Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
344 am EDT Sat Aug 2 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 3:30 am Saturday...conditions remain favorable for periods
of heavy rain today and tonight..so will be keeping the resent
Flood Watch up through the near term and beyond. A nearly
stationary front is analyzed over our NC and SC coastal counties
this morning. Model consensus has this front wavering back and
forth through the period...pushing northwest later this morning and then
back towards the coast overnight. At the upper levels a long-wave
trough will maintain its hold over eastern Continental U.S. As a series of
weak disturbances round its base and move NE over the eastern
Carolinas. Water vapor loops show a tropical plume of moisture
continuing to advect NE over the forecast area. Model soundings
also continue to show a deeply moist column through the
period...with a moderately unstable airmass and p/west values in the
2 inch range. All elements thus remain in place for widespread
shower and thunderstorm activity with the attendant heavy rain
threat continuing today and overnight.
Extensive cloud cover and precipitation will limit maximum
temperatures to the middle 80s today. Overnight lows will hover in
the lower to middle 70s.
Short term /Sunday through Monday night/...
as of 3 am Saturday...some question as to whether or not Flood
Watch will remain in effect until its current expiration time of
Sunday evening. Through much of Sunday moisture remains copious
with precipitable water values 2.00-2.2 inches. What may be lacking however is
deep forcing for ascent. Best positive vorticity advection appears over by 18z and the
upper right entrance divergence on the wane. Model guidance quantitative precipitation forecast
now looking more lackluster. There is little value in making
changes to the watch at this point however...due to the
uncertainty involved and also the possibility that should Saturday
turn out wet as anticipated then by Sunday even minor rain amounts
may lead to some flooding issues with the saturated soils. Deepest
moisture shifting east some on Monday and the threat for heavy
rain may do the same. For now have discounted the large wave shown
in the WRF. The model is seeming having trouble resolving the
upper low currently in the Bahamas and Bertha...and allowing for
the former to become the dominant circulation. Rain chances will
diminish but linger nevertheless into Monday night as the weak middle
level trough axis remains to our west and the surface boundary can
still be made out near the coast on surface forecasts. Daytime highs
very suppressed again on Sunday but show some recovery towards
climatology by Monday.
Long term /Tuesday through Friday/...
as of 3 PM Friday...weakening middle level troughiness remains to our
west Tuesday and Wednesday. There should be an increasingly
westerly flow developing instead of southwesterly flow however
yielding a trend towards more climatological temperatures and rain
chances. As the trough moves off the coast on Thursday a weak
front may push through but it is tough to tell this far out if it
has any real effects on sensible weather. Building middle level ridge
over Gomex Thursday and Friday with weak/typical surface flow
should bring fewer thunderstorms and higher temperatures.
Aviation /08z Saturday through Wednesday/...
as of 06z...light rain is winding down near kflo/klbt. Ceilings are
IFR at those terminals and expected to remain so through
14-15z...with a good chance of LIFR ceilings/IFR visibilities by 08z.
Convection is increasing at the coastal terminals...with some
isolated lightning strikes just offshore myr.
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 an upper
impulse. This should allow for an increase in convection at the
coastal terminals early this morning with isolated thunder.
IFR/LIFR conditions will eventually spread east and affect the
coastal terminals except kilm towards 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 3:30 am Saturday...little change over the waters from
present conditions today and tonight. A nearly stationary front
will remain inland or just near the coast today and
tonight...keeping winds southerly and in the 10 to 15 knots
range...with seas of 2 to 4 feet. Expect extensive shower and
thunderstorm activity over the waters as a tropical plume of
moisture moves north across the waters.
Short term /Sunday through Monday night/...
as of 3 am Saturday...southerly winds expected for most of the
period with a frontal boundary weakening very near the coast. The
surface trough associated with the boundary will keep wind speeds
fairly light especially come Monday as the front weakens even
more. There is a model solution that is currently being discounted
as erroneous...it generates a strengthening low that moves
parallel to the coast. This solution would imply a turn to a more
northerly flow and higher wind speeds along with building seas.
This will only occur if the upper low now in the Bahamas generates
a surface low that ends up dominating the wind fields over
tropical system Bertha...which will be passing even further
offshore. There could be a complex interaction between the
two...but the current forecast is for the well offshore Bertha to
keep its identity. Any swells associated with this system will
likely impact the area just beyond the short term period.
Long term /Tuesday through Wednesday/...
as of 3 am Saturday...Bertha makes its closest approach...and it
isn't going to be a very close one...on Tuesday. Winds should
retain their southerly component but may vary from SW to southeast. A
little swell energy to affect the local area with some slightly
higher seas...but this will obviously hinge on the strength and
track. For now it seems we may avoid any headlines. Back to climatology
norms on Wednesday with west Atlantic high pressure only weakly
exerting influence locally for a light SW flow.
SC...Flood Watch through Sunday evening for scz017-023-024-032-033-
NC...Flood Watch through Sunday evening for ncz087-096-099-105>110.