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-- Discussion containing changed information from previous version are highlighted. --
066
FXUS62 KCHS 150310
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1010 PM EST Wed Nov 14 2018

.SYNOPSIS...
Low pressure will affect the area into Thursday with cool and
dry high pressure then returning through this weekend. A cold
front could move through early next week with a few showers
followed by cool and dry high pressure once again into the
middle of next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A broad and weak area of low pressure over north-central Florida
will travel north-northeast and into our nearby Georgia Atlantic
waters after midnight, reaching near the Charleston County coast
around 12Z Thursday. During this transition, forcing will become
maximized with deep moisture and strong dynamics in place due to
a 40-50 kt low level jet and difluence associated with the upper
jet passing inland over the Southeast. This will lead to
widespread moderate rains developing, along with pockets of
occasional heavy rains. Localized minor flooding will become a
concern. We considered adding mention of t-storms over the South
Carolina coastal zones, but with the track of the surface low to
mainly stay over the ocean, we opted not to include. Still a
stray t-storm is possible late. Rain cooled conditions have
prompted us to lower temps, both hourly and for minimum temps a
bit in many areas. However, with the track of the low
approaching late, we have shown rising temps over parts of
Charleston and Berkeley County. Gusty winds will persist,
especially over the coastal corridor, as speeds reach as high as
30 or 35 mph.

Previous discussion...
A deep and tropical-like plume of moisture will extend across
the area, with PWat as much as 170-180% of normal for mid
November. This along with increasing and strengthening
isentropic ascent with cool air damming in place to our north-
northwest, and increasing forcing from an approaching wave of
low pressure from Florida, which hugs the coast as it rides
northeast, will lead to widespread rainfall all areas. A strong
low level jet and difluence from the upper jet will further lead
to large scale forcing for ascent, and potentially some locally
heavy rains.

Our evening update as slowed down the onset of rainfall over to
the locations mainly over the north and east counties until the
late evening and overnight, with likely to categorical PoP west
and southwest.

Depending upon if any instability get move onshore of the
coastal plain of the area overnight as the coastal warm front
attempts to move onshore, there could be a risk of isolated
t-storms, and higher rainfall rates. This could result in the
potential for localized flooding.

The strength of the low level jet and the packed gradient
between the in-situ wedge and the approaching low will lead to
northeast and east winds as high as 30-35 mph along the coastal
corridor.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Relatively calm conditions will prevail through the period as low
pressure pulls away from the region and high pressure builds in from
the west. Rain will quickly end from southwest to northeast through
the day Thursday with dry conditions prevailing Thursday Night into
Saturday. Clearing conditions will ensue Thursday in the wake of the
low with clear to mostly clear skies prevailing thereafter.
Temperatures will only warm into the mid-upper 50s Thursday and
Friday then moderate into the mid 60s by Saturday. Lows Friday Night
will range from the mid 30s well inland to the mid-upper 40s at the
beaches. Could see patchy to scattered frost develop across the
far interior just before daybreak Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Dry weather will prevail through early next week as cooler high
pressure moves into the area. A weak area of low pressure may
develop offshore and cause a few showers mainly near the coast.
Temperatures should mostly stay near normal.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Rain has been slow in developing at and near KCHS and KSAV this
evening, but eventually it will develop and overspread the
terminals during the late evening and overnight as lift
increases ahead of an approaching wave of low pressure from the
south and southwest. MVFR conditions early in the valid 00Z TAF
cycle will lower to IFR as the rain occurs, and continues into
at least Thursday morning. As the low pulls away the rest of
Thursday, the rain will end, and there should be at least some
improvement back into the MVFR range after 15-16Z.

An additional concern tonight will be winds, both surface and in
the lower levels. NE winds will be gusty at the surface as the
pressure pattern tightens between an inland wedge and the
approaching wave. Also, a 45-50 kt jet will traverse the area
for a few hours from about 04-09Z, leading to low level wind
shear at both terminals.

Extended Aviation Outlook: No concerns.

&&

.MARINE...
Overnight: Low pressure will ride north-northeast through the
area, passing through all but the AMZ350 waters prior to
daybreak. There is a strong pinching of the gradient between
this approaching feature and an inland wedge that will generate
NE winds as high as 25-30 kt with gusts near or in excess of 35
kt across most of the Atlantic waters. As a result we have
Small Craft Advisory headlines in effect for AMZ350, AMZ352 and
AMZ374. Across the AMZ354 waters and in Charleston Harbor we
have strong Small Craft Advisory conditions, for NE winds of
20-25 kt with some higher gusts. Seas will be about as high as
they can get in the absence of tropical weather; 8-12 ft in the
Atlantic, with 2-3 foot waves in Charleston Harbor. Based on the
recent radar trends and elevated instability expected across
the coastal waters, we have added mention of a slight chance of
t-storms across the outer Georgia waters through the night,
which will expand into the Charleston County Atlantic waters
after midnight as the surface low approaches.

Thursday through Monday: Conditions will gradually improve across
the local marine area Thursday as low pressure moves away from the
area. Seas are expected to drop below Small Craft Advisory
thresholds Thursday morning across the nearshore waters and Thursday
afternoon for the Georgia offshore waters Thursday evening. From
Friday on, northwest winds will turn northeast over the weekend with
speeds 15 kt or less. Seas will range 2-4 ft from Friday through
Monday.

High surf: Gale conditions will cause elevated seas to continue,
as the offshore seas within 20 nm reach as high as 8-11 ft, and
5 foot breakers occur in the surf zone, especially along the
northeast and east facing beaches. A High Surf Advisory remains
in effect.

&&

.TIDES/COASTAL FLOODING...
Strengthening northeast winds will lead to increasing positive
tidal anomalies tonight. The high tide after midnight may
experience departures around 1.5 ft MLLW at both Downtown
Charleston and Fort Pulaski. While this is below our coastal
flood criteria, there remains a concern that steady rains
falling around that time may result in a mix of minor fresh and
salt water flooding.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Surf Advisory until 5 AM EST Thursday for GAZ117-119-139-
     141.
SC...High Surf Advisory until 5 AM EST Thursday for SCZ051.
     High Surf Advisory until 8 AM EST Thursday for SCZ048>050.
MARINE...Gale Warning until 1 AM EST Thursday for AMZ352-374.
     Gale Warning until 5 AM EST Thursday for AMZ350.
     Small Craft Advisory until 10 AM EST Thursday for AMZ354.
     Small Craft Advisory until 4 AM EST Thursday for AMZ330.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...