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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 181457

Area Forecast Discussion
National Weather Service Charleston SC
1057 AM EDT Wed Sep 18 2019

A cold front will advance through southern areas early today. 
High pressure will then build south into the region later today 
and continue into early next week. 


Today: A backdoor cold front will continue to shift south over parts 
of Southeast Georgia late this morning and into early afternoon. 
South of the front, MLCAPE around 1500 J/kg and PWATs around 1.75 
inches should support isolated to scattered showers and thunderstorms,
especially near coastal locations in Southeast Georgia where 
moisture convergence is enhanced. The bulk of precip should come
to an end across most locations as the front shifts south of 
the Altamaha River early this afternoon. However, a few showers 
could linger well behind the front as high pressure builds across
the region from the north. Temps will be noticeably cooler once
fropa occurs, especially compared to the previous day. In 
general, high temps should peak in the lower 80s across Southeast
South Carolina and low/mid 80s before fropa in Southeast Georgia.

Tonight, a wedged ridge of high pressure is forecast to build 
southwest along the east facing slopes of the Appalachians
tonight. The ridging should support steady northeast winds
across the CWA tonight. The northeast winds will likely result
in a gradually lowering of low level thicknesses and cooling h85
temps across the region. The combination of cooling llvl thermal
profiles and clearing sky will yield below normal low
temperatures tonight. Using a blend of cooler MOS, I will
forecast low temperatures to range from the upper 50s across
inland SC to the low to mid 60s across SE GA.


Thursday: Surface high pressure will dominate the eastern seaboard. 
Very dry air aloft will reside across the forecast area as Pwats 
will mainly be less than 1 inch. Dry weather is on tap plenty with 
abundant sunshine across most of the area. Atlantic stratocu and 
coastal afternoon cumulus are expected. There could be a potential 
for a few very light showers or sprinkles to brush far south coastal 
GA, but measurable rain potential looks quite low. Cooler temps are 
on tap with highs from the upper 70s north to lower 80s south. The 
coastal corridor will also see breezy conditions, especially closer 
to the beaches and barrier islands.

Friday: Models continue to hint at a weak coastal trough just off 
the GA coast. Latest data also progs a decent amount of isentropic 
ascent into southeast GA. Pwats will increase slightly over 1 inch 
and light patchy showers could certainly develop. Patchy showers 
further inland to the south of I-16 are also possible after mid 
afternoon. We have some slight chance POPs in that area with low-end 
chance POPs along the GA coastal corridor. We should see more clouds 
across the area although northern SC zones may still see a mostly 
sunny day, especially inland. 

Saturday: Deep layered ridging will continue to expand across the 
forecast area. We anticipate a dry day with scattered stratocu 
more prevalent along coastal GA with the onshore flow. Temps
will begin a warming trends with highs in the mid 80s with upper
80s to the west of I-95.


Deep layered ridging will persist into Monday and then tend to break 
down thereafter. Models hint at a weak front and stronger northwest 
flow aloft by mid-week, however the depth of dry-layered air was 
still enough to keep mentionable POPs out of the forecast. Temps are 
expected to run above climo each day with a return to some 90 degree 
high temps early next week inland and southern zones.


A backdoor front will continue to shift south of the terminals late 
this morning with high pressure building in its wake. A few showers 
could develop across the SAV terminal late morning into early 
afternoon, resulting in brief MVFR conditions. VCSH remain at the 
SAV terminal until 15Z, but could be needed until 17Z. The combination
of mixing and a weak pressure gradient should support gusts near
20 kts at KCHS and KSAV this afternoon. Clearing sky and decreasing
winds are expected across the terminals this evening.

Extended Aviation Outlook: VFR conditions will prevail.


Today and Tonight: A backdoor cold front will slide south of the 
marine zones late this morning into early afternoon with high 
pressure building across the waters in its wake. Gusty northeast 
winds are expected  behind the front as cold air advection 
occurs from the north and the pressure gradient tightens. The 
combination of wind and sea conditions will be highlighted with 
Small Craft Advisories for all marine zones outside of the 
Charleston harbor today though tonight, mainly due to higher 
seas associated with long period swells near 11 seconds. In 
general, northeast winds will gust up to 20-25 kts while seas 
build to 5-7 ft in nearshore waters and 7-10 ft in offshore 
Georgia waters (highest tonight).

Northeast winds will dominate throughout the week as high 
pressure anchors to the north. Small Craft Advisory conditions 
for all coastal waters into Friday evening for the nearshore 
waters and well into Saturday night for the offshore Georgia 
waters. We may need to issue a SCA for the Charleston Harbor on 
Thursday as periods of near 25 kt wind gusts are possible. 

The pressure gradient is forecast to weaken during the weekend as 
the surface high bridges closer to the marine waters. Seas will 
gradually subside with time as well. By Monday, winds may become 
light and variable, before becoming south to southwest later in the 

Rip Currents: A Moderate Risk of rip currents is in place today for 
all beaches due to lingering long period swells and increasing 
longshore currents due to strengthening northeast winds behind a 
departing front. The rip current risk will remain elevated through 
the end of the week as northeast winds and strong longshore currents 


Low chances for minor coastal flooding around the times of high
tide through late week, especially along the South Carolina coast.


MARINE...Small Craft Advisory until 8 PM EDT Friday for AMZ350-352.
     Small Craft Advisory until 4 AM EDT Sunday for AMZ374.
     Small Craft Advisory until 8 PM EDT Friday for AMZ354.