Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 201513
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
1113 AM EDT SAT SEP 20 2014

.SYNOPSIS...
DEVELOPING LOW PRESSURE OFF FLORIDA WILL LIFT NORTH THROUGH THE
WEEKEND...PASSING JUST OFF THE CAROLINA COASTS. THIS LOW PRESSURE
WILL REMAIN JUST FAR ENOUGH OFFSHORE SUCH THAT IMPACTS WILL BE
LIMITED...BUT SHOWERS AND SOME INCREASED WIND IS
LIKELY...ESPECIALLY ALONG THE COAST. A COLD FRONT WILL CROSS THE
AREA MONDAY...WITH COOL HIGH PRESSURE FOLLOWING BEHIND IT THROUGH
THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1015 AM SATURDAY...LATEST SATELLITE IMAGERY AND 88D RADAR
IMAGERY CONTINUE TO ILLUSTRATE THE PCPN JUST OFFSHORE FROM THE ILM
CWA COASTLINE AND THE WESTERN EDGE OF THE CLOUD SHIELD BASICALLY
ALONG THE I-95 CORRIDOR. LATEST MODEL SOUNDINGS CONTINUE TO SHOW
THE DRIER IN THE LOW TO MID LEVELS AND IS EVIDENT WHEN PCPN TRIES
TO MAKE ITS PUSH ONSHORE ACROSS THE ILM CWA COASTLINE. SOUNDINGS
DO MOISTEN UP WITH THE NAM QUITE ZEALOUS WITH PWS ABOVE 2.0
INCHES. FOR NOW...WILL CONTINUE THE OVERALL PCPN/CLOUD
TRENDS...BUT JUST MAKE CLOUD AND PCPN COVERAGE SHARPER...IE.
HIGHEST ALONG THE IMMEDIATE COAST AND ADJACENT WATERS...AND
LOWEST ALONG AND WEST OF THE I-95 CORRIDOR. IN ADDITION...HAVE
UPDATED AFTN MAXES...UP TO A CAT LOWER ESPECIALLY ALONG THE
IMMEDIATE COAST.

PREVIOUS DISCUSSION...............................................
AS OF 630 AM SATURDAY...NO CHANGES TO THE FORECAST WITH THE LATEST
UPDATE. PREVIOUS DISCUSSION FOLLOWS:

MODELS IN DECENT AGREEMENT THAT CYCLOGENESIS WILL OCCUR ALONG A
STALLED FRONT OVER THE BAHAMAS...WITH THE DEEPENING LOW MOVING
NORTHEAST AND OFFSHORE OF THE EAST COAST TODAY AND TONIGHT. WHILE
DETAILS DIFFER...A CONSENSUS OF GUIDANCE HAS THE LOW CENTERED
SOUTHEAST OF BEAUFORT NC BY DAYBREAK ON SUNDAY. THE EASTERN
CAROLINAS WILL BE ON THE BACKSIDE OF THE LOW WITH A MOIST
NORTHEAST FLOW EARLY IN THE PERIOD BECOMING MORE NORTHERLY AFTER
MIDNIGHT AS THE LOW MOVES OFFSHORE. THE MAIN FORECAST CHALLENGE
WILL BE EXTENT AND AMOUNT OF PRECIPITATION. BASED ON CURRENT TRACK
AND MODEL SOUNDINGS WILL INTRODUCE HIGH CHANCE TO LIKELY POPS
ALONG THE COAST...WITH CHANCES INCREASING THROUGH THE AFTERNOON
AND EARLY EVENING HOURS AND THEN DECREASING AGAIN AFTER MIDNIGHT
AS THE LOW PULLS AWAY TO THE NE. THERE WILL BE A SUBSTANTIAL
GRADIENT OF POPS...WITH CHANCES RAPIDLY DECREASING AS ONE MOVES
INLAND...AND WITH OUR FAR INLAND COUNTIES REMAINING DRY THROUGH
THE PERIOD.

QPF TOTAL FORECAST IS TRICKY AND WILL DEPEND UPON EXACT TRACK OF
LOW. THE NAM IS THE MOST BULLISH IN THIS REGARD WITH A NEARLY
SATURATED MOISTURE PROFILE LATE THIS AFTERNOON AND EVENING. DUE TO
THE UNCERTAINTIES INVOLVED WILL BE ADOPTING A MIDDLE-GROUND
APPROACH...WITH QPF EVENT TOTALS RANGING FROM BETWEEN A QUARTER AND
A HALF AN INCH ALONG THE COAST TO ZERO WELL INLAND. MODEL SOUNDINGS
ALSO INDICATE A TRANSITION IN PRECIP TYPE FROM MORE CONVECTIVE EARLY
ON TO STRATIFORM OVERNIGHT.

