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Tropical Storm Helene Forecast Discussion Number 36
2018-09-16 10:43:14| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Sep 16 2018 431 WTNT43 KNHC 160843 TCDAT3 Tropical Storm Helene Discussion Number 36 NWS National Hurricane Center Miami FL AL082018 500 AM AST Sun Sep 16 2018 Helene's cloud pattern is certainly looking less and less like a tropical cyclone this morning. Based on conventional satellite imagery and AMSU data, Helene is quickly undergoing an extratropical transition, and this dynamic process is expected to be completed later today, as the cyclone moves away from the Azores. The initial intensity is lowered to 45 kt, and is based primarily on 2326 UTC ASCAT-A wind retrievals. Cold (22C) sea surface temperatures and strong westerly shear will continue to disrupt Helene's vertical structure and should cause the cyclone to complete the extratropical transition in 12 hours, or sooner. The initial motion is estimated to be northeastward, or 50/22 kt, within the ferocious mid-latitude westerlies. The global models are in remarkably good agreement with Helene accelerating northeastward and becoming absorbed in a large baroclinic zone extending over northern United Kingdom in 72 hours, and the official forecast reflects this scenario. Earlier 2326 UTC METOP-A ASCAT scatterometer data indicated that the 34 kt and 50 kt wind radii, particularly in NW and NE quadrants, had decreased considerably. Accordingly, an adjustment was made on this advisory. 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 athttps://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 16/0900Z 42.5N 28.4W 45 KT 50 MPH 12H 16/1800Z 44.5N 24.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 17/0600Z 47.4N 18.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 17/1800Z 50.8N 10.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 18/0600Z 55.1N 3.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 19/0600Z...ABSORBED BY A FRONT $$ Forecaster Roberts
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