898 
fxus62 kilm 201912 
afdilm 


Area forecast discussion 
National Weather Service Wilmington NC 
310 PM EDT Wednesday Aug 20 2008 


Synopsis... 
a ridge of high pressure will build north of the area and persist 
through the weekend. Tropical Storm Fay will remain south of the 
region...and eventually weaken over the deep south. Otherwise... 
conditions will remain mostly dry with seasonal temperatures through 
the period. 


&& 


Near term /through tonight/... 
as of 3 PM Wednesday...forecast dilemma will continue to be the area 
of low level convergence and associated showers that have basically 
set up just off the southeast coast of Brunswick County and extending back 
to the southwest through Georgetown and Williamsburg counties. The 
activity has decreased a bit the past few minutes...and looking at 
RUC low level convergence at 925mb...it appears to have a handle on 
things. The trend is for this area to continue to dissipate as the 
convergence disappears. This trend is reflected in the pop 
grids/forecast through the evening hours. After 0600 UTC...used a 
more broad based approach with the low level convergence increasing 
once again via the GFS. Probability of precipitation remain low with the best chances across 
the south and east over the coastal waters. 


Generally used a blend of guidance regarding overnight lows. Do 
expect winds to keep the boundary layer at least partially 
mixed...with winds of 5-10 miles per hour common with slightly higher values 
along the coast. This should mitigate the fog threat as 
well...although my thoughts this time yesterday were similar. 


&& 


Short term /Thursday through Friday night/... 
as of 3 PM...500 mb ridge will become centered over Virginia during Thursday 
and linger through Friday night. Deeper moisture will be available 
across the southern zones with stronger easterly low-level inflow 
in place. Low-level moisture is a little more limited across the 
northern areas per time height cross sections. Speed convergence 
will persist along the coast with Fay to the south and high pressure 
ridging in from the north. The speed convergence along with marginal 
instability will support widely scattered to scattered 
showers/tstms...with the best chances setting up across ilm/S 
southern zones this period. 


Otherwise...expect breezy/windy conditions Thursday and Friday with 
mixing of stronger easterly low-level flow a good bet each day. 
Winds expected to be highest across the coastal SC zones. As for 
temperatures....continue to favor a blend toward the cooler met numbers for 
the highs...and a straight blend for the lows. 


&& 


Long term /Saturday through Wednesday/... 
as of 3 PM...large upper ridge elongated from SW to NE will stretch 
across most of the eastern U.S. By Saturday. Forecast soundings show 
very dry air above about 600mb on account of this feature. Despite 
the fact that most of the flow below 500mb will be easterly little 
more than a few tropical-like showers should be able to make it 
onshore. Since most of them will not be measurable probability of precipitation have been 
kept in the slight chance range. Not much changes into Sunday...the 
low level easterly flow may become even shallower while the middle and 
upper dry air persists. Over the weekend as Fays circulation moves 
farther west a tremendously long easterly fetch around Atlantic high 
pressure develops. This is prognosticated to bring increasing swell energy 
to area beaches over the weekend and into Monday. This should 
prolong/enhance the rip current threat. 


The ridging will weaken Monday through Wednesday at the middle levels. 
This should decrease the capping and middle level dryness leading to 
better but still quite small rain chances across the region as both 
the sea breeze and a weak Piedmont trough serve as convective foci. 
Forecast soundings still show pretty weak lapse rates so any storms that 
do develop may not be significant rainmakers. 


&& 


Aviation /18z Wednesday through Sunday/... 
current forecast on track with gusty east winds this afternoon. Time 
height shows dry air aloft...however could see some widely scattered 
showers south of a flow to cre line. Did put a mention of MVFR fog 
toward morning...but this may be pessimistic with some weak to 
moderate mixing. Continued east northeast flow for Thursday with a 
slightly better chance for precipitation over the southern terminals in the 
afternoon. 


Outlook though Sunday...isolated storms possible Thursday...with 
scattered storms expected Friday as the coastal trough moves 
onshore. Isolated convection Saturday and Sunday. 


&& 


Marine... 
near term /through tonight/... 
as of 3 PM Wednesday...still expecting small craft conditions to 
develop across our southern waters...zone 256...this evening via six 
foot seas. These seas will develop from a combination of wind waves 
with the increased gradient and swell already developing from Fay. 
If anything the wavewatch guidance is lagging a bit with the 
increase as 41004 is reporting six footers currently. Winds however 
initiated a bit high and this should keep a 6:00 PM/2200 UTC start 
for small craft conditions on track. Still expecting a range of 
20-25 knots by Thursday morning across all waters...increasing from 
15-20 knots this afternoon. 


Short term /Thursday through Friday night/... 
as of 3 PM...easterly fetch will persist across the coastal 
waters with Fay to the south and a ridge building in from the north. 
This pattern will lead to a continuation of rough seas...and the 
Small Craft Advisory will remain in place for all of the coastal 
waters. Reefcast plots and the latest wna output both show seas 
building into the 6-8 feet range through the period. 


Long term /Saturday through Monday/... 
as of 3 PM...period will be characterized by an unusually long 
eastern fetch around large Atlantic high pressure. Nearshore vs 
offshore range in significant wave height will be a bit lower than 
normal for August as seas will be pushed directly towards the coast. 
Wind waves averaging 2 to 4 feet with an approximate period of 7 seconds 
will be accompanied by a 1 to 2 feet swell in the 12-14 second range. 


&& 


Rip currents... 
wavewatch guidance not advertising any long-period swell...but am 
still concerned about rip current risk through this period. The long 
easterly fetch is a pattern that favors rips...and any swell 
generated by Fay would end up at a right angle to wind wave 
action. Even with Fay no longer over water by the 
weekend...Sat/sun will be days 4 and 5 of a continuous and 
sometimes frisky onshore flow...a pattern that lends itself to 
increased rip current threats. 


&& 


Ilm watches/warnings/advisories... 
SC...none. 
NC...none. 
Marine...Small Craft Advisory from 6 PM this evening to 6 am EDT 
Saturday for amz256. 


Small Craft Advisory from 2 am Thursday to 6 am EDT Saturday 
for amz250-252-254. 


&& 


$$ 


Synopsis...srp 
near term...heden 
short term...srp 
long term...mbb 
aviation...dl 

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