SEASONAL TEMPERATURES WILL PREVAIL. HAVE LEANED TOWARDS THE RECENTLY
BETTER-PERFORMING GFS GUIDANCE FOR THIS PERIOD...WITH HIGHS IN THE
LOWER 80S AND OVERNIGHT LOWS IN THE MID 60S FOR MOST PLACES.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 300 AM SATURDAY...LOW PRESSURE MOVING JUST OFF THE COAST SUNDAY
MORNING WILL RACE NORTHEAST THROUGH THE DAY. SUNDAY MORNING MAY
STILL BE UNSETTLED WITH CLOUDS AND RAIN SHOWERS ALONG THE
COAST...BUT RAPID DRYING WILL OCCUR ON N/NW WINDS DURING THE
AFTN...AND THE SECOND HALF OF SUNDAY WILL LIKELY BE PRETTY NICE WITH
LOTS OF SUNSHINE AND HIGHS IN THE LOW TO MID 80S. FORECAST PROFILES
ARE VERY DRY SUNDAY NIGHT...BUT WINDS WILL BEGIN TO BACK TO THE SW
AS HIGH PRESSURE RIDGES UP INTO THE AREA...AND THUS LOWS SUNDAY
NIGHT WILL LIKELY BE A BIT ABOVE CLIMO...A DEGREE OR TWO EITHER SIDE
OF 65.

MONDAY WILL BE A TRANSITIONAL DAY...STARTING WARM BUT COOLING OFF
LATE AS A COLD FRONT CROSSES THE AREA. FROPA IS NOW EXPECTED TO BE
EARLY MONDAY...CROSSING OFFSHORE BY THE AFTN...BUT A STRONG VORT
IMPULSE WILL ROTATE OVERHEAD ALONG OR JUST BEHIND THE COLD FRONT
CAUSING SOME SHOWERS...PRIMARILY ALONG THE COAST. NO STRONG STORMS
ARE EXPECTED...BUT PVA COMBINED WITH 300-500 J/KG OF SBCAPE WILL
SUPPORT ISOLATED TSTMS BENEATH THIS VORT LOBE. VERY DRY AIR FLOODS
IN BEHIND THIS FEATURE MONDAY NIGHT...USHERING IN ASTRONOMICAL FALL
WHICH OCCURS AROUND 1030PM MONDAY NIGHT. HIGHS MONDAY WILL BE IN THE
LOW 80S...WITH SOME MID 80S IN THE SOUTHEAST ZONES...FOLLOWED BY A
COOL NIGHT AS LOWS DROP TO NEAR 60...OR SLIGHTLY BELOW FAR NW
COUNTIES.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 300 AM SATURDAY...THE EXTENDED BEGINS WITH BEAUTIFUL FALL
WEATHER...WHICH IS APPROPRIATE SINCE TUESDAY IS THE FIRST FULL DAY
OF ASTRONOMICAL FALL (EQUINOX ON MONDAY NIGHT). COLD FRONT WILL BE
WELL OFFSHORE...WITH COOL CANADIAN HIGH PRESSURE BUILDING ACROSS
MOST OF THE EAST COAST AND RIDGING DOWN INTO THE SOUTHEAST. WHILE
THE FIRST HALF OF THE EXTENDED LOOKS QUITE GORGEOUS...WITH TEMPS
JUST BELOW CLIMO AND LOW HUMIDITY...THERE IS SOME UNCERTAINTY LATE
IN THE WEEK AS THE HIGH TAKES ON A WEDGE-TYPE SETUP ALLOWING FOR
INCREASED LOW-LEVEL E/NE FLOW TO FLOOD INTO THE REGION. THIS WILL
LIKELY PRODUCE ENHANCED LOW-LEVEL CLOUDINESS AND POSSIBLE
SHOWERS...MAINLY ALONG THE COAST...LATE IN THE PERIOD. BEST CHANCE
WILL BE ALONG THE EASTERN SC ZONES...BUT WILL FOLLOW THE INHERITED
TREND OF RAISING SCHC POP THU/FRI FOR THE ENTIRE COAST ON D6/D7 WITH
A MINOR DIURNAL ENHANCEMENT.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
AS OF 12Z...A TREMENDOUS AMOUNT OF CLOUDS AND CONVECTION OFFSHORE.
ONE BATCH MAY MOVE INTO ILM IN TWO TO THREE HOURS...BUT MOST WILL
STAY OFFSHORE THROUGH MUCH OF THE DAY. LOW PRESSURE WILL DEEPEN AND
MOVE UP THE COAST TONIGHT...WITH A BETTER CHANCE OF RAIN EXPECTED.
NORTHEAST FLOW WILL CONTINUE...BECOMING GUSTY BY MID MORNING. THE
NAM APPEARS TO BE WAY OVERDONE WITH NUMEROUS SHOWERS AND IFR
CONDITIONS THIS AFTERNOON. WILL LEAN MORE TOWARD THE GFS SOLUTION.

