Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
926 PM EDT Friday Aug 1 2014
a stationary front will linger near the southeast coast through the
middle of next week...steering Tropical Storm Bertha out to sea...
and also bringing unsettled weather to the local area. A Piedmont
trough will then prevail through late next week.
Near term /until 6 am Saturday morning/...
the coastal fnt is lurking across the eastern portions of the forecast
area this evening and will remain the primary focus for shower/thunderstorm
development overnight as a moist/southerly flow interacts with it.
Already seeing signs of showers reforming off the Charleston County
coast. Convective activity just S of the Altamaha river will likely
impact parts of long-McIntosh through midngt. Could see an isolated
flood threat there...mainly in low-lying and poor drainage areas.
Other than making minor adjustments to near term probability of precipitation...the forecast
is on track.
Need to watch for low stratus and perhaps some fog developing late
tonight along the western periphery of the front...where increased
subsidence is expected. Considerable cloud cover will only allow
temperatures to fall to lows in the lower to middle 70s tonight.
Short term /6 am Saturday morning through Monday/...
a broad and persistent deep-layered trough will prevail over the
eastern United States...while a stationary front holds nearby and
probably just off the local coast into next week. A deep influx of
both Gulf and Atlantic sub-tropical moisture will continue...with
precipitable waters climbing near or greater than 2 inches...near the 75th
percentile for early August. Various waves of upper divergence
associated with the right entrance ageostrophic circulation of the
upper jet will occur...while surface and low level convergence
associated with the front and other developing mesoscale-scale boundaries
will provide plentiful large scale forcing for ascent. Probability of precipitation will be
as high as 60-70 percent each day. Coverage will taper
overnight...but with the front still nearby and abundant
moisture...probabilities will remain highest near the coast.
Rain will be heavy at times and localized flooding will be cause for
a concern with a weak storm motion. Flash flood advisories and/or
warnings may be required as a result. The severe risk is quite low
given considerable cloud cover and poor lapse rates.
Extensive cloud cover and elevated rain chances will keep daytime
highs down below seasonal norms...while night time lows will be
close to climatological levels.
Long term /Monday night through Friday/...
drier...more seasonable weather will return by middle week as the front
meanders offshore and dissipates. Atlantic high pressure will
gradually reestablish itself across the region with more a more
typical convective pattern expected. Highs will be in the upper 80s
to lower 90s with lows in the Lower-Middle 70s. Tropical Storm Bertha
is forecast to remain offshore as it curves well off the southeast
Aviation /02z Saturday through Wednesday/...
there will be a increased risk for MVFR and possibly IFR
conditions overnight as low-level moisture slowly builds
underneath the nocturnal inversion. Current data suggests there
may be enough middle-level cloudiness in place to keep ceilings/visibilities
above both alternate and airfield minimums...although alternates
may be required. Transient shower activity could occur at just
about anytime overnight into Saturday morning...but the best
chances look to occur at kchs...roughly 15-18z...possibly earlier.
Shower activity is possible at ksav but confidence is not high
enough at this time to include a mention.
Extended aviation outlook...periods of IFR/MVFR likely through
Tuesday in rain showers/thunderstorms and rain as a stationary front lingers nearby. Still a
chance of temporary flight restrictions in rain showers/thunderstorms and rain next Wednesday.
tonight...a nearly stationary front will remain just inland of the
coast...resulting in south-southeast winds through the night.
Wind speeds could be upwards of around 15 knots...before diminishing a
bit overnight. Seas will range 2-4 feet...highest over the outer
Georgia waters. Showers and thunderstorms should increase in
Saturday through Sunday...a stationary front will persist over or
near the local waters during this time with fluctuations in wind
speeds and directions dependent upon where the front actually aligns
itself. On average winds will be mainly southeast Saturday/Saturday
night...easterly Sunday/Sunday night. Speeds will remain held under
15 knots and seas no higher than 3 or 4 feet.
Monday through Wednesday...swells generated by Tropical Storm Bertha
could impact the waters Monday into Wednesday as it curves well
offshore of the southeast U.S. Coast. There is a possibility that
combined seas could reach Small Craft Advisory thresholds during this
period...but its a bit too far to really pin that down this far out.
Seas will be capped at 4-5 feet for now.
Given the proximity to the stationary front and a rich flow of
sub-tropical moisture...periodic showers and T-storms will occur
into next week. Some of these storms will be strong with frequent
lightning...gusty winds and heavy downpours. As a result...mariners
are advised to monitor National oceanic and atmospheric administration weather radio all hazards and/or
appropriate vhf channels for weather updates and information.