Coastal Flood in Virginia, October 28 to 30, 2021

AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
256 PM EDT Thu Oct 28 2021

.SYNOPSIS...
A strong storm system will approach and cross the region later
tonight into Saturday. Clouds and widespread rain will spread
across the area tonight and persist through Friday. In addition,
gusty winds are expected on Friday...especially close to the
coast. Calmer conditions are expected by Sunday as the storm
system moves well off to the northeast and high pressure begins
to build across the region.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 300 PM EDT Thursday...

This afternoon, mid and high level clouds are on the increase
across the region as weak WAA ensues out ahead of the next
system. In addition, some lower clouds have worked into the
eastern half of the region due to onshore flow. Expect most
locations in our area to remain dry through the late
afternoon/early evening hours, except for perhaps our far SW
(I-85 corridor SW of the RIC/Tri- Cities area), which might
experience a few showers right before sunset. PoPs bump up
fairly quickly from the SW after 00z/8 pm this evening to
likely/categorical through the overnight hours, with first slug
of overrunning moisture/WAA lift across the area ahead of the
approaching occluding front. WPC has continued Marginal Risk of
Excessive Rainfall across our far NW tier of counties for
tonight on into Friday, with amounts likely to be terrain
enhanced, owing to a stout 40-60kt SSE LLJ late tonight into Fri
morning. Expect rain will fall moderately to heavily at times
late tonight/overnight from the RIC metro to the piedmont and
south central VA. Storm total QPF is 0.75"-1" along the coast,
and 1"-1.5" just inland. Some locally heavier totals are likely
especially NW of RIC. Temperatures do not fall much tonight due
to the extensive moisture/cloud cover with lows forecast in the
50s to near 60 for most tonight, with lower to middle 60s
across coastal NE NC and eastern portion of Hampton Roads.

Have maintained the categorical PoPs area-wide through Friday
morning, before mid-level dry slot noses in from the south and
begins to taper off the first wave of rainfall. This will allow
us to drop back to chance PoPs for mainly scattered showers
during the afternoon across the south, with periods of rain
continuing mainly north of I-64 and over the eastern shore into
Friday evening. The trend continues with the GFS preferred over
the NAM, which is a bit slower and a bit more
amplified/aggressive with pushing the triple point farther north
across the Tidewater area as it pushes offshore. This would
allow the warm sector and some modest instability (~500-1000
j/kg MLCAPE) to set up over the Hampton Roads area, and bring a
more substantial second wave of precipitation to the area. The
GFS solution would confine meager instability (aob ~500 j/kg
MLCAPE) only across our far SE counties.

Given the impressive wind fields aloft, it would not take much
instability to present at least a low-end threat for bowing
line segments and perhaps even a quick, spin-up tornado threat.
So while the quicker GFS remains the preferred solution at this
point, will maintain thunder wording for the entire area Friday
morning into the early afternoon (south) and through the
afternoon (VA Peninsulas northward) given this dynamic system
and its very strong winds aloft. SPC has the much of the eastern
half of the region in a Marginal Risk of severe weather for
Friday with the mention of damaging wind gusts and the
possibility for an isolated tornado. Thinking the greatest
severe thereat for our neck of the woods will be during the mid
to late morning hours across the southeast, spreading further
north into the afternoon hours.

Next threat is the synoptic wind. NWP continues to show strong
E winds ramping up quickly along and just north of the occluded
front Friday. This likely results in wind gusts up to 45 mph (50
mph Eastern Shore) across Hampton Roads and Atlantic coast, as
well as the VA Peninsulas through the northern neck. In fact,
guidance suggests that the easterly wind will only become
stronger as the front moves north and the gradient tightens up a
bit further. Thus, while not overly confident, would not be
shocked to see a gust or two of ~50 KT north of WAL Friday aftn.

Highs in the 60s back into the piedmont and along the eastern
shore, with highs in the lower to middle 70s east of I-95 to the
Hampton Roads area.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 300 PM EDT Thursday...

Still cannot rule out a few showers continuing into Fri night,
especially across the north and northwest, which will be
closest to the surface and upper low. However, any widespread
rainfall not expected due to previously referenced drying aloft.
The vertically stacked low pressure crosses the central
Appalachians and pushes across the local area up early Saturday,
then heads north into the northeast CONUS through the weekend.
With the cool air aloft associated with the upper low and plenty
of moisture available, will need to keep chance PoPs across
especially western portions of the region for scattered showers
on Saturday.

