[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 150900
TCDAT2

Hurricane Ophelia Discussion Number  25
NWS National Hurricane Center Miami FL       AL172017
500 AM AST Sun Oct 15 2017

Although the satellite appearance of Ophelia has been slowly
degrading this morning, the cyclone remains an impressive hurricane
due to it being over the relatively cool waters of the northeastern
Atlantic. A testament to Ophelia's strength is a late arriving buoy
report 25 nmi southeast of the center of the eye from around 0200Z,
which indicated that the pressure in the southeastern portion of the
large eye or eyewall was 970.9 mb. However, Dvorak intensity
estimates have been steadily decreasing since that buoy report, so
the intensity has been lowered to 90 kt for this advisory.

Ophelia continues to accelerate and the hurricane is now moving
050/30 kt. Water vapor imagery indicates that a deepening trough
just to west of Ophelia is moving quickly eastward, and that the
cyclone is now well embedded within the deep-layer southwesterly
flow on the east side of the trough. As a result, Ophelia is
expected to turn toward the north-northeast by tonight and be
accompanied by a slight increase in forward speed. The NHC model
guidance remains in excellent agreement on Ophelia reaching the
southern coast of Ireland in 24-30 hours, and then move across
the remainder of the country Monday night, and then move across
Northern Ireland and northern Great Britain on Tuesday.

Ophelia is forecast to become a post-tropical cyclone by 24 hours
when extratropical transition should be completed, although the
transition to an extratropical cyclone could occur as early as 12
hours. Regardless of the exact timing, post-tropical cyclone Ophelia
is forecast to remain a powerful storm with hurricane-force winds
when it reaches Ireland on Monday.  The system is forecast to
occlude and interact with land, which should cause a faster rate of
weakening in 48 to 72 hours, with dissipation expected shortly
thereafter.

Although the center of Ophelia is not forecast to reach Ireland or
the UK until Monday, strong winds and rains will arrive well in
advance of the cyclone center. Residents in those locations should
consult products from their local meteorological service for more
information on local impacts.

KEY MESSAGES:

1. Ophelia is expected to be a powerful extratropical cyclone with
hurricane force winds Monday while it moves near Ireland and the
United Kingdom.  Direct impacts from wind and heavy rain in portions
of these areas are 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  15/0900Z 39.0N  18.3W   90 KT 105 MPH
 12H  15/1800Z 43.0N  15.1W   85 KT 100 MPH
 24H  16/0600Z 49.0N  11.5W   80 KT  90 MPH...POST-TROP/EXTRATROP
 36H  16/1800Z 54.0N   8.6W   60 KT  70 MPH...POST-TROP/EXTRATROP
 48H  17/0600Z 57.7N   4.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  18/0600Z 60.8N    .1W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  19/0600Z...DISSIPATED

$$
Forecaster Stewart
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