096
FXUS02 KWBC 240638
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
238 AM EDT Tue Sep 24 2024

Valid 12Z Fri Sep 27 2024 - 12Z Tue Oct 01 2024

...Potential Tropical Cyclone Nine to bring impactful heavy rain,
high wind, and coastal flooding threat to the Central to Eastern
Gulf Coast/Southeast ahead/with landfall as Hurricane Thursday...


...Guidance/Predictability Assessment...

The main forecast story remains the threat and impacts associated
with impending Potential Tropical Tropical Cyclone Nine. All eyes
will be on the pattern over the eastern U.S. ino later this week.
Recent guidance has come into better agreement in depicting a
split flow pattern with an upper-trough lifting northward over the
Northeast as a cut-off upper-low drops southward over the Middle
Mississippi Valley/Ozarks Region/ArkLaTex. This upper-low then
lingers in the general vicinity into the weekend as upper-ridging
moves in to the north over the Great Lakes/southeastern Canada. At
the same time, the official National Hurricane Center (NHC)
forecast track for Potential Cyclone Nine brings the system
northward across the Florida Panhandle Region as a Hurricane and
into the Southeast on Thursday. The GFS/ECMWF and the UKMET have
trended over the past few runs to consistently depict Potential
Tropical Cyclone Nine remaining a separate entity for a longer
period of time after moving inland, moving northward into the
Appalachians/Upper Ohio Valley through the day Friday. The system
is then eventually absorbed into the upper-low by early Saturday
over the Middle Mississippi Valley. The CMC remains an outlier with
the upper-low absorbing the system faster. Specifics on the exact
track of the system, the upper-low to the west, and the timing in
which the energy is absorbed will be important to the overall QPF
footprint, which will likely stretch from the Southeast, robustly
north into favored terrain of the southern/central Appalachians
and back westward through the Ohio Valley into the Ozarks Region.

The position/strength of the upper-low not surprisingly becomes
less defined by the latter part of the period late this
weekend/early next week. Differences increase with the overall
pattern elsewhere by the end of the period as well with the very
uncertain potential for more amplified northern-stream shortwave
energy over the northern Rockies/High Plains suggested by the
deterministic guidance, particularly recent GFS runs. However, the
00 UTC GFS has strongly trended toward the rest of guidance. The
WPC forecast includes a blend of the GFS/ECMWF/UKMET for Friday and
Saturday given good overall agreement with respect to the track of
Potential Tropical Cyclone Nine and the handling of the cutoff low
to the west. Swictched to the GEFS/ECENS means for the latter part
of the period as uncertainty the overall pattern grows.

...Weather/Hazards Highlights...

The NHC and the Weather Prediction Center among others continue to
monitor Potential Tropical Cyclone Nine. The official NHC track
brings the system northward into the Gulf of Mexico to threaten
maritime interests and the central to eastern Gulf Coast/Southeast
mid-late week, with the system set to move inland Thursday.
Confidence is growing in a large system that will bring significant
rainfall/winds/surf/coastal flooding for the central to eastern
Gulf Coast/Florida, with impactful weather possible through the
Southeast, and wrapping back into the Mid-South late week into the
weekend. The Day 4/Friday ERO period features Nine proximity and
moisture feed into the southern Appalachians as well as over the
Ozark Region under the influence of the slow moving closed-low,
with both regions covered with Slight Risks Outlook threat areas. A
similar area depicted for the Day 5/Saturday ERO shows a scaling
down ERO version as Nine weakens and dissipates. However, ample
lingering deep tropical moisture will remain to fuel the elongated
Marginal threat area. More certain local focus closer to occurance
would likely lead to Slight Risk issuance upgrades, especially
given earlier period heavy rainfall will create saturated soils.

Elsewhere, the Washington coastal ranges and Cascades will be an
exception with enhanced rain late week with Pacific system
passages, with some additional modest potential downstream later
into the northern Rockies. Warmer than average temperatures are
expected to translate from the Northern Plains east into the
Midwest later this week into the weekend following upper-level
ridging, with anomalies decreasing by early next week. Cooler than
average temperatures are expected centered around the Ozarks Region
under the influence of the upper- low aloft, also returning closer
to average by early next week as the upper-low dissipates.

Schichtel


Additional 3-7 Day Hazard information can be found on the WPC medium
range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw
























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