ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Tropical Storm Norma Discussion Number 12 NWS National Hurricane Center Miami FL EP172017 300 AM MDT Sun Sep 17 2017 A pair of ASCAT passes between 0400 and 0500 UTC showed that Norma is weaker than previously estimated. The maximum winds in both passes were around 40 kt, so the initial intensity has been conservatively lowered to 45 kt. The new NHC intensity forecast is a little lower than the previous one because of the lower initial intensity, but otherwise the reasoning behind the forecast is unchanged. Norma is already embedded within a fairly dry environment, and will be moving over progressively cooler SSTs over the coming days. Steady weakening is likely, and Norma is now forecast to become a remnant low by 96 h. There has been a significant shift in the track guidance. The GFS and various GFS-derived models have come into better agreement with the ECMWF, and now depict a track farther away from the Baja California peninsula. Beyond day 3, there is still a fair amount of disagreement on the extent to which a ridge to the east will turn the tropical storm or its remnants back toward the north. The ECMWF continues to insist that the cyclone will come to a near halt, while the GFS shows the remnant low continuing well to the north. The new NHC forecast remains close to the various consensus aids, but hedges toward the ECMWF. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 20.5N 110.4W 45 KT 50 MPH 12H 17/1800Z 21.1N 110.7W 40 KT 45 MPH 24H 18/0600Z 21.7N 111.3W 40 KT 45 MPH 36H 18/1800Z 22.1N 112.1W 35 KT 40 MPH 48H 19/0600Z 22.4N 113.0W 35 KT 40 MPH 72H 20/0600Z 22.9N 114.3W 30 KT 35 MPH 96H 21/0600Z 23.5N 114.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 22/0600Z 24.0N 114.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky NNNN
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