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Chill falls over the Atlantic as the official season heads towards close
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| #939178 (Received by flhurricane at: 4:57 AM 09.Sep.2018) TCDAT3 Tropical Storm Helene Discussion Number 8 NWS National Hurricane Center Miami FL AL082018 500 AM AST Sun Sep 09 2018 Satellite imagery indicates that Helene continues to become better organized with an increase in banding overnight. A couple of recent microwave images show that the inner core continues to organize with a low-level ring evident and indication that a banding-type eye is forming. Dvorak satellite T-numbers have increased and support an initial intensity of 55 kt. Helene is forecast to remain over SSTs of 27-28C during the next couple of days. The upper-level wind pattern is also expected to be quite favorable, and these conditions should support steady intensification. Slightly cooler waters and increasing southwesterly shear from an upper-level trough to the northwest of Helene are likely to put an end to the intensification process by day 3. After that time, Helene is forecast to move closer to the aforementioned trough with southwesterly shear and drier mid-level air likely to result in weakening by day 4 and 5. The NHC intensity forecast is near the IVCN intensity consensus model, but it is a little more conservative than the FSSE and HCCA models. The tropical storm is moving westward or 270 degrees at 12 kt. A deep-layer ridge to the north of the storm should steer Helene westward to west-northwestward during the next couple of days. By mid-week, Helene is expected to approach a weakness in the ridge between 40-50W longitude and the cyclone is predicted to turn northwestward, then north-northwestward by the end of the period. The track guidance is in fairly good agreement on this scenario, but there is some spread later in the period as to exactly what longitude the northwesterly turn takes place. The NHC forecast is between the various dynamical model solutions and is close to the HFIP corrected consensus model. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 13.2N 24.0W 55 KT 65 MPH 12H 09/1800Z 13.4N 26.0W 65 KT 75 MPH 24H 10/0600Z 14.0N 28.9W 75 KT 85 MPH 36H 10/1800Z 14.7N 31.9W 85 KT 100 MPH 48H 11/0600Z 15.4N 34.5W 90 KT 105 MPH 72H 12/0600Z 17.4N 38.3W 80 KT 90 MPH 96H 13/0600Z 20.5N 41.0W 65 KT 75 MPH 120H 14/0600Z 25.0N 42.5W 50 KT 60 MPH $$ Forecaster Brown |