By Sunday morning, the upper trough will be far enough to our
north to allow for some drying...with late day clearing leading
to partly to mostly sunny skies and a pleasant Halloween night.
Highs Sunday in mid to upper 60s on Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
As of 300 PM EDT Thursday...

Generally quiet weather is expected for next week as upper flow
becomes quasi-zonal in advance of the deep upper trough over
the Canadian prairies into the northern plains states. A weak
cold front will attempt to move through the area by midweek, but
latest guidance continues to indicate that very little moisture
will be available with this system. Maintained PoPs at slight
chance or less for now. Overall, temps will be seasonable with
mid 60s to around 70 Monday and Tuesday, falling to the upper
50s to low/mid 60s on Wednesday. Early morning lows in the 40s
to low 50s.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
As of 135 PM EDT Thursday...

This afternoon, some pockets of MVFR ceilings have worked into
eastern portions of the area (mainly impacting ORF and PHF) due
to onshore flow. The cloud deck will continue to spread to the
west through this afternoon with ceilings from 3000 to 3500 ft.

Meanwhile, a potent area of low pressure will continue to
approach the region from the SW with easterly winds increasing
ahead of this feature through this afternoon/evening. Widespread
showers and degraded flight conditions (in the form of MVFR to
IFR ceilings and MVFR visbilities) are expected to overspread
the region from south to north later this evening through
tonight and will persist through the remainder of the forecast
period. Gusty east to southeast winds are expected tomorrow,
especially closer to the coast. Gusts to 30 knots are possible
at KRIC/KSBY, and ~35-45 kt possible across SE coastal
terminals.

Outlook: Unsettled flying conditions continue through tomorrow
night into Saturday, as upper level low pressure pushes across
the area. Some episodes of VFR are possible on Saturday, but the
more widespread improving conditions will not occur until
Sunday and Monday.

&&

.MARINE...
As of 400 AM EDT Thursday...

Early morning surface analysis shows weak high pressure ridging down
the east coast between departing low pressure now well into the
Atlantic and another strong low centered over northern Arkansas.
Winds across the waters are generally from the NNE 10-15 kt. Waves
in the bay are 1-3 ft (highest near the mouth of the bay) with seas
offshore remaining elevated in the 5-8 ft range.

Very busy couple of days on tap for marine interests across the
region. Aforementioned high pressure will translate offshore today
into tonight. Flow transitions to NE and E with time today as the
ridge axis moves offshore. This will usher in a period of onshore
flow that strengthens considerably this evening and tonight as low
pressure approaches from the west. Hoisted SCA headlines for for all
waters from this evening into early Friday as conditions are
expected to go downhill through the night. Winds increase 15-20 kt
this evening and further increase to 20-25 kt with gusts to 30 kt
after midnight. Winds will continue to increase towards daybreak on
Friday with most areas averaging 25-30 kt with gusts to 35 kt. The
core of the strongest winds will come during the day on Friday with
improving conditions expected after the strong surface low crosses
the region mid to late afternoon. Opted to upgrade the Ches Bay and
coastal waters to a Gale Warning starting at 7am Friday but some
uncertainty continues for the Currituck Sound and lower James river
where a Gale Watch remains in effect. Will let the day shift take a
closer look at these areas. The upper James as well as the York and
Rappahannock rivers look to stay just below Gale thresholds so have
raised SCA flags for those waters. However, given strong easterly
winds and favorable orientation, the York and Rappahannock rivers
may require an upgrade to Gale Warnings in subsequent forecasts.

In addition to the Gale force wind gusts, seas will rapidly build
due to the strong onshore flow. Seas build to 9-12 feet across the
northern waters (12 ft+ out 20 nm) and 7-10 feet south. Seas remain
elevated in excess of 5 feet through much of the weekend. Waves in
the bay will range from 3-5 ft across our northern bay zones but 5-7
ft waves will impact the lower bay as larger waves come in from the
open Atlantic. Calmer conditions are expected Saturday into early
next week.

&&

.TIDES/COASTAL FLOODING...
As of 600 AM EDT Thursday...

Coastal Flood Watches remain in effect for areas along the northern
half of the Chesapeake Bay and the Atlantic coast north of Cape
Charles Light.

