Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 190126
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
926 PM EDT Wed Sep 18 2019

.SYNOPSIS...
High pressure will provide noticeably cooler and drier
conditions through late week and will prevail through early
next week. A cold front could push into the region around the
middle of next week. 

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Tonight: High pressure will build across the region in wake of 
a cold front shifting south of the area. Few to scattered clouds
should then clear across the area from north to south during 
the first half of the night. Weak cold air advection associated 
with dry high pressure building across the area should help 
maintain a 5-10 mph northeast wind overnight. However, cold air 
advection and drier air will likely support cooler temps, with 
lows eventually dipping into the upper 50s to around 60 well 
inland (coolest in Southeast South Carolina) and mid/upper 60s 
near the coast.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Cooler/drier high pressure will prevail through this period. The 
only wrinkle will be for isolated/scattered showers which will cross 
coastal waters and develop onshore within an E/NE low-level flow 
regime. Slight chance PoPs are limited to far southern/coastal 
counties through Thursday, then coverage of slight chance/chance 
PoPs expands somewhat later Thursday night through Friday as a 
coastal trough becomes more pronounced, with highest PoPS across 
southern/coastal counties. Limited instability does not justify any 
mention of thunderstorms through this period. Friday night through 
Saturday, guidance suggests that the surface high will expand and 
will push the chance for showers south of the region. 

Otherwise, high temperatures in the upper 70s north and lower to mid 
80s south will warm into the middle/upper 80s Saturday away from the 
beaches. Thursday night, low temperatures will average 55-60F away 
from t he coast and 65-70F on the beaches. Late Friday night, 
temperatures will fall into the upper 50s to middle 60s inland and 
will bottom out in the upper 60s to middle 70s on the coast. The 
most noticeable change will be the drier air mass featuring daytime 
dewpoints in the 50s/60s through this period.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
00Z TAFs: VFR. Expect gusty northeast winds Thursday afternoon.

Extended Aviation Outlook: VFR conditions will prevail.

&&

.MARINE...
Tonight: High pressure will build across coastal waters through
tonight behind a departing cold front to the south. A fair 
amount of cold air advection associated with a northeast wind 
along with long period swells near 11 seconds will result in 
ongoing Small Craft Advisories for all waters outside the 
Charleston Harbor through tonight. Some guidance suggests winds 
could increase toward daybreak Thursday, necessitating a Small 
Craft Advisory in the Charleston Harbor. In general, northeast 
winds will gust to 20-25 kts while seas build up to 5-7 ft in 
nearshore waters and 7-10 ft in offshore Georgia waters.

A tight northeast gradient enhanced by high pressure centered north 
of the waters will maintain hazardous winds/seas through Friday. 
Northeast winds averaging 20-25 knots with gusts to 30 knots will 
contribute to combined seas topping out at 5-8 feet nearshore waters 
and 8-12 feet beyond 20 nm, with worst conditions Thursday through 
Thursday night. Small Craft Advisories are in effect for all waters 
outside Charleston Harbor, and wind gusts could approach SCA levels 
even on the Harbor Thursday.  

Friday and especially Friday night, the pressure gradient/ 
associated winds will relax. While SCA seas could persist into the 
weekend over the outer GA waters, overall we can expect a much more 
tranquil regime this weekend into early next week. Long period swell 
created by offshore TC Jerry could reach coastal waters by early 
next week.  

Rip Currents: High risk of rip currents on all beaches through 
Thursday evening due to strong northeast winds and at least a 
2-3 ft/11 second period swell created by offshore Hurricane 
Humberto. An elevated risk for rip currents will then continue 
through at least the end of this week.

&&

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

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...High Rip Current Risk through Thursday evening for GAZ117-119-
     139-141.
SC...High Rip Current Risk through Thursday evening for SCZ048>051.
MARINE...Small Craft Advisory until 8 PM EDT Friday for AMZ350-352-354.
     Small Craft Advisory until 4 AM EDT Sunday for AMZ374.

&&

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