Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1148 AM EDT Sat Aug 31 2019 Valid 12Z Tue Sep 03 2019 - 12Z Sat Sep 07 2019 ...Hurricane Dorian forecast to affect Florida and parts of the Southeast U.S. next week... ...Overview... Upper ridging over the Four Corners/Southern Plains and western Atlantic will help to funnel Hurricane Dorian northward near/along the Florida coast Tues-Wed. As troughing in the northern stream swings through the Great Lakes Wednesday, it will begin to tug Dorian northeastward near/along the Carolina coast as additional height falls push through Ontario Friday. Troughing off the west coast will slowly ease inland and be replenished upstream. ...Guidance Evaluation and Preferences... Models/ensembles continue to gravitate towards a more common solution off the west coast and near Florida with the larger players in the forecast, with some differences remaining with regards to timing/track/strength. In the Midwest, consensus agrees on a sub-1000mb low in northern Minnesota Tue lifting into Canada and dragging its cold front eastward/southeastward into the southern Appalachians late Wed/early Thu. Models show better agreement with shortwave energy farther north than in previous runs, which translates to a more agreeable frontal position through the Northeast and Ohio Valley. With Dorian, models are trending faster as Dorian gets pulled north-northeastward along the Florida/Southeast coasts. The 06Z GFS and 00Z CMC are by far the fastest, followed by the 00Z GFS and the 00Z UKMET/ECMWF. The 15Z NHC track was closest to a blend of the 00z GFS/ECMWF/UKMET, but a slightly faster solution is not unreasonable given the trend. By next Fri/Sat, enough height falls should dig south toward Dorian (assuming it will be that far north) to start to tug it northeastward as the surface front lies astride the cyclone. A split between the 00Z GFS and 00Z ECMWF would bring Dorian (likely in extratropical transition) a couple hundred miles off the New England coast by next Saturday but ensemble spread remains broad so confidence is low. Please consult the forecasts from the National Hurricane Center for the latest information on Dorian as changes in the short term track/speed will have large affects on the forecast for late next week. The WPC blend for this cycle of the progs used a blend of the 00Z GFS/ECMWF/UKMET plus WPC continuity (which was good for both Dorian and the rest of the CONUS), with some contributions from the ECENS/GEFS means after Day 5 to help with timing differences of the second trough approaching the West Coast late next week. ...Sensible Weather... Dorian will bring strong winds, heavy rain/flooding, and storm surge to parts of Florida and into the Southeast per the current forecast but will be closely tied to its proximity to the coast. Northern Plains into the Great Lakes and Northeast will see cooler temperatures (10-15F below average) Tue-Thu behind a cold front that will sink toward the Southeast. Should Dorian lift northeastward as expected later next week, the heavy rain threat would follow through coastal NC as the system moves offshore. Quite uncertain of any effects on New England later next week. Away from Dorian, rainfall coverage should be fairly limited over the lower 48, with the exception being along/ahead of the northern tier cold front and in the Pacific Northwest as the upper trough moves into WA/OR. The Southwest/Four Corners states may see isolated to scattered rain but with generally light amounts. Santorelli/Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml