Scientific Forecaster Discussion
fxus61 kakq 170857
Area forecast discussion
National Weather Service Wakefield Virginia
457 am EDT Tue Sep 17 2019
a backdoor cold front will slide south across the lower mid
Atlantic region this morning. Surface high pressure gradually
builds down into the region from the north tonight through
Thursday. Meanwhile, Hurricane Humberto is forecast to track
well east of the southeast coast through midweek.
Near term /until 6 PM this evening/...
as of 355 PM EDT Tuesday...
The current surface analysis places a backdoor cold front over
ern PA and central NJ, with high pressure centered NE of the
Great Lakes. Meanwhile, Hurricane Humberto is slowly tracking
east-northeast well off the southeast coast. Partly to mostly cloudy and
mild early this morning with temperatures ranging from the mid
60s to low 70s. There is some patchy fog and stratus over
interior S-central Virginia and NE NC.
The backdoor cold front will drop swd through the region today.
High- res data suggest some showers develop along the boundary.
However, coverage is limited and primarily over the Piedmont.
Pops are 30-40% west of I-95, and 20% or less east of I-95. There is
some instability over the Piedmont and there is a slight chc of
tstms. Becoming mostly cloudy with high temperatures range from
the mid/upper 70s NE to the low 80s S and SW. Becoming breezy
along the coast as a NE wind increases behind the front.
Short term /6 PM this evening through Wednesday night/...
as of 355 PM EDT Tuesday...
Drier air builds in from the NE tonight as high pressure builds
across New England. Clouds decrease from NE to SW, with any
lingering showers quickly dissipating early in the evening.
Forecast lows range from the mid 50s to low 60s as some low-
level mixing should inhibit full radiational cooling.
High pressure continues to build swd from the eastern Great
Lakes/New England Wednesday. Forecast soundings show some
lingering low level moisture with the onshore flow, which should
result in partly cloudy conditions along the coast, with mostly
sunny conditions farther inland. However, dry conditions should
prevail with limited deep layer moisture. Comfortable
temperatures are expected (highs only 75-80f) and dewpoints
falling into the 50s for most areas. Rather breezy along the
coast, due to the cooler airmass over the warm water and a
strong pressure gradient between the high to the north and Humberto
well offshore. Pleasant Wednesday night with lows in the low/mid
50s inland, and upper 50s/low 60s closer to and along the
Long term /Thursday through Monday/...
as of 115 PM EDT Monday...
Cooler, drier conditions look to persist for the mid to latter
portion of the week. Ridge of sfc high pressure will extend
along the eastern Seaboard into the southeastern US Thu-Fri.
Aloft, the region will remain on the periphery of an upper level
ridge of high pressure, which will rebuild over the region from
the southwest during the upcoming weekend, bringing a gradual
warm-up late in the weekend into early next week.
Warm days and cool nights persist through much of the period.
High temperatures Thursday and Friday will be near to slightly
below seasonal averages with highs in the upper 70s to lower
80s. Overnight lows falling back into the low to mid 50s inland
(though a smattering of upper 40s possible in typical cool
spots Thu/Fri mornings)...with low to mid 60s at the coast. The
warming trend begins Saturday into early next week, with high
pressure at the surface and building heights aloft. Above
average temperatures likely prevail through this period with
highs in the mid/upper 80s to around 90 degrees.
Aviation /09z Tuesday through Saturday/...
as of 155 am EDT Tuesday...
A backdoor cold front will push in from the NE later this
morning resulting in NE onshore flow. This will bring the
potential for occasional MVFR cigs behind the boundary
(primarily after 12z). A NE wind of 8-12kt will prevail inland
later this morning into the aftn, and will be stronger toward
the coast, 12-15kt with gusts of 20-25kt. There is a slight chc
for showers later this morning into the aftn. High pressure
builds in from the northeast tonight, with the sky gradually
clearing, although some scattered SC could linger toward the coast.
Some scattered to occasionally broken cumulus are possible Wednesday
(especially toward the coast) as onshore flow continues. High
pressure settles into the region Thursday through Saturday
bringing VFR, mostly clear, and dry conditions.
as of 355 am EDT Tuesday...
