685 
FXUS62 KCHS 230956
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
456 AM EST Fri Nov 23 2018

.SYNOPSIS...
A low pressure system will move through tonight through
Saturday. A cold front will then move through Monday followed
by high pressure. 

&&

.NEAR TERM /THROUGH TONIGHT/...
Pre-dawn: Strong high pressure centered over New England 
continues to wedge south into the forecast area, resulting in a 
tightening pressure gradient and increasing breezes across the 
region. Breezy to windy conditions were ongoing on the beaches 
and barrier islands but latest indications were too borderline 
for wind advisories but we will monitor trends with the pinching
gradients. Rains were still off the coast and skies ranged from
mainly clear to the north of I-16, to cloudy conditions along 
coastal areas from Hilton Head southward through immediate 
coastal GA. The strong northeast flow may be responsible for 
some significant coastal flooding around high tide this 
morning, please see the tides/coastal flooding section.

Today: A very complicated synoptic setup both surface and aloft
as strong thermal and moisture gradients dominate the southeast
states from north to south in the lower levels, anchoring tight
low level pressure fields. Aloft, an upper jet segment extending 
across Florida will exit offshore while a strengthening jet digs
into the Gulf Coast region. The forecast today continues to 
show unsettled weather developing along southern coastal areas 
and gradually spreading north and inland this afternoon. Clouds
are expected to increase during the morning hour as isentropic 
ascent builds while warm air advection spread atop the wedge 
inversion. Temps will likely reach max levels by early in the 
afternoon before thickening clouds and rains tend to develop 
over more land areas. We kept most areas shy of 60 degrees 
throughout the day, lowering some readings over southeast GA 
from the previous forecast. Inland areas closer to the CSRA and 
SC Midlands may keep dry all day as models initially keep rains 
along and east of I-95. The tight pressure gradient will keep 
cool northeast flow going with breezy to windy conditions on the
beaches and barrier islands where winds could frequently gust 
over 30 mph.

Tonight: A progressive mid level short wave will move from
the Southern Plains into the western Carolinas by 12Z on
Saturday. Models break out more in the way of widespread
rains, especially across coastal areas and nearly all of
Southeast SC. There is some uncertainty on how far coastal
trough can move inland after midnight, perhaps only into
SC coastal zones where low level moisture and convergence
would be maximized. A few models suggest an inch of rain is
possible overnight in this area but most should fall after
this evening's high tide and prior to Saturday's morning
high tide. We continue to indicate likely to categorical
POPs with temps ranging from the mid to upper 40s inland
to the lower/mid 50s coast. Some lightning strikes could
occur close the coast as the stronger upper forcing moves
through but we mainly tstms for the adjacent waters again
on this package.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
Low pressure will quickly pull northeast away from the forecast area 
Saturday. Latest guidance indicates rain will end from southwest to 
northeast, generally by early afternoon, though some model variation 
exists. Behind the low, a noticeably drier atmospheric column will 
be in place for much of Sunday with moisture levels increasing late 
in advance of a developing low pressure system over the central 
plains. This system will track northeast across or near the Great 
Lakes, pulling the next cold front through the forecast area Monday. 
As the front nears, moisture levels will increase greatly Sunday 
night into Monday, and slight chance POPs are warranted during this 
period considering increasing lift as the upper trough
approaches.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
Based on the latest guidance, rain chances diminish by Monday 
afternoon behind the cold front, with dry high pressure persisting 
through at least mid-next-week. Coastal troughing could develop 
by late next week, increasing precipitation chances.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
VFR for much of the night at both KCHS and KSAV with conditions
dropping to MVFR mid-late morning Friday. Gusty winds >20 kt will
be possible at both terminals late tonight and will linger 
through the end of the 00Z TAF period. Risk for shower activity
will increase quickly after 20, especially at KSAV where we 
introduced some rain late. We have rain breaking out at KCHS
toward the end of the 06Z TAF cycle.

Extended Aviation Outlook: Flight restrictions likely into Saturday 
as low pressure impacts the area. Surface conditions look to improve 
Sunday but brief flight restrictions will be possible overnight 
Sunday into Monday as a cold front crosses the region. VFR 
conditions are then expected to prevail at both terminals into mid-
next-week.

&&

.MARINE...
Hazardous conditions are expected over the marine waters today 
with Gale Warnings in effect. We extended the Gales to mid
afternoon with an SCA for the Charleston Harbor. Seas will build
to 7-9 ft near shore and up to 11 ft offshore. The winds will
tend to subside across GA waters tonight as the coastal front
moves closer. Winds should remain strong and gusty this evening
along SC waters but also tend to subside late as a wave of low
pressure rides along the coast. 

A continuing tight surface pressure gradient will lead to Small
Craft Advisory conditions over the nearshore coastal waters 
through late Saturday and offshore Georgia waters through early 
Sunday. Another round of Small Craft Advisories will be possible
Monday as a cold front crosses the waters. High pressure will 
then persist into mid-next-week.

High Surf: Local surf height guidance shows a possible window 
this morning of 5 ft breakers along the SC/GA coast. We will 
monitor for the potential of a High Surf Advisory. Some beach 
erosion is possible given the above normal tides.

&&

.TIDES/COASTAL FLOODING...
Strong northeast flow had developed along the coast overnight.
Based on the latest forecast trends, it appears the chances for
major coastal flooding were increasing given latest guidance.
Tides are expected to peak 7.8-8.2 ft MLLW in Charleston Harbor 
and 9.9-10.3 ft at Fort Pulaski. We have upgraded the Coastal 
Flood Watch to Warning this morning. Expect Hwy 80 between 
Wilmington Island and Tybee Island will be closed due to 
saltwater inundation. A Coastal Flood Advisory was also issued 
for Tidal Berkeley County.

Strong onshore flow through tonight combined with increasing 
astronomical effects will likely result in minor to moderate 
coastal flooding with the morning high tide Saturday. Coastal 
Flood Advisories are expected.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Coastal Flood Warning until 10 AM EST this morning for GAZ117-
     119-139-141.
SC...Coastal Flood Warning until 10 AM EST this morning for 
     SCZ048>051.
     Coastal Flood Advisory until 10 AM EST this morning for SCZ052.
MARINE...Gale Warning until 4 PM EST this afternoon for AMZ350-352-354-
     374.
     Small Craft Advisory until 1 AM EST Saturday for AMZ330.

&&

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