acquiring a rather subtropical appearance, and Norman's increasingly shallow warm core as depicted by the FSU phase-space diagrams. The new intensity forecast continues to weaken Norman, and makes it a post-tropical gale center in 36 hours. If Norman does not regain deep convection near the LLCC soon, it will likely be declared post-tropical considerably sooner than shown in this forecast. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 26.0N 154.4W 50 KT 60 MPH 12H 09/0000Z 27.4N 154.8W 45 KT 50 MPH 24H 09/1200Z 29.1N 154.9W 40 KT 45 MPH 36H 10/0000Z 31.2N 154.7W 40 KT 45 MPH...POST-TROPICAL 48H 10/1200Z 32.9N 154.5W 35 KT 40 MPH...POST-TROPICAL 72H 11/1200Z 34.5N 155.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 12/1200Z 35.5N 156.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 13/1200Z...DISSIPATED $$ Forecaster Jacobson NNNN
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