486
FXUS61 KAKQ 270031
AFDAKQ

AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
831 PM EDT Thu Sep 26 2024

.SYNOPSIS...
Hurricane Helene intensifies this evening, making landfall on
the Florida Gulf Coast early tonight. The remnants of Helene
will then pass well west of the area on Friday. Drier conditions
briefly return on Saturday, followed by unsettled weather
Sunday through next Tuesday.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
As of 330 PM EDT Thursday...

Key Message:

- Isolated to scattered showers redevelop this afternoon,
  mainly W of I-95, with only a slight chance to the east.

- Widespread showers and isolated thunderstorms expected Friday,
  associated with the remnants of Tropical Cyclone Helene. Heavy
  rain and brief tornadoes are the main threats.

The main wx story regionally (and nationally) remains Hurricane
Helene in the eastern Gulf of Mexico. As of a 230 PM special NHC
advisory, max sustained winds have increased to near 120 mph.  Ahead
of Helene, high pressure is gradually shifting further offshore from
Atlantic Canada, leading to rather light SE/ESE flow over the
region. An expansive shield of precip extends northward from Helene,
with a predecessor (PRE) rainfall event ongoing in the higher
terrain of SC/NC/VA. Aloft, a sprawling upper low is situated over
the mid MS Valley. Temps are generally around 80 F this afternoon
and highs will average 80-82, except upper 70s along the immediate
coast. Light radar echoes are noted over our far western counties,
but this does not appear to be reaching the ground as of this
writing. For the rest of this afternoon into this evening, showers
currently over central NC are forecast to spread northward into our
SW and W counties as rich tropical moisture advances ahead of
Helene. The highest coverage remains W of our area, but have 30-40%
PoPs W of I-95, with 10-20% PoPs further E.

Helene will make landfall in the FL Big Bend region tonight, moving
inland along the southern spine of the Appalachians Friday morning.
The remnant sfc circulation will then interact with the upper low
over the MS Valley, eventually pivoting NW into the OH Valley.
Isolated-scattered showers or light rain are expected through around
sunrise, with the bulk of the rain forecast to hold off until the
late morning and afternoon hours Friday. Rain chances ramp up
quickly heading into this timeframe and PoPs of 70-90% have been
continued areawide. Per the latest consensus across the CAMs, the
bulk of the precip will be associated with a northward/northeastward
pivoting band of heavier showers and embedded thunderstorms along a
warm front-type feature. Given the tropical moisture source, PWATs
of at least 2-2.2" will overspread the region and very heavy rain
can be expected in any shower or storm. The duration of heavy rain
is expected to remain on the shorter side, so aerial rain totals
will range from 0.25-1.0" across the area (highest across the
Piedmont). However, the very heavy rain rates could quickly drop an
inch or two of rain in localized areas. There could be isolated
instances of flash flooding in urban areas, but the overall flooding
risk remains marginal per the latest WPC excessive rainfall outlook.

The other side to the forecast, and perhaps the more concerning
aspect, is the tornado potential. With sfc dew points surging into
the mid 70s and temps in the upper 70s or lower 80s, there could be
a narrow axis of higher sfc-based instability along and just ahead
of the line of showers/storms. Forecast sounding show large, looping
hodographs with plentiful 0-1 and 0-3 km SRH. If enough instability
can be realized, a tornado threat could materialize. The highest
threat is over central and southern VA and NE NC, where SPC has
expanded the slight risk. A marginal risk borders the slight risk to
the N and it is questionable how much destabilization there will be
in these areas. The lowest tornado threat appears to be on the
Eastern Shore. With strong winds aloft (850 and 925 mb winds of ~60
and ~40 kt, respectively), any convective core could also mix down
some of these winds to the sfc, especially if low-level lapse rates
can be sufficiently steepened in areas that see sfc heating and/or
cloud breaks. Highs Friday range from the lower 80s across the E and
S, with mid-upper 70s across the W and N. Skies average mostly
cloudy to overcast. Lows Friday night in the mid-upper 60s, with
slowly clearing skies and PoPs tapering off (though a few
showers may remain).

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
As of 355 PM EDT Thursday...

Key Messages:

- Mainly rain-free and warm/humid Saturday.

- Cloudier and slightly cooler Sunday, with chances for a few
showers returning.

On Saturday, the remnants of (weakening) Helene will be located well
off to our west over western KY and the remnant sfc circulation will
slowly fill in underneath the upper low. Drier weather returns
outside of some low- end rain chances across the NW late. High temps
warm into the low-mid 80s under a mostly sunny sky. Lows Sat night
in the mid 60s.

