Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 161618
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1218 PM EDT Wed Aug 16 2017

...HEAT ADVISORY FOR COASTAL AREAS OF SOUTHEAST SOUTH CAROLINA
AND SOUTHEAST GEORGIA...

.SYNOPSIS...
Atlantic high pressure will remain in control as troughing
persists across the Mid-Atlantic region and inland into late
week. A cold front will approach this weekend, likely falling
apart early next week as high pressure returns.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The forecast is on track. 16/16z heat indices were already
approaching 110 in a few spots along the coast, so the Heat
Advisory was recently updated to move the start time to the
current time. Still looks like max heat indices will peak
108-113, although a few spots could approach Excessive Heat
Warning criteria of 115, especially along the lower South
Carolina coast where the pinned sea breeze will make some
inland progression very late in the afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
Tonight: Another warm and muggy overnight is on tap. We
maintained a late night chance of convective rains along the SC
beaches close to a weaker land breeze.

Thursday through Saturday: For the most part, ridging will
dominate aloft while the surface pattern features a lee-side
trough and Atlantic high pressure extending across FL into the
Gulf of Mexico. The main mechanisms for convection will be the
sea breeze and the proximity to the inland trough, although
boundary interactions will come into play as coverage increases
each afternoon. This will allow for scattered PoP`s each day,
with activity to wind down with nocturnal influences each night.
Steering flow is weak and PWat is at least 2 inches, and this
will support the risk for locally heavy downpours, but no
widespread flooding concerns are anticipated.

Our 850 mb temps average 19-20C, above the 90th percentile for mid
August, while 925 mb temps are as high as 26-27C, or about as high
as they can get this time of year. This will support max temps above
normal, but exactly how hot depends on the onset of diurnal
convection. For now we have lower and middle 90s each day inland
from the immediate coast, with lows at best only down into the mid
and upper 70s.

Heat Indices will be as high as 106-108F Thursday, 105-107F Friday
and 103-105F Saturday. Not quite to Heat Advisory thresholds, but
certainly making for unbearable/uncomfortable outdoor conditions
where there can be an increased risk for heat disorders with
prolonged outside exposure and/or strenuous activity.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
A cold front upstream will attempt to approach but will likely fall
apart as it runs into a strong blocking ridge both surface and
aloft. The typical instability along with sufficient moisture and
meso-scale boundary interactions will support a chance of mainly
diurnally driven convection each day through the extended period,
including Monday the day of the total solar eclipse. Above average
heights, 925 and 850 mb temps and low level thickness will allow for
a continuation of above normal highs and lows.

&&

.AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
Primary concerns:
* None - VFR.

Extended Aviation Outlook: Temporary flight restrictions can occur
in scattered diurnal convection through Sunday.

&&

.MARINE...
Today through Saturday: The coastal waters will lie in a general
SW`erly flow along the fringes of Atlantic high pressure, as a
Piedmont trough persists inland over the SE. While afternoon sea
breeze influences and nocturnal low level jetting will give a
boost to winds, speeds on average will be no more than 15-18 kt.
Seas will hold at or below 3 or 4 ft. Expect isolated to scattered
showers and t-storms through the entire period.

Sunday through Monday: A cold front upstream will never reach the
waters as high pressure holds firm, keeping winds and seas below any
SCA conditions. Isolated to scattered showers and t-storms will
again prevail.

&&

.EQUIPMENT...
The temperature sensor at the Downtown Charleston observation
site (KCXM) has failed. Technicians are working to resolve the
problem. Temperature and dewpoint data will not be available
until the sensor is replaced.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 7 PM EDT this evening for GAZ116>119-
     138>141.
SC...Heat Advisory until 7 PM EDT this evening for SCZ045-047>052.
MARINE...None.

&&

$$



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