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Subtropical Storm Oscar Forecast Discussion Number 2
2018-10-27 10:39:29| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Oct 27 2018 000 WTNT41 KNHC 270839 TCDAT1 Subtropical Storm Oscar Discussion Number 2 NWS National Hurricane Center Miami FL AL162018 500 AM AST Sat Oct 27 2018 Oscar's convective pattern has not changed much since the previous advisory. The surface center is displaced just to the southeast of a burst of deep convection, and other convective elements extend along a broken band over the eastern part of the circulation. Although satellite classifications have not increased, a drifting buoy (47546) near Oscar's center recently reported a pressure of 998.8 mb, implying a significant drop in the cyclone's central pressure from the previous estimate. Based on pressure-wind relationships, this low pressure would equate to maximum winds around 45 kt, and that is set as the initial intensity for this advisory. Oscar is careening around the northern side of a mid- to upper-level low, and its initial motion is now west-northwestward, or 300/10 kt. As the circulation becomes more vertically aligned in the coming days, the cyclone is forecast to be pushed westward to west-southwestward by the flow on the back side of a trough that is dropping southward over the eastern Atlantic. After 48 hours, Oscar is expected to recurve sharply and accelerate toward the north Atlantic ahead of an approaching mid-latitude trough. The global models have come into much better agreement on Oscar's eventual recurvature and acceleration, and confidence in the NHC track forecast has increased. In fact, the 00Z guidance suite required a significant increase in Oscar's forecast forward speed on days 4 and 5, and the new NHC track forecast is much faster than the previous one at the end of the forecast period, jumping northward by about 10 degrees of latitude. This new forecast is close to the TVCN multi-model consensus and HCCA model on day 5, but it's still not as fast as the 00Z GFS and ECMWF guidance. Gradually decreasing shear and warmer waters ahead of Oscar should allow for a steady increase in intensity during the next few days, and the cyclone is also expected to take on a more tropical convective pattern in about 36 hours. The intensity models are showing a little more intensification than before, and the new NHC intensity forecast has been nudged upward, showing Oscar becoming a hurricane in 3-4 days. Still, this forecast lies near the lower bound of the intensity guidance, and additional upward adjustments may be required in future advisories. Now that most of the models are showing more acceleration of Oscar toward the north Atlantic later in the forecast period, there is also more definitive consensus that Oscar will become an extratropical low by day 5, and that is now indicated in the official forecast. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 27.3N 47.0W 45 KT 50 MPH 12H 27/1800Z 27.1N 49.1W 45 KT 50 MPH 24H 28/0600Z 26.2N 52.0W 50 KT 60 MPH 36H 28/1800Z 25.7N 54.6W 55 KT 65 MPH...TROPICAL CYCLONE 48H 29/0600Z 25.9N 56.6W 60 KT 70 MPH 72H 30/0600Z 28.4N 57.4W 65 KT 75 MPH 96H 31/0600Z 35.0N 52.0W 70 KT 80 MPH 120H 01/0600Z 45.0N 39.0W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg
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