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Hurricane Norman Forecast Discussion Number 19
2018-09-01 22:54:42| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Sat Sep 01 2018 538 WTPZ41 KNHC 012054 TCDEP1 Hurricane Norman Discussion Number 19 NWS National Hurricane Center Miami FL EP162018 200 PM PDT Sat Sep 01 2018 Since the previous advisory, a well-defined closed eye has remained apparent in microwave satellite data, and a cloud-filled eye has appeared in visible satellite imagery during the past couple of hours. Satellite intensity estimated haven't changed since the previous advisory, so the initial intensity remains 90 kt, which is supported by a 1501Z SATCON estimate of 88 kt and a Dvorak CI value of T5.0/90 kt. Norman's initial motion estimate is now 275/12 kt based on microwave and visible satellite eye position estimates. There are no significant changes to the previous track forecast and reasoning. The hurricane is expected to be steered by a strong deep-layer subtropical ridge to the north, resulting in a westward motion for the next 12-24 hours, followed by a west-northwestward motion at a faster forward speed. The latest model guidance is tightly packed about the previous forecast track through 96 hours, with much less divergence after that compared to previous model runs. Therefore, the new forecast track is essentially just an extension of the previous advisory track, and lies close to a blend of the HCCA, FSSE, and TVCE consensus track models. The GFS and ECMWF models are forecasting the 15-20 kt of vertical wind shear that has been affecting Norman to steadily decrease for the next 60-72 hours, possibly becoming near zero if the ECMWF upper-level wind forecasts verify. Since the hurricane is expected to remain over 27 deg C and warmer SSTs for the next 48 hours, only slow weakening is forecast and that is due mainly to occasional intrusions of drier and more stable air coming in from the northwest, where a large field of cold-air stratocumulus clouds is currently lurking close by. The HWRF and HMON models continue to forecast Norman to re-strengthen into a major hurricane during the next 24 hours, but this scenario is being discounted at this time due to Norman's proximity to the aforementioned stratocumulus cloud field. By 72 hours, increasing southwesterly shear and cooler SSTs should combine to induce more significant weakening. The NHC intensity forecast is similar to the HCCA and IVCN consensus model forecasts. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 16.3N 125.1W 90 KT 105 MPH 12H 02/0600Z 16.6N 127.0W 90 KT 105 MPH 24H 02/1800Z 17.4N 130.1W 85 KT 100 MPH 36H 03/0600Z 18.2N 133.2W 85 KT 100 MPH 48H 03/1800Z 19.1N 136.5W 80 KT 90 MPH 72H 04/1800Z 20.4N 142.0W 70 KT 80 MPH 96H 05/1800Z 21.4N 146.4W 65 KT 75 MPH 120H 06/1800Z 22.2N 149.6W 60 KT 70 MPH $$ Forecaster Stewart
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