Parts of the U.S. Government are closed. However, because the information this site provides is necessary to protect life and property, it will be updated and maintained during the Federal Government shutdown. For critical weather information, please visit www.weather.gov. To learn more, see www.commerce.gov.
ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM HURRICANE SANDRA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP222015 200 PM MST WED NOV 25 2015 Sandra's intensification has continued at a rapid pace. The hurricane now has a clearer eye in infrared satellite imagery that is completely surrounded by a white ring on the Dvorak enhancement curve. Dvorak estimates from TAFB and SAB were T5.5/102 kt and T5.0/90 kt, respectively, although data-T numbers were up to 6.0. The UW-CIMSS ADT scheme has been flopping between different scene types, but when it has used an eye pattern it has yielded estimates in the 5.5-6.0 range. Based on these numbers, the initial intensity is raised to 100 kt, making Sandra a category 3 hurricane. There have now been 9 major hurricanes over the eastern North Pacific Ocean during the 2015 season, which is a record for that basin. Some additional strengthening is anticipated since Sandra will be moving over sea surface temperatures between 29 and 30 degrees Celsius and within a low-shear environment for another 24 hours or so. However, it is hard to tell how much longer rapid intensification (RI) will last. The SHIPS RI index has fallen a bit since earlier today, but it still shows about a 50 percent chance of a 30-kt increase in winds over the next 24 hours. Strengthening is still shown in the NHC forecast for another 12 hours, with some weakening beginning in 24-36 hours once the shear increases. Southwesterly shear increases to well over 30 kt beyond 48 hours, and rapid weakening is expected as Sandra approaches the Baja California peninsula and western mainland Mexico. The NHC intensity forecast is a little higher than the guidance for the first 12-24 hours, but then it is very similar to the IVCN intensity consensus thereafter. Sandra appears to have turned northwestward with an initial motion of 305/7 kt. The hurricane is beginning to move around the western extent of a subtropical ridge located over southern Mexico, and it should recurve to the north and northeast during the next several days as a mid-/upper-level trough pushes the ridge eastward. The track guidance remains in relatively good agreement through 24 hours, with some divergence thereafter as the ECMWF model (on the western edge of the guidance) takes a wider and slower turn while the GFS (on the eastern edge) take a sharper and faster turn. The difference in these models is due to their depiction of Sandra's vertical integrity once the shear increases. The ECMWF shows a strongly tilted and shallower system by day 3 while the GFS maintains a deeper vertical circulation even in the face of 50 kt of shear. The NHC track forecast remains close to the model consensus aids, but it is a little slower than the previous forecast due to the latest ECMWF forecast, which seems like a more realistic solution at this time. Although Sandra is forecast to weaken, it is too soon to know exactly how it will affect portions of the southern Baja California peninsula or the west coast of mainland Mexico. Since the forecast has slowed down a bit, a watch may not be required until tonight or on Thursday for portions of Mexico. Regardless, interests in those areas should continue to monitor the progress of Sandra. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 13.0N 109.9W 100 KT 115 MPH 12H 26/0600Z 14.0N 110.6W 110 KT 125 MPH 24H 26/1800Z 15.7N 111.1W 105 KT 120 MPH 36H 27/0600Z 17.5N 111.2W 90 KT 105 MPH 48H 27/1800Z 19.3N 110.8W 75 KT 85 MPH 72H 28/1800Z 23.1N 108.6W 40 KT 45 MPH 96H 29/1800Z 27.0N 107.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 30/1800Z...DISSIPATED $$ Forecaster Berg NNNN