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Hurricane Oscar Forecast Discussion Number 11
2018-10-29 15:34:47| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Mon Oct 29 2018 000 WTNT41 KNHC 291434 TCDAT1 Hurricane Oscar Discussion Number 11 NWS National Hurricane Center Miami FL AL162018 1100 AM AST Mon Oct 29 2018 Oscar's convective cloud pattern has continued to improve since the previous advisory, with a small, cloud-filled eye now apparent in visible satellite imagery and also in a recent SSMI/S microwave pass. In addition, cirrus outflow has been expanding in all quadrants, especially in the eastern semicircle. The initial intensity of 75 kt is based on a Dvorak satellite intensity estimate of T4.5/77 kt from TAFB, a Data-T-number of T4.5/77 kt from SAB, and an NHC objective intensity estimate of T4.4/75 kt. It is also worth noting that bursts of lightning activity in the eastern eyewall have been occurring since around 1100 UTC. The initial motion estimate is now 285/06 kt. Oscar has slowed its forward motion significantly and has made the advertised turn toward the west-northwest. A motion toward the northwest is expected by late afternoon today as the hurricane rounds the southwestern periphery of a deep-layer ridge. A turns toward the north and then toward the north-northeast are forecast on Tuesday as Oscar moves north of the ridge axis ahead of an eastward-moving deep-layer trough currently approaching Bermuda. The trough is expected to continue advancing eastward over the next couple of days, accelerating Oscar toward the northeast at forward speeds near 25 kt on Wednesday through Friday. Although a strong shortwave trough is still forecast to dig southward to the west of Oscar on Wednesday, none of the model guidance shows the hurricane being captured any longer, and instead keep the cyclone as a separate entity that accelerates northeastward into the mid-latitude westerlies as a strong extratropical cyclone. The official track forecast is similar to the previous advisory, and lies close to an average of the corrected-consensus models HCCA and FSSE and the simple consensus models TVCA and TVCX. Deep-layer (850-200 mb) shear calculations by the SHIPS model and UW-CIMSS are at least 25 kt from the northwest, which clearly is not negatively affecting the improving cirrus outflow. This is likely due to the large 1000-km domain that the SHIPS model uses to compute vertical wind shear. Furthermore, most of the cloud top temperatures within the outflow layer appear to be mostly below the 200-mb level, and closer to the 250-mb level. The large shear values are resulting in much less intensification forecast by the SHIPS and LGEM statistical-dynamical intensity models. As a result, the official intensity forecast leans more toward the HCCA and FSSE models, which are weighing more heavily the stronger intensity forecasts provided by the HWRF, HMON, and Navy COAMPS-TC models, which have Oscar strengthening to just below major hurricane status in 24-36 hours. By 48 hours and beyond, sharply decreasing SSTs along with increasing southwesterly shear ahead of a deep-layer trough are expected to cause Oscar to gradually weaken and transition to a strong extratropical low in 60-72 hours. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 25.8N 58.4W 75 KT 85 MPH 12H 30/0000Z 26.8N 58.7W 85 KT 100 MPH 24H 30/1200Z 28.7N 58.0W 90 KT 105 MPH 36H 31/0000Z 31.4N 56.1W 90 KT 105 MPH 48H 31/1200Z 35.0N 52.6W 80 KT 90 MPH 72H 01/1200Z 43.0N 43.7W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 02/1200Z 50.0N 30.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 03/1200Z 55.0N 15.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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