Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 041439
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
1039 AM EDT TUE AUG 4 2015

.SYNOPSIS...
AN AREA OF LOW PRESSURE WILL SLOWLY SLIDE UP THE COAST TODAY
BRINGING PERIODS OF SHOWERS AND THUNDERSTORMS. THIS MAY LEAD TO
PERIODS OF HEAVY RAINFALL ALONG THE COAST. MORE TYPICAL SUMMERTIME
CONDITIONS WILL DEVELOP WEDNESDAY THROUGH FRIDAY. A COLD FRONT
MOVING CLOSER TO THE AREA WILL INCREASE THE CHANCE OF SHOWERS AND
THUNDERSTORMS ONCE AGAIN THIS WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1030 AM TUESDAY...WEAK LOW JUST OFF THE COAST EAST OF
GEORGETOWN SOUTH CAROLINA CONTINUES TO CAUSE SHOWERS AND
THUNDERSTORMS ACROSS THE AREA THIS MORNING. CONVECTION OVER LAND
HAS INCREASED IN THE LAST FEW HOURS DUE TO AN INCREASE IN LOW
LEVEL CONVERGENCE AND MOISTURE. DID NOT MAKE WHOLESALE CHANGES TO
THE PREVIOUS FORECAST BUT DID TRIM/TWEAK POP GRADIENT AND VALUES
BASED ON RECENT RADAR TRENDS. THIS RESULTED IN A SLIGHT LOWERING
OF POP/QPF ALONG THE COAST AS WELL AS AN INCREASE IN POP/QPF
ACROSS PORTIONS OF INLAND NC.

CANNOT RULE OUT SOME LIGHT PRECIP ACROSS PORTIONS OF SC THIS AM AS
THE LOW LIFTS NORTHEAST BUT CHANCES ARE RAPIDLY DIMINISHING. THE
NORTH TO NORTHWEST FLOW AT THE LOW LEVELS AND WEAK SURFACE
DIVERGENCE MAKE SIGNIFICANT CONVECTION DURING THE NEXT FEW HOURS
UNLIKELY. CONVECTION MAY REDEVELOP THIS AFTERNOON IF THE LOW
DEPARTS QUICKLY AND HEATING RESULTS IN SURFACE BASED INSTABILITY.
THERE IS HOWEVER A FAIR AMOUNT OF DRY AIR ALOFT AROUND THE
PERIPHERY OF THE MOISTURE PLUM WHICH WILL BE WORKING ITS WAY OVER
THE AREA.

PREVIOUS DISCUSSION FROM 630 AM FOLLOWS:
ANOTHER WET DAY FOR THE COASTAL CAROLINAS AS SFC LOW PRESSURE
CREEPS N-NE ALONG THE IMMEDIATE SOUTHEAST U.S. COAST...REACHING
THE ILM SC CWA THIS AFTERNOON...AND THE ILM NC CWA THIS EVENING
AND OVERNIGHT. THE LOW WILL BE ACCOMPANIED BY UPPER SUPPORT THAT
WILL AID IN DRAWING IN THE RICH MOISTURE...PWS IN EXCESS OF 2
INCHES...FROM OFF THE ATLANTIC AS SEEN VIA LATEST KLTX VWP IN THE
LOW TO MID LEVELS. AT THIS POINT...MODELS INDICATE THE BULK OF THE
HEAVIEST RAIN AND UPPER DYNAMICS TO REMAIN JUST OVER THE ADJACENT
ATLANTIC WATERS AS IT PASSES BY THE ILM CWA.

