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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 162255

Area Forecast Discussion
National Weather Service Charleston SC
655 PM EDT Mon Sep 16 2019

Hurricane Humberto will continue to move away from the coast
through mid week. A cold front will advance through the area
Wednesday, followed by high pressure into early next week. 


Satellite imagery shows clearing skies over land areas earlier 
than expected, so we adjusted the forecast to account for this 
over the next few hours. Dew points are also running lower than
expected across the entire area, so we trended these down
through most of the night. With lower dew points, there is
the concern temperatures will be lower. But we're opting to 
monitor the temperature trends before making any chances to the
overnight lows.

Otherwise, drying/subsidence enhanced on western periphery of 
departing Hurricane Humberto will support a tranquil night. 
After a very warm late afternoon/early evening, under clear 
skies temperatures by daybreak will range from 65-70F inland to 
the middle 70s on the beaches.


Tuesday: As Hurricane Humberto accelerates away from the area, the 
pressure gradient across the area will weaken. Sinking motion across 
the area in the wake of Humberto combined with compressional heating 
ahead of a backdoor cold front will help low level temperatures and 
thickness values to increase. As a result, with abundant sunshine it 
will be rather hot especially for mid September. Raised high 
temperatures a degree or two in most areas away from the coast with 
highs generally in lower to mid 90s away from the coast. Heat 
indices will only reach 95 to 100 away from the coast as low level 
dew points mix out a bit during the afternoon. Moisture and cloud 
cover increase Tuesday night and there could be a shower or two 
along the coast during the later half of the night. However, will 
maintain a silent 10 percent pops in the forecast due to the 
expected limited coverage. 

Wednesday: As the backdoor cold front pushes through the area from 
north to south, there could be a few showers. Cooling temperatures 
aloft support some instability especially during the afternoon. As a 
result, think there could be a few thunderstorms along and ahead of 
the front. Kept it dry in the north where the front will move 
through before any instability can develop. Limited moisture and 
instability should keep rain chances in the slight chance category. 
Cooler and drier air will advect into the area from the north behind 
the front. High temperatures should range from 80-85 across 
southeast South Carolina to the upper 80s across mainly interior 
southeast Georgia. As the back door cold front pushes south of the 
area, the threat for precipitation will end in the south Wednesday 
evening. It will be much cooler by Thursday morning with lows 
ranging from near 60 in the north away from the coast to near 70 
along the coast in southeast Georgia. 

Thursday: Cooler and less humid conditions are expected for all 
areas with highs ranging from the upper 70s along the South Santee 
River to the mid 80s to the west of I-95 and south of I-16. Breezy 
conditions are likely near the coast, especially for the beaches and 
barrier islands.


Deep layered ridging will persist over the region late week 
into early next week, bringing near climo temps and dry weather 
for the forecast area.


VFR through the 18Z TAF period. N/NE winds could gust around 20
knots at times until late this afternoon. 

Extended Aviation Outlook: Patchy fog is possible around the 
terminals around daybreak Wednesday, flight restrictions appear 
unlikely at this time. Otherwise, VFR.


Tonight: The latest observations from buoy 41008 have winds
generally under 10 kt. We lowered the wind forecast in this
general area to better account for this in the next few hours.
Buoy 41004 indicated seas were a foot lower than the forecast,
so we also accounted for this. We remain borderline for needing
a Small Craft Advisory for seas in AMZ352, so we'll maintain it.
The other zones (AMZ350 and AMZ354) didn't need any changes
with their advisories. Those zones could have NE winds as high 
as 25 kt with hazardous seas.

TC Humberto will continue to impact the coastal waters on Tuesday 
and Tuesday night with large swells and modest northeast winds. The 
swells will begin to decrease by Wednesday, but the northeast winds 
will increase behind the backdoor cold front on Wednesday prolonging 
the small craft advisory conditions for AMZ350 and AMZ374. Looks 
like significant improvement in marine conditions is unlikely until 
late week especially for AMZ350 and AMZ374. The gradient and overall 
winds and seas should subside this weekend as broad high pressure 
blankets the southeast states.

Rip Currents: We maintained a high risk for rip currents at all
beaches into this evening due mainly to earlier rip current
reports and continued elevated/long period swell emanating from
Hurricane Humberto. The rip current risk will then remain 
elevated throughout at least midweek as the large swells from 
Hurricane Humberto continue. The rip current risk could remain 
elevated perhaps through the end of the week as northeast winds 
and the longshore currents strengthen behind the backdoor cold 


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


GA...High Risk for Rip Currents until 8 PM EDT this evening for GAZ117-
SC...High Risk for Rip Currents until 8 PM EDT this evening for 
MARINE...Small Craft Advisory until 6 AM EDT Tuesday for AMZ352.
     Small Craft Advisory until 6 PM EDT Friday for AMZ350.
     Small Craft Advisory until 8 PM EDT Saturday for AMZ374.