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Potential Tropical Cyclone Five Forecast Discussion Number 1
2021-06-30 22:54:51| National Hurricane Center (Atlantic)
Issued at 500 PM AST Wed Jun 30 2021 000 WTNT45 KNHC 302054 TCDAT5 Potential Tropical Cyclone Five Discussion Number 1 NWS National Hurricane Center Miami FL AL052021 500 PM AST Wed Jun 30 2021 Satellite imagery indicates that the convection associated with the low pressure area over the central tropical Atlantic is becoming better organized. However, earlier scatterometer data showed that the circulation was elongated and not well defined. Since the system is about 48 h away from the Lesser Antilles and is expected to become a tropical storm before reaching the islands, advisories are being initiated at this time on Potential Tropical Cyclone Five. The initial intensity is set to 30 kt based on the scatterometer data and satellite intensity estimates from TAFB and SAB. The initial motion is 285/18. The disturbance is currently on the south side of a strong subtropical ridge, and for the next 72 h the system should move rapidly west-northwestward. Indeed, the forward speed may exceed 25 kt as the system moves through the Lesser Antilles. There is excellent agreement in the guidance on this part of the forecast track. After 72 h, the system is expected to approach a weakness in the ridge caused by a mid-latitude trough over the eastern United States. The should cause the system to slow its forward speed and turn more northwestward. The track guidance become more diverse during this time in regards to how far north the system will turn, and this part of the NHC forecast track is most similar to the GFS and UKMET forecasts. Note that the track forecast is more uncertain than usual since the system does not yet have a well-defined center. The disturbance is currently in a favorable upper-level wind pattern. However, most Atlantic systems in this area moving near 25 kt have trouble strengthening, and there are indications that the fast forward speed may produce some westerly shear. Thus, the NHC intensity forecast for the first 72 h is near the lower edge of the intensity guidance. After 72 h, the intensity forecast becomes highly uncertain due to possible land interaction and differences in the model forecasts of the upper-level winds. This portion of the NHC intensity forecast maintains a constant 50-kt intensity due to the level of uncertainty. Key Messages: 1. The system is expected to become a tropical storm before reaching the Lesser Antilles and tropical storm conditions are possible beginning Friday in portions of the Windward and southern Leeward Islands. 2. Heavy rainfall will move quickly across the Windward and southern Leeward Islands, including Barbados, on Friday. Isolated flash flooding and mudslides are possible. 3. There is a risk of wind and rainfall impacts in portions of the Virgin Islands, Puerto Rico, Hispaniola, Cuba, the Turks and Caicos and the southeastern Bahamas through early next week, although the forecast is more uncertain than usual since the system does not have a well-defined center. Interests in these areas should monitor the system's progress and updates to the forecast. 4. Interests in Florida should monitor updates to the forecast for this system, but it is too soon to determine what if any impacts could occur there next week given the uncertainty in the long-range forecast. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 9.6N 43.7W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 01/0600Z 10.2N 46.6W 35 KT 40 MPH...TROPICAL CYCLONE 24H 01/1800Z 11.1N 51.0W 40 KT 45 MPH 36H 02/0600Z 12.4N 56.0W 45 KT 50 MPH 48H 02/1800Z 13.8N 61.2W 45 KT 50 MPH 60H 03/0600Z 15.4N 66.3W 50 KT 60 MPH 72H 03/1800Z 17.0N 70.9W 50 KT 60 MPH 96H 04/1800Z 20.0N 77.0W 50 KT 60 MPH...INLAND 120H 05/1800Z 22.5N 81.5W 50 KT 60 MPH...INLAND $$ Forecaster Beven
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