POPS WILL BE ORIENTED LOWEST INLAND...ALONG AND WEST OF THE I-95
CORRIDOR...TO HIGHEST ALONG THE IMMEDIATE CAROLINA COASTS. THE
GROUNDS HAVE BEEN ABSORBING THE RECENT RAINS LIKE A SPONGE OF
LATE...AND WILL CONTINUE TO DO SO TODAY. EVENTHOUGH FFG VALUES
ACROSS THE COASTAL COUNTIES HAVE DECREASED SOME...ITS JUST NOT
LOW ENOUGH TO WARRANT A FLOOD WATCH AT THIS TIME GIVEN THE CURRENT
QPF FORECAST FOR THE COASTAL CAROLINAS AT ONE HALF TO 1 INCH. WITH
PWS PROGGED AT 2+ INCH AMOUNTS...THE FA STILL COULD EXPERIENCE
ISOLATED HIGHER AMOUNTS FROM THE STRONGER AND MORE EFFICIENT
CONVECTION. OVERALL...WILL LIKELY OBSERVE NUISANCE TYPE FLOODING
OR PONDING OF WATER ACROSS THOSE NORMALLY PRONE AND VULNERABLE
LOCATIONS. HAVE HIGHLIGHTED THIS FLOOD POTENTIAL IN THE HAZARDOUS
WEATHER OUTLOOK. MAX TEMPS TO REACH THE 90S WELL INLAND...AND IN
THE LOW TO MID 80S ALONG THE COAST. MIN TEMPS TO RANGE AROUND 70
INLAND TO THE UPPER 70S TO NEAR 80 AT THE COAST.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 300 AM TUESDAY...HOT SUMMER WEATHER FOR THE SHORT TERM AS
BERMUDA HIGH PRESSURE COMBINES WITH MID-LEVEL RIDGING...CREATING
MORE TYPICAL SUMMERTIME WEATHER. WEDNESDAY LOOKS TO BE A VERY HOT
DAY WITH WIDESPREAD MID AND UPR 90S ACROSS THE AREA. THIS IS DUE
TO VERY WARM 850MB TEMPS ADVECTING EAST INTO THE CAROLINAS...AND
COMBINING WITH A WARM/DRY DOWNSLOPE FLOW...SO EVEN COASTAL
SECTIONS WILL RISE WELL INTO THE 90S AS THE SEA BREEZE GETS
PINNED. ISOLATED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE
WEDNESDAY...BUT DRIER AIR BEHIND THE DEPARTING LOW FROM TUESDAY
WILL PREVENT ANYTHING BEYOND JUST A FEW STORMS. LOWS WEDNESDAY
NIGHT WILL BE QUITE WARM...MID AND UPR 70S...POSSIBLY NEAR 80 ON
THE BRUNSWICK COUNTY COAST.

SIMILAR WEATHER FOR THURSDAY ALTHOUGH NOT QUITE AS HOT AS THE
THICKNESSES BEGIN TO DECREASE AND MID-LEVEL FLOW BECOMES MORE SWLY.
TEMPS ARE STILL EXPECTED TO BE ABOVE NORMAL...LOW 90S AT THE COAST
AND MID 90S INLAND...BUT LIKE A FEW DEGREES COOLER THAN WEDNESDAY.
STORM COVERAGE WILL BE SLIGHTLY HIGHER TOO THANKS TO GREATER
INSTABILITY ON HIGHER DEWPOINTS AND STEEPER LAPSE RATES...BUT ONLY
LOW-CHC POP IN A TYPICAL SUMMERTIME REGIME IS WARRANTED. ANOTHER
WARM NIGHT EXPECTED THURSDAY NIGHT WITH LOWS REMAINING AT LEAST 5
DEGREES ABOVE CLIMO...MID 70S ACROSS THE AREA.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 300 AM TUESDAY...PATTERN CHANGE BEGINS FRIDAY AS TROUGHING
ACROSS THE EASTERN CONUS RE-AMPLIFIES IN RESPONSE TO RIDGING
EXPANDING ACROSS THE GREAT PLAINS. THIS WILL BE LED BY A POTENT
VORT DRIVING A COLD FRONT INTO THE AREA ON FRIDAY...ALTHOUGH
GUIDANCE HAS NOW DIVERGED ON THE TIMING AND PROGRESSION OF THIS
SURFACE FEATURE. FOLLOWING WPC PROGS AS A REASONABLE
SOLUTION...THE FRONT WILL APPROACH FRIDAY AND THEN LIKELY STALL
THROUGH THE WKND...SIMILAR TO WHAT WE JUST EXPERIENCED THIS PAST
WKND. HOWEVER...THE LONGWAVE TROUGH SHOULD BE A BIT DEEPER AND
THUS THE FRONT HAS A BETTER CHANCE OF MOVING OFFSHORE
SATURDAY...SO WILL OPTIMISTICALLY SHOW AT LEAST SOMEWHAT DRIER AIR
SUNDAY AND MONDAY WITH TEMPS ACTUALLY BELOW CLIMO...AFTER
SEASONABLE BUT WITH GOOD CHANCES FOR SHOWERS/TSTMS FRIDAY AND
SATURDAY.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
AS OF 12Z...LOW PRESSURE TRACKING STEADILY UP THE COAST THIS
MORNING. THE HRRR MODEL DISPLAYS THIS FEATURE FAIRLY WELL...WITH
CONVECTION  ALONG THE COAST THROUGH THE MORNING HOURS. WINDS COULD
GUST TO NEAR 30 KTS IN THE STRONGEST CONVECTION...WITH INTERMITTENT
IFR VISIBILITIES. THE INLAND TERMINALS WILL NOT SEE MUCH IN THE WAY
OF CONVECTION...AS MOST OF THE MOISTURE RESIDES ON THE EAST SIDE OF
THE LOW. GIVEN ENOUGH HEATING THIS AFTERNOON HOWEVER COULD TRIGGER
SOME MAINLY ISOLATED SHOWERS INLAND. MOST OF THE ACTIVITY WILL END
BY MID TO LATE AFTERNOON AS THE LOW TRACKS OUT OF THE REGION.

