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| #946153 (Received by flhurricane at: 10:45 PM 27.Oct.2018) TCDAT1 Tropical Storm Oscar Discussion Number 5 NWS National Hurricane Center Miami FL AL162018 1100 PM AST Sat Oct 27 2018 Satellite imagery shows that convection associated with Oscar has become better organized, with increased banding around the low- level center. In addition, recent scatterometer data indicate that the system now has a relatively small wind field with a radius of maximum winds of about 25 n mi. Although the cyclone is still tangled up with the upper-level low to the point where it has not yet developed the anticyclonic outflow of a tropical cyclone, the convection and the wind field now justify calling the system a tropical storm. The initial intensity has been raised to 55 kt based on the scatterometer data, and it is possible this is a little conservative. The initial motion is a somewhat uncertain 240/17, as the short-term motion has been more toward the southwest or south. For the next several hours, Oscar should continue to pivot around the upper-level low to its east. Thereafter, it should turn more westward with a decrease in forward speed on the south side of a large ridge over the North Atlantic. After about 36 h, a large deep-layer trough moving eastward across the western Atlantic should cause Oscar to turn northwestward and northward, followed by recurvature into the westerlies and acceleration. The track guidance is generally in good agreement with this scenario, although by 120 h there is some spread in both the direction and forward speed after recurvature. The new forecast track is near the various consensus models, and the early part of it is shifted a little to the south of the previous forecast due to the current location and motion. The global models suggest that the core of Oscar should mostly avoid nearby strong upper-level winds through 24-36 h, and then encounter strong upper-level divergence associated with the deep-layer trough. While the environment is not ideal for a tropical cyclone, conditions appear favorable for additional intensification, and the intensity forecast now calls for Oscar to reach hurricane strength in about 24 h. Interaction with the trough after 72 h should start extratropical transition, which should be complete between 96-120 h. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 25.7N 51.4W 55 KT 65 MPH 12H 28/1200Z 25.2N 54.1W 60 KT 70 MPH 24H 29/0000Z 25.1N 56.5W 65 KT 75 MPH 36H 29/1200Z 25.8N 58.2W 70 KT 80 MPH 48H 30/0000Z 27.2N 58.6W 75 KT 85 MPH 72H 31/0000Z 32.5N 55.5W 75 KT 85 MPH 96H 01/0000Z 41.0N 47.0W 70 KT 80 MPH 120H 02/0000Z 48.5N 32.0W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven |
