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Hurricane OPHELIA


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Hurricane Ophelia Discussion Number  19
NWS National Hurricane Center Miami FL       AL172017
500 PM AST Fri Oct 13 2017

Ophelia's eye has become better defined over the past 6 hours.
Although cloud tops near the inner core of the hurricane are warmer
than 24 hours ago, a ring of -50 deg C or colder cloud tops still
surrounds the eye.  Dvorak current intensity estimates have not
changed substantially, and a blend of objective and subjective
classifications still supports an initial intensity of 85 kt.

Little change in strength is expected while Ophelia remains a
hurricane, since the relatively cool SSTs along the hurricane's path
will likely be offset by low shear and cold upper-level temperatures
for the next 36 h.  Extratropical transition will likely begin
shortly after that time, as Ophelia begins to interact with a large
upper-level trough approaching from the west.  The dynamical
guidance suggests that Ophelia will deepen in response to the
trough, and although the forecast does not explicitly show it, I can
not rule out that Ophelia will briefly intensify as it undergoes
extratropical transition.  By 72 hours, the cyclone is expected to
occlude and begin weakening, though the expansion of the wind field
will result in impacts over portions of the British Isles,
regardless of its exact location or strength.  By 96 hours,
continued weakening and interaction with land will likely cause the
surface circulation to become ill-defined, and dissipation is
expected shortly thereafter.

Ophelia is beginning to accelerate toward the east-northeast and the
initial motion estimate is 060/11 kt.  Very little change has been
made to the official track forecast.  Ophelia is still expected to
continue picking up speed on an east-northeast heading while passing
south of the Azores during the next 24 to 36 hours.  By 48 hours,
interaction with the aforementioned upper-level trough will cause
Ophelia to turn toward the northeast and approach Ireland and the
western UK in about 72 h.  The track guidance is tightly clustered,
especially through 72 h, and the new NHC track forecast is close to
the various multi-model consensus aids.  Although the center of
Ophelia is not expected to reach Ireland or the UK until about day
3, wind and rain effects will arrive well in advance of the cyclone
center.  Individuals in those locations should consult products from
their local meteorological service for more information on local
impacts.

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 Ophelia's 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.

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 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  13/2100Z 32.3N  31.8W   85 KT 100 MPH
 12H  14/0600Z 33.4N  29.5W   80 KT  90 MPH
 24H  14/1800Z 35.2N  25.4W   80 KT  90 MPH
 36H  15/0600Z 38.2N  20.3W   80 KT  90 MPH
 48H  15/1800Z 43.1N  16.0W   80 KT  90 MPH
 72H  16/1800Z 53.2N  10.4W   65 KT  75 MPH...POST-TROP/EXTRATROP
 96H  17/1800Z 60.5N   2.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  18/1800Z...DISSIPATED

$$
Forecaster Zelinsky

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