292
FXUS62 KRAH 261908
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
305 PM EDT Thu Sep 26 2024

.SYNOPSIS...
Hurricane Helene will move across the eastern Gulf of Mexico this
afternoon and cross the Florida Big Bend coast tonight. 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 /TONIGHT THROUGH FRIDAY/...
As of 305 PM Thursday...

Overview: Hurricane Helene`s track has changed little, and is still
forecast to make landfall in the Big Bend region of Florida this
evening as a major hurricane. Helene should weaken to a tropical
storm by Friday morning as it approaches the Atlanta metro area,
then become nearly stationary over central Tennessee as it weakens.
Rainfall this afternoon is still primarily due to a boundary that
has been persistent over the Appalachian Mountains over the last two
days. The bulk of this afternoon and this evening`s rainfall will be
from the Triangle west, but it appears that by midnight, most of the
forecast area should actually be dry, with all of the rain to the
west and south of the area. Rainfall will then quickly ramp up late
tonight into Friday morning, which is when the heaviest rainfall
rates are expected in addition to the greatest severe weather threat
due to a band of moderate to heavy rainfall associated with Helene.
Despite limited instability considering the time of day, strong wind
shear will bring an increased risk for tornadoes late tonight, but
more likely Friday morning. The high-resolution model guidance
continues the trend of moving the primary band of rain out of the
region slightly more quickly, and it appears that the bulk of the
rain should move north into Virginia by early Friday afternoon. An
isolated shower or thunderstorm could persist through the afternoon
hours along the VA/NC border. Overnight lows should be near 70, with
daytime highs ranging from the upper 70s across the north to the mid
80s in the southeast. A separate hydrology section is below.

Wind impacts: As Helene undergoes its extratropical transition, wind
gusts should increase across much of central NC late tonight through
Friday. The strongest winds with Helene will be near the center of
the circulation itself, but there should also be a core of stronger
winds associated with the band of precip that moves through the area
Friday morning/afternoon. 12Z HREF 90th percentile shows wind gusts
in the 35-40mph range from early Friday morning into the afternoon
hours. Bumped up wind speeds and gusts closer to the NBM 90-95th
percentile and have issued a Wind Advisory for a good portion of
central NC from midnight tonight through 6pm Friday. While it will
certainly be breezy, the northern Coastal Plain should be far enough
away from the strongest winds to warrant a Wind Advisory based on
today`s guidance.

&&

.SHORT TERM /FRIDAY NIGHT/...
As of 305 PM Thursday...

After the weather of the last couple days, Friday night`s weather
will be quiet. An isolated shower or thunderstorm could persist
through the evening hours north of US-64, but the rest of the night
should be dry. Wind speeds will also start to come down, with values
below 5 mph in most locations by the end of the night. Lows will be
in the 60s.

&&.

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 1214 PM Thursday...

The anomalous mid-level trough expected to eject TC Helene northward
today will linger over the TN Valley Saturday. The mid-upper level
trough/low will then slowly shift east across the Mid-Atlantic
through middle of this week. The system will pull offshore by
Wednesday, followed by mid-level ridging and nwly flow aloft.

Saturday: As the remnants of Helene continues to weaken over
Tennesse Saturday, anomalous moisture associated with this system
will consolidate well to the north and west of central NC. This will
promote a primarily dry day across our area. The only exception is
that a few models suggests the potential for some isolated to
scattered showers across the NC/VA border Saturday afternoon.
Overall though, most guidance keeps central NC dry Saturday.
Otherwise, daytime highs in the lower to mid 80s is expected.

Sunday through Thursday: 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). Ensembles
seem to be in good agreement bringing in some drier dew points into
the 50s Thursday into the weekend as high pressure extends down the
east coast.

Temperature wise, we`ll generally see upper 70s to lower 80s through
Wednesday.  There continues to be a signal for a cool down Thursday
into the weekend. For now will highlight daytime highs in the mid to
upper 70s and overnight lows in the mid to upper 50s.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
As of 140 PM Thursday...

A mixture of largely MVFR to VFR conditions in SHRA is expected to
start the TAF period. At GSO/INT, a gradual lowering of CIG to IFR
is expected by 21z as conditions deteriorate in showers. The main
forecast challenge in the near-term is the potential for TSRA at the
eastern sites of RDU/FAY/RWI, roughly between 18-20z and 00-02z,
earliest at FAY and latest at RWI, per the latest CAM guidance.
Confidence was too low to include TSRA at GSO/INT in the first 6
hours but cannot be ruled out. Rain showers and some embedded storms
will continue into late evening, but there is a good signal in the
guidance for a break in the shower activity between 03-06z before
the the main line of potential severe storms tracks in Fri morning
into early Fri afternoon. Even with the lull in precipitation
overnight, conditions are forecast to lower to IFR in most places,
with the exception of perhaps FAY/RWI. Some LIFR is also possible at
GSO/INT overnight. Wind will increase early Fri, accompanied by
LLWS, out of the ESE with sustained of 15-20 kt and gusts of 30-40
kt. As the line of strong to severe storms tied to remnant Helene
approaches the terminals, roughly between 12 and 18z Fri, conditions
will range between IFR to MVFR, with a gradual improvement Fri
afternoon to VFR.

Outlook: VFR conditions are largely expected later Fri into Sat,
though early morning fog is possible. A chance of showers/storms
will return Sun into Tue with a persistent upper-low near the region.

&&

.HYDROLOGY...
As of 305 PM Thursday...

Will issue a Flood Watch for the Piedmont and Sandhills region of
central NC for tonight through 6pm Friday.

Multiple rounds and bands of rain and thunderstorms will spread
north across central NC through Friday. Given recent wet
conditions, streamflows across Central North Carolina are
significantly above normal per 714 day USGS stream flows. NASA
SPoRT soil moisture percentiles are above the 90th percentile in the
010 cm and 040 cm layer across the southern coastal plain. In
addition, 1-3 hr hour Flash Flood Guidance is essentially below 2
inches across most of the Piedmont.

While the heaviest rain associated with Helene will be focused
across the foothills and mountains, a general 1-3 inches with
embedded heavier rain rate will cause a risk of flash flooding
through late Friday afternoon. This will be especially true where
creeks and streams are already swollen, and there are even some
areas with ongoing road closures owing to rainfall over the past 2
to 3 days. Lower rainfall totals and a reduced threat of locally
heavy rain across the northern and central Coastal Plain results in
a reduced flood threat and have omitted those locations from the
watch.

Main stem river flooding is not expected to be as significant of an
issue based on the 1-3 inch rain forecast, although heavy rates in
the vicinity of the Rocky River near Norwood, which drain from west
to east and may see heavier rain upstream, and also the routing of
significantly heavier rainfall in the upper reaches of the Yadkin
River may cause some flooding in the Yadkin basin. The Neuse and Tar
are also abnormally high with the Neuse at Smithfield currently in
minor flood.

&&

.CLIMATE...

Record High Minimum Temperatures:

September 26:
KGSO: 69/2005
KRDU: 73/1993
KFAY: 73/1930

September 27:
KGSO: 69/2011
KRDU: 73/2011
KFAY: 73/2017

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday afternoon for NCZ007-021>025-
038>042-073>077-083>086-088-089.
Wind Advisory from midnight tonight to 6 PM EDT Friday for
NCZ007-021>025-038>042-073>077-083>086-088-089.

&&

$$
SYNOPSIS...MWS
NEAR TERM...Green/Leins
SHORT TERM...Green
LONG TERM...Luchetti
AVIATION...Kren
HYDROLOGY...Blaes
CLIMATE...RAH