EXTENDED OUTLOOK...GUSTY NORTHEAST WINDS WILL BECOME NORTHWEST
AND DECREASE SUN AS LOW PRESSURE MOVES NE FURTHER AWAY FROM THE
TERMINALS. OTHERWISE VFR SUN THROUGH WED WITH A CHANCE OF A SHOWER
WITH A COLD FRONT ON MONDAY.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 1030 AM SATURDAY...LATEST OMR AND BUOY REPORTS HAVE THE
HIEST WINDS AND SEAS BASICALLY ACROSS THE OUTER WATERS 10-20 NM
OUT...INCLUDING NEAR SHORE WATERS FROM CAPE FEAR NWRD. BASICALLY A
SOLID NE 15 KT...OCCASIONALLY UP TO 20 KT SUSTAINED. PROGGED SFC
PRESSURE PATTERN KEEPS THE LOW OFFSHORE AS IT MOVES NE-WARD ALONG A
COASTAL TROF...WITH ITS CLOSEST APPROACH LATE TONIGHT AND EARLY
SUNDAY. SIGNIFICANT SEAS WILL HAVE ANOTHER FOOT OR 2 TO BUILD FROM
CURRENT VALUES...WITH 4 TO 7 FOOT AT ITS PEAK. WIND DRIVEN WAVES
TO MAKE-UP THE MAJORITY OF THE SIG. SEAS WITH DOMINANT PERIODS
BETWEEN 4 AND 6 SECONDS.

PREVIOUS DISCUSSION................................................
AS OF 630 AM SATURDAY...NO CHANGES TO THE FORECAST WITH THE LATEST
UPDATE. PREVIOUS DISCUSSION FOLLOWS:

A LOW PRESSURE CENTER DEVELOPING OVER THE BAHAMAS WILL MOVE
NORTHEAST UP THE COAST AND WILL PASS EAST OF THE WATERS TONIGHT.
PRESENT NE WINDS WILL BACK TO THE NORTH...BECOMING MORE OFFSHORE
AFTER MIDNIGHT AS THE LOW MAKES ITS MOVE UP THE COAST. THESE
OFFSHORE WINDS WILL ALLOW SEAS TO DROP BY A FOOT OR SO LATE IN THE
PERIOD. THIS MAY ALLOW SEAS TO DECLINE BELOW THE 6 FT CRITERIA FOR
THE SMALL CRAFT ADVISORY PRESENTLY IN EFFECT...BUT DUE TO
UNCERTAINTY REGARDING EXACT TRACK AND DEVELOPMENT OF LOW...WILL BE
KEEPING THE ADVISORY IN FORCE THROUGH THE PERIOD.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 300 AM SATURDAY...3-5 FT SEAS WILL BOOKEND THE SHORT TERM...AS
ELEVATED WINDS DRIVE HIGHER WAVE HEIGHTS BOTH SUNDAY MORNING AND
THEN AGAIN MONDAY NIGHT. LOW PRESSURE MOVING WELL OFFSHORE WILL
CREATE ELEVATED NORTHERLY WINDS OF 10-20 KTS THE FIRST HALF OF
SUNDAY...BUT AS THIS SYSTEM PULLS OFF TO THE NORTHEAST...WINDS WILL
BACK TO THE SW AND EASE TO AROUND 10 KTS. A COLD FRONT WILL CROSS
THE WATERS MONDAY AFTN...TURNING WINDS QUICKLY TO THE NW BUT AT
STILL RELATIVELY LIGHT SPEEDS...BEFORE A NE SURGE DEVELOPS AT THE
END OF THE PERIOD DRIVING WINDS TO 15-20 KTS ONCE AGAIN AT THE END
OF THE PERIOD. SEAS MUCH OF SUNDAY AND MONDAY WILL BE 1-3 FT WITH A
VARIABLE SPECTRUM...WITH THE AFOREMENTIONED HIGHER SEAS BEING
CONFINED TO THE FIRST AND LAST 6 HRS OF THE PERIOD.

LONG TERM /TUESDAY THROUGH WEDNESDAY/...
AS OF 300 AM SATURDAY...HIGH PRESSURE RIDGING DOWN THE EAST COAST
WILL WORK IN TANDEM WITH A DEVELOPING COASTAL TROUGH THROUGH
MID-WEEK TO PRODUCE AN EXTENDED PERIOD OF NE WINDS. THE NE SURGE
THAT DEVELOPS JUST BEFORE THIS PERIOD WILL PERSIST...AND THEN
STRENGTHEN AS THE GRADIENT TIGHTENS BY WEDNESDAY...DRIVING WINDS UP
TO 20 KTS OR MORE BY WEDNESDAY. THIS EXTENDED PERIOD OF NE WIND WILL
CAUSE DETERIORATING MARINE CONDITIONS...AND AN SCA WILL LIKELY BE
NEEDED AS WAVE HEIGHTS RISE TO 6 FT OR MORE TUESDAY NIGHT AND
WEDNESDAY.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT SUNDAY FOR AMZ250-252-254-
     256.

&&

$$
SYNOPSIS...JDW
NEAR TERM...DCH/REK
SHORT TERM...JDW
LONG TERM...JDW
AVIATION...DL



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