Chesapeake Bay/Tidal Rivers: Tidal anomalies continue to rapidly
increase across the Chesapeake Bay this morning with anomalies now
in excess of 2 ft at Bishops Head and Lewisetta. A series of strong
flood tides have been observed at Cape Henry (~2kt), with multiple
flood tides (and very little to no ebb tide) expected to continue
according to CBOFS guidance. Additionally, CBOFS water level
guidance has Lewisetta, Bishops Head, and Cambridge hitting minor
flood thresholds during high tide this morning. Therefore, the
forecasts have been nudged upward, well into minor flood
range for the southern shore of the Potomac and Bay-side of the
MD Eastern Shore, and a Coastal Flood Advisory has been issued
for these locations. Another Coastal Flood Advisory has been
issued for the James River and the Peninsula vicinity to account
for minor flooding expected at Jamestown, Sewells Pt, Yorktown,
and Norfolk this afternoon into the early evening. A Coastal
Flood Advisory has also been issued for Lancaster, Middlesex,
and Mathews counties from 2pm through late evening to cover
expected minor coastal flooding as anomalies continue to rise.

In addition, the next low pressure system approaches the region late
today into Friday, turning the winds to the east (gale force) which
will allow for additional water up the Chesapeake Bay. All of these
factors are setting the stage for a significant coastal flood event
for especially the northern Chesapeake Bay tidal sites beginning
this evening and persisting into the weekend. Guidance continues to
show the highest tide during the late Friday evening/Friday night
timeframe with locations such as Cambridge, Bishops Head, and
Lewisetta approaching or surpassing Major Flood Stage. The remainder
of the upper Bay tidal sites will be reach Moderate Flood Stage.
Water levels will be slow to recede with elevated tides expected
into the weekend. The southern Bay/river sites will also likely
reach at least Minor Flood Stage (likely Moderate at Jamestown).

Atlantic Coast: Minor/nuisance flooding is expected to continue at
Ocean City over the next couple of tidal cycles, and the Coastal
Flood Advisory has been extended through 4 PM Thursday afternoon.
More significant flooding, high-end minor to moderate, is expected
later Friday evening at Ocean City, Chincoteague, Wachapreague, and
Oyster. Large waves in excess of 8 to 10 feet will enhance the
flooding threat and may also lead to beach/dune erosion issues.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...Coastal Flood Warning until 6 PM EDT Saturday for MDZ021>023.
     High Surf Advisory from 7 AM to 10 PM EDT Friday for MDZ025.
     Wind Advisory from 7 AM to 7 PM EDT Friday for MDZ024-025.
     Coastal Flood Watch from Friday morning through Saturday
     morning for MDZ024-025.
     Coastal Flood Advisory until 4 PM EDT this afternoon for
     MDZ024-025.
NC...Wind Advisory from 4 AM to 2 PM EDT Friday for NCZ102.
     High Surf Advisory from 4 AM to 4 PM EDT Friday for NCZ102.
VA...Coastal Flood Advisory until 8 PM EDT this evening for VAZ084-
     089-090-093-095>097-523>525.
     Wind Advisory from 4 AM to 2 PM EDT Friday for VAZ095-098.
     High Surf Advisory from 4 AM to 4 PM EDT Friday for VAZ098.
     Coastal Flood Warning until 6 PM EDT Saturday for VAZ099.
     High Surf Advisory from 7 AM to 10 PM EDT Friday for VAZ099-
     100.
     Wind Advisory from 7 AM to 7 PM EDT Friday for VAZ099-100.
     Coastal Flood Watch from Friday morning through Saturday
     morning for VAZ100.
     Wind Advisory from 7 AM to 4 PM EDT Friday for VAZ077-078-
     084>086-523-525.
     Coastal Flood Warning until noon EDT Saturday for VAZ075-077-
     078-085-086.
MARINE...Gale Warning until 4 PM EDT Friday for ANZ630>632-634>636-654-
     656-658.
     Gale Warning until 7 PM EDT Friday for ANZ650-652.
     Gale Warning until 1 PM EDT Friday for ANZ633-637-638.

&&

SYNOPSIS...AJB/MAM
NEAR TERM...AJB/MAM
SHORT TERM...AJB/MAM
LONG TERM...AJB/MAM
AVIATION...AJB
MARINE...AJB/LKB/RHR
TIDES/COASTAL FLOODING...

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