Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
927 PM EDT Sat may 23 2015
high pressure will extend across the region through next week. A
coastal trough will linger over the coastal waters through Sunday
Near term /until 6 am Sunday morning/...
quiet weather tonight. Subtle coastal trough is taking shape
offshore. Isolated showers over the Georgia offshore waters will
linger for a few more hours before slowly dissipating. Could see
few sprinkles reach the upper Georgia coast by sunrise...but
measurable rainfall is unlikely at this time. Adjusted hourly temperatures and
sky cover based on short term trends and incoming high resolution
data. No major changes were made with the late evening update.
Short term /6 am Sunday morning through Tuesday/...
models in good agreement that high pressure ridging will prevail
this period and with limited moisture/forcing in place rain chances
will be low. On Sunday the best chances will be across southeast
Georgia where low-level moisture will be a bit greater and the
northern end of a possible coastal trough offshore could reach. Some
showers could linger Sun night and push into SC south of Beaufort
along the trough. For Monday the best rain chances will be dependent
on the trough position which should be pushing north of
Charleston...but will generally be across inland areas as the sea
breeze pushes through in the afternoon. By Tuesday the best rain
chances should again be inland along the progressive sea breeze.
Temperatures should be near to slightly below normal Sunday before
climbing to or even slightly above normal Monday/Tuesday.
Long term /Tuesday night through Saturday/...
a weak upper ridge will persist over the southeast states while a
weak upper trough sits to the west and a large closed upper low
exists near Bermuda. A weak surface high will build down the eastern
Seaboard...keeping dewpoints in the low to middle 60s. A slightly
weaker cap over inland areas will support isolated showers and thunderstorms
during the afternoon Wednesday through Friday. Thereafter the upper
ridge will rebuild over the area...suppressing convection and likely
yielding a dry weekend. Temperatures will warm through the upper 80s into
the lower 90s late week into the weekend.
Aviation /02z Sunday through Thursday/...
Extended aviation outlook...MVFR ceilings will be possible through
middle week...mainly at ksav late night through around noon each day.
initialized the Georgia offshore zone with a Small Craft Advisory
per 18z ww4 output. Also included isolated showers for a few more
hours. The rest of the forecast is on track.
Tonight...high pressure will continue to sit off the middle Atlantic
coast and will drive the persistent easterly flow across the local
waters. The pressure gradient remains modestly tight...and this will
keep winds in the 15-20 knots range everywhere outside of the
Charleston Harbor. The long fetch easterly flow will help to
gradually build seas as well. By late tonight...expect 3-5 feet out to
20 nm...and 5-6 feet beyond. As a result of 6 feet seas beyond 40 nm in
the outer Georgia waters...a Small Craft Advisory will be issued
starting late tonight. Models show a bit of a developing coastal
trough through the night...and there is a low chance for some shower
development in the outer reaches of the outer Georgia waters.
Probability of showers is too low to mention in the forecast at this
Sunday through Thursday...Atlantic high pressure to persist keeping
a solid onshore flow through the period. Conditions will remain a
bit worse than normal given the enhanced pressure gradient and
persistent fetch...likely reaching advisory levels beyond 20 nm
through Sun night. Charleston Harbor may also see marginal advisory
conditions with gusts near 25 knots Sunday and possibly Monday as the
sea breeze helps increase winds near the coast.
Rip currents...strong onshore winds and some lower period swell
energy are expected at the coast Sunday and we decided to lean
toward a moderate risk for all beaches given the rip current reports
from today and Holiday weekend.
Marine...Small Craft Advisory until 8 am EDT Monday for amz374.