Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 310525
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
125 AM EDT MON AUG 31 2015

.SYNOPSIS...
A WAVE OF LOW PRESSURE WILL MOVE NORTH FROM FLORIDA ALONG THE
CAROLINA COASTLINE THROUGH MONDAY NIGHT. TROPICAL MOISTURE STREAMING
NORTHWARD INTO THE CAROLINAS WILL BRING A GOOD CHANCE OF RAIN
THROUGH TUESDAY. WEAK HIGH PRESSURE WILL COVER THE AREA THE
REMAINDER OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
AS OF 130 AM MONDAY...NO CHANGES TO THE FORECAST WITH THE LATEST
UPDATE. PREVIOUS DISCUSSION FOLLOWS:

DESPITE OVERALL FAVORABLE SYNOPTIC CONDITIONS A HOLE IN RADAR
ECHOES HAS OPENED UP ACROSS THE AREA. UPSTREAM BETWEEN CHARLESTON
AND SAVANNAH NEW SHOWERS ARE FORMING...AND THESE SHOULD ADVECT
NORTHWARD INTO THE FORECAST AREA OVER THE NEXT 3- 4 HOURS.
EASTERLY WINDS ARE INCREASING QUITE A BIT ACROSS THE SAME
AREA...WITH ENHANCED LOW-LEVEL CONVERGENCE LIKELY HELPING TRIGGER
THE SHOWERS. POPS WILL REMAIN HIGH WITH THE BEST COVERAGE SHIFTED
INTO THE 3-6 AM TIMEFRAME. I HAVE TRIMMED BACK QPF BASICALLY TO
WHAT WAS IN THERE PRIOR TO MY LAST UPDATE...0.2" TO 0.5" AREAL
COVERAGE. NO CHANGES TO TEMPERATURES. SOME THOUGHTS FROM 730 PM
FOLLOW...

WATER VAPOR SATELLITE IMAGERY SHOWS A PLUME OF DEEP TROPICAL
MOISTURE MOVING NORTH ACROSS FLORIDA AND ACROSS THE EASTERN
CAROLINAS. PRECIPITABLE WATER VALUES IN EXCESS OF 2.0 INCHES
PEAK AT 2.5 INCHES NEAR CONVECTION OFF THE GEORGIA COAST. THIS IS
MOISTURE ASSOCIATED WITH FORMER TROPICAL STORM ERIKA. AT THE SURFACE
A WAVE OF LOW PRESSURE EXTENDING NORTHWARD FROM FLORIDA INTO THE
CAROLINA COASTAL PLAIN SHOULD SHARPEN UP OVERNIGHT. DUSTING OFF MY
WINTERTIME ISENTROPIC LIFT PROCEDURES AND EXAMINING THE 310K THETA
SURFACE (NEAR 700 MB) REVEALS A GOOD AMOUNT OF LIFT DEVELOPING
OVERNIGHT... SUFFICIENT TO PRODUCE RAIN OR SHOWERS ACROSS
THE ENTIRE FORECAST AREA.

FORECAST SOUNDINGS SHOW A WARM NOSE APPEARING AROUND 650 MB
OVERNIGHT IN THE MIDST OF A WARM ADVECTION JET OUT AHEAD OF A RATHER
IMPRESSIVE UPPER DISTURBANCE MOVING NORTH THROUGH THE SOUTHERN
APPALACHIANS. NEAR AND ABOVE THIS WARM NOSE LAPSE RATES ARE GREATER
THAN MOIST ADIABATIC AND I HAVE INCLUDED THE MENTION OF ISOLATED
THUNDERSTORMS IN THE FORECAST.

WITH SUCH HIGH PRECIPITABLE WATER VALUES AND SUPPORT FOR
PRECIPITATION PROVIDED BY BOTH SYNOPTIC AND CONVECTIVE
TRIGGERS...LOCALIZED HEAVY RAINFALL COULD DEVELOP OVERNIGHT.
TEMPERING THIS HEAVY RAIN THREAT WILL BE THE FACT
THE  BEST LIFT SHOULD OCCUR AT A RATHER HIGH ALTITUDE (AT AND ABOVE
700 MB) WITH MOISTURE EXISTING BELOW THIS LAYER NOT DIRECTLY BEING
INVOLVED IN PRECIP GENERATION.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY NIGHT/...
AS OF 3 PM SUNDAY...PRIMARY HEADLINE REMAINS GOOD RAIN POTENTIAL
SETTING UP FOR NE SC AND SE NC AS AN UPPER LOW EVIDENT IN VAPOR
CHANNEL THIS AFTERNOON DRIVES DEEP TROPICAL MOISTURE NORTHWARD.
MARINE CONVECTIVE SYSTEMS CURRENTLY OFFSHORE OF FLORIDA AND
GEORGIA WILL TRANSPORT A RICH SUPPLY OF DISTURBED AIR OVER A
NOCTURNALLY BUOYANT OCEAN LATE TONIGHT INTO MONDAY MORNING. RAIN
CHANCES MAY CUT OFF SHARPLY INLAND MONDAY AS DRY AIR INTRUSION
ENTRAINED INTO THE UPPER LOW SPREADS MORE CAPPING INLAND. DUE TO
HIGH PRECIPITABLE WATERS IN PLACE OVER THE NEXT 36-48 HOURS
HOWEVER...RAIN MAY BE HEAVY AT TIMES THROUGH AT LEAST TUESDAY
MORNING...AND FAVORED CLOSER TO THE COAST. WPC QPF GRAPHICS
THROUGH WED 00Z/TUE 8PM SHOW 2-3 INCHES ALONG THE SC COAST AND
1-2 INCHES ELSEWHERE...BUT LESS THAN AN INCH WEST OF I-95.
CLOUDS WILL KEEP MAXIMUMS BELOW NORMAL MONDAY AND TUESDAY FOR
THE EASTERN AND CENTRAL ZONES BUT CLOSER TO AVERAGE WELL INLAND.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
AS OF 3 PM SUNDAY...THE UPPER LOW ACROSS THE GULF COAST...WHICH
WAS HELPING FUNNEL DEEP MOISTURE ASSOCIATED WITH THE REMNANTS OF
ERIKA...WEAKENS BY THE START OF THE PERIOD. IT LOOKS LIKE WHAT IS
LEFT OF ERIKA WILL BE A DRIFT ACROSS GEORGIA MID AND LATE WEEK
GIVEN THE WEAK PRESSURE PATTERN. A TROUGH WILL EXTEND NE ALONG THE
COAST...AND THIS WILL HELP TO KEEP UNSETTLED WEATHER ACROSS THE
CAROLINAS MID WEEK.

AN UPPER RIDGE WILL BEGIN TO EXPAND ACROSS THE SOUTHEAST AND
SOUTHERN TIER OF THE COUNTRY MID AND LATE WEEK. OVERALL...
PRECIPITABLE WATER VALUES ARE HIGHER MID WEEK...SLOWLY LOWERING LATE
WEEK AND FOR THE WEEKEND. THIS SUGGESTS HIGHER POPS...ESPECIALLY WED-
THU TIME FRAME AND LOWEST POPS DURING THE WEEKEND. HOWEVER...SURFACE
HIGH PRESSURE TO OUR N MAY RIDGE STRONGLY TO OUR W...THUS ALLOWING
FOR A COASTAL TROUGH TO DEVELOP/STRENGTHEN. THIS SCENARIO WOULD BRING
AT LEAST SCATTERED CONVECTION TO THE COAST OR JUST OFFSHORE EVEN
LATE IN THE PERIOD. AT THIS TIME...NOT SEEING ENOUGH SIGNALS TO GO
ABOVE CHANCE CATEGORY THROUGHOUT ALTHOUGH LATER FORECASTS MAY FIND
JUSTIFICATION FOR AT LEAST LIKELY POPS AS THE FINER DETAILS IN BOTH
TIME AND SPACE CRYSTALLIZE.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
AS OF 06Z...A MIXTURE OF VFR/MVFR/IFR EXPECTED OVERNIGHT INTO THE
EARLY MORNING HOURS AS ISOLATED TO SCATTERED SHOWERS...LOWER
CIGS...AND AREAS OF FOG AFFECT THE AREA. CONDITIONS GRADUALLY
IMPROVE LATER ON MONDAY.

LATEST RADAR DEPICTS SHOWERS MOVING ACROSS PORTIONS OF THE
FORECAST AREA...WITH OBSERVATIONS SEEING A MIXTURE OF VFR/MVFR
SHRA ACTIVITY...LOW CIGS AND AREAS OF FOG. EXPECT THIS TO CONTINUE
THROUGH THE OVERNIGHT HOURS...WITH RAINFALL INCREASING AS THE
ATMOSPHERIC COLUMN INCREASINGLY BECOMES SATURATED. WINDS WILL BE
LIGHT. AFTER DAYBREAK...SHOWERS WILL CONTINUE WITH A GRADUAL
IMPROVEMENT OF CONDITIONS TO MVFR/AREAS OF VFR IN THE MORNING
HOURS. SOUTHEAST WINDS WILL INCREASE TO AOB 10 KTS WITH GUSTS
ALONG THE COAST UP TO 18 KTS THROUGH THE LATE MORNING HOURS. BY
AFTERNOON EXPECT VFR WITH LINGERING CLOUDS...TAPERING OFF OF -SHRA
ACTIVITY...AND SOUTHEAST WINDS.

EXTENDED OUTLOOK...SLOW MOVING LOW PRESSURE MOVING UP THE COAST
WILL GIVE US UNSETTLED WEATHER THROUGH WEDNESDAY...WITH
INTERMITTENT SHOWERS AND MVFR/IFR CEILINGS. A BIT BETTER FOR
THURSDAY AND FRIDAY WITH ISOLATED MAINLY AFTERNOON SHOWERS.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 130 AM MONDAY...NO CHANGES TO THE FORECAST WITH THE LATEST
UPDATE. PREVIOUS DISCUSSION FOLLOWS:

WIND SPEEDS ARE INCREASING RAPIDLY BETWEEN CHARLESTON AND
SAVANNAH IN ADVANCE OF THE WAVE OF LOW PRESSURE OVER FLORIDA. I
HAVE INCREASED FORECAST WIND SPEEDS BY ABOUT 5 KNOTS ACROSS THE
SOUTH CAROLINA WATERS AFTER MIDNIGHT...WITH 15-20 KNOTS NOW
EXPECTED NEAR AND SOUTH OF MYRTLE BEACH. THIS COULD BUILD SEAS AS
HIGH AS 4 FEET BY 6 AM. DISCUSSION FROM 730 PM FOLLOWS...

A WEAK BUBBLE OF HIGH PRESSURE CENTERED NEAR CAPE LOOKOUT WILL
DISSIPATE OVER THE NEXT SEVERAL HOURS AS A DEVELOPING WAVE OF LOW
PRESSURE MOVES NORTH FROM FLORIDA. MOISTURE ASSOCIATED WITH FORMER
TROPICAL STORM ERIKA IS INVOLVED IN THIS SYSTEM...AND WILL BRING A
RAINY NIGHT FOR MARINERS ALONG THE CAROLINA COAST. RAIN CHANCES ARE
100 PERCENT...WITH THE HEAVIEST ACTIVITY EXPECTED AFTER MIDNIGHT AS
STORMS OFF THE GEORGIA COAST MOVE NORTHWARD. A WARM FRONT WILL
SHARPEN UP JUST INLAND FROM THE COAST OVERNIGHT...WITH SOUTHEAST
WINDS INCREASING TO NEAR 15 KNOTS ALONG THE SC COAST...10-15 KT FOR
NC. SEAS CURRENTLY RANGING FROM 2-3 FEET (PRIMARILY IN 10 SECOND
SOUTHEAST SWELL) MAY BUILD BY ANOTHER FOOT OVERNIGHT.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 3 PM SUNDAY...MARINE CONDITIONS WILL WORSEN INTO MONDAY AS
RAIN REDUCES VSBYS AND SE WINDS KEEP SEAS ELEVATED 3-4 FT SEAS AND
AS HIGH AS 5 FT OUTER PORTION. AN EXERCISE CAUTION STATEMENT MAY
BE NEEDED FOR THE SC WATERS WHERE STRONGER SE WINDS OF 17-21 KT
MAY OCCUR MUCH OF MONDAY. ISOLATED TSTMS WILL LIKELY GREET THE
WATERS MONDAY MORNING AND AGAIN INTO TUESDAY. SEAS MONDAY AND
TUESDAY ESE WAVES 3-5 FT EVERY 8-9 SECONDS...HIGHEST OFFSHORE.
SE WIND CHOP WILL BE STRONGEST MONDAY ALONG THE SC COAST AND AN
EXERCISE CAUTION STATEMENT MAY BE NEEDED.

LONG TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 3 PM SUNDAY...A WEAK PRESSURE GRADIENT IS EXPECTED ACROSS
THE WATERS MID AND LATE WEEK. A TROUGH IS EXPECTED TO EXTEND NE
ALONG THE SOUTHEAST COAST FOR MUCH OF THE PERIOD. THIS FEATURE
LOOKS MOST PRONOUNCED WED- