Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington NC
1111 PM EDT Tuesday Jul 7 2015
Bermuda high pressure will bring typical summertime heat and
humidity to the Carolinas the remainder of the week. A cold front
will approach from the north this weekend...but should stall
across northern North Carolina...with above-normal temperatures
Near term /until 6 am Wednesday morning/...
as of 1030 PM Tuesday...continued with no probability of precipitation for the ilm County Warning Area
for the remainder of this evening through the pre-dawn Wednesday hours.
This based on the latest kltx 88d reflectivity display and
trends. In addition to the radar trends...no upper support available
to aid in firing up convection overnight...and also the warm
temperatures displayed around 600mb when looking at model soundings for
locations across the ilm County Warning Area. Should see skies become mostly clear
across the forecast area overnight due to the debris convective clouds
scouring out. Right now...banking on the debris cirrus/cs well
upstream to become less opaque as it moves across the forecast area within
north to northeast flow in the upper levels.
A weak low level SW 20-25 knots jet to develop by late this evening
..and should keep winds active across the forecast area...Up to 5 miles per hour
inland...and up to 10g15mph along the immediate coasts. Have kept
fog on the sideline for the time being.
Short term /6 am Wednesday morning through Thursday night/...
as of 300 PM Tuesday...deep high pressure will continue to cover
the Carolinas through the period. At 200 and 300 mb the ridge will
be to our north...at 500 and 700 mb the ridge will run across
southern South Carolina...and at the surface the ridge should be
displaced a little farther south across Georgia. Any upper-level
disturbances will be forced on a path well north of the Carolinas.
850 mb temperatures should stabilize around +19c...perhaps approaching
+20c inland on Thursday. This should translate to highs both days
in the middle 90s along the I-95 corridor...with 89-93 near the
Westerly flow across the Appalachians plus hot temperatures will
enhance the Piedmont trough significantly. This will increase the
typical pressure drop from the coast to the Piedmont region of the
Carolinas by 2-3 mb above typical with a Bermuda high offshore...
with a corresponding increase in afternoon/evening seabreeze wind
speeds and overnight low level jetting. For this reason I have
trended the forecast toward warmer low temperatures than what MOS
guidance is suggesting.
Precipitation chances appear quite slim through the period. We'll have
the seabreeze boundary plus the Piedmont trough...but these
features along don't imply more than about 10-15% convective
coverage. The 12z NAM is going on our a limb indicating an mesoscale convective system
diving east-southeastward across North Carolina Wednesday
evening...but this specific idea is not indicated in the bulk of
other models at this time.
Long term /Friday through Tuesday/...
as of 300 PM Tuesday...500 mb ridge will shift west across the area
from the western Atlantic Friday becoming centered over the
south-Central Plains by Sunday. At the surface...high pressure off
the southeast coast and inland trough will prevail. During the
weekend the trough may shift off the coast temporarily...however
in the meantime the chance for mainly diurnal convection will
exist each day with slightly higher chances Saturday given the
position of surface trough and more-so Tuesday as an upper trough
is prognosticated to evolve across the eastern United States. Regarding
maximum/min temperatures did not stray too far from mex numbers which are
approximately a category above climatology. The heat index will likely
exceed 100f each afternoon...but should remain just below advisory
Aviation /03z Wednesday through Sunday/...
as of 00z...expect VFR through the valid period with potential for
isolated rain showers/thunderstorms and rain Wednesday afternoon with the influence of the
sea breeze and Piedmont trough.
VFR prevails this evening with southerly winds at or below 12 kts and
occasional gusts up to just under 20 kts. Expect winds to subside
just before midnight...becoming sustained around 5 kts. Few/scattered middle
to high clouds will linger across the area this evening...nearly
clearing overnight. On Wednesday...expect south-southwest winds at or below
10 kts with gusts around 20 kts along the coast...and afternoon
rain showers/thunderstorms and rain possible along sea breeze.
Extended outlook...chance of showers and thunderstorms each
day...with brief periods of MVFR/IFR possible. Otherwise VFR.
near term /through tonight/...
as of 1030 PM Tuesday...looking at SW 10 to 15 knots becoming a
solid SW 15 after midnight. This will continue through the pre-dawn
Wednesday hours up until daybreak Wednesday. The modest SW winds are a result
of a low level SW 15 to 25 knots jet...that will occasionally mix
down to the ocean surface.
Significant seas will hang around 3 feet...occasionally up to 4 feet
across the outer waters off Cape Fear if the higher winds just off
the deck are able to mix down to the ocean surface. A bonafide 2 to
2.5 foot southeast ground swell at 8 to 9 second periods will dominate
the significant seas. The spectral density charts for buoys across
the local waters illustrate the higher energy associated with this
southeast ground swell when compared to locally produced wind driven
Short term /Wednesday through Thursday night/...
as of 300 PM Tuesday...Bermuda high pressure offshore and a
Piedmont trough inland will maintain a southwesterly wind through
the period. As inland temperatures soar well into the 90s we
expect a strong seabreeze circulation to develop both days with
afternoon/evening wind speeds increasing to 15-20 knots. Wind speeds
will gradually diminish late at night and veer more westerly.
Precipitation potential appears quite low. The morning hours may
have the best chance of isolated showers...with the afternoon
seabreeze sweeping up any remaining activity and throwing it well
inland. Seas should average 3-5 feet in a combination of
southeast 10-second swell and local 4-second wind waves...highest
during the evenings.
Long term /Friday through Sunday/...
as of 300 PM Tuesday...southwest flow will prevail Friday...then the
flow may veer to an offshore direction Saturday as a weak trough
moves off the coast. Southwest to southerly flow will become
established once again during Sunday. Seas are expected to peak
around 4 feet across the outer waters Friday evening...then again by
Sunday evening. Otherwise seas 3 feet or less through the long term.