705
FXUS02 KWNH 220738
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
337 AM EDT Sun Sep 22 2024

Valid 12Z Wed Sep 25 2024 - 12Z Sun Sep 29 2024

...Tropical System Development threat from the Caribbean may
impact the Gulf of Mexico and Central to Eastern Gulf
Coast/Southeast by late week...


...Guidance/Predictability Assessment...

It remains the case that there is quite alot of uncertainty
surrounding the upper level pattern over the CONUS mid to late
week. While unresolved, this also has huge implications for the
eventual track of a possible tropical system through the Gulf of
Mexico. This may help to pull any sort of tropical development in
the Gulf northward a little faster than previous thoughts and
latest guidance from NHC reflected this. Very little confidence in
any of the specifics associated with the overall medium range flow
pattern over the CONUS and, of course, Gulf of Mexico tropical
activity as models continue to flip-flop. There also remains
uncertainty late week as a cut off low tries to form over or off
the Northeast Coast, and timing inconsistencies Pacific energies
move into and onward from the West/Northwest.

The WPC medium range product suite was mainly derived from a
blend of the 18 UTC GEFS mean, 12 UTC ECMWF ensemble mean and
especially the 12 UTC ECMWF for much of this forecast period.
These solutions were reasonably clustered/compatible, and also
importantly best fit latest NHC guidance on a possible formation
and northward track of a tropical system into the Gulf of Mexico
late week. However, recent model runs continue to suffer from much
less than normal cycle to cycle continuity, both with interacting
flow evolution over the lower 48 and with any tropical development.

...Weather/Hazards Highlights...

Upper trough energy exiting the Great Lakes/Ohio Valley midweek
may be further enhanced by uncertain reinforcing energy into later
week over the Northeast. Wavy frontal systems will also focus
deepening moisture to fuel a threat of showers/thunderstorms with
runoff issues given slowed motion and possible closed low. WPC
Excessive Rainfall Outlook (ERO) Marginal Risk areas shift from the
Mid-Atlantic through New England Day4/Wednesday and Day/5 Thursday.

Meanwhile, NHC and WPC will continue to monitor possible tropical
development in the Caribbean over the next few days that may lift
into the Gulf of Mexico to threaten maritime interests and the
central to eastern Gulf Coast/Southeast mid-late week. Given
planned development, ultimate timing and track remains quite
uncertain in guidance. Even so, the vast bulk of recent guidance
offers a growing signal for impactful weather, including a threat
for heavy rainfall/winds/surf for the central to eastern Gulf
Coast, with impactful weather possible through the Southeast/East
late week/weekend. The WPC Day 5/Thursday ERO introduced Marginal
and Slight Risk area given NHC and incorporating latest 00 UTC
model trends that support widespread heavy rainfall development.

Out West, most areas should stay dry. The Washington coastal
ranges/Cascades will be an exception with growing daily enhanced
rain potential with Pacific system energy and moisture approaches.

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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