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Hurricane Ophelia Forecast Discussion Number 16
2017-10-13 04:50:21| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Thu Oct 12 2017 000 WTNT42 KNHC 130250 TCDAT2 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. 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 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 $$ Forecaster Blake
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