825 
WTNT42 KNHC 122037 
TCDAT2 
 
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. 
 
KEY MESSAGES: 
 
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 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