Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 060241 AFDILM AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WILMINGTON NC 1040 PM EDT TUE MAY 5 2015 .SYNOPSIS... A LOW PRESSURE SYSTEM IS EXPECTED TO FORM NEAR THE BAHAMAS WEDNESDAY...AND MEANDER OFF THE SOUTHEAST U.S. COAST THROUGH THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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AS OF 1030 PM TUESDAY...NO SIGNIFICANT CHANGES ARE NEEDED TO THE FORECAST WITH THIS LATE EVENING UPDATE. THE COAST IS IN BETWEEN CIRRUS BANDS WITH MAINLY CLEAR SKIES CURRENTLY...BUT THICKER CIRRUS SHOULD BUILD BACK IN OVER THE NEXT FEW HOURS. DISCUSSION FROM 730 PM FOLLOWS... HIGH PRESSURE OFF THE CAROLINA COAST EXTENDS A RIDGE AXIS WESTWARD BETWEEN 34-35 DEGREES LATITUDE. LOW PRESSURE DEVELOPING IN THE BAHAMAS IS PUSHING A STREAM OF CIRRUS CLOUDINESS NORTH ALONG THE COAST. GFS/CANADIAN 200 MB MOISTURE PROGS SHOW THIS CIRRUS WILL PROBABLY BE WITH US THROUGH THE NIGHT EAST OF I-95...AND I HAVE INDICATED PARTLY CLOUDY SKIES IN THE FORECAST AS A RESULT. THE MOISTURE IS THIN ENOUGH VERTICALLY THAT IT SHOULD HAVE LITTLE IMPACT ON TEMPERATURES. MOS GUIDANCE (IN PARTICULAR THE GFS MOS GUIDANCE) HAS BEEN TOO WARM RECENTLY. OVER THE PAST TWO NIGHTS THE GFS MOS HAS SCORED ERRORS OF +4 TO +6 DEGREES AT ILM...LBT AND CRE. DESPITE THE CIRRUS CLOUDINESS...THIS FACT PLUS THE PRESENCE OF THE RIDGE AXIS AND A LONG PERIOD OF LIGHT TO CALM WINDS HAS LED ME TO REDUCE FORECAST LOWS BY SEVERAL DEGREES FOR LOCATIONS NORTH AND WEST OF MYR/CRE. NO OTHER SIGNIFICANT CHANGES ARE NEEDED. DISCUSSION FROM 300 PM FOLLOWS... ONSHORE FLOW WILL WEAKEN DURING THE EVENING AND ANY CUMULUS WILL DISSIPATE WITH THE LOSS OF HEATING. SKIES OVERNIGHT WILL BE MOSTLY CLEAR WITH SOME THIN HIGH CLOUDS POSSIBLE FROM THE AREA OF DISTURBED WEATHER FAR TO THE SOUTH. OTHERWISE... TIME HEIGHT CROSS SECTIONS INDICATE A DRY COLUMN IN THE H85-5 LAYER. WITH MOSTLY CLEAR SKIES AND LIGHT WINDS THINK A BLEND TOWARD THE COOLER MET NUMBERS WILL WORK TONIGHT...WHICH IS A NOTCH BELOW CLIMO.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... AS OF 300 PM TUESDAY...FORECAST REMAINS ESSENTIALLY UP IN THE AIR DEPENDING IF AND WHEN THE SUBTROPICAL ENTITY DEVELOPS AND ITS MOVEMENT THEREAFTER. GUIDANCE IS STILL ADVERTISING VARIOUS SCENARIOS THAT COULD PRODUCE EITHER A LOT OF WIND AND RAIN OR VERY LITTLE OF BOTH. PRUDENCE CALLS FOR KEEPING THE SLOWLY INCREASING TREND OF POPS THROUGH FRIDAY MORNING. THIS ALONG WITH SLIGHTLY COOLER TEMPERATURES AND INCREASING CLOUD COVER. THIS APPROACH IS IN GOOD AGREEMENT WITH WPC GRAPHICS AS WELL. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 300 PM TUESDAY...CONSIDERABLE UNCERTAINTY REMAINS REGARDING THE LOW THAT WILL DEVELOP IN THE BAHAMAS TONIGHT INTO TOMORROW AND WHAT THE LOCAL IMPACTS WILL BE. THIS UNCERTAINTY SHOULD DECREASE ONCE DEVELOPMENT GETS UNDERWAY ESPECIALLY ESPECIALLY IF SOME OF THE CIRCULATION GETS PERIPHERALLY SAMPLED BY FL RAOBS. THERE HAS BEEN AN INTERESTING TREND IN 12Z GUIDANCE TOWARDS THE SYSTEM AFFECTING THE REGION, EVEN THE PREVIOUSLY EAST-OUTLYING ECMWF...THOUGH THAT MODEL INDICATES THE SYSTEM IS A FEW DAYS SLOWER THAN WRF/GFS. AT THIS POINT THERE SEEMS LITTLE VALUE IN MAKING MUCH OF A CHANGE TO THE FORECAST. WITH A DIRECT IMPACT SEEMING MORE POSSIBLE THAN IT WAS BEFORE ITS TEMPTING TO ZERO IN ON A DAY WHERE HIGH POPS AND HEAVY RAIN CAN BE ADVERTISED BUT THE VAST DIFFERENCES IN TIMING PRECLUDE DOING SO AT THIS TIME. AS FOR THE THERMAL STRUCTURE OF THE SYSTEM THE FL STATE PHASE DIAGRAMS KEEP IT WEAKLY SYMMETRIC WARM CORE ON SOME MODELS WHILE OTHERS BRING IT TO THE BORDER BETWEEN WARM AND COLD...THUS A HYBRID SYSTEM APPEARS MOST LIKELY. THIS SYSTEM IS REALLY THE ONLY MAJOR PLAYER OF THE LONG TERM...WHICH WILL OTHERWISE FEATURE SEASONABLE TO MILD AFTERNOONS AND RELATIVELY WARM NIGHTS. THIS WILL OBVIOUSLY BE MODULATED BY CLOUD COVER ASSOCIATED WITH THE STORM AND SO MAY NEED TWEAKING ONCE WE HAVE A BETTER FEEL FOR THE TRACK AND TIMING. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 00Z...HIGH PRESSURE WILL REMAIN IN CONTROL FOR AT LEAST THE NEXT 24 HOURS. HAVE ADDED SOME MVFR FOG AT CRE AND FLO. A CIRRUS CEILING WILL INHIBIT FOG FORMATION...HOWEVER VERTICAL MOISTURE PROFILES AND LIGHT WINDS AT THE BOUNDARY LAYER ARE FAVORABLE. LIGHT MAINLY SOUTHEAST FLOW IS EXPECTED OVERNIGHT. WEDNESDAY...MORE OF THE SAME WITH A BROKEN CIRRUS CEILING AND EAST SOUTHEAST FLOW. EXTENDED OUTLOOK...LOW CONFIDENCE REMAINDER OF EXTENDED DUE TO UNCERTAINTY IN TRACK OF SUB-TROPICAL LOW APPROACHING THE TERMINALS. VFR LIGHT RAIN DEVELOPING EARLY THU WITH TEMPO MVFR BY THU AFTERNOON. RAIN/MVFR/WINDS FRI WITH TEMPO IFR. SAT TEMPO SHOWERS/MVFR. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... AS OF 1030 PM TUESDAY...NO SIGNIFICANT CHANGES ARE NEEDED TO THE FORECAST AT THIS TIME. ANY SE WINDS RESULTING FROM THIS AFTERNOON`S SEABREEZE CIRCULATION SHOULD BACK AROUND TO THE EAST WITHIN A FEW HOURS. CURRENT BUOY OBS OF 2-3 FEET SUPPORT THE CURRENT FORECAST. DISCUSSION FROM 300 PM FOLLOWS... NORTHEAST TO EAST FETCH WILL PERSIST THROUGH TONIGHT WITH HIGH PRESSURE CENTERED OFFSHORE AND LOWERING PRESSURE IN THE VICINITY OF THE BAHAMAS. SEAS WILL GRADUALLY BUILD AS A RESULT OF THE PRESSURE GRADIENT...WITH CHOPPY 3-4 FT CONDITIONS POSSIBLE BY EARLY WEDNESDAY. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 PM TUESDAY...MUCH LIKE THE PUBLIC PART OF THE FORECAST...THE COASTAL WATERS FORECAST IS HIGHLY DEPENDENT ON THE DEVELOPMENT OF THE SYSTEM NOW FESTERING IN THE CARIBBEAN. CONTINUED TO ADVERTISE THE INCREASING TREND OF NORTHEAST WINDS THROUGH THE PERIOD CULMINATING IN STRONG SMALL CRAFT CONDITIONS EARLY FRIDAY MORNING. SAME TREND WITH SEAS WITH 2-4 FEET EARLY TOMORROW INCREASING TO 4-6 FEET BY FRIDAY MORNING. LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 300 PM TUESDAY...EXPECTING ADVISORY CONDITIONS FOR MOST OF THE PERIOD BUT WITH CONSIDERABLE UNCERTAINTY REGARDING THE TRACK AND SPEED OF WHAT MAY END UP BEING A HYBRID TROPICAL SYSTEM AFFECTING THE REGION. THIS SYSTEM WILL ALSO HAVE A SAY AS TO WHICH TYPE OF ADVISORY/HEADLINE ENDS UP MATERIALIZING. FOR NOW IT LOOKS LIKE SCA FOR SOME SEAS AND MAYBE WINDS. BUT THERE IS A CHANCE THAT AT SOME POINT NHC STARTS ADVISORIES AND WE COULD BE LOOKING AT TROPICAL HEADLINES. THE UNCERTAINTY WILL START TO DECREASE TONIGHT INTO TOMORROW AS THE SYSTEM DEVELOPS GRADUALLY IN THE BAHAMAS. ONCE IT DOES THE MODEL GUIDANCE SHOULD START HAVING AN EASIER TIME RESOLVING THE TRACK.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...NONE. NC...NONE. MARINE...NONE. && $$ SYNOPSIS...SHK NEAR TERM...SRP/TRA SHORT TERM...SHK LONG TERM...MBB AVIATION...MRR MARINE...CRM

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