Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
233 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 next Tue/Wed. As troughing in the northern
stream swings through the Great Lakes Wednesday, it will begin to
tug the system 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 have gravitated toward a more common solution off
the west coast and near Florida with the larger players in the
forecast, but differences remain in timing/track/strength of said
features. In the west, 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. Most disagreement lied in Canada but this also
translated into differences in frontal timing from the Northeast
through the Ohio Valley (quicker GFSs, slower
ECMWF/UKMET/Canadian). Ensembles suggest somewhat of a quicker
pattern in the northern stream, so the 18Z GFS was not
unreasonable. To the south, 03Z NHC track was closest to the 18Z
GFS followed by the 12Z UKMET/ECMWF which was a good blended
starting point over the CONUS as well. 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. Split between the 18Z GFS and 12Z
ECMWF would bring Dorian (likely in extratropical transition) near
the 40N/70W benchmark by next Saturday but ensemble spread was
encompassed in a nearly 1000km by 1000km area so confidence was
low. Please consult the latest information on Dorian from the
National Hurricane Center as changes in the short term track/speed
will have large affects on the forecast for late next week.
...Sensible Weather...
Dorian will bring strong winds, heavy rain/flooding, and storm
surge to parts of Florida into the Southeast per the current
forecast but will be 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.
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