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Chill falls over the Atlantic as the official season heads towards close
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| #906806 (Received by flhurricane at: 4:46 PM 12.Oct.2017) 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 $$ Forecaster Zelinsky |
