000 WTPZ42 KNHC 141439 TCDEP2 Tropical Storm Norma Discussion Number 1 NWS National Hurricane Center Miami FL EP172017 900 AM MDT Thu Sep 14 2017 The convective structure of the area of disturbed weather well to the south of the Baja California peninsula has continued to increase in organization, with an elongated band wrapping around the southern and eastern sides of the circulation. Dvorak intensity estimates have increased to T3.0/45 kt from TAFB and T2.0/30 kt from SAB, so the system is now classified as a 35-kt tropical storm. Since Norma has just recently consolidated, its motion is a little uncertain, but the best estimate is slowly northward, or 360/4 kt. Norma is located to the northwest of a mid-level ridge that extends westward from Central America, but it is also due south of a blocking high centered over northwestern Mexico. As a result, the storm is expected to only drift slowly northward for the next 48 hours or so. After 48 hours, a more pronounced northward motion is forecast, but there is a lot of spread among the track models regarding exactly how fast Norma moves north and if it moves east or west at all. On the eastern side of the guidance envelope, the GFS has a weaker ridge over Mexico and a deeper trough off the California coast, which would cause Norma to turn northeastward near the southern part of the Baja California peninsula. On the western side of the guidance, the ECMWF maintains a stronger ridge, forcing Norma to turn northwestward to the west of the Baja California peninsula. Until the evolving pattern becomes clearer, the NHC track forecast is between these two extremes and lies closest to the HFIP Corrected Consensus Approach (HCCA). Norma is over very warm waters and should remain in a low-shear environment for at least the next 48-72 hours. As a result, steady strengthening is anticipated, and Norma could reach hurricane strength within about 36 hours. Strengthening should continue through 48-72 hours until vertical shear begins to increase, and a weakening trend is likely to occur on days 4 and 5. The NHC intensity forecast closely follows the SHIPS guidance and the ICON intensity consensus, and it is slightly below the HCCA output. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 17.2N 109.5W 35 KT 40 MPH 12H 15/0000Z 17.7N 109.5W 45 KT 50 MPH 24H 15/1200Z 18.1N 109.5W 55 KT 65 MPH 36H 16/0000Z 18.4N 109.4W 65 KT 75 MPH 48H 16/1200Z 18.9N 109.4W 75 KT 85 MPH 72H 17/1200Z 21.0N 110.1W 75 KT 85 MPH 96H 18/1200Z 23.5N 111.0W 65 KT 75 MPH 120H 19/1200Z 25.5N 110.5W 55 KT 65 MPH $$ Forecaster Berg