Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
741 PM EDT Friday Aug 1 2014
a trough will remain stalled near the coast through the weekend.
This will bring a heightened risk for flooding as widespread showers
and thunderstorms plague the area for much of the weekend. The
airmass will only slowly dry out during the middle and later
portions of next week.
Near term /through tonight/...
as of 730 PM Friday...the coastal trough/warm front made pretty good
inland progress earlier today...reaching the Interstate 95 corridor
from Lumberton down through Florence. The boundary is stalling and
is expected to drop back toward the South Carolina coast late
tonight...with at least some potential it could reach Myrtle Beach
before daybreak. Focused convergence along the front has led to a
line of showers and embedded T-storms from Bladen County through
Marion...Florence to near Orangeburg SC. An eastward advancing upper
disturbance near the Savannah River should help nudge the front and
a collocated deep moisture channel eastward tonight...reaching the
Changes with this update were fairly minor...with tweaks to wind
directions and hourly probability of precipitation/weather most significant. Previous discussion
from 300 PM follows...
Trough remains stalled along the coast while deep Gulf moisture
continues to spread northeast. Along with low level convergence
associated with the boundary...weak divergence aloft continues. This
coupled with moderate instability...cape is 1000-1500 j/kg...has
been producing showers and thunderstorms across much of the area.
Expect activity to continue and increase in coverage for the
remainder of the afternoon. Loss of diurnal heating should bring
about a decrease in coverage but do not think activity will
completely disappear this evening.
Trough will remain stalled along or just inland of the coast with
precipitable water values hanging around 2 inches overnight.
Additionally there appears to be a weak deformation zone east of the
area. This feature will slowly drift west this evening and overnight
as the middle level western Atlantic ridge expands. Based on this have
held onto likely pop along the coast all night but drop inland areas
to high chance around middle night. Middle level pattern and lack of
surface low in eastern Texas suggests the trough will remain stalled
along the coast through the end of the period and this is where the
highest quantitative precipitation forecast should be found.
Cloud cover and moisture along with boundary layer winds will keep
lows near to above climatology. West of the boundary lows will be close to
climatology...around 70. On the east side of the boundary modest onshore
flow will keep temperatures in the middle 70s.
Short term /Saturday through Sunday night/...
as of 300 PM Friday...a Flood Watch is in effect through Sunday. A
coastal trough will remain positioned along the Carolina coast
this period. While some of the models are indicating the trough
will very slowly move inland...the middle-level flow suggests
otherwise. An extremely deep S/SW flow will remain locked in place
along with a moist column through a very deep layer. The persistent
upper diffluence within the entrance region of jet streak across
the northeast and the low level convergence along the trough will
provide the necessary lift for a large scale...significant
rainfall event. We are expecting total rainfall amounts to average
2 to 4 inches with upwards of 4 and 5 inches along coastal Cape
Fear. However...higher amounts are possible and given the ground
is wet from a very wet July...we feel the risk for significant
flooding is high enough to warrant a Flood Watch.
The clouds...rain...and lowered thicknesses will keep highs below
normal for early-August...but at the same time maintain normal or
slightly above normal lows. Expect highs in the lower to middle 80s
both days...and lows in the lower to middle 70s.
Long term /Monday through Friday/...
as of 300 PM Friday...mid-level trough axis will remain west of
the area Monday and Tuesday...resulting in a continued ample
supply of moisture to enhance the potential for showers and thunderstorms.
Surface convergence will be provided by the stalled frontal
boundary which will linger along the coast as well as weak waves
of low pressure which models indicate may develop along the
boundary. Expect temperatures will be held in check by cloud cover
Monday...but less so Tuesday-Wednesday. The middle-level trough axis
will slowly transition east and allow some drier air to filter in
by midweek...so although probability of precipitation will be included each day...trend
will be downward. Another weak frontal boundary will drop into the
area Thursday and linger into Friday...so slight/low chance probability of precipitation
will be warranted those days as well.
Aviation /00z Saturday through Wednesday/...
as of 00z...a narrow band of rain showers/isolated thunderstorms and rain is occurring along a
frontal boundary from near kflo to klbt. Ceilings are MVFR/tempo IFR at
kflo/klbt. No precipitation is currently occurring at the coastal
terminals. Tempo MVFR ceilings have been occurring at kcre/kmyr. The
current conditions should continue for the next several hours. A
weak upper impulse should move through this evening ending the
precipitation at kflo/klbt and increasing the precipitation
potential at the coastal terminals.
Model solutions vary widely on the evolution of the frontal boundary
near kflo/klbt...thus confidence is low. At this time will swing the front
back towards the coast with the passage of the upper impulse. This
should allow for IFR/LIFR to eventually affect all terminals except
ilm before sunrise. Highest confidence of LIFR/IFR ceilings/visibilities will
be at kflo/klbt.
LIFR/IFR ceilings improve to MVFR by middle morning. Rain showers/thunderstorms and rain re-develop
by late morning...with best potential for thunderstorms in the vicinity along the boundary
near the coastal terminals.
Extended outlook...shra/tsra likely with periods of MVFR conditions
through Tuesday as a front stalls and finally dissipates over the
eastern Carolinas. A chance of showers continues on Wednesday late.
near term /through tonight/...
as of 730 PM Friday...the warm front/coastal front has moved inland
through Elizabethtown and Whiteville with south winds reported at
all weather observation stations along the coast. Models are showing the
boundary may reverse course overnight and drop back down toward the
coast. My latest forecast brings it fairly close to Myrtle Beach
again late tonight. The pressure gradient is awfully "baggy" in the
vicinity of the front and this should result in wind speeds
diminishing overnight...particularly along the South Carolina coast.
Winds of 10-15 knots should continue along North Carolina coast much
of the night. Seas are currently 3 feet at the Sunset Beach
buoy...and just under 4 feet at the nearshore Wrightsville Beach
buoy and offshore Lejeune buoy...necessitating only a slight
increase in wave forecasts. Previous discussion from 300 PM
Coastal trough stalled near the coast keeps southeast flow in place
over the waters through the end of the period. Little change to the
gradient is expected and winds will remain in the 10 to 15 knots range.
Prolonged onshore flow will keep seas 3 to 4 feet.
Short term /Saturday through Sunday night/...
as of 300 PM Friday...a coastal trough will likely not move much
through the period and we expect the trough will be over the area
or just to the west through Sunday night. The wind direction on the
west side of the trough will be more northerly while winds on the
east side will be more southerly. At this time...expect the wind
direction across the waters will be predominately from a S or southeast
direction. The proximity of the trough should keep wind speeds
from exceeding 10 to 15 knots. Seas will be 3 to 4 feet with perhaps
some 5 feet seas developing across the outermost waters late in the
weekend. A still rather weak 9 to 11 second southeast swell will be present.
Long term /Monday through Wednesday/...
as of 300 PM Friday...surface flow is expected to remain
relatively light as the pressure gradient will remain weak through
the period. However there is uncertainty in the wind direction
during this time as a stalled frontal boundary will linger along
the coast. A 3 to perhaps 4 foot swell with 11 second period will
be possible Tuesday-Wednesday from Bertha...which is currently
forecast to be moving northward well off the Carolina coast at
SC...Flood Watch through Sunday evening for scz017-023-024-032-033-
NC...Flood Watch through Sunday evening for ncz087-096-099-105>110.