Area Forecast Discussion
Issued by NWS Wakefield, VA

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FXUS61 KAKQ 032000
AFDAKQ

AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
400 PM EDT Mon Aug 3 2020

.SYNOPSIS...
Tropical cyclone Isaias impacts the region later tonight into
Tuesday afternoon. This will bring heavy rain, breezy to windy
conditions, and a threat of tornadoes toward the coast. More
typical summer-like conditions return by the middle of the week.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 230 AM EDT Monday...

Current wv imagery places a deep trough in vicinity of the
Great Lakes and Mississippi Valley, with a ridge over the
subtropical wrn Atlantic. Meanwhile, TS Isaias is located about
115mi S of Charleston, SC moving nwd about 13mph. An initial
band of showers/tstms has lifted nwd through the region this
aftn producing brief heavy rain and wind gusts of 35-40mph.
There is a lull S of this band, with additional showers/tstms
crossing the Albemarle Sound and moving into NE NC as of 330pm.
Temperatures are largely in the upper 70s to low 80s in the wake
of the pcpn, but highs did reach the mid 80s to around 90F
prior to the rain, and RIC has hit 90F once again. Occasional
showers/tstms are expected to progress through the area this
evening producing brief heavy rain.

TS Isaias is expected to make landfall along the nrn SC coast
later this evening into the early overnight hours, and then
increase in speed and turn NNE as it feels the effect of the
trough to the W. A 130-140kt upper jet at 200mb is forecast to
develop over the St. Lawrence Valley by Tuesday morning placing
the Mid-Atlantic region in the RRQ of the jet. This will result
in strong forcing for ascent and will combine with rich tropical
moisture bringing a threat for heavy rainfall/flooding to the
region. The heaviest rain should shift to left of track, so the
rain threat is more inland with lesser amounts of rain toward
the immediate coast. The Flash Flood Watch remains in effect for
the same locations. Forecast amounts remain 3-6" with locally
higher amounts for areas in the FF Watch. 03/12z HREF does have
a signal that some of this rain could fall on the order of 3hrs,
with the potential for some rainfall rates greater than 1" an
hour. WPC has a large portion of the area in a moderate risk for
excessive rainfall. Breezy to windy conditions develop later
tonight into Tuesday morning, with the latest data suggesting
the strongest wind occurs as some drier air mixes in on the srn
flank of the low. Wind gusts of 55-70mph are possible E of I- 95
toward the coast. Strong low-level shear and SRH are expected E
of the track bringing a tornado potential initially to NE NC/SE
VA later tonight and spreading nwd along the coast Tuesday. The
tornado potential and the extent will be dependent on how much
destabilization is able to occur E of the track along with the
location of any surface boundaries. SPC has the area from NE
NC/SE VA to the Delmarva in a slight risk for severe weather.

Conditions improve from SW-NE later Tuesday aftn. Forecast
highs are generally in the low/mid 80s after morning lows in the
upper 60s to mid 70s.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 400 PM EDT Monday...

Conditions settle down Tuesday night through Thursday as Isaias
moves well NE of the region. There is a chc of diurnal
showers/tstms Wednesday/Thursday aftn. Seasonal temperatures
with lows in the upper 60s/low 70s Tuesday/Wednesday night,
followed by highs in the upper 80s/low 90s Wednesday/Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 400 PM EDT Monday...

Going with a blend of the 12Z/03 GFS and 12Z/03 ECMWF for the
extended period. Until a shortwave trough to the west of the
area Thu night, combined with a lingering frontal boundary over
ESE portions of the region, move off the coast, there will
continue to be chc to likely PoPs from Thu night through Sat
across much of the CWA. Only slight to small chc PoPs for Sat
night into Mon morning, as high pressure tries to build in from
the NW or N. Increasing chances again Mon aftn into Mon evening,
esply inland/Piedmont locations. Highs will range from the mid
80s to near 90 through the period, with lows in the upper 60s to
mid 70s.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
As of 200 PM EDT Monday...

An initial band of showers/tstms ahead of Isaias is moving nwd
across the region bringing brief IFR conditions in vsby and wind
gusts to 30-35kt. Additional showers/tstms are forming over ern
NC and are expected to move nwd across the region through 00z
bringing additional showers/tstms and the potential for IFR
conditions in heavy rain and locally strong wind gusts.
Otherwise, expect SCT-BKN CU of 3.5-5.0kft and a light southerly
wind. Heavy rain, breezy to windy conditions (gusts in excess of
50kt toward the coast), and reduced cigs/vsby are expected
later tonight into Tuesday as Isaias impacts the region. Vsby to
IFR is likely and periods of LIFR are possible. Conditions are
expected to improve from SW- NE later Tuesday aftn. Conditions
transition back to more diurnal showers/tstms Wednesday through
Saturday.

&&

.MARINE...
As of 400 PM EDT Monday...

