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Hurricane Ophelia Discussion Number 16
NWS National Hurricane Center Miami FL AL172017
1100 PM AST Thu Oct 12 2017
Remarkably, the hurricane has continued to strengthen this evening.
Satellite images indicate that cloud tops in the eyewall have cooled
in the past several hours, with a warm eye remaining. Dvorak
estimates from TAFB, SAB and CIMSS range between 90 to 95 kt, so the
initial intensity is raised to 90 kt.
It seems that the marginal SSTs that Ophelia has been moving over
have been offset by the cold upper-level temperatures and low shear
environment. SSTs only slightly cool in the next 24 hours with
similar shear conditions, so a minor decrease in strength is in the
forecast. After that time, while the hurricane should move over
colder waters, it will likely be accelerating to the northeast and
experiencing favorable mid-latitude jet dynamics, which will help to
maintain the cyclone's intensity. All of the guidance show
extratropical transition by 3 days with the cyclone keeping
hurricane-force winds, as indicated in the new forecast. Little
change was made to the previous prediction, except to account for
the higher initial wind speed.
Ophelia is finally moving, estimated at 6 kt to the east-northeast.
This general motion with an increase in forward speed is expected
for the next couple of days as the hurricane gets picked up by a
large mid-latitude trough. Confidence in the track forecast remains
fairly high for the first 72 h, although the spread increases after
that time. The GFS-based guidance generally then show a more
northward track to the west of Ireland then over the far North
Atlantic, while the UKMET/ECMWF show a track over Ireland and Great
Britain then eastward and dissipating over northern Europe.
The forecast is close to the consensus at long range, but some large
changes could be required for later forecasts.
While the NHC track keeps the center of Ophelia south and east
of the Azores, tropical-storm-force winds are possible throughout
the Azores by Saturday night 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.
FORECAST POSITIONS AND MAX WINDS
INIT 13/0300Z 30.7N 34.7W 90 KT 105 MPH
12H 13/1200Z 31.2N 33.5W 90 KT 105 MPH
24H 14/0000Z 32.2N 31.1W 85 KT 100 MPH
36H 14/1200Z 33.7N 27.5W 80 KT 90 MPH
48H 15/0000Z 36.0N 23.0W 80 KT 90 MPH
72H 16/0000Z 45.0N 14.5W 75 KT 85 MPH...POST-TROP/EXTRATROP
96H 17/0000Z 56.0N 7.0W 55 KT 65 MPH...POST-TROP/EXTRATROP
120H 18/0000Z 64.0N 0.5W 50 KT 60 MPH...POST-TROP/EXTRATROP