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Potential Tropical Cyclone Six Forecast Discussion Number 4
2018-08-31 10:36:59| National Hurricane Center (Atlantic)
Issued at 500 AM AST Fri Aug 31 2018 322 WTNT41 KNHC 310836 TCDAT1 Potential Tropical Cyclone Six Discussion Number 4 NWS National Hurricane Center Miami FL AL062018 500 AM AST Fri Aug 31 2018 Even though the circulation is gradually becoming less elongated, there is still relatively little deep convection near the estimated center of circulation. Instead, most of the convection remains confined to the monsoon trough southwest of the center, where low-level convergence is strongest. Therefore, the system is not quite yet being designated as a tropical cyclone. Global model fields suggest that the low should detach from the monsoon trough within the next 12 hours, which would likely allow deep convection to form closer to the center. Assuming that happens, the system is also forecast to strengthen and become a tropical storm by this afternoon while it approaches the southern Cabo Verde Islands. Although vertical shear is expected to be relatively light for much of the forecast period, sea surface temperatures ahead of the system are marginal, and the low will likely move over a minimum of oceanic heat content in 48-72 hours. Adding on top of that a drier mid-level environment, only gradual strengthening is anticipated through day 5. A majority of the intensity models agree on this scenario, with the exception of the HWRF model, which brings the system close to major hurricane strength at the end of the forecast period. Since that solution is discounted at the moment, the NHC intensity forecast is below the HCCA guidance and closest to the intensity consensus. The low appears to have turned west-northwestward with an initial motion of 285/10 kt. A mid-level high centered west of the Canary Islands should continue to steer the disturbance west-northwestward at a faster clip for the next 4 days or so. By the end of the forecast period, a weakness in the ridge over the eastern Atlantic could cause the system to turn northwestward. The new NHC track forecast is a little slower than the previous one during the first 72 hours and then a little to the west on days 4 and 5 to better match the latest guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 13.6N 21.4W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 31/1800Z 14.2N 23.1W 35 KT 40 MPH...TROPICAL STORM 24H 01/0600Z 14.8N 25.6W 40 KT 45 MPH 36H 01/1800Z 15.5N 28.3W 45 KT 50 MPH 48H 02/0600Z 16.2N 30.9W 50 KT 60 MPH 72H 03/0600Z 17.4N 36.2W 55 KT 65 MPH 96H 04/0600Z 19.0N 41.0W 60 KT 70 MPH 120H 05/0600Z 21.5N 45.0W 65 KT 75 MPH $$ Forecaster Berg
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