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Tropical Storm Helene Forecast Discussion Number 29
2018-09-14 16:41:56| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Fri Sep 14 2018 774 WTNT43 KNHC 141441 TCDAT3 Tropical Storm Helene Discussion Number 29 NWS National Hurricane Center Miami FL AL082018 1100 AM AST Fri Sep 14 2018 Conventional satellite imagery and a 1147 UTC METOP-B AMSU microwave image show a deep convective curved band wrapping around the surface circulation in the west semicircle. Additionally, a recent 1148 UTC ASCAT-B scatterometer pass indicates that Helene is a little stronger than earlier estimated. The data showed a number of 60 kt winds in the northeast quadrant. Based on these data, Helene is still classified as a tropical cyclone, and the initial intensity is bumped up to 60 kt for this advisory. The large-scale models and the statistical intensity guidance indicate little change in strength during the next 36 hours or so. After that time, some gradual weakening is forecast as Helene completes extratropical transition while passing just to the north of the Azores Islands. The ECMWF, UKMET, and the CMC all show Helene absorbed by a larger baroclinic system just beyond the 72 hour period, as the cyclone moves over Ireland and the United Kingdom. The initial motion is estimated to be northward, or 010/20 kt, within the deep-layer southerly flow produced by a mid-tropospheric trough to the west. A north-northeast to northeast turn is expected over the weekend as the cyclone quickly moves within the mid-latitude westerlies. Only a slight adjustment to the left of the previous track forecast was made through 48 hours. The NHC official forecast is based primarily on the TVCN multi-model consensus. An orange wind warning is in effect 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 14/1500Z 32.9N 36.3W 60 KT 70 MPH 12H 15/0000Z 35.5N 35.5W 60 KT 70 MPH 24H 15/1200Z 38.4N 33.4W 55 KT 65 MPH 36H 16/0000Z 40.7N 30.0W 50 KT 60 MPH 48H 16/1200Z 42.7N 25.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 17/1200Z 47.4N 16.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 18/1200Z...ABSORBED BY FRONT $$ Forecaster Roberts
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