000 WTPZ42 KNHC 170244 TCDEP2 Tropical Storm Norma Discussion Number 11 NWS National Hurricane Center Miami FL EP172017 900 PM MDT Sat Sep 16 2017 Norma's structure hasn't changed over the past 6 hours. A sprawling band of deep convection extends well out from the center, but the tropical storm still appears to lack an inner core. The intensity has been held at 55 kt based on the Dvorak current intensity estimate from TAFB, but that could be generous given that the earlier reconnaissance flight struggled to find winds that high, and the the Final-T number from TAFB was a little lower. Norma has continued moving slowly north, but a turn toward the north-northwest is expected overnight. The global models agree for the next 2 days that a deep-layer ridge extending westward over central Mexico will keep Norma on a north-northwest or northwest heading. Beyond that time, there is considerable spread in the guidance. The ECMWF forecasts that the ridge will weaken sufficiently to cause Norma to stall off the coast of the Baja California Peninsula. On the other hand, the GFS maintains the ridge long enough to force Norma farther north, and into a fairly dry and stable environment. The official forecast splits these scenarios, and is based mostly on the TVCX consensus aid. Recent total precipitable water imagery suggests that some dry air may be wrapping into the circulation, and this will likely contribute to further weakening. The reliable intensity models all indicate that steady weakening will occur throughout the forecast period. By day 5, SSTs below 26 C and very dry air should cause the tropical storm to become a remnant low. If Norma takes the faster and farther north track of the GFS, it is likely that it will become a remnant low sooner than indicated. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 20.2N 110.1W 55 KT 65 MPH 12H 17/1200Z 20.9N 110.4W 50 KT 60 MPH 24H 18/0000Z 21.8N 110.8W 45 KT 50 MPH 36H 18/1200Z 22.4N 111.5W 45 KT 50 MPH 48H 19/0000Z 22.7N 112.1W 40 KT 45 MPH 72H 20/0000Z 23.0N 112.7W 35 KT 40 MPH 96H 21/0000Z 23.5N 113.2W 30 KT 35 MPH 120H 22/0000Z 24.5N 113.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky