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#906806 (Received by flhurricane at: 4:46 PM 12.Oct.2017)

Hurricane Ophelia Discussion Number 15
NWS National Hurricane Center Miami FL AL172017
500 PM AST Thu Oct 12 2017

Ophelia`s structure has continued to improve during the afternoon.
The eye of the hurricane has cleared and is surrounded by a ring of
cloud tops colder than -55 deg C. Dvorak classifications from TAFB
and the UW-CIMSS ADT have increased accordingly, and on that basis
the initial intensity has been increased to 85 kt. Ophelia is
nearly stationary, which could cause the hurricane to stop
strengthening, or even weaken slightly during the next 12 to 24
hours due to upwelling effects. That said, the intensity guidance
is in good agreement that Ophelia will remain at hurricane strength
for the next 48 h while it remains in a fairly unstable, low-shear
environment. Beyond that time, extratropical transition will begin,
though baroclinic forcing will likely keep post-tropical Ophelia
near hurricane strength as it approaches Ireland and the UK. The
new intensity forecast is very similar to the previous advisory, and
is generally close to the multi-model intensity consensus.

Although Ophelia is currently stationary, a mid-latitude trough
should cause it to begin moving toward the east-northeast within
about 24 hours. The cyclone will then accelerate on that heading in
the faster mid-latitude westerly flow ahead of the trough, before
turning toward the northeast around day 3 as extratropical
transition occurs and the hurricane becomes entangled with the
southern extent of the trough. Confidence in the track forecast is
fairly high for the first 72 h, and all of the dynamical guidance is
tightly clustered through this period. The model spread increases
substantially at 96 h and beyond. As a post-tropical cyclone,
Ophelia will continue to interact with the southern extent of the
trough, and should turn toward the northeast as a result of this
interaction. However, the details of this turn vary greatly from
model to model. The new NHC forecast has been nudged slightly
toward the east at this time range, closer to the UKMET and ECMWF
models, as well as the corrected consensus aids HCCA and FSSE.

While the track guidance keeps the center of Ophelia south and east
of the Azores, tropical-storm-force winds are possible throughout
the Azores by Sunday due to an approaching front. In addition, the
wind field of Ophelia will likely expand as the cyclone begins
extratropical transition, and 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.


1. Ophelia is expected to transition to a hurricane-force post-
tropical cyclone by Monday when it moves near Ireland and the
United Kingdom. While post-tropical Ophelia will likely bring some
direct impacts from wind and heavy rain to portions of these areas,
as well as dangerous marine conditions, given the forecast
uncertainty at these time ranges it is too soon to determine the
exact magnitude, timing and location of the impacts. Residents in
Ireland and the United Kingdom should monitor the progress of
Ophelia for the next several days. For more information on local
impacts, residents of Ireland should refer to products issued by Met
Eireann and residents in the United Kingdom should refer to products
issued by the Met Office.


INIT 12/2100Z 30.4N 35.5W 85 KT 100 MPH
12H 13/0600Z 31.0N 34.6W 85 KT 100 MPH
24H 13/1800Z 31.9N 32.6W 80 KT 90 MPH
36H 14/0600Z 33.2N 29.6W 75 KT 85 MPH
48H 14/1800Z 35.0N 25.6W 75 KT 85 MPH
72H 15/1800Z 42.6N 17.1W 75 KT 85 MPH
96H 16/1800Z 53.0N 10.0W 65 KT 75 MPH...POST-TROP/EXTRATROP
120H 17/1800Z 62.5N 2.0W 55 KT 65 MPH...POST-TROP/EXTRATROP

Forecaster Zelinsky