Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 030606
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
206 AM EDT MON AUG 3 2015

.SYNOPSIS...
LOW PRESSURE WILL MOVE NORTHEASTWARD ACROSS THE FLORIDA PANHANDLE
TONIGHT AND ALONG AN OLD STATIONARY FRONT ON MONDAY AND
TUESDAY...BRINGING INCREASING CHANCES OF SHOWERS AND
THUNDERSTORMS TO THE COASTAL CAROLINAS. THE LOW WILL MOVE AWAY
FROM THE AREA TUESDAY NIGHT...WITH TYPICAL SUMMER WEATHER EXPECTED
WEDNESDAY THROUGH NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
AS OF 1030 PM SUNDAY...LINE OF SHOWERS HEADING TOWARDS THE COAST
IS NOW FROM 15 TO 20 NM OFFSHORE AND SHOULD BE SKIRTING BALD HEAD
ISLAND SHORTLY. STILL EXPECTING A GRADUAL RAMPING UP OF POPS
THROUGH THE EARLY MORNING HOURS AS THE LOW PRESSURE SYSTEM
CURRENTLY OVER NORTHERN FLORIDA MOVES NE ALONG A STALLED FRONTAL
BOUNDARY.

BOTH THE GFS AND NAM SHOW LOW LEVEL WIND FIELDS BACKING WITH HEIGHT
THUS INCREASING CONVERGENCE BASICALLY ALONG THE COAST...THIS OCCURS
AFTER 0600 UTC. THE GFS HAS BACKED OFF SLIGHTLY WITH THE 1200 RUN
WHILE THE NAM REMAINS THE MOST AGGRESSIVE. I AM CONTINUING TO
ADVERTISE GOOD CHANCE POPS ALONG THE IMMEDIATE COAST WITH MUCH
HIGHER AMOUNTS OFFSHORE. FOLKS WEST OF I-95 WILL PROBABLY MISS OUT
ENTIRELY. THE NAM IS ADVERTISING 0.25 TO 0.50 FOR THE SIX HOUR
PERIOD WHILE THE GFS JUST UNDER A TENTH. MY EXPERIENCE SHOWS THAT
ALTHOUGH MOST AREAS...ALONG THE COAST RECEIVE RAINFALL...THE QPF IS
LIGHT AS THE HEAVIER ACTIVITY RESIDES JUST OFFSHORE. THIS IS
PROBABLY WHAT WE WILL SEE THROUGH 1200 UTC. I LIKE THE SLIGHTLY
WARMER GFS/MAV NUMBERS FOR LOWS WITH ALL OF THE CLOUD COVER
MOVING IN.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY NIGHT/...
AS OF 300 PM SUNDAY...THE BIG PLAYER IN THE MONDAY-TUESDAY
TIMEFRAME IS THE LOW CENTERED NEAR THE GULF COAST ABOUT 50 MILES
SOUTHEAST OF TALLAHASSEE FLORIDA. WHILE MODEL SOLUTIONS ARE ALL
OVER THE PLACE WITH REGARD TO TIMING...THE 12Z GFS APPEARS TO HAVE
TO HAVE A SUPERIOR FORECAST WITH ITS SLOWER NORTHEASTWARD MOVEMENT
ALONG THE OLD STATIONARY FRONT. THE 12Z NAM AND 12Z CANADIAN
MODELS IN PARTICULAR ARE FAR TOO FAST AND HAVE BEEN ENTIRELY
DISCOUNTED FOR THIS FORECAST.

A SURGE OF DEEP TROPICAL MOISTURE AHEAD OF THE LOW WILL REACH THE
CAROLINA BEACHES MONDAY MORNING. PRECIPITABLE WATER VALUES WILL
EXCEED TWO INCHES ALONG THE COAST...WHILE SOUTHERLY/ONSHORE FLOW
SHOULD INCREASE LOW-LEVEL CONVERGENCE ALONG THE STATIONARY FRONT.
A SUBTLE 300 MB DISTURBANCE MOVING ACROSS NORTHERN NC AND OFF THE
COAST MONDAY MORNING WILL HELP ENHANCE UPPER LEVEL DIVERGENCE
ACROSS OUR AREA...AND IT WOULD NOT BE SURPRISING AT ALL TO SEE
GOOD COVERAGE OF STORMS ONGOING AT DAYBREAK. HEAVY RAINFALL IS
EXPECTED AND THERE IS SOME POTENTIAL OF FLOODING...ESPECIALLY
WITHIN 50 MILES OF THE COAST BENEATH THE DEEP MOISTURE CHANNEL.

ONSHORE WINDS WILL CONTINUE MONDAY NIGHT INTO TUESDAY AS THE LOW
APPROACHES THE AREA. I HAVE HELD OFF INCREASING POPS BEYOND 50
PERCENT FOR EITHER PERIOD NOT KNOWING HOW SYMMETRIC CONVECTION
WILL BE DISTRIBUTED AROUND THE LOW...AND TO ACCOUNT FOR MESOSCALE
SUBSIDENCE AREAS AROUND LARGE CONVECTIVE STRUCTURES POTENTIALLY
DEVELOPING OUT OVER THE GULF STREAM. TUESDAY NIGHT THE LOW SHOULD
BE MOVING NORTHEAST OF THE AREA. DRIER AIR WRAPPING IN BEHIND THE
CIRCULATION SHOULD HELP ERODE CLOUDS AND KILL PRECIPITATION
CHANCES. EXTRATROPICAL STORM SURGE GUIDANCE SHOWS SURGE VALUES
REMAINING UNDER HALF A FOOT AT THE BEACHES...AND WE ARE MOVING
PAST THE FULL MOON WHICH SHOULD PREVENT COASTAL FLOODING ISSUES.

FARTHER INLAND ALONG AND WEST OF THE INTERSTATE 95 CORRIDOR (WHERE
RAIN IS BADLY NEEDED) THE BULK OF THIS EVENT WILL REMAIN TOO FAR
EAST. POPS ARE ONLY 10-30 PERCENT AND DAYTIME TEMPERATURES SHOULD
RUN 5-8 DEGREES WARMER THAN AT THE COAST.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
AS OF 3 PM SUNDAY...RAIN CHANCES WILL REMAIN QUITE MINIMAL FOR MOST
OF WEDNESDAY BUT LATE IN THE DAY SOME WEAK CYCLONIC CURVATURE MAY
IMPINGE UPON US FROM THE WEST. AS THIS CONTINUES INTO THURSDAY WITH
THE AID OF DAYTIME HEATING THE RADAR SHOULD LIGHT UP PRETTY NICELY
IN THE AFTERNOON EVEN THOUGH THE GFS IS NOT TOO ENAMORED WITH THE
IDEA. THE LOWERED HEIGHTS AND ADDED CLOUDS SHOULD TEMPER THE HEAT
EVEN IF ONLY BY A FEW DEGREES. FROM THERE RAIN CHANCES SHOULD
INCREASE EVEN FURTHER ON FRIDAY AS BOTH A COLD FRONT AND STRONGER
ENERGY ALOFT APPROACH FROM POINTS NORTH AND WEST. THERE MAY EVEN BE
A HEALTHY WAVE ALONG THE FRONT WHICH COULD LEAD TO QUITE A BIT OF
RAIN. THE FRONT WILL BE DECELERATING MAKING FIGURING OUT HOW QUICKLY
WE DRY OUT DIFFICULT. WILL JUST SHOW A SLOW DECREASE IN RAIN CHANCES
DURING THE LATTER PART OF THE WEEKEND. WE SHOULD ALSO SEE A RETURN
OF MORE SEASONABLE DAYTIME HIGHS LATE IN THE PERIOD WHEREAS AREAS
AWAY FROM THE WATER MAY FLIRT WITH HEAT ADVISORY CRITERIA WEDNESDAY
AND THURSDAY.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
AS OF 06Z...SURGE OF PRECIPITATION MOVING UP AND ALONG THE SE
U.S. COAST. FORECAST ISSUE OF THE DAY WILL BE THE SURFACE LOW
ACROSS THE NE GULF OF MEXICO MOVING/DRIFTING NE INTO NRN
FLORIDA...AND THEN INTO GEORGIA WITHIN THE NEXT 24 HOURS.
PWAT AMOUNTS INCREASE TO ABOUT 2.25 INCHES ACROSS MAINLY THE
COASTAL AREAS AS PER THE MODEL SOUNDINGS BUT REMAINING LESS THAN
2 INCHES INLAND. MODELS SHOW SHARP DECREASE IN THE PRECIPITATION
SHIELD AS YOU MOVE WESTWARD...WITH INTERSTATE 95 ACTING LIKE THE
DIVIDING LINE BETWEEN PCPN OR NO PCPN. ANY SHIFT IN THE MODELS
JUST 30 MILES EITHER WAY CAN HAVE A SIGNIFICANT IMPACT ON THE
FORECAST. WILL MAINLY HEDGE WITH MVFR PERHAPS IFR ALONG THE
COASTAL TERMINALS DURING THE DAY WITH PERIODS OF RAIN SOME OF
WHICH MIGHT BE HEAVY AND VFR/MVFR INLAND WITH SOME SHWRS. MOST
OF THE ACTIVITY WILL BE ALONG THE COAST. CONFIDENCE IN FORECAST
CONDITIONS ARE LOW AS MODELS DIFFER WITH SPEED AND STRENGTH OF
LOW COMING OUT OF THE GOM.

EXTENDED OUTLOOK...PREDOMINANTLY VFR THROUGH THE PERIOD WITH A
SLIGHT CHANCE AFTERNOON SHRA/TSRA.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 1030 PM SUNDAY...LATEST OBS SHOW SOUTHERLY WINDS AT AROUND
15 KTS WITH 4 FT SEAS. THIS FITS IN WELL WITH THE LATEST
FORECAST WHICH PROJECTS A GRADUAL TIGHTENING OF THE GRADIENT
OVERNIGHT...WITH SEAS INCREASING UP TO 5 FT. PREVIOUS DISCUSSION
FROM THIS AFTERNOON FOLLOWS:

THE PRESSURE GRADIENT WILL INCREASE SLIGHTLY THROUGH THE LATER
AFTERNOON AND OVERNIGHT HOURS. THE OVERALL PATTERN IS STILL
RELATIVELY WEAK HOWEVER (41013 IS CURRENTLY REPORTING CALM WINDS)
AND WINDS WILL LOSE THE SEA BREEZE INFLUENCE OF A SE DIRECTION AND
GO MORE SOUTHWEST. SPEEDS SHOULD SETTLE NICELY INTO A 10-15 KNOT
RANGE. SEAS WILL INCREASE FROM 2-4 FEET TO 3-5 FEET AFTER 0600 UTC
VIA THE SUBTLE INCREASE IN WINDS AND A DECENT SWELL COMPONENT
REMAINING IN THE MIX.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300 PM SUNDAY...A ROUGH COUPLE OF DAYS FOR THE MARINE
COMMUNITY IS COMING UP AS LOW PRESSURE CENTERED ABOUT 50 MILES
SOUTHEAST OF TALLAHASSEE FLORIDA MOVES ACROSS THE COASTAL
CAROLINAS. THE GFS MODEL IS THE BASIS FOR OUR FORECAST...SHOWING
A MUCH SLOWER MOVEMENT OF THE LOW THAN THE NAM OR CANADIAN
MODELS.

SOUTH WINDS WILL INCREASE TO 15-20 KT MONDAY INTO TUESDAY AHEAD OF
THE LOW. MULTIPLE WAVES OF SHOWERS AND THUNDERSTORMS WILL MOVE
ACROSS THE AREA...ACCOMPANIED BY LOW VISIBILITY IN HEAVY RAIN AND
POSSIBLE SQUALLY WIND GUSTS. THE LOW WILL MOVE NORTHEAST OF CAPE
FEAR TUESDAY NIGHT...WITH LIGHTER OFFSHORE WINDS DEVELOPING
OVERNIGHT.

SEAS WILL BUILD TO 4-6 FEET MAINLY IN 6 SECOND SOUTH WAVES
PRODUCED BY THE FETCH BEGINNING NEAR JACKSONVILLE FL AND ENDING AT
OUR BEACHES. SMALL CRAFT ADVISORIES WILL LIKELY BE NEEDED.

LONG TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 3 PM SUNDAY...BERMUDA HIGH PRESSURE AND WEAK PIEDMONT
TROUGHINESS THE MAIN PLAYERS ON WEDNESDAY. SOUTHWESTERLY WINDS A
LITTLE ON THE LIGHT SIDE POSSIBLY CAPPED AT 10 KNOTS. THE TROUGH
WILL BE STRONGER ON THURSDAY OPENING THE FORECAST UP TO A MORE
TYPICAL 10 TO 15 KT AND POSSIBLY DECREASING THE NEARSHORE/OFFSHORE
WAVE HEIGHT GRADIENT EVER SO SLIGHTLY. A COLD FRONT WILL BE
APPROACHING ON FRIDAY THOUGH ITS SPEED IS A BIT UNCERTAIN
ESPECIALLY SINCE IT MAY BE DECELERATING. THERE MAY BE A SLIGHT
LATE PERIOD VEERING AND INCREASE IN WIND SPEED.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.

MARINE...NONE.

&&

$$
SYNOPSIS...TRA
NEAR TERM...REK/SHK
SHORT TERM...TRA
LONG TERM...MBB
AVIATION...DCH/MAC



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