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Subtropical Storm Oscar Forecast Discussion Number 1
2018-10-27 04:33:56| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Oct 26 2018 000 WTNT41 KNHC 270233 TCDAT1 Subtropical Storm Oscar Discussion Number 1 NWS National Hurricane Center Miami FL AL162018 1100 PM AST Fri Oct 26 2018 Satellite imagery and scatterometer data indicate the circulation of the broad low pressure area over the central Atlantic has become better defined, with a low-level center developing to the south of a convective burst. The scatterometer data indicate 35-40 kt winds about 70-90 n mi from the center, and satellite imagery shows that the cyclone is entangled with a developing upper-level low. Based on these factors, advisories are being initiated on the latest in this year's series of subtropical storms, Oscar. Due to the recent development of the center, the initial motion is an uncertain 335/8. The track guidance is in excellent agreement that Oscar should should turn sharply westward and west- southwestward during the next 24 h as it pivots around the north side of the upper-level low, with this general motion continuing through about 48 h. After that, the cyclone should turn more westward at a slower forward speed as it approaches a weakness in the subtropical ridge. A northeastward motion appears likely from 72-120 h due to a mid-latitude trough approaching Oscar from the west. However, there are significant differences in the forward speed between the GFS, ECMWF, and UKMET models that make this part of the forecast low confidence. Overall, the forecast track is close to the TVCN consensus model, and it splits the difference between the divergent global models late in the forecast period. Gradual strengthening is forecast as Oscar remains in the deep-layer cyclonic flow of the upper-level low during the first 36-48 h. After that time, the global models suggests the system will have a chance to develop a tropical cyclone outflow pattern, and based on this the forecast calls for Oscar to become a tropical cyclone near the 48 h point. Interaction with the aforementioned mid-latitude trough may allow some additional intensification before Oscar encounters stronger shear near the 120 h point. The FV3 model shows a much weaker Oscar than the other dynamical models, and it is possible that dry air entrainment may hamper development through the forecast period. Thus, the intensity forecast is below the intensity consensus and on the weaker side of the intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 26.7N 45.7W 40 KT 45 MPH 12H 27/1200Z 27.2N 47.2W 45 KT 50 MPH 24H 28/0000Z 26.6N 50.3W 50 KT 60 MPH 36H 28/1200Z 25.6N 53.2W 50 KT 60 MPH 48H 29/0000Z 25.3N 55.3W 55 KT 65 MPH...TROPICAL CYCLONE 72H 30/0000Z 26.5N 57.5W 60 KT 70 MPH 96H 31/0000Z 30.0N 55.5W 60 KT 70 MPH 120H 01/0000Z 34.0N 50.0W 55 KT 65 MPH $$ Forecaster Beven
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