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| #906940 (Received by flhurricane at: 10:37 PM 13.Oct.2017) TCDAT2 Hurricane Ophelia Discussion Number 20 NWS National Hurricane Center Miami FL AL172017 1100 PM AST Fri Oct 13 2017 The eye of Hurricane Ophelia continues to be remarkably distinct on satellite and remains surrounded by a ring of deep convection. An average of objective and subjective Dvorak numbers still support an initial intensity of 85 kt. The hurricane has managed to move through an area of relatively low shear and maintain its intensity so far. This is about to change in a day or so when a cold front reaches the circulation of the hurricane and the shear increases substantially. By then, any increase in intensity should be triggered by baroclinic forces as the cyclone becomes extratropical. The NHC forecast calls for Ophelia to become extratropical in about 48 hours and dissipate or absorbed by another large low beyond 4 days. Given that the cyclone is forecast to become extratropical, the wind field should expand, resulting in impacts over portions of the British Isles regardless of its exact location or strength. By 96 hours, Ophelia should have weakened due to the interaction with land, causing the surface circulation to become ill-defined, and dissipation is expected shortly thereafter. Now that the cyclone is well embedded in the mid-latitude westerlies, it is moving faster toward the east-northeast or 060 degrees at 17 kt. An additional increase in forward speed is anticipated as a large high-latitude trough accelerates the westerly flow. Track models are in very good agreement and this increases the confidence in the NHC forecast which is in the middle of the tight guidance envelope. Although the center of Ophelia is not expected to reach Ireland or the UK for another 2-3 days, wind and rain effects will arrive well in advance of the cyclone center. Individuals in those locations should consult products from their local meteorological service for more information on local impacts. Tropical-storm-force winds are possible throughout the Azores beginning Saturday night primarily due to an approaching cold front. However, any track deviation to the left could bring stronger winds associated with Ophelia`s circulation 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 become a hurricane-force post-tropical cyclone by Monday before it moves near Ireland and the United Kingdom. Direct impacts from wind and heavy rain in portions of these areas are likely, along with dangerous marine conditions. For more details on the magnitude, timing, and location of impacts from post-tropical Ophelia, residents in 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 14/0300Z 33.0N 30.6W 85 KT 100 MPH 12H 14/1200Z 34.3N 27.9W 80 KT 90 MPH 24H 15/0000Z 36.5N 23.2W 80 KT 90 MPH 36H 15/1200Z 40.3N 17.7W 75 KT 85 MPH 48H 16/0000Z 46.0N 14.0W 75 KT 85 MPH...POST-TROP/EXTRATROP 72H 17/0000Z 56.0N 7.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 18/0000Z 62.0N 1.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 19/0000Z...DISSIPATED $$ Forecaster Avila |
