Hurricane Ophelia Discussion Number  18
NWS National Hurricane Center Miami FL       AL172017
1100 AM AST Fri Oct 13 2017

The eye of Ophelia has become a bit more apparent in visible and
infrared imagery during the past couple of hours, but the cloud tops
around the eye have also warmed recently. The initial intensity is
set to 85 kt based on a blend of the latest subjective and objective
Dvorak CI and Final-T numbers. The hurricane will remain in an
environment of marginal SSTs and light to moderate shear for the
next day or so, which suggests little change in intensity during
that time. By 36 hours, the shear will begin to increase as a
powerful upper-level trough approaches from the west, but Ophelia
should remain at hurricane force during extratropical transition as
it undergoes a favorable interaction with the aforementioned trough
and takes on a warm seclusion structure. The transition process
is expected to be complete by 72 hours, and post-tropical Ophelia
should gradually weaken as the cyclone occludes beneath the upper
trough. The low-level circulation of Ophelia is expected to
dissipate over Scandinavia by day 5.

The initial motion estimate is 060/10. The track forecast reasoning
remains unchanged from the previous advisory. Ophelia should move
east-northeastward ahead of the approaching upper-level trough with
a steady increase in forward speed through the next 24 hours. The
hurricane should turn northeastward by 48 hours followed by a
north-northeastward motion at days 3 and 4. The track model guidance
is in good agreement on this overall scenario, but there are some
differences in forward speed beyond 48 hours. The new NHC track
is similar to the previous one and lies between the latest TVCA
multi-model consensus and the HCCA corrected consensus aid through
the forecast period. On this track, the center of Ophelia is
expected to move southeast of the Azores during the next 36 hours
and then move near or over Ireland and the western part of the UK in
3 to 4 days. Given the expected increase in the size of Ophelia's
wind field during extratropical transition, impacts from strong
winds and rain are becoming increasingly likely over portions of the
British Isles regardless of the exact track of the center.

While the NHC track continues to keep the center of Ophelia south
and east of the Azores, tropical-storm-force winds are possible
throughout the Azores beginning late Saturday or Saturday night due
to an approaching cold front. Any deviation to the left of the
forecast track could bring stronger winds to the islands. Interests
in the Azores should refer to products issued by the Azores Weather
Forecast and Watch Center.

A 1242 UTC ASCAT-B pass was helpful in analyzing the 34-kt wind
radii around Ophelia.

KEY MESSAGES:

1. Ophelia is expected to become a hurricane-force post-tropical
cyclone by Monday before it moves near Ireland and the United
Kingdom. Direct impacts from wind and heavy rain in portions of
these areas are becoming more likely, along with dangerous marine
conditions. For more details on the magnitude, timing, and location
of impacts from post-tropical Ophelia, residents in Ireland should
refer to products issued by Met Eireann, and residents in the United
Kingdom should refer to products issued by the Met Office.

FORECAST POSITIONS AND MAX WINDS

INIT  13/1500Z 31.8N  32.9W   85 KT 100 MPH
12H  14/0000Z 32.6N  30.9W   85 KT 100 MPH
24H  14/1200Z 34.1N  27.3W   85 KT 100 MPH
36H  15/0000Z 36.5N  22.6W   80 KT  90 MPH
48H  15/1200Z 40.7N  17.9W   80 KT  90 MPH
72H  16/1200Z 51.0N  11.5W   70 KT  80 MPH...POST-TROP/EXTRATROP
96H  17/1200Z 60.0N   4.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  18/1200Z...DISSIPATED

$$
Forecaster Brennan