Early morning surface analysis shows Hurricane Humberto a few
hundred miles east of the Georgia/SC coastline, with high pressure over
the nrn Great Lakes. A weak backdoor cold front was entering the
nrn marine zones, where 5-10 kt NE winds prevail. Winds remain
variable (aob 10 kt) over the remainder of the area. Seas are 3
ft north/3-4 ft S, with 1 ft waves on the Bay.
The aforementioned backdoor cold front will cross the region
today, allowing winds to turn to the NE across all marine
zones. In addition, winds ramp up during the day today as the
pressure gradient tightens between the area of high pressure to
the north and Humberto to the S. By late aftn, NE winds increase to
17-20 kt (sustained) on the Bay and lower James River/20-25 kt
on the ocean and Currituck Sound. Additionally, seas increase to
5-6 ft (w/ 2-4 ft waves on the ches bay) by this evening. The
high becomes centered over nrn New England by Wed am as Humberto
continues to track to the east-northeast. Winds increase slightly (by a
few knots) tonight and a few gusts to 30 kt are likely over the
mouth of the ches Bay/srn coastal waters by late tonight/Wed am.
The potential for ~30 kt gusts in these areas continues through
the day on Wed. Sustained winds of ~20 kt on the Bay/25 kt on
the ocean are expected on Wed (lasting through the first part of
Wed night). There is a chc that scas may be needed for the
upper rivers for a time on Wed, with at least a few gusts of ~20
kt likely. Seas build from 5-7 ft early Wed am to 7- 10 ft by
00z Thu (highest S of the Virginia/NC border). Scas have been extended
through 7 PM Wed for the ches Bay, lower James River and
Currituck Sound (and may need to be extended further in
subsequent forecast packages). Went ahead and extended the Small Craft Advisory
for the ocean through 7 PM Thu (due to very high confidence in
seas remaining aoa 5 ft).
On Thursday, the high is expected to build south-southwest toward the area
as Humberto continues to slowly pull away to the east-northeast. This will
finally allow for winds to turn to the north slowly diminish from
Thu am-Thu night. The current forecast has wind gusts dropping
below Small Craft Advisory thresholds by late Thu evening. The high is expected
to settle into the region from Fri-Sat before moving to the southeast
of the area on sun. Winds are expected to become light (aob 10
kt) by late Fri and remain that way through much of the weekend.
However, seas (and waves near the mouth of the bay) will be
slow to diminish. Scas may potentially be needed for the mouth
of the ches Bay through Fri/ocean through Sat (due to
as of 455 am EDT Tuesday...
A strong NE wind will push tidal anomalies to 1.0-1.5ft above
normal by Wednesday and Thursday. This has the potential to
produce minor tidal flooding, particularly on the south and west
sides of the ches Bay, James River, and associated tributaries.
In addition...with the persistent NE wind/swell...water likely
gets trapped in the upper ches Bay by Thu. This will lead to
steadily increasing anomalies on the Bayside of the lower Maryland ern
shore. Minor tidal flooding will likely occur in vulnerable
areas of southern Dorchester County by the high tide Thursday
evening, with a chc of minor flooding at Cambridge/Crisfield.
Water levels are forecast to crest just above minor flood
thresholds at bishop's head by late Wed aftn.
The current forecast keeps water levels just below minor flood
thresholds along the Atlantic coast of MD, VA, and NC. However,
there is a slight chc that water levels exceed minor flood
thresholds on the Oceanside of the Virginia ern shore/NC during the
higher astronomical tides on Wed/Thu.
A high rip current risk is forecast today, which will likely
continue through at least midweek, as swell from Humberto
propagates toward the coast.
kdox radar remains offline due to an equipment issue. Technicians
at the site hope to have needed parts tomorrow, with a return
to service by late tomorrow or tomorrow night. Further updates
will be passed along as they become available...and will also be
available through site free text message (ftmdox).
Marine...Small Craft Advisory from 1 PM this afternoon to 7 PM EDT
Wednesday for anz630>632-634-638.
Small Craft Advisory from 10 am this morning to 7 PM EDT
Wednesday for anz633.
Small Craft Advisory from 10 am this morning to 7 PM EDT
Thursday for anz650-652-654-656-658.