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| #906859 (Received by flhurricane at: 4:58 AM 13.Oct.2017) TCDAT2 Hurricane Ophelia Discussion Number 17 NWS National Hurricane Center Miami FL AL172017 500 AM AST Fri Oct 13 2017 Ophelia`s eye has become cloud filled during the past several hours, and an 0330 UTC GCOM microwave pass indicated that the hurricane only had about half an eyewall, with nearly all of the deep convection located over the eastern part of the circulation. However, the initial intensity remains 90 kt based on Dvorak CI numbers of 5.0 from TAFB and SAB. The initial motion estimate is a little faster toward the east-northeast, or 070/7 kt, with Ophelia embedded in the flow ahead of a large mid-latitude trough pushing east of Atlantic Canada. As this trough swings eastward over the north Atlantic, Ophelia is expected to continue accelerating and turn northeastward by day 3 and north-northeastward by day 4. There is high confidence in the track forecast for the first 48 hours while Ophelia remains a tropical cyclone. Although there is some model divergence after 48 hours once Ophelia becomes extratropical, the global models remain relatively tightly clustered through day 4, and they all agree that Ophelia will track very close to the western shores of the British Isles on days 3 and 4. As such, very little change was made to the NHC official forecast compared with the previous advisory. There is significantly more spread in Ophelia`s track by day 5, with the GFS moving Ophelia over the North Sea while the ECMWF and UKMET turn the cyclone eastward over Norway. However, NHC`s graphical product suite cannot handle forecast points east of the Prime Meridian, so the official forecast now cuts off after day 4. Vertical shear over Ophelia may decrease a bit over the next 24 hours, and the hurricane will remain over marginally warm waters for the next day or two. Hence, only slight weakening is anticipated through 48 hours, and Ophelia is forecast to remain a tropical cyclone during that period. Ophelia is then expected to merge with an approaching cold front and develop into a warm seclusion by day 3 to the southwest of Ireland, with baroclinic forcing likely helping to maintain the cyclone`s intensity for about a day. Some weakening is anticipated after day 3 while Ophelia moves near the British Isles, but strong winds are becoming increasingly likely over portions of Ireland and United Kingdom regardless of the cyclone`s exact intensity. While the NHC track continues to keep 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. KEY MESSAGES: 1. Ophelia is expected to transition to a hurricane-force post- tropical cyclone by Monday before 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 13/0900Z 31.1N 33.9W 90 KT 105 MPH 12H 13/1800Z 31.8N 32.5W 85 KT 100 MPH 24H 14/0600Z 33.1N 29.7W 85 KT 100 MPH 36H 14/1800Z 35.0N 25.5W 80 KT 90 MPH 48H 15/0600Z 37.9N 20.8W 80 KT 90 MPH 72H 16/0600Z 47.9N 13.7W 75 KT 85 MPH...POST-TROP/EXTRATROP 96H 17/0600Z 57.5N 6.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 18/0600Z...EAST OF THE PRIME MERIDIAN $$ Forecaster Berg |
