476
FXUS62 KRAH 260616
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
216 AM EDT Thu Sep 26 2024

.SYNOPSIS...
Tropical Cyclone Helene will move across the eastern Gulf of Mexico
today and cross the Florida Big Bend coast this evening. After
landfall, Helene is expected to turn northward across Georgia
tonight, then northwestward while slowing over the Tennessee Valley
on Friday and Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1100 PM Wednesday...

Central NC remains under S/SW flow aloft between an upper ridge of
high pressure centered near Bermuda and a closed low centered over
southern Illinois. Meanwhile Hurricane Helene is centered over the
far southern Gulf of Mexico. Regional radar imagery depicts a large
swath of showers and storms extending from the FL panhandle into GA
and the Appalachians. Despite a fairly moist air mass across central
NC this evening, with PW values in the 1.6 to 1.9 inch range and
decent 925-850 mb moisture transport, a lack of forcing is keeping
any showers and storms largely to our north and west. This will
mostly continue overnight, but as the mid/upper low drops south and
the offshore ridging nudges slightly east, weak height falls and an
area of upper divergence will begin to move in from the west. So
some isolated to widely scattered showers may get into the western
Piedmont, but the solid heavy rain axis should stay to our west. Low
stratus is expected again overnight, with northern and western areas
favored. Low temperatures will again be quite mild with all the
cloud cover and high dew points, generally upper-60s to lower-70s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 235 PM Wednesday...

On Thursday morning, Hurricane Helene should be intensifying over
the Gulf of Mexico as it moves north, likely to make landfall along
the Florida Gulf Coast Thursday evening. Scattered showers and
isolated thunderstorms will continue Thursday morning along the
leftover boundary from today, slowly expanding to the east Thursday
afternoon. Have maintained likely pops across western counties
Thursday afternoon. As Helene weakens to a tropical storm by the
time it reaches northern Georgia Friday morning, rainfall will
expand farther across the forecast area Thursday night, with the
greatest coverage and intensity of rainfall likely to occur Thursday
night and Friday morning. 12Z models indicate that rain could come
to an end a little quicker than previously forecast as the dry slot
moves in from the south - likely pops will continue north of US-64
Friday afternoon, but pops should become more scattered across the
south in the afternoon, and all locations should be dry by late
Friday night.

While there is still spread as to the exact time of Helene once it
makes landfall, the overall trend across central North Carolina has
been a reduction in rainfall totals. A general one to two inches of
rainfall is expected, with greater amounts to the west. The maximum
wind gusts remain generally unchanged, ranging from 20-25 mph across
the east to 30-35 mph in the west. There have been some locations
that have received as much as five inches of rain in the last three
days. Considering how wet the ground is in some locations, despite
wind gusts that are expected to remain below tropical storm status,
there is the potential for many more trees to come down than would
be expected for the given wind speeds. The preceding rainfall will
also increase the risk for flash flooding and river flooding,
although there is not enough confidence in higher rainfall rates to
issue a flood watch. There will also be a risk for tornadoes on
Friday with ample moisture and instability for thunderstorms. This
threat will be evaluated more closely tonight and Thursday once
additional high-resolution model guidance is available.

High temperatures will range from the mid 70s in the northwest to
the mid 80s in the southeast. Low temperatures will range from the
upper 60s to the mid 70s Thursday night, then be in the mid to upper
60s Friday night as clouds clear out Friday night.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 244 PM Wednesday...

The mid-upper low/trough expected to pull Hurricane Helene northward
will linger over the TN Valley Saturday before slowly oozing
northeast through the Mid-Atlantic through early next week.

Saturday: The remnants of Helene will likely have moved over TN by
Saturday morning. The anomalous moisture associated with this system
will have congealed well to the north and west of central NC,
promoting a primarily dry day on Saturday. By Saturday evening,
however, some models suggest some of that anomalous moisture may
trickle back into our northwest Piedmont. As such, maintained a low-
end slight chance for showers Saturday afternoon and evening.
Otherwise, daytime highs in the lower to mid 80s is expected.

Sunday through Wednesday: As the mid-upper low slowly migrates
across the mid-Atlantic through early next week, additional daily
showers and thunderstorms will be possible.  Will maintain low
slight to chance PoPs each day for now, with highest chances across
the north where better moisture will pool and upper forcing for
ascent appears strongest.  There does seem to be good consensus that
the upper trough will shift offshore through Wednesday, behind which
nwly flow aloft will usher in drier air by mid-week (mean ensembles
suggest <1 inch PWAT may encompass our area by Thursday morning).

Temperature wise, we`ll generally see upper 70s to lower 80s through
Wednesday.  There is a signal for a potential cool down Wednesday
night into Thursday, but confidence is low at this point.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
As of 215 AM Thursday...

Moist sely flow into a front over the wrn Carolinas and VA will
favor a gradual development and expansion of mainly MVFR-IFR
ceilings from the front ewd and across the NC Piedmont this morning,
and also a chance of showers throughout cntl NC through tonight. In
addition to the showers, a shield of stratiform rain will precede
Hurricane Helene and overspread cntl NC later today-tonight. Sely
surface winds may occasionally gust into the teens kts with diurnal
heating/mixing today, then further increase with the approach of
Helene tonight.

Outlook: Periodic rain bands will bring occasionally sub-VFR
conditions in moderate to heavy rain with isolated storms, along
with frequent gusts over 20 kts late tonight-Fri morning. Low level
wind shear may also occur esp at FAY/INT/GSO early Fri morning, but
confidence is low. Conditions will improve to VFR from S to N Fri,
lasting through Sat. A chance of showers/storms will return esp to
the NW Sun into Mon.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...MWS
NEAR TERM...Danco
SHORT TERM...Green
LONG TERM...Luchetti
AVIATION...MWS/Hartfield