Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 181928 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 328 PM EDT THU SEP 18 2014 .SYNOPSIS... HIGH PRESSURE WILL EXTEND DOWN INTO THE CAROLINAS FROM THE NORTH AS LOW PRESSURE DEVELOPS OFF THE SOUTHEAST COAST AND MOVES NORTHWARD INTO THE WEEKEND. THE NEXT COLD FRONT WILL MOVE THROUGH THE AREA MONDAY NIGHT FOLLOWED BY COOL AND DRY HIGH PRESSURE DURING THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 PM THURSDAY...SCATTERED TO NUMEROUS SHOWERS AND SOME THUNDERSTORMS OFFSHORE CONTINUE TO MOVE AWAY FROM THE CAROLINAS THIS AFTERNOON. ISOLATED SHOWERS HAVE DEVELOPED ALONG THE CONVERGENT RESULTANT SEABREEZE THIS AFTERNOON. THERE HAVE BEEN A COUPLE BRIEF LIGHTNING STRIKES IN THIS ACTIVITY. HIGH PRESSURE NOSING SOUTHWARD IS PROVIDING A LITTLE MORE SUBSIDENCE AS COMPARED TO WED AS IT CONTINUES TO SLOWLY BUILD SOUTHWARD AND THIS IS AIDING IN SUPPRESSING CONVECTION. VERY WEAK DISTURBANCES EMBEDDED IN WNW FLOW DO NOT APPEAR SUFFICIENT TO ENHANCE CONVECTION. SLIGHTLY LOWER AFTERNOON TEMPS AND SLIGHTLY HIGHER MID-LEVEL TEMPS HAVE LOWERED THE INSTABILITY AS COMPARED TO WED...WITH MIXED LAYER CAPE VALUES IN THE RANGE OF 1000-1500 J/KG. DOWNDRAFT CAPE VALUES STILL REMAIN SIGNIFICANT AND SO ANY ISOLATED STRONG CONVECTION DOES HAVE THE POTENTIAL TO PRODUCE GUSTY WINDS. WILL MAINTAIN 20 TO 30ISH POPS INTO EARLY EVE THROUGHOUT AND THEN SHOW THE CONVECTION ENDING. HOWEVER...CONVECTION WILL AGAIN BLOSSOM ACROSS THE WARM ATLANTIC WATERS TONIGHT...SOME OF WHICH MAY SCRAPE THE IMMEDIATE COAST AFTER MIDNIGHT. STRATUS MAY AGAIN FILL IN OVERNIGHT INLAND AS A SUBSIDENCE INVERSION TRAPS A CONTINUOUS SUPPLY OF MOISTURE BELOW 2 KFT ON LOW-LEVEL EASTERLY FLOW. MODEL SOUNDINGS SHOW THE INVERSION WILL BE MOST PRONOUNCED INLAND. ALONG THE COAST...OFFSHORE STRATOCUMULUS IS EXPECTED TO AFFECT THE COAST AND THIS IS IS REPRESENTED IN MODEL SOUNDINGS WITH BASES/CEILINGS AROUND 3 KFT. OVERNIGHT LOWS WILL AGAIN BE IN THE LOWER TO MID 60S...PERHAPS UPPER 60S AT THE BEACHES. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 300 PM THURSDAY...HIGH PRESSURE WILL RIDGE DOWN THROUGH THE INLAND CAROLINAS IN A TYPICAL WEDGE-LIKE FASHION WHILE LOW PRESSURE OFF THE SOUTHEAST COAST STRENGTHENS AS IT TRACKS NORTHWARD FRI THROUGH SATURDAY. THE MID TO UPPER TROUGH PULLS OFF TO THE NORTHEAST LEAVING A WEAKNESS IN THE MID TO UPPER LEVELS OVER GA/SC COAST. THE SFC LOW WILL TRACK NORTH REACHING EAST OF THE CAPE FEAR COAST BY SAT NIGHT. THE INCREASING E-NE FETCH AHEAD OF THE SYSTEM SHOULD AFFECT MAINLY COASTAL SECTIONS WITH CLOUDS AND POSSIBLE SHOWERS. THE NAM CONTINUES TO BE MUCH SLOWER WITH THE EVOLUTION OF THIS LOW...NOT REACHING THE CAPE FEAR COAST UNTIL LATE SUNDAY. THEREFORE KEEPING A MORE EASTERLY FETCH...BEING MORE AGGRESSIVE WITH ITS ONSHORE PUSH OF MOISTURE WITH PCP WATER VALUES UP TO 1.8 INCHES OVER PORTIONS OF LOCAL FORECAST AREA FRI INTO SAT. THE GFS HOLDS THE MOISTURE CLOSER TO THE COAST IN A TIGHTER MORE NE FLOW AROUND THE LOW WITH MOIST AIR IN