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Tropical Storm Nora Forecast Discussion Number 6
2021-08-27 04:51:11| National Hurricane Center (East Pacific)
Issued at 1000 PM CDT Thu Aug 26 2021 000 WTPZ44 KNHC 270251 TCDEP4 Tropical Storm Nora Discussion Number 6 NWS National Hurricane Center Miami FL EP142021 1000 PM CDT Thu Aug 26 2021 A large area of deep convection has developed over the southern and western portions of Nora's circulation over the past several hours. Almost all of the convection is displaced to the southwest of Nora's center by some moderate northeasterly shear. Based on the slightly improved satellite appearance of the cyclone, the initial intensity is raised to 40 kt for this advisory. This is in best agreement with the objective UW-CIMSS ADT and SATCON estimates of around 40 kt. Nora has turned a bit to the right and accelerated slightly this evening, and it is now moving west-northwestward or 295/10 kt. The mid-level ridge over the southern United States that is steering Nora is being eroded by a shortwave trough over the Rocky Mountains. In response, Nora is expected to turn toward the northwest on Friday and then the north-northwest on Saturday. This will bring the center of the cyclone close to the southwestern coast of Mexico. The ECMWF and UKMET as well as almost all the ECMWF ensemble members keep Nora offshore, passing just offshore of Cabo Corrientes before moving toward the entrance to the Gulf of California and Baja California Sur. However, the GFS and many of its ensemble members still show Nora moving inland over southwestern Mexico on Saturday. Overall, the multi-model track guidance consensus changed little this cycle, and so the official NHC track forecast remains very close to the previous one. The extended forecast still shows Nora moving near or over Baja California Sur and the Gulf of California on days 4 and 5. However, it is worth noting that the degree of uncertainty in this portion of the forecast is above average. The moderate northeasterly wind shear over Nora is expected to diminish over the next 12-24 h, which should allow the cyclone to intensify within a moist and unstable environment over SSTs around 29 deg C. Thus, Nora is forecast to strengthen over the next few days and become a hurricane on Saturday. Of course, this is highly dependent on Nora remaining offshore and not moving inland over mainland Mexico. Since the NHC track forecast keeps Nora offshore, the official intensity forecast lies on the high end of the intensity guidance and is closest to the ECMWF-based SHIPS and LGEM models. In this case, the normally reliable intensity consensus aids are of limited use since several of the consensus members bring Nora inland. Weakening is forecast on days 4-5 due to expected land interaction with Baja California Sur. The government of Mexico has extended the Tropical Storm Warning northward from Manzanillo to Cabo Corrientes, and issued a Tropical Storm Watch north of Cabo Corrientes to San Blas. Additional watches and warnings may be required on Friday. Key Messages: 1. Nora is forecast to strengthen to a hurricane on Saturday while it is near the coast of southwestern Mexico, and a hurricane watch and tropical storm warning are in effect for portions of that area. Interests along the southwestern coast of Mexico should closely monitor the progress of this system and updates to the forecast. 2. Heavy rain associated with Tropical Storm Nora is expected across coastal sections of the Mexican states of Oaxaca, Guerrero, Michoacan, Colima, and Jalisco. Life-threatening flash flooding and mudslides may occur. 3. Nora is forecast to be near or over the southern portion of Baja California Sur as a hurricane early next week, bringing a risk of wind and rain impacts to that area. Given the above average uncertainty in the forecast, it is still too soon to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 14.1N 102.6W 40 KT 45 MPH 12H 27/1200Z 14.9N 103.6W 45 KT 50 MPH 24H 28/0000Z 16.3N 104.7W 55 KT 65 MPH 36H 28/1200Z 18.0N 105.6W 60 KT 70 MPH 48H 29/0000Z 19.9N 106.5W 65 KT 75 MPH 60H 29/1200Z 21.5N 107.5W 70 KT 80 MPH 72H 30/0000Z 22.7N 108.7W 75 KT 85 MPH 96H 31/0000Z 24.4N 110.6W 65 KT 75 MPH...NEAR BAJA CAL SUR 120H 01/0000Z 26.0N 112.1W 45 KT 50 MPH...OVER BAJA CAL SUR $$ Forecaster Reinhart/Cangialosi
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