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