ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Hurricane Norma Discussion Number 11 NWS National Hurricane Center Miami FL EP172023 300 AM MDT Fri Oct 20 2023 Earlier low-frequency microwave images indicated that significant degradation of Norma's eye has occurred during the past few hours, particularly in the south part of the inner core. Although the outflow aloft is still quite impressive, there is evidence in the UW-CIMSS shear analysis of modest southerly shear below 250 mb which is apparently affecting Norma's vertical structure. Subsequently, the initial intensity is lowered to 100 kt for this advisory and is based on a blend of the subjective and objective intensity estimates from TAFB, SAB, and UW-CIMSS. Gradual weakening should continue through the period as a result of increasing south-southwesterly vertical wind shear produced by an amplifying mid- to upper-level trough approaching the Baja California peninsula, and a progressively inhibiting thermodynamic surrounding environment with mid-tropospheric relative humidity values of less than 50 percent. Despite the forecast weakening trend, Norma will likely be a hurricane while it approaches the southern portion of Baja California Sur on Saturday. The initial motion is estimated to be north-northwestward, or 330/6 kt. Norma is expected to move between mid-level subtropical high-pressure east of the cyclone and the above mentioned trough to the northwest and north during the next couple of days. By mid-period, Norma should turn north-northeastward to northeastward with a reduction in forward speed while approaching the west-central coast of Mexico. The official track forecast lies between the TVCE simple deterministic model consensus and the HFIP HCCA, and is similar to the previous forecast with a slight adjustment to the south of it beyond the 48-hour period. The initial wind radii have been adjusted slightly based on a recent METOP-B scatterometer overpass. Key Messages: 1. A Hurricane Warning is in effect for the far southern portion of the Baja California peninsula, where Norma is expected to bring hurricane conditions on Saturday when it passes near or over the area. Tropical storm conditions are also expected within the tropical storm warning areas in Baja California Sur on Saturday. 2. Heavy rains from Norma will begin to impact the far southern portions of California Baja Sur later today, continuing through Sunday. This rainfall may produce flash and urban flooding, along with possible mudslides in areas of higher terrain. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 18.8N 108.6W 100 KT 115 MPH 12H 20/1800Z 19.7N 109.2W 90 KT 105 MPH 24H 21/0600Z 21.2N 109.7W 85 KT 100 MPH 36H 21/1800Z 22.4N 109.6W 70 KT 80 MPH 48H 22/0600Z 23.3N 109.2W 60 KT 70 MPH 60H 22/1800Z 23.6N 108.4W 50 KT 60 MPH 72H 23/0600Z 23.9N 107.8W 45 KT 50 MPH 96H 24/0600Z 25.3N 106.6W 25 KT 30 MPH...POST-TROP/INLAND 120H 25/0600Z...DISSIPATED $$ Forecaster Roberts NNNN
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Page last modified: Monday, 18-Dec-2023 12:10:25 UTC