[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 141438
TCDAT2

Hurricane Ophelia Discussion Number  22
NWS National Hurricane Center Miami FL       AL172017
1100 AM AST Sat Oct 14 2017

During the past few hours, Ophelia's satellite presentation has
improved significantly. The eye has become even more distinct
with a temperature of 16 deg C, and has been surrounded by very
deep convection. T-numbers from TAFB and SAB have reached 5.5 on the
Dvorak scale, and the objective numbers from CIMMS have been
oscillating around T5.8 and T5.9 recently. Based on these estimates,
the initial intensity has been increased conservatively to 100 kt,
making Ophelia a category 3 hurricane on the SSHS.  Ophelia is a
quite intense and rare hurricane for its location in the
northeastern Atlantic. Increasing shear and cold waters will
soon begin to impact Ophelia, and the hurricane should begin to
acquire extratropical characteristics in about 36 hours or sooner.
Although some weakening is anticipated, Ophelia is expected to reach
the British Isles as a powerful extratropical cyclone with hurricane
force winds. Dissipation is forecast in about 4 days after the
system moved over these Isles.

Satellite fixes indicate that Ophelia is moving toward the northeast
or 055 degrees at 22 kt. The hurricane is well embedded within the
southwesterly flow associated with the southern extension of a large
mid-latitude trough, and this pattern should continue to steer the
cyclone northeastward and north-northeastward with increasing
forward speed for the next 2 to 3 days until dissipation. Track
models are in excellent agreement and the guidance envelope is quite
tight. The NHC forecast is not different from previous ones, and it
is very close to the HFIP corrected consensus HCCA and the
multi-model ensemble TVCX.

Given that Ophelia is forecast to become extratropical, the wind
field should expand, resulting in impacts over portions of the
British Isles regardless of its exact location or strength.

Although the center of Ophelia is not forecast to reach Ireland or
the UK for another couple of days, wind and rains 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
after Ophelia passes to the south and east later today and tonight
as a cold front moves through 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 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  14/1500Z 34.8N  26.6W  100 KT 115 MPH
 12H  15/0000Z 36.5N  23.0W   95 KT 110 MPH
 24H  15/1200Z 40.5N  18.0W   90 KT 105 MPH
 36H  16/0000Z 46.5N  14.0W   85 KT 100 MPH...POST-TROP/EXTRATROP
 48H  16/1200Z 51.5N  11.0W   75 KT  85 MPH...POST-TROP/EXTRATROP
 72H  17/1200Z 59.0N   6.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 96H  18/1200Z...DISSIPATED

$$
Forecaster Avila
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