Conditions turn more unsettled more Sunday as the upper low/trough
over the OH Valley translates eastward. Therefore, expecting more in
the way of cloudiness and chances for showers (especially NW). Some
uncertainty surrounds rainfall coverage, with the 12z GFS showing
more precip than the ECMWF. The GFS solution would lead to cooler
high temps vs. the ECMWF. For now, will go with NBM highs, which is
a few degrees cooler than Saturday and in the upper 70s-low 80s (mid
80s possible far SE). Lows Sun night in the 60s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 330 PM EDT Thursday...

Key Messages:

- Multiple low-end chances of rain Sunday through Tuesday early from
  the post tropical remnant of Hurricane Helene.

- Drier and cooler air arrives mid to late next week.

The latest model guidance indicates the remnant low of Hurricane
Helene will gradually shift to the east through Tue after stalling
near the TN valley on Sunday. This will keep conditions unsettled,
with chcs for showers and a few tstms. High temperatures Mon-Wed
will be in the mid-to-upper 70s with lows in the low 60s Mon-Tue
night. A dry cold front is expected around Tuesday night. There is
some model differences on the timing, but cooler overnight lows in
the low-to-mid 50s across the piedmont and inland and upper 50s near
the coast for Wed-Thur night are possible. After the cold front,
significantly lower humidities are expected.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 825 PM EDT Thursday...

Just isolated to sctd showers were lifting nwrd across our extrm
wrn counties this evening. SBY already had IFR CIG. Any VFR CIGs
late this evening will gradually become MVFR or IFR (locally
LIFR) at all TAF sites late tonight through late Fri morning,
in advance of bands of showers associated with tropical cylone
Helene. MVFR/IFR conditions then expected at all TAF sites from
Fri aftn into Fri evening, as bands of showers, possible tstms
move through the area. Higher winds will be possible in any
stronger showers or storms. After sunrise, ESE winds will pick
up and gust to at least 20-25 kt in the aftn into the evening.

Outlook: Fri night and Sat will be drier with mainly VFR
conditions. A chc of showers is possible with unsettled wx Sun-
Mon.

&&

.MARINE...
As of 400 PM EDT Thursday...

- Small Craft Advisories have been extended across all waters for
Friday for increasing southeast winds.

- Southeast winds increase on Friday bringing Small Craft conditions
in the Chesapeake Bay, Rivers and Currituck Sound.

East to Southeast flow persists this afternoon with winds generally
10 kt. Southeast winds will gradually increase after midnight and
continue to increase through Friday morning as Helene pushes
north.

Major Hurricane Helene continues to intensify and accelerate
northward and is forecast to make landfall along the Florida Big
Bend later tonight. Helene will continue to move quickly north into
Georgia early Friday then into Tennessee later Friday.

Winds increase to 15-20 kt with gusts to 25 to 30 kt Friday into
Friday evening and SCA headlines have been hoisted for all waters.
The gradient relaxes early Saturday as the remnant circulation from
Helene gets shunted NW on the northern periphery of an upper level
low over Tennessee. Waves in the bay increase quickly to 2-3 ft
Friday with 3-4 ft in afternoon. Calmer conditions are expected on
Saturday and even into early Sunday. Seas will likely remain
elevated though so SCAs may linger into Sat and Sun for the ocean
waters.

A secondary low may develop along the coast late Sunday into Monday
bringing a potential return on SCA conditions to the Bay early next
week.

High rip current risk continues for all beaches today and Friday
given 3-5 ft nearshore waves and swell periods 10-12 seconds.

&&

.TIDES/COASTAL FLOODING...
As of 4 PM EDT Thursday...

Key Messages:

-Tidal departures continue to fall across the region.

- Coastal flooding persists at Bishops Head and Tangier and
  will continue for the next several high tides.

- Back Bay of VA Beach will likely go into minor flooding Friday as
southeast winds increase.

Tidal departures continue to fall this afternoon, but remain highest
(1.5-1.75 ft) in the upper Chesapeake Bay from Tangier to Bishops
Head. Water levels will fall further at most locations over the next
24 to 48 hours.

Lastly, will continue to watch areas adjacent to the Currituck Sound
(including Back Bay of VA Beach) and the Albemarle Sound through
Friday as SE winds could push already elevated water levels up
further into minor flooding thresholds.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...Coastal Flood Advisory until 8 AM EDT Saturday for MDZ021-022.
NC...None.
VA...Coastal Flood Advisory until 1 AM EDT Friday for VAZ075-077.
MARINE...Small Craft Advisory from 7 AM Friday to midnight EDT Friday
     night for ANZ630>638.
     Small Craft Advisory until 1 AM EDT Saturday for ANZ650-652-
     654-656-658.

&&

$$

SYNOPSIS...LKB/SW
NEAR TERM...SW
SHORT TERM...LKB/SW
LONG TERM...KMC
AVIATION...KMC/TMG
MARINE...AJZ/RHR/JAO
TIDES/COASTAL FLOODING...AKQ