Late this afternoon, Tropical Storm Isaias was moving northward
off the coast of GA, with high pressure well offshore of the
Mid- Atlantic coast. Winds are generally S-SW at 5-15 kt with
seas of ~3 ft and waves of 1-2 ft on the bay. Isaias will
significantly impact the area waters from late tonight-Tuesday.
Tropical Storm Warnings remain in effect for all marine zones.

Fairly high confidence forecast with respect to Isaias, as
models are now in very good agreement with respect to timing. In
general, the 12z/03 models (especially some of the CAMs)
continue to show a modest increase in strength over the next
12-24 hours vs the previous forecast, resulting in a slightly
stronger wind field for our area. The latest NHC track is faster
and shows Isaias making landfall just S of the NC/SC border
late this evening before moving to just east of Raleigh. Isaias
will likely track NNE just to the west of the Chesapeake Bay on
Tuesday morning before quickly exiting to the N/NE Tue
afternoon. Isaias is expected to be a strong tropical storm as
it tracks through the area, so TS Warnings remain in effect for
the ocean, bay, Currituck Sound, and all of the rivers. Still
looks like the most likely timing for tropical storm conditions
will be from around 2 AM through 2 PM Tuesday. The earliest
onset of TS conditions will be across srn marine zones, with the
latest onset of TS conditions occurring across nrn marine
zones. There is the potential for sustained winds of 40-50 kt
with gusts up to 60-65 kt during this timeframe. The strongest
winds will generally be from the S or SE across the marine area
(E of the center of Isaias). However, there are some hints that
there will be a brief (~1 hour) period of 50-65 kt gusts as
winds turn to the west on the back side of Isaias at the tail
end of the event as drier air mixes into the boundary layer.
This will be something to watch for closely (and has been
modeled by a good portion of the CAMs). Given that Isaias will
be gaining forward speed as it tracks through the area, tropical
storm conditions will last no more than 6-8 hours or so at any
given location. Dangerous waves/seas (could see seas of 12- 15
ft w/ waves of 6-9 ft on the bay) are expected through the
duration of tropical storm conditions. Seas quickly decrease Tue
evening in the wake of Isaias. Sub-SCA conditions return on Wed
and are expected to last through Fri. Please see the latest
advisories from the National Hurricane Center concerning the
track of Hurricane Isaias.

&&

.TIDES/COASTAL FLOODING...
As of 530 AM EDT Monday...

Tidal flooding is possible across parts of the area on Tuesday-early
Wednesday morning as TS Isaias tracks NNE through the area. Strong S
to SE winds for a 6-8 hour period will result in rapidly rising
water levels across the mid/upper Ches Bay (especially the bayside
of the Lower MD Ern Shore) and also in areas on the north side of
the Albemarle/Currituck Sounds. In coordination with neighboring
offices, Coastal Flood Watches remain in effect for the bayside
of the Lower MD Ern Shore, VA Northern Neck, all counties in NE
NC north of the Albemarle Sound, and VA Beach (for sound side
flooding). There is the potential for water levels to exceed
moderate flood thresholds in the watch area on Tuesday. The
latest guidance shows lower potential for water to be trapped in
the northern Ches Bay, but the forecast will continue to show
minor to low-end moderate flooding on the bayside of the Lower
Ern Shore early Wed AM. Thus, the Coastal Flood Watch for the
Lower Ern shore runs through ~06z Wed. Watches for NE NC/VA
Beach run through Tuesday evening.

While a watch has been issued for Northumberland/Westmoreland,
confidence remains quite low that Lewisetta will reach moderate
flood thresholds.

&&

.CLIMATE...
As of 230 AM EDT Monday...

RIC official had a high temperature of 90F Mon which made it 25
consecutive days of 90+F temperatures (the 2nd longest streak in
the period of record). The longest streak on record is 27 days
in 1995.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...Flash Flood Watch from 10 PM EDT this evening through Tuesday
     evening for MDZ021>023.
     Tropical Storm Warning for MDZ021>025.
     Coastal Flood Watch from late tonight through late Tuesday
     night for MDZ021>023.
NC...Flash Flood Watch from 10 PM EDT this evening through Tuesday
     evening for NCZ012>014-030.
     Tropical Storm Warning for NCZ012>017-030>032-102.
VA...Flash Flood Watch from 10 PM EDT this evening through Tuesday
     evening for VAZ048-060>062-064>069-075>090-092-093-096-
     509>524.
     Tropical Storm Warning for VAZ064-075>090-092-093-095>100-
     511>525.
     Coastal Flood Watch from late tonight through late Tuesday
     night for VAZ099.
     Coastal Flood Watch from 2 AM EDT Tuesday through Tuesday
     evening for VAZ098.
     Coastal Flood Watch from late tonight through Tuesday evening
     for VAZ075-077.
MARINE...Tropical Storm Warning for ANZ630>638-650-652-654-656-658.
&&

$$
SYNOPSIS...AJZ/ALB
NEAR TERM...AJZ
SHORT TERM...AJZ/ALB
LONG TERM...TMG
AVIATION...AJZ
MARINE...ERI
TIDES/COASTAL FLOODING...AKQ
CLIMATE...AKQ



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