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Tropical Storm Helene Forecast Discussion Number 28
2018-09-14 10:52:54| National Hurricane Center (Atlantic)
Issued at 500 AM AST Fri Sep 14 2018 163 WTNT43 KNHC 140852 TCDAT3 Tropical Storm Helene Discussion Number 28 NWS National Hurricane Center Miami FL AL082018 500 AM AST Fri Sep 14 2018 Helene is looking increasingly like an extratropical cyclone, with a rain shield extending from its northwest quadrant and a line of clouds to the southeast, probably associated with a convergence zone, that looks like a developing a front. However, earlier ASCAT data suggested that the cyclone still had a compact wind field with maximum winds of around 55 kt on the west side, and the most recent available AMSU data still showed a distinct warm core. The extratropical transition (ET) process will likely be completed within the next 48 h, around the time that Helene will likely pass near or over the Azores. While this process occurs, little weakening is forecast by the various dynamical models, but gradual weakening should occur once ET is completed. By the end of the forecast period, nearly all of the global models depict the cyclone being absorbed into a larger mid-latitude low pressure system over the far northeast Atlantic. Helene continues to accelerate northward, and the initial motion is 010/20 kt. Almost no change has been made to the track forecast. Helene is still forecast to move quickly northward to north-northeastward between a mid-level ridge to its east and a sharp mid-latitude trough to its west. A northeastward turn should occur over the weekend as Helene reaches the northern extent of the ridge and becomes embedded within the mid-latitude westerlies. The official track forecast remains near the various consensus aids. The government of Portugal has issued an orange wind warning for the Azores, equivalent to a tropical storm warning. Tropical Storm conditions with gusty winds and heavy rains are likely over the weekend as Helene passes the islands, regardless of whether the cyclone is a tropical storm or post-tropical. Helene is expected to be a post-tropical cyclone when it approaches Ireland and the United Kingdom in a few days. Interests in those locations should consult products from their local meteorological service for information about potential impacts from Helene. Local forecasts and warnings for the UK can be found on the website of the UK Met Office at https://www.metoffice.gov.uk/. Local forecasts and warnings for Ireland can be found on the website of Met Eireann at https://www.met.ie/. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 30.6N 36.0W 55 KT 65 MPH 12H 14/1800Z 33.4N 35.3W 55 KT 65 MPH 24H 15/0600Z 36.7N 33.8W 55 KT 65 MPH 36H 15/1800Z 39.3N 30.8W 55 KT 65 MPH 48H 16/0600Z 41.3N 26.9W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 17/0600Z 45.5N 17.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 18/0600Z 51.5N 8.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 19/0600Z...DISSIPATED $$ Forecaster Zelinsky
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