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Tropical Depression Nine Forecast Discussion Number 4
2018-09-08 16:57:36| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sat Sep 08 2018 571 WTNT44 KNHC 081457 TCDAT4 Tropical Depression Nine Discussion Number 4 NWS National Hurricane Center Miami FL AL092018 1100 AM AST Sat Sep 08 2018 The structure of Tropical Depression Nine is improving as the ongoing shear diminishes, with the convection getting closer to the low-level center. However, recent scatterometer data indicates that the system has not yet become a tropical storm, and the initial intensity remains 30 kt. The cyclone is still moving fairly slowly, with the initial motion now 300/5. The subtropical ridge to the north of the cyclone is forecast to steer the system westward with an increasing forward speed for at least the next 2-3 days. After that time, there is some uncertainty in the track forecast due to the formation of a mid- to upper-level trough over the central Atlantic. The Canadian and UKMET models forecast the cyclone to slow down and turn northwestward near the end of the forecast period due to the trough, while the ECMWF and GFS show a continued westward motion. The track forecast follows the ECMWF/GFS scenario and shows a faster westward motion than the previous forecast. The new forecast also lies near the various consensus models. With the shear diminishing, conditions are becoming more favorable for the cyclone to strengthen during the next 72 h. However, there are still concerns about dry air entraining into the system. The new intensity forecast is similar to the previous forecast with the cyclone becoming a tropical storm in about 12 h and a hurricane in about 72 h. After 72 h, the system is expected to encounter another round of shear, which is expected to cause some weakening. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 14.6N 36.0W 30 KT 35 MPH 12H 09/0000Z 14.7N 36.9W 35 KT 40 MPH 24H 09/1200Z 14.8N 38.5W 40 KT 45 MPH 36H 10/0000Z 14.8N 40.8W 50 KT 60 MPH 48H 10/1200Z 14.8N 43.5W 60 KT 70 MPH 72H 11/1200Z 14.5N 49.0W 75 KT 85 MPH 96H 12/1200Z 14.5N 55.0W 80 KT 90 MPH 120H 13/1200Z 14.5N 60.0W 75 KT 85 MPH $$ Forecaster Beven
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