298
FXUS61 KAKQ 261936
AFDAKQ

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

.SYNOPSIS...
Hurricane Helene intensifies today, 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 405 AM EDT Thursday...

Key Messages:

- Helene weakens and tracks well west of the area Friday,
  bringing the potential for moderate to locally heavy rain and
  a tornado threat (mainly to southern VA and NE NC zones).

- Mainly rain-free and warm/humid Saturday.

Rain chances rapidly increase after daybreak Friday, with PoPs
rising to likely to categorical over the W/SW 1/2 of the area,
overspreading the entire CWA by late morning or early aftn. The
overall trends with respect to total QPF are similar or slightly
lower compared to the previous model cycle. The ensemble means
are less than 0.50" over the NE portion of of the CWA to ~1.00"
over the western piedmont, but as usual much higher local
amounts will be possible. Perhaps the greater concern will be
for a tornado threat sometime from later Fri morning through Fri
aftn as instability develops across NC and into at least
southern portions of VA. Ample low level shear will be in place
with strong SSW flow aloft and SE low level winds, yielding
large, curving hodographs. Farther north, the amount of
instability will be less so the threat is lower. Uncertainty in
the exact track of Helene makes the severe threat somewhat
uncertain, but there is enough consensus for SPC to have NE NC
into a Day Slight Risk (primarily for the 5% TOR threat), with a
marginal (2% TOR threat) into southern and central VA (roughly
to the I-64 corridor). A dry slot moves in from the south late
Fri aftn/Friday evening into Friday night, bringing an end to
the precip. On Saturday, the remnants of (weakening) Helene will
be located well off to our west over western KY. Drier weather
returns outside of some low- end rain chances across the NW
late.

&&

.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 /20Z THURSDAY THROUGH TUESDAY/...
As of 230 PM EDT Thursday...

Scattered showers remain to the NW of RIC. High clouds from
Hurricane Helene with VFR conditions are present across the area.
Some lower clouds (around 2,000ft) are present across most of the
area, but they are mainly scattered. Winds are primarily SE at 5-
10kt. MVFR CIGs will begin overnight with the piedmont reaching
lower heights first. Patchy fog near SBY and PHF is possible before
sunrise. Cloud heights will decrease throughout the day to IFR and
locally LIFR as rain chcs increase. There is a chc for scattered
storms/tstms starting tomorrow afternoon but timing and coverage are
uncertain. Locally reduced visibility and higher winds are expected
in any shower or storm. After sunrise, winds will pick up and gusts
around 20kt are possible across the area.

Outlook: The direct impacts of Hurricane Helene and its remnant low
are somewhat uncertain, but Friday afternoon and into overnight has
a continuing chc of storms. While Friday is likely wet, Saturday
will be drier. A chc of showers is possible with unsettled wx Sun-
Mon.

&&

.MARINE...
As of 405 AM EDT Thursday...

Key Messages:

- Small Craft Advisories have been extended into late Friday for all
Atlantic zones due to persistent seas above 5 ft.

- Southeast winds increase on Friday bringing the potential for
Small Craft conditions in the Chesapeake Bay, lower James River, and
Currituck Sound.

High pressure has moved off the eastern Canadian coast with
Hurricane Helene making northward progress into the eastern Gulf of
Mexico. Winds are generally E or SE at 5-10 kt across the local
waters. Waves are mainly 1-2 ft in the Chesapeake with 2-3 ft near
the mouth. Seas range from 3-5 ft, highest away from the immediate
coast.

Southeast flow has overspread the waters as high pressure well to
the north continues to translate eastward/offshore. This has allowed
near-shore wave heights to finally fall below 5 ft but have
maintained SCA headlines for all coastal waters as heights remain 4-
5 ft farther offshore. Hurricane Helene continues to intensify over
the extremely warm waters of the eastern Gulf. The storm is forecast
to make landfall along the Florida Big Bend early this evening.
Helene continues quickly north tonight into Georgia. SE winds 5-10
kt continue today and tonight before the gradient strengthens
locally on Friday. Winds increase to 15-20 kt with gusts to 25 kt on
Friday into Friday evening and SCA headlines are likely for the
Chesapeake Bay, lower James, and Currituck Sound. The gradient
relaxes early Saturday as the remnant circulation from Helene gets
shunted NW on the northern periphery of an upper level low. Waves in
the bay increase to 2-3 ft with 3-4 ft likely near the mouth Friday
afternoon and evening. Calmer conditions are expected on Saturday
and even the seemingly never-ending SCA headlines for the coastal
waters may even be allowed to expire. For now, have only extended
the ongoing coastal waters SCAs for an additional six hours into
Friday night with less confidence that 5 ft seas will persist toward
sunrise Saturday. Uncertainty increases for Sunday into next week
with the 00z GFS the most bullish on some of Helene`s energy
combining with the lingering upper low to result in the development
of another area of (non-tropical) low pressure along the NC coast.
Will show ENE winds increasing to around 15 kt for now pending
better agreement in the models.

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 405 AM EDT Thursday...

Key Messages:

-Tidal departures continue to fall across the region.

- Coastal flood advisories have been issued for the next two high
tide cycles for the tidal Potomac and Rappahannock as well as bay
side portions of the MD Eastern Shore.

Tidal departures continue to fall this morning, but remain highest
(1.5-1.75 ft) in the upper Chesapeake Bay, along the tidal Potomac
and Rappahannock, and on the bay side of the MD Eastern Shore.
Coastal flood advisories have been issued through late this evening.
Water levels fall further to end the week and any nuisance-minor
flooding will likely be constrained to tidal Potomac and bay side of
the MD Eastern Shore. Latest guidance does show the potential for
increasing anomalies late Friday across the middle and upper bay
with the potential for minor to locally moderate coastal flooding at
Bishop`s Head and Lewisetta.

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

As of 405 AM EDT Thursday:

Consecutive high tides reaching at least Minor Flood with this event:

- Lewisetta (P.O.R. since 1979): 18 (with several more to come),
previous record was 8 in Oct 2021, Oct 2019, Oct 2015.

- Cambridge (P.O.R. since 1980): 13 (with this morning`s high tide
unlikely to reach minor flood), previous record was 5 in Oct 2021,
Oct 2019, Sep 2018, Oct likely 2011.

Consecutive high tides reaching at least Moderate Flood with this
event:

- Lewisetta (P.O.R. since 1979): 7 (with additional moderate flood
unlikely), ***tying the record of 7 in Oct 2015***

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...Coastal Flood Advisory until 8 AM EDT Saturday for MDZ021-022.
NC...None.
VA...None.
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/LKB
MARINE...RHR
TIDES/COASTAL FLOODING...