A TIGHTER GRADIENT BETWEEN THE COAST AND INLAND. WILL NEED TO WATCH HOW THIS LOW EVOLVES AS IT MAY EVEN TAKE ON SOME TROPICAL CHARACTERISTICS OVER THE NEXT COUPLE OF DAYS. FOR NOW WILL MAINTAIN MAINLY SHALLOW MOISTURE WITH CLOUDS AND PCP CONFINED CLOSER TO THE COAST AND SPREADING NORTHWARD AS LOW APPROACHES. AS WINDS STRENGTHEN THERE MAY BE INCREASED CONVERGENCE AND MORE WIDESPREAD SHWR CHANCES BUT UNCERTAINTY EXISTS AS TO HOW FAST AND HOW CLOSE TO COAST THE LOW WILL MOVE AND THEREFORE WILL KEEP BRUNT OF ACTIVITY ALONG AND OFF SHORE. CLOUD COVER MAINLY ALONG THE COAST AND EAST-NORTHEAST FLOW WILL KEEP HIGH TEMPERATURES NEAR TO SLIGHTLY BELOW CLIMO THROUGH THE PERIOD. LOWS WILL END UP NEAR TO SLIGHTLY ABOVE CLIMO...A COMBINATION OF CLOUD COVER AND LINGERING LOW LEVEL MOISTURE. && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 300 PM THURSDAY...BIGGEST QUESTION MARK DURING THE EXTENDED INVOLVES A LOW PRESSURE MOVING ALONG THE COAST SUNDAY. GFS/CMC/NAM SUGGEST THAT A HYBRID/WARM-CORE LOW PRESSURE SYSTEM WILL BE JUST OFF THE NC COAST SUNDAY MORNING...WHILE THE ECMWF SHOWS BARELY A TROUGH MOVING TO THE NORTHEAST. TIMING DIFFERENCES EXIST...AS THE NAM IS QUITE SLOW COMPARED TO THE OTHER GUIDANCE...AND IS LIKELY TOO SLOW SINCE ANY LOW PRESSURE SHOULD BE PICKED UP AND SLUNG TO THE NE BY A SECONDARY TROUGH DROPPING INTO THE GREAT LAKES. THE GFS SEEMS TO BE A CONSISTENT COMPROMISE...AND IS FAVORED FOR THE EXTENDED. THIS SUGGESTS THAT WHILE RAPID DRYING WILL OCCUR DURING SUNDAY...THE FIRST PART OF THE DAY WILL BE CLOUDY AND POSSIBLY UNSETTLED WITH SHOWERS...ESPECIALLY ALONG THE COAST. AS THIS SYSTEM PULLS AWAY...RAPID DRYING WILL OCCUR AND THE SECOND HALF OF SUNDAY WILL BE SUNNY WITH SEASONABLE TEMPERATURES. A VERY BRIEF PERIOD OF WAA DEVELOPS LATE SUNDAY INTO MONDAY BEFORE A STRONGER COLD FRONT CROSSES THE CAROLINAS LATE MONDAY. THIS FRONT NOW LOOKS TO BE MOISTURE STARVED DUE TO SUCH A BRIEF PERIOD OF MOIST ADVECTION AHEAD OF IT...AND THUS ONLY A SCHC OF SHOWERS IS EXPECTED WITH SOME ENHANCED CLOUD COVER. THIS WILL RAPIDLY CLEAR AND DRY BY TUESDAY...AND SOME BEAUTIFUL FALL WEATHER WILL OVERSPREAD THE REGION WITHIN CANADIAN HIGH PRESSURE FROM LATE TUESDAY THROUGH THE REST OF THE PERIOD. HIGHS AND LOWS ARE EXPECTED TO BE A FEW DEGREES BELOW CLIMO...BUT LOW HUMIDITY AND LOTS OF SUNSHINE WILL PRODUCE GREAT WEATHER AS THE CALENDAR TICKS OFFICIALLY INTO ASTRONOMICAL FALL. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 18Z...WEAK HIGH PRESSURE IS AFFECTING THE TERMINALS WITH A FRONT WELL TO THE SOUTH. COASTAL TERMINALS ARE VFR EXCEPT TEMPO MVFR HAS OCCURRED AT KMYR/KCRE OVER THE PAST SEVERAL HOURS. SHOWERS ARE OCCURRING ALONG A RESULTANT BOUNDARY NEAR KCRE/KMYR. VFR IS EXPECTED AT ALL TERMINALS THROUGH THIS EVENING...EXCEPT EARLY THIS AFTERNOON TEMPO MVFR WILL POTENTIALLY OCCUR AT KCRE/KMYR WITH SHOWER ACTIVITY. ISOLATED SHOWERS ALSO POSSIBLE LATER THIS AFTERNOON AND EARLY THIS EVENING NEAR KLBT...BUT CONFIDENCE IS LOW. SHOWER ACTIVITY SHOULD DISSIPATE DURING THE EVENING BUT WILL CONTINUE OFFSHORE OVERNIGHT. OVERNIGHT THERE IS INCREASING CONFIDENCE MVFR CONDITIONS WILL OCCUR. MVFR COULD CONTINUE INTO THE MID-MORNING HOURS AS ISOLATED SHOWERS DEVELOP TERMINAL-WIDE. EXTENDED OUTLOOK...VFR FRIDAY AFTERNOON WITH ISOLATED SHOWERS AND THUNDERSTORMS. RAIN/TEMPO MVFR COASTAL AREAS SAT...WITH GUSTY NORTHEAST WINDS TERMINAL-WIDE EXPECTED SAT/SUN AS A LOW PRESSURE AREA MOVES NORTHEAST ALONG THE COAST. VFR SUN. && .MARINE... NEAR TERM /THROUGH TONIGHT/... AS OF 300 PM THURSDAY...HIGH PRESSURE WILL RIDGE MORE STRONGLY SOUTHWARD. AN ENE TO NE PUSH WILL KEEP WINDS SPEEDS UP TO AROUND 15 KT TONIGHT. SEAS OF 3 TO 4 FT WILL BE COMMON WITH PERHAPS A SMALL AREA OF 5 FT SEAS ACROSS THE OUTER FRINGES OF THE NORTHERNMOST WATERS. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 300 PM THURSDAY...WINDS WILL WILL INCREASE THROUGH FRI IN PINCHED GRADIENT FLOW BETWEEN WEDGE OF HIGH PRESSURE INLAND AND LOW PRESSURE DEVELOPING OFF THE SOUTHEAST COAST. NE WINDS WILL INCREASE UP TO 20 KT WITH HIGHER GUSTS THROUGH FRI INTO FRI NIGHT. AS NE WINDS INCREASE THROUGH FRI...SEAS WILL REACH SCA THRESHOLDS INTO FRI EVE...ESPECIALLY NORTH OF CAPE FEAR...BUILDING TO 4 TO 6 FT. SEAS WILL REMAIN LOWER CLOSE TO THE COAST SOUTH OF CAPE FEAR WHERE NE FLOW IS BLOCKED. HIGH PRESSURE WILL WEAKEN INLAND AS HIGH SHIFTS FARTHER OFF THE NEW ENGLAND COAST LOSING ITS GRIP. THIS SHOULD HELP GRADIENT WINDS TO DIMINISH AND SEAS TO LOWER THROUGH SATURDAY...BUT AS LOW MOVES NORTHWARD CLOSER TO THE LOCAL WATERS...NE WINDS SHOULD INCREASE ONCE AGAIN...POSSIBLY REACHING SCA THRESHOLDS ONCE AGAIN. LONG TERM /SUNDAY THROUGH TUESDAY/... AS OF 300 PM THURSDAY...LOW PRESSURE WILL BE MOVING UP THE COAST ON SUNDAY...AND WILL BE JUST OFFSHORE...EAST OR NORTHEAST...OF THE WATERS TO START THE PERIOD. THIS LOW WILL MOVE AWAY DURING SUNDAY...WITH WINDS BACKING FROM NE TO NW...AND THEN WEST BY MONDAY MORNING. STILL SOME UNCERTAINTY INTO THE STRENGTH AND TRACK OF THIS LOW PRESSURE...BUT ATTM IT LOOKS LIKE IT WILL BE WEAK ENOUGH AND FAR ENOUGH OFFSHORE TO KEEP WINDS TO 15 KTS OR LESS REGARDLESS OF DIRECTION ON SUNDAY. SEAS WILL FEATURE HIGHLY VARIABLE DIRECTIONS ON SUNDAY WHICH WILL MAKE A CONFUSED SPECTRUM...BUT WAVE HEIGHTS WILL FALL FROM 3-5 FT EARLY TO 2-3 FT BY MONDAY MORNING. OF COURSE...IF THIS LOW PRESSURE BECOMES STRONGER OR MOVES CLOSER...CONDITIONS COULD END UP BEING WORSE THAN CURRENTLY FORECAST. A BRIEF PERIOD OF W/SW WINDS MONDAY WILL QUICKLY BECOME NW BEHIND A COLD FRONT WHICH WILL CROSS THE WATERS LATE IN THE DAY...FOLLOWED BY A NE SURGE ON TUESDAY WITH WINDS AGAIN RISING TO 15 KTS. LOW-AMPLITUDE SEAS OF 1-2 FT MONDAY WILL RISE SLOWLY DURING TUESDAY AS THE NE WINDS INCREASE...BECOMING 3-5 FT LATE IN THE PERIOD. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...COASTAL FLOOD ADVISORY FROM 5 PM THIS AFTERNOON TO 8 PM EDT THIS EVENING FOR NCZ107. MARINE...NONE. && $$ NEAR TERM...RJD SHORT TERM...RGZ LONG TERM...JDW AVIATION...RJD/MRR

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