Hurricane Ophelia

000
WTNT42 KNHC 150240
TCDAT2

Hurricane Ophelia Discussion Number  24
NWS National Hurricane Center Miami FL       AL172017
1100 PM AST Sat Oct 14 2017

Ophelia remains an impressive hurricane in infrared satellite
imagery.  The hurricane continues to exhibit a large well-defined
eye within a ring of cold cloud tops.  However, the overall cloud
pattern has started to elongate and there has been a slight erosion
of the area of cloud tops over the west and southwest portions of
the circulation as dry air and a frontal boundary encroaches on the
hurricane.  Satellite intensity estimates from all agencies
continue to support an intensity of 100 kt.  The aforementioned
changes in the cloud pattern and an expansion of the wind field as
noted by an earlier ASCAT overpass suggest that extratropical
transition has begun.  The wind field is expect to significantly
expand over the next 12 to 24 hours, which is likely to lead to a
gradual decrease in the maximum winds.  Ophelia is forecast to
complete extratropical transition within 24 hours, but it is
expected to remain a powerful post-tropical cyclone with
hurricane-force winds as it approaches 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.

Ophelia is moving northeastward, or 055/24 kt ahead of a
mid-latitude trough moving over the northeastern Atlantic.  The
hurricane should continue to accelerate northeastward tonight, then
turn north-northeastward with an additional increase in forward
speed by late Sunday and Sunday night.  After the system occludes in
a couple of days, it should begin to slow down. The track guidance
is in good agreement, and the updated NHC track forecast is very
close to the previous advisory.

Although the center of Ophelia is not forecast to reach Ireland or
the UK until Monday, wind 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.

Tropical-storm-force winds are possible throughout the Azores
tonight behind a cold front that has moved through the islands in
the wake of Ophelia. 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  15/0300Z 37.3N  21.5W  100 KT 115 MPH
 12H  15/1200Z 40.1N  17.7W   90 KT 105 MPH
 24H  16/0000Z 45.7N  13.8W   80 KT  90 MPH...POST-TROP/EXTRATROP
 36H  16/1200Z 51.4N  10.6W   70 KT  80 MPH...POST-TROP/EXTRATROP
 48H  17/0000Z 56.0N   7.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  18/0000Z 60.0N   2.0W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  19/0000Z...DISSIPATED

$$
Forecaster Brown

Hurricane Ophelia Discussion Number  27
NWS National Hurricane Center Miami FL       AL172017
500 PM AST Sun Oct 15 2017

Ophelia's cloud structure is declining rapidly, and microwave and
shortwave IR imagery indicate that the low-level and mid-level
centers are becoming separated.  However, some deep convection is
still present near Ophelia's center, and an SSMIS pass from 1827 UTC
indicated that the hurricane still has an inner core that is
separated from a front to the north and west.  The estimated maximum
winds have been decreased slightly to 75 kt given the overall decay
of the cloud structure.  However, the cyclone's favorable position
relative to an upper-level jet streak is likely contributing to
deepening of the low as the wind field expands substantially.  Only
a slight decrease in the maximum winds is therefore expected before
the post-tropical cyclone reaches Ireland.  After that time,
interaction with land while the cyclone occludes should cause it to
weaken more rapidly.  Around 48 h, the cyclone's circulation is
likely to become ill-defined and dissipate near the western coast of
Scandinavia.

Ophelia has continued to move toward the north-northeast, and the
initial motion estimate remains 025/33 kt.  There has been no change
to the track forecast reasoning since Ophelia is already embedded
within the flow associated with a large mid-latitude trough.  This
should keep Ophelia on a north-northeast heading as it passes over
Ireland and the UK on Monday.  The dynamical guidance remains in
very good agreement on the track of Ophelia, and very little change
has been made to the track forecast.

Since Ophelia will be post-tropical as it approaches Ireland and the
UK, strong winds and rain will arrive over land areas sooner than
the center. For more information on local impacts, consult products
from local meteorological services in Ireland and the United Kingdom
for more information.

KEY MESSAGES:

1. Ophelia is expected to be a powerful extratropical cyclone with
hurricane force winds 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.

2. Individuals are urged to not focus on the exact track of Ophelia
since strong winds and heavy rainfall will extend well outside of
the NHC forecast cone.


FORECAST POSITIONS AND MAX WINDS

INIT  15/2100Z 44.6N  13.3W   75 KT  85 MPH
 12H  16/0600Z 49.2N  11.3W   70 KT  80 MPH...POST-TROP/EXTRATROP
 24H  16/1800Z 54.3N   7.5W   55 KT  65 MPH...POST-TROP/EXTRATROP
 36H  17/0600Z 58.5N   2.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
 48H  17/1800Z...DISSIPATED