Post Tropical Storm Helene 17/18 Sep 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