Extended Forecast Discussion NWS Weather Prediction Center College Park MD 132 AM EDT Sat Sep 08 2018 Valid 12Z Tue Sep 11 2018 - 12Z Sat Sep 15 2018 ...Florence likely to impact a portion of the East Coast next week... ...Pattern Overview... Strong upper ridging over the northern Pacific and the northwestern Atlantic off the New England coast will favor the maintenance of a positively tilted trough along the west coast of the lower 48. Current tropical storm Florence is forecast to strengthen to a major hurricane between the Bahamas and the Outer Banks next week and is likely to impact at least part of the Southeast/Mid-Atlantic starting as early as late Wednesday but perhaps still into next weekend. Please consult the National Hurricane Center for the latest information. ...Guidance/Predictability Assessment... Overall, the amplified pattern remains well-handled by the ensemble guidance but with uncertainty atop the ridge in the Pacific that translates toward the Pacific Northwest. To the east, the strength and shape of the blocking upper high will dictate where Florence will track, but the slowly narrowing ensemble consensus appears to take the system into the Southeastern US but the range of possibilities still extends from Florida northward to at least the Mid-Atlantic which includes a chance of recurving just offshore. With broad WSW flow from mid-continent to the Atlantic, the typical acceleration of a transitioning tropical system may be delayed as the longwave pattern remains rather stuck. A blend of the deterministic models sufficed for the early portion of the period but then transitioned to an 18Z GFS/12Z ECMWF/18Z GEFS blend to account for the coordinated preference in the east but also to dampen the perhaps overzealous ECMWF off the Pac NW with subsequent/reinforcing troughing Thu/Fri. ...Weather Highlights/Hazards... Biggest impacts will be in the east with the forecast taken verbatim. Heavy rain, damaging winds, coastal flooding, storm surge, etc. are real possibilities for coastal and then inland locations. The heavy rain threat will continue inland with a continued tropical fetch on the system's east side. A track inland without a defined acceleration into the westerlies has the potential for a large area of 5-10"+ inches of rain over a few days. Many factors will determine location/amounts/timing but that won't be resolved for a few more days at the least. A second area of rain will exist over the northern and northwestern Gulf Coast under a weakness aloft. With plenty of moisture to work with, several inches of rain are possible over the period. Temperatures will generally be cooler than average in the Northwest under the trough but near to above average elsewhere (especially for minimum temperatures which may be near record warm values in the east). Fracasso WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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