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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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