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Tropical Storm Helene Forecast Discussion Number 3
2018-09-08 04:45:00| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Sep 07 2018 187 WTNT43 KNHC 080244 TCDAT3 Tropical Storm Helene Discussion Number 3 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Fri Sep 07 2018 A very timely ASCAT pass indicated that the winds associated with the depression have increased to 35 kt, and also that the center was a little east of the location previously indicated. This is very common in systems during the formative stage. Based on the ASCAT data, the system has been upgraded to Tropical Storm Helene, the eighth named storm of the season. The satellite presentation has also improved during the past several hours, and now the cyclone has large cyclonically curved convective bands to the south of the center. The outflow is fair in all quadrants. Helene will be moving over warm waters and within an environment of light shear through the next 3 to 4 days, and most of the guidance responds to that environment by gradually strengthening the cyclone. The NHC forecast follows the trend of the intensity consensus, and brings Helene to hurricane intensity in about 3 days. Currently, Helene is embedded within a southwest monsoon-type flow, and is moving toward the west at about 9 or 10 knots. However, as the cyclone moves away from the African coast, it will become steered by the easterly flow around the subtropical ridge and should then increase in forward speed. Most of the track models are in extremely good agreement, at least for the next 3 days when the confidence in the forecast is high. At the long range, a mid-level trough is expected to develop over the central Atlantic, forcing the cyclone to turn more to the northwest and even north later on. The NHC forecast is in the middle of the guidance envelope and basically on top of the corrected consensus HCCA. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 13.6N 18.5W 35 KT 40 MPH 12H 08/1200Z 13.8N 19.9W 35 KT 40 MPH 24H 09/0000Z 14.3N 22.3W 40 KT 45 MPH 36H 09/1200Z 14.8N 25.0W 50 KT 60 MPH 48H 10/0000Z 15.4N 28.0W 55 KT 65 MPH 72H 11/0000Z 17.0N 33.9W 65 KT 75 MPH 96H 12/0000Z 18.5N 39.0W 65 KT 75 MPH 120H 13/0000Z 20.5N 42.5W 60 KT 70 MPH $$ Forecaster Avila
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