978 
FXUS62 KCHS 110854
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
454 AM EDT Sat Aug 11 2018

.SYNOPSIS...
Low pressure will persist near the region through the weekend.
A weak front could drift into the area during the middle of
next week. High pressure will then prevail during the second
half of the week before weak low pressure returns next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Pre-dawn: Mainly quiet conditions with a spotty shower possible
as a very weak short wave traverses the forecast area. The land
breeze should ensure that any significant convection occurs off
the coast. A very warm and humid summer morning with readings 
close to 80 degrees along the coastal corridor to the mid 70s 
well inland. 

Today: Ridging of the past couple of days has weakened and a broad
upper trough was settling across GA and the Carolinas. Mean low
level flow will back to a more southwest component and this alone
suggests weaker capping today with potential for enhanced moisture
convergence along the sea breeze corridor this afternoon and 
early evening. Moisture is forecast to deepen today in the 850-500
MB layer and PWATs rise above 2 inches forecast across most of 
the area. There will be some mid and high level clouds around 
this morning and temps will warm to around 90 not long after 
midday at many areas. We maintained highs in the low to mid 90s 
with the sea breeze coming off the SC beaches quicker today, 
readings will be not be quite as warm along the ocean front.

Convection: Since convective temps are in the 90-91 degree range
early on, showers and tstms initiation most areas after 18Z 
with the main focus along the sea breeze corridor. Isolated to 
scattered convection is expected to develop from mid to late 
afternoon with increasing coverage late in the day as outflow 
boundaries and the sea breeze interact. We maintained chance 
POPs averaging near 40 percent most areas inland from U.S 17. 
DCAPE values as high as 800-1000 J/kg are displaced off to the 
west this afternoon but soundings certainly support potential 
for some strong updrafts which could result in precip-loaded 
microbursts and an isolated severe wind threat. If upstream 
convection arrives from the W-NW late, the severe risk would be 
greater well inland.

Tonight: Convective rains could linger into the evening hours
many areas with coverage dependent on the extent of the sea
breeze convection during the late day hours. Areas along and
east of I-95 may see isolated to scattered showers and storms
redevelop past the midnight hour. This would be due to coastal 
moisture convergence and the arrival of another weak mid level 
short wave. Lows should average mid 70s inland and upper 70s 
close to the coast.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Sunday: A fairly unsettled weather pattern is anticipated to start 
off the week as a nearly cutoff mid/upper lvl low shifts over the 
Ohio River Valley. South of this feature, a weak sfc trough will 
extend over much of the Mid-Atlantic and Southeast states, just 
inland and to the north of the area for much of the day. A light 
southwest flow along with abundant sfc heating should support high 
temps in the lower 90s away from the coast and PWATs that approach 
near 1.75 to 2.00 inches. The setup suggests scattered showers and 
thunderstorms developing near the trough axis earlier in the day, 
before activity drifts into inland areas during the afternoon and/or 
evening. A few showers and/or thunderstorms can not be ruled out 
along the seabreeze as well. Precip activity should wane during 
early night hours due to the loss of daytime heating. Overnight lows 
should range in the low/mid 70s. 

Monday: The center of a mid/upper lvl low will likely advance over 
the Northeast and Mid-Atlantic states, helping a sfc trough and/or 
weak front slowly shift toward the region from the north. Guidance 
suggests a fairly pronounced h5 shortwave sweeping along the 
southern base of the mid/upper low, shifting over Southeast South 
Carolina earlier in the day, then over Southeast Georgia later in 
the day. Ahead of this shortwave, a southwest flow will likely 
advect deep moisture into the region, characterized by PWATs near 
2.0 inches over most areas, while sfc temps warm into the lower 90s, 
helping SBCAPE approach 1500-2500 J/kg. These unstable conditions in 
combination with forcing associated with the arriving shortwave and 
some upper lvl divergence associated with a passing h25 jet could 
lead to a fairly active afternoon/evening in regards showers and 
thunderstorms, some of which could be organized and potentially 
strong/severe. Strong wind gusts and heavy rainfall would be the 
primary threat with thunderstorms. Most activity should shift 
offshore during early overnight hours. Overnight lows should range 
in the low/mid 70s. 

Tuesday: Chances of showers and thunderstorms should persist into 
the afternoon as a sfc trough and associated weak front gradually 
shift toward the Southeast coast. However, convective activity 
should trend towards coastal locations and eventually offshore as 
the parent mid/upper lvl low to the north shifts off the Mid-
Atlantic and Northeast coast while the weak sfc front attempts to 
push off the Southeast coast. High temps should peak in the lower 
90s outside shower and thunderstorm activity. 

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Drier conditions are anticipated mid week as high pressure builds 
over the region Wednesday/Thursday while sfc low pressure is less 
pronounced inland. Other than a few afternoon showers/thunderstorms, 
the pattern should support slightly warmer conditions with high 
temps peaking in the low-mid 90s. Higher precip chances could return 
next weekend as the sfc trough becomes more pronounced inland 
while a front shifts toward the Mid-Atlantic states.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions will prevail at the KCHS/KSAV terminals. We have 
introduced VCTS late afternoon into early evening on this cycle
as the trough pattern in the mid levels appears to be enough
to allow for the potential scattered sea breeze convection.

Extended Aviation Outlook: Brief flight restrictions are possible 
each afternoon/evening with showers and thunderstorms. Otherwise, 
VFR conditions are expected at both CHS and SAV terminals. 

&&

.MARINE...
Persistence forecast for the most part, southwest synoptic flow
will back south over GA waters this afternoon with enough
gradient to support flow increasing back to 15 kt with some
higher gusts at time. Along the SC coast, winds will also build
to 15 kt with occasional G20 kt possible later in the day and 
this evening. Through Tonight, seas will generally average 2 to
3 ft. Tstms look more likely after midnight tonight with some
strong storms possible locally. Storm motions should mainly 
be side or slightly offshore with coverage more prevalent beyond
20 NM.

Sunday through Thursday: Conditions are expected to remain 
below Small Craft Advisory levels through the middle of next 
week. However, a somewhat tightened pressure gradient between 
low pressure inland and high pressure offshore will support 
southwest/south winds near 15-20 kt through much of the week. 
Shower and thunderstorm coverage should also increase over 
coastal waters on Monday, especially as a weak front attempts to
shift offshore by the middle of the week. Seas will range 
between 2-4 ft into Tuesday, then slowly subside to 1-3 ft mid 
to late week.

Rip Currents: While we are forecasting a Low Risk of rip currents 
at the beaches today, due to astronomical influences it won't 
take but a little higher wind than now forecast to bump the risk
into the moderate range during the afternoon hours.

&&

.TIDES/COASTAL FLOODING...
The Perigean Spring Tide due to the New Moon and the Perigee 
will contribute to elevated high tide levels into early next 
week. The evening high tides could produce shallow coastal 
flooding, mainly over the weekend. Coastal Flood Advisories are 
possible.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

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