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| #909422 (Received by flhurricane at: 11:05 PM 06.Nov.2017) TCDAT4 Tropical Storm Rina Discussion Number 4 NWS National Hurricane Center Miami FL AL192017 1100 PM AST Mon Nov 06 2017 Despite the low-level center being exposed to the west of the deep convection, a pair of ASCAT-A and ASCAT-B passes between 00Z and 01Z showed an area of 30-35 kt winds east of the cyclone's center. Based on the ASCAT data, the depression is upgraded to a tropical storm with the initial intensity set at 35 kt. The rather disorganized cloud pattern is consistent with the approximately 20 kt of westerly shear analyzed by UW-CIMSS and the SHIPS model. The environment is only expected to be marginally conducive for intensification via diabatic processes, with the shear expected to remain near 20 kt and the SSTs cooling along the forecast track. After 24 to 36 hours, cooling upper-tropospheric temperatures and increasing upper-level divergence suggest that Rina will maintain its intensity as it begins extratropical transition, which should be complete between by 72 hours. The new NHC intensity forecast is similar to the previous one and is close to the HWRF and HCCA aids. The official forecast shows Rina dissipating by 96 hours in agreement with global model fields. The exposed low-level center and ASCAT passes result in high confidence in the initial position, and Rina has begun to move more steadily, with an initial motion estimate of 010/06. Rina should continue to accelerate northward and north-northeastward during the next 36 to 48 hours between a mid-level ridge to the east and an upper-level trough to the west. After 48 hours, Rina is forecast to accelerate further as it enters the mid-latitude westerlies. The track model guidance has shifted left this cycle, and the along-track spread is quite large by 72 hours, with the GFS more than 500 n mi northeast of the ECMWF at that time. The new NHC track forecast has been adjusted westward and a bit slower, and lies close to a blend of the GFS and ECMWF solutions to the east of the TVCA multi-model consensus. Confidence in the details of the track forecast is lower than usual given the large model spread. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 30.4N 49.9W 35 KT 40 MPH 12H 07/1200Z 32.4N 49.6W 40 KT 45 MPH 24H 08/0000Z 35.4N 49.0W 45 KT 50 MPH 36H 08/1200Z 39.0N 48.0W 45 KT 50 MPH 48H 09/0000Z 42.3N 46.2W 45 KT 50 MPH 72H 10/0000Z 51.0N 36.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 11/0000Z...DISSIPATED $$ Forecaster Brennan |