EXTENDED OUTLOOK...PREDOMINANTLY VFR THROUGH THE PERIOD WITH
DIURNALLY DRIVEN SHRA/TSRA.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 1030 AM TUESDAY...SLOW MOVING WEAK LOW IS RESULTING IN
SOUTHWEST FLOW AROUND 20 KT ACROSS MUCH OF THE NEAR SHORE WATERS.
THIS HAS PUSHED SEAS CLOSE TO 8 FT IN SOME AREAS AND THE SCA
CONTINUES FOR ALL ZONES. SURFACE ANALYSIS IS SHOWING PINCHED
GRADIENT JUST AHEAD OF THE LOW...RIGHT WHERE BUOYS ARE REPORTING
THE HIGHEST WINDS/SEAS. THIS AREA OF ENHANCED WINDS SHOULD SLIDE
OFF TO THE NORTHEAST AS THE LOW SLOWLY LIFTS NORTH-NORTHEAST
TODAY. ONLY MINOR ADJUSTMENTS NEEDED TO PREVIOUS FORECAST.

PREVIOUS DISCUSSION FROM 630 AM FOLLOWS:
HAVE POSTED A SMALL CRAFT ADVISORY FOR ALL WATERS FOR TODAY
THROUGH THE MAJORITY OF TONIGHT. THIS IN RESPONSE TO A SFC LOW
MOVING N BY NE...MOVING ACROSS THE IMMEDIATE SC AND NC COASTS THIS
AFTERNOON AND EVENING RESPECTIVELY. ENOUGH OF A TIGHTENED SFC PG
DEVELOPS TO PRODUCE S-SW WINDS IN THE 15 TO 25 KT SPEEDS. GUSTS
OVER 30 KT REMAINS POSSIBLE ESPECIALLY IF ANY MIXING FROM ALOFT
DOWN TO THE OCEAN SFC OCCURS. LATEST MODELS AND THE KLTX VWP
INDICATE 25 TO 35 KT WINDS JUST OFF THE OCEAN SFC. THE LOW WILL
MOVE AWAY FROM THE AREA WATERS AFTER MIDNIGHT... LEAVING A SW-WSW
10-20 KT WIND IN ITS WAKE.

SIGNIFICANT SEAS WILL BUILD TO 4 TO 7 FT..WITH THE 7 FOOTERS
RESERVED FOR THE LOCAL WATERS OFF CAPE FEAR. THIS MAY BE A
CONSERVATIVE SEAS FORECAST CONSIDERING THE 1 TO 3 FOOT UNDERLYING
SE GROUND SWELL AT 10-11 SECOND PERIODS. OVERALL...DOMINANT
PERIODS WILL RUN 7 SECONDS...INDICATIVE OF WIND DRIVEN WAVES
DOMINATING THE SEAS.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 300 AM TUESDAY...BERMUDA HIGH PRESSURE WILL BE THE DOMINANT
FEATURE THIS PERIOD CREATING SW WINDS ACROSS THE WATERS. WIND
SPEEDS WILL BE 10-15 KTS MOST OF THE PERIOD...BUT A SHARPENING
PIEDMONT TROUGH EACH EVENING WILL HELP WINDS ACROSS THE WATERS
RISE UP TOWARDS 20 KTS BRIEFLY WED AND THU EVE...BEFORE FALLING
BACK AGAIN EACH NIGHT. THESE WINDS WILL BE THE PREDOMINANT DRIVER
OF SEAS...WITH A 5 SEC SW WIND CHOP CREATING 3-4 FT SEAS...UP TO 5
FT AT TIMES DURING THE STRONGEST WINDS EACH EVENING.

LONG TERM /FRIDAY THROUGH SATURDAY/...
AS OF 300 AM TUESDAY...TYPICAL BERMUDA HIGH PRESSURE REMAINS
RIDGED ACROSS THE WATERS FRIDAY...AHEAD OF A COLD FRONT WHICH WILL
APPROACH FROM THE NW AND THEN DROP ACROSS THE WATERS LATE
SATURDAY. THIS COLD FRONTAL PASSAGE WILL DRIVE A WIND SHIFT TO THE
NW LATE. SEAS WILL BE DRIVEN PREDOMINANTLY BY THE WINDS...WITH 3-4
FT SEAS EXPECTED FRIDAY...FALLING TO 2-3 FT SATURDAY AS THE SPEEDS
EASE WITH THE FRONTAL PASSAGE.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 3 AM EDT WEDNESDAY FOR AMZ254-256.
     SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR AMZ250-252.

&&

$$

NEAR TERM...III
SHORT TERM...JDW
LONG TERM...JDW
AVIATION...43


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