Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1001 am EDT sun may 24 2015
high pressure will extend across the region through next weekend.
Near term /through tonight/...
late this morning...the forecast area remains almost directly
under the center of the deep ridge aloft. High pressure centered
well off the middle Atlantic coast continues to drive a persistent
onshore easterly flow through the day. It will be quite similar to
Saturday...with just a bit more low level moisture noted in model
time heights. Sounds continue to show a prominent subsidence
inversion around 800 mb...and that will keep the forecast dry
through the day. There will likely be a bit more diurnal cumulus
as well as some advecting in off the Atlantic in the easterly
flow. Otherwise...another quiet day. No changes to high
temperatures...upper 70s to low 80s closer to the coast...ranging
to middle 80s well inland in some places.
Tonight...the ridge aloft begins to weaken a bit and drift slowly
east. Models indicate weak isentropic lift along 300k may play a
part in expanding some nocturnal stratocu fields along coastal
south Georgia northward with time to the west of I-95. We cannot
rule out a few sprinkles to the south of I-16 late. Otherwise...
patchy clouds...continued quiet weather and lows ranging from the
middle 60s well inland to the middle 70s beaches and barrier island.
Short term /Monday through Wednesday/...
the upper level ridge will gradually shift off the eastern Seaboard
Monday through Wednesday while the center of the surface high sinks
south. On Monday the best Theta-E will exist over southeast Georgia where
temperatures will rise into the upper 80s and dewpoints approach 70. This
should produce enough surface-based cape to overcome the middle-level
cap in spots and support isolated convection. Tuesday will be a
similar story with the best chance for convection across inland
locales. Slightly better coverage of showers and thunderstorms is expected
Wednesday as the upper ridge breaks down further and some shortwave
energy approaches our western zones late in the day. We bumped probability of precipitation
into the 30 percent range far inland with 20s elsewhere. Temperatures will
warm into the middle/upper 80s each day.
Long term /Wednesday night through Saturday/...
a weak upper shortwave will move across the area on Thursday though
instability parameters do not look terribly impressive. Slightly
better coverage of showers and thunderstorms expected during the afternoon
especially inland. A slightly drier high pressure system moves in
from the northeast Friday through Sunday...minimizing rain chances.
Highs will mainly be in the upper 80s to around 90 degrees.
Aviation /14z Sunday through Thursday/...
VFR should continue to prevail through 12z Monday. Onshore flow
will be gusty at times late morning until sunset during the
warmest parts of the day. Gusts could exceed 20 knots at times...
especially at ksav Post sea-breeze. A few models hint MVFR ceilings
may impact ksav late tonight...not enough evidence to forecast
toward the end of the 12z taf cycle Monday morning at this point.
Extended aviation outlook...MVFR ceilings will be possible
through middle week...mainly at ksav late night through around noon
a relatively steady-state persistence coastal waters forecast
with onshore flow averaging 15-20 knots through tonight with some
diurnal fluctuations along the land/sea interface. There is a
small concern that marginal Small Craft Advisory conditions may
develop with short windows for 25 knots gusts and/or 6 feet seas in
the 15-20 nm range but for now we only have an advisory going for
20-60 nm Georgia waters for 5-6 feet seas through tonight.
Atlantic high pressure will maintain onshore flow and winds
generally at or below 15 knots. A slight wind enhancement expected each
afternoon along the coast as the sea breeze develops. Seas as high
as 5 feet over outer portions Monday will gradually drop to no higher
than 4 feet by Tuesday.
Rip currents...persistent onshore flow in the 15-20 knots range and
2-3 feet 7-8 second swells are expected at the coast today and we
maintained a moderate risk for all beaches. Similar conditions
are likely Monday and the rip current risk may be enhanced once
Marine...Small Craft Advisory until 8 am EDT Monday for amz374.