000 WTPZ44 KNHC 291445 TCDEP4 Hurricane Nora Discussion Number 16 NWS National Hurricane Center Miami FL EP142021 900 AM MDT Sun Aug 29 2021 Nora has a healthy satellite appearance this morning. The deep convection near and to the west of the estimated center is maintaining a fairly large central dense overcast with very cold infrared cloud tops. Recent ATMS and SSMIS microwave data indicate Nora still has a pronounced mid-level eye structure, with the center very near the coast of extreme southern Sinaloa. A blend of the UW-CIMSS objective ADT estimate and 12 UTC subjective Dvorak classifications from TAFB and SAB support holding the initial intensity at 65 kt for this advisory. The estimated initial motion of Nora is north-northwestward or 345/9 kt, although this is somewhat uncertain due to the lack of in-situ observations. A mid-level ridge should continue to steer the tropical cyclone generally north-northwestward to northwestward during the next few days. This motion will bring the center over the eastern Gulf of California and very near or over the coast of west-central Mexico. The official NHC track forecast is adjusted just slightly to the right of the previous one, in line with the latest track guidance. Nora's intensity forecast remains highly dependent on whether the center moves inland over mainland Mexico or along the Gulf of California, parallel to the west-central coast of Mexico. Given the slight eastward track adjustment, the official NHC intensity forecast shows gradual weakening over the next few days due to at least intermittent land interaction as Nora skirts the coast. This is consistent with the general intensity guidance consensus, which no longer supports strengthening given Nora's proximity to land. Due to the complex geography of western Mexico, even a slight eastward deviation from the forecast track would result in more rapid weakening as Nora moves further inland. Conversely, a more northwestward motion over the warm Gulf of California waters could allow Nora to remain a stronger tropical storm early this week. As previously mentioned, confidence in the intensity forecast is lower than normal. Key Messages: 1. Nora is forecast to be at or near hurricane strength while it moves near the coasts of Nayarit and Sinaloa today and into Monday, and hurricane warnings or watches are in effect for portions of that coastline. Interests in these areas should closely monitor the progress of Nora and subsequent updates to the forecast. 2. Heavy rain associated with Nora is expected across the west coast of Mexico from the states of Colima northward to southern Sonora. This rain will likely result in life-threatening flash flooding and mudslides across these regions. Rainfall from Nora is likely to spread into the southwestern U.S. and central Rockies during the middle to latter portion of the week, bringing the potential for flash flooding to the region. 3. Nora is forecast to move north-northwestward to northwestward near or over the Gulf of California Tuesday and Wednesday, bringing a risk of wind impacts to portions of the Mexican states of Baja California Sur, northern Sinaloa, and Sonora. Given the above-average uncertainty in the intensity forecast, confidence is not high enough to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 23.3N 106.4W 65 KT 75 MPH 12H 30/0000Z 23.8N 106.9W 60 KT 70 MPH...NEAR THE COAST 24H 30/1200Z 24.3N 107.5W 55 KT 65 MPH...NEAR THE COAST 36H 31/0000Z 24.9N 108.2W 55 KT 65 MPH...NEAR THE COAST 48H 31/1200Z 25.6N 109.0W 50 KT 60 MPH...NEAR THE COAST 60H 01/0000Z 26.5N 109.6W 50 KT 60 MPH...NEAR THE COAST 72H 01/1200Z 27.5N 110.0W 40 KT 45 MPH...INLAND 96H 02/1200Z 29.5N 111.2W 30 KT 35 MPH...INLAND 120H 03/1200Z...DISSIPATED $$ Forecaster Reinhart