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Tropical Storm Miriam Forecast Discussion Number 14
2018-08-29 16:34:56| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Wed Aug 29 2018 957 WTPZ45 KNHC 291434 TCDEP5 Tropical Storm Miriam Discussion Number 14 NWS National Hurricane Center Miami FL EP152018 800 AM PDT Wed Aug 29 2018 Although Miriam remains a sheared tropical cyclone, recent geostationary satellite data and a 1002 UTC AMSR2 microwave overpass indicates that there has been some improvement in the structure of the cyclone. The microwave data showed an increase in banding over the eastern portion of the circulation and less separation between the convection and the low-level center. Therefore, the initial intensity is increased to 60 kt, which is a blend of the most recent subjective Dvorak classifications and objective T-numbers from UW/CIMSS. The northwesterly shear over the cyclone appears to have abated slightly, and a further slight reduction in shear could allow Miriam to reach hurricane strength within the next 24-36 h. Most of the intensity guidance agrees, and the NHC intensity forecast has been increased slightly for the first 36 h. After that time, increasing shear and cooler waters are expected to cause Miriam to weaken fairly quickly and the system is forecast to become a remnant low by day 4. Miriam continues to move westward or 275/10 kt. The cyclone is approaching the western edge of the subtropical ridge, and the global models indicate that Miriam will slow down and turn west-northwestward very soon. By Thursday, a large mid- to upper-level trough to the northeast of the Hawaiian Islands is expected to cause Miriam to turn northwestward, then northward through 72 hours. At days 3 and beyond, there continues to be significant model differences with the ECMWF still taking Miriam faster and much farther northward, while the GFS moves a much weaker Miriam westward. Since Miriam is forecast to weaken and become a shallow system around that time, the NHC forecast leans toward the more westward scenario, but is not as far south and west as the GFS. The new NHC track is south of the various consensus aids at day 5, and is in best agreement with the GFS ensemble mean and UKMET model. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 14.2N 139.4W 60 KT 70 MPH 12H 30/0000Z 14.4N 140.6W 65 KT 75 MPH 24H 30/1200Z 15.1N 141.6W 65 KT 75 MPH 36H 31/0000Z 16.3N 142.0W 65 KT 75 MPH 48H 31/1200Z 17.9N 142.1W 60 KT 70 MPH 72H 01/1200Z 21.0N 142.9W 45 KT 50 MPH 96H 02/1200Z 23.8N 145.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 03/1200Z 26.7N 149.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown
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