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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 180551
AFDCHS

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

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

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
As of 150 AM: I will issue a quick update to align PoP and Wx
with recent radar trends. Generally keeping SCHC to CHC PoPs
along and south of the Savannah River. Otherwise, the current
forecast appears in good shape.

Previous Discussion:
Quick Update to add slight chance POPs to Allendale County and
surrounding areas. Radar shows isolated thunderstorms
approaching this area. The HRRR indicates they should persist
for at least the next 2-3 hours. We may need to expand this
areal coverage further, depending on the future radar trends.

Otherwise, a cold front will move south and should make it 
toward the Altamaha River near daybreak as Hurricane Humberto 
well offshore continues to move farther away. Some showers are 
expected to develop as moisture, instability and convergence 
increase a bit. Can't rule out some weak storms but any thunder 
should mainly be confined to around the GA coast where the 
greatest instability is expected. Temperatures should fall to 
around 70 north and west toward the Pee Dee/Midlands with lower 
to mid 70s south and east toward the coast and GA Coastal 
Empire.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH FRIDAY/...
Wednesday: Models in good agreement that the backdoor front will 
move through the area from north to south during the day. Models 
show some increase in moisture associated with the front and this is 
supported by cloud cover across Virginia at the present time. Some 
minor instability is expected to develop mainly in the afternoon 
across southeast Georgia. Threat for precipitation is low enough in 
the north due to the early arrival of the front that it was left out 
of the forecast. Highest rain chances will be in the south. Threat 
for precipitation will end by late afternoon. Made some minor 
adjustment to lower high temperatures from the Allendale/Walterboro 
areas south to near Savannah. Maintained highs in the mid to upper 
80s southwest of this area, but have some concern that cloud cover 
may be sufficient enough to keep the high temperatures from getting 
that high. Highs will mainly be in the lower 80s in the north and 
along southeast South Carolina Coast. Drier air will move in behind 
the front with lows Wednesday night ranging from near 60 in the 
north to near 70 along the southeast Georgia Coast.  

Thursday: Drier air will continue to overspread the area in the wake 
of the cold front. The only exception will be along the southeast 
Georgia Coast near the Altamaha River where a few very light marine 
showers could brush the coast. Brisk northeast winds are expected 
along the coast. High temperatures area wide will be rather mild 
and this combined dew point temperatures in the 50s inland to the 
lower to mid 60s at the coast will make for a rather pleasant day. 
Highs should range from the upper 70s near the South Santee River to 
the mid 80s across far inland portions of southeast Georgia. A few 
light marine showers are possible in southeast Georgia mainly east 
of I-95 Thursday night.   

Friday: As surface high pressure begins to build from the Mid-
Atlantic states into the western Atlantic, surface winds will become 
more onshore especially from Beaufort County south and this will 
allow the threat for some light marine showers to spread further 
inland especially across southeast Georgia. Highs should range from 
near 80 along the coast to the mid 80s far inland where more 
sunshine is expected and there is basically no threat for 
precipitation.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Deep layered ridging will persist over the weekend and then 
tend to break down during the first part of next week. Models 
continue to show dry weather prevailing through the entire 
period. High temps are expected to warm slightly above climo 
during the period, however overnight temps should continue to 
fall into the 60s each night away from the ocean as the 
atmosphere remains quite dry.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
A backdoor cold front will slide south across KCHS early this
morning and KSAV during the early daylight hours. The approach
and passage of the cold front may support a few showers near
KSAV this morning, I will highlight with VCSH at KSAV. High
pressure is expected to build across the terminals through the
afternoon. The combination of mixing and a weak pressure
gradient should support gusts near 20 kts at KCHS this
afternoon. Clearing sky and decreasing winds are expected across
the terminals this evening.

Extended Aviation Outlook: VFR conditions will prevail.

&&

.MARINE...
Tonight: A cold front will move south through most, if not all,
of the waters with winds picking up from the northeast behind 
it. Seas will also build as a result and Small Craft Advisories
are in effect for all waters except Charleston Harbor and the
nearshore GA waters.

Wednesday through Sunday: Northeast winds will dominate 
throughout the week in the wake of the backdoor cold front that 
moves through the waters on Wednesday. The combination of 
increasing seas and winds will result in 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. Looks like the best threat for Small craft 
Advisory conditions to occur in Charleston Harbor will be on 
Thursday. Later shifts will need to further evaluate and if 
necessary issue an advisory there. 

Rip Currents: Moderate Risk through Wednesday due to lingering 
elevated long period swells and increasing longshore currents 
due to strengthening northeast winds. 

The rip current risk will remain elevated through the end of the 
week as northeast winds and strong longshore currents continue.

&&

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

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 8 PM EDT Friday for AMZ352.
     Small Craft Advisory until 4 AM EDT Sunday for AMZ374.
     Small Craft Advisory until 8 PM EDT Friday for AMZ350.
     Small Craft Advisory from 11 AM this morning to 8 PM EDT 
     Friday for AMZ354.

&&

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