Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1131 am EDT Monday Aug 31 2015
a surface trough will lift north of the area through this
afternoon. On the periphery of Atlantic high pressure...a weak
trough of low pressure will meander over the southeast most of
this week. Late this week into next weekend...low pressure will
develop over the Atlantic while weak inland high pressure expands
south and east into the region.
Near term /through tonight/...
rains are shifting northeast past the area...so have adjusted
probability of precipitation to account for earlier transition out of the area. Localized
flooding is still possible given the significant amount of
rainfall for Charleston and Berkeley counties. While high tide has
receded...ponding of water remains. We have adjusted winds to
better reflect the passage of the low.
The environment behind the low will be fairly benign for additional
convective development. The greatest chances for additional
convection will be near the coast of Georgia if sufficient
heating occurs with diminishing sky cover...so we have updated
probability of precipitation to reflect this general area. The temperature curve may require
additional adjustment to delay warming due to remaining
considerable cloud cover...which will also require adjustments to
sky cover... probability of precipitation...and winds to reflect a weaker or nonexistent
seabreeze. For now we have left earlier high temperature forecast as is.
Re-evaluation may be required with future updates.
Tonight...a much quieter night is expected with partly cloudy
skies for most areas. Although low stratus/fog could be a
concern. An exception could be across southeast Georgia as scattered
showers redevelop as deep moisture increases and a middle level vorticity
axis pokes north from Florida.
Short term /Tuesday through Thursday/...
Tuesday through Thursday...an upper ridge will build over the region
from the southeast. However...vorticity/associated enhanced moisture
trapped within the ridge will drift over the southeast and will
contribute to scattered showers/thunderstorms especially midday into
the evening. Per 850-500 mb moisture forecasts...highest PM pop are
focused across southern counties...but the north/south probability of precipitation gradient
remains subtle. Also...guidance differs regarding the
track/orientation of vorticity...in part provided by the remnants of
Erika...and this will impact day to day pop trends. For
now...slightly greater afternoon/evening probability of precipitation are in place for
Wednesday...as high as 40-50 percent...as compared with Tuesday and
Thursday. Despite the prevalence of clouds...daytime highs should
recover into the upper 80s/lower 90s each day.
Each night...probability of precipitation should diminish over land/away from the immediate
coast per typical diurnal trends...while probability of precipitation could increase over
coastal waters each night. Low temperatures in the 70s will remain
common each night.
Long term /Thursday night through Sunday/...
a longwave upper trough is prognosticated to advance into the region from
the west late this week. Then...this feature could become cut-off
over the southeast as a blocking pattern develops next weekend
through early next week. Meanwhile...high pressure will gradually
build into the region from the north...producing a persistent/long
fetch onshore flow. By late weekend/early next week...a coastal
trough could develop. This pattern should support unsettled
conditions...justifying at least chance probability of precipitation during the day and
persistent nighttime probability of precipitation especially near the coast and across
adjacent coastal waters...as well slightly cooler high temperatures
in the middle to upper 80s.
Aviation /15z Monday through Friday/...
kchs...lingering MVFR conditions this morning will give way to VFR
for this afternoon...with only small chances for MVFR ceilings late
Ksav...IFR conditions in stratus...improving conditions to VFR
this afternoon into the evening. There could be some MVFR ceilings
late tonight as deep moisture increases once again.
Extended aviation outlook through Friday...mainly VFR. Brief flight
restrictions could occur mainly within showers/thunderstorms.
a weak wave of low pressure will move north of the area shortly.
The flow is offshore behind the wave...but could become onshore if
sufficient insolation occurs to develop a seabreeze. Seas up to 6
or 7 footers persist over amz350 and amz374 waters where small
craft advisories remain in effect. The gradient will slacken this
afternoon as the flow becomes S or SW. Elevated seas will
diminish tonight as the flow becomes somewhat variable from north
Tuesday through Saturday. A weak pressure pattern will translate to
winds/seas below Small Craft Advisory thresholds through this
period. Winds will remain dominated by the sea breeze each
afternoon/evening and by the land breeze each overnight/early
morning...mainly less than 15 knots through the period. Seas will of
2-4 feet Tuesday will subside to 1-3 feet Wednesday through late week.
Conditions could begin to deteriorate as high pressure builds from
the north next weekend.
Rip currents... an elevated risk for rip currents exists today and could
persist Tuesday. An elevated risk for rip currents could develop
again next weekend.
the coastal Flood Advisory has been canceled. Another one may be
needed this evening to account for higher than normal tides.
Marine...Small Craft Advisory until 5 PM EDT this afternoon for amz374.
Small Craft Advisory until 8 PM EDT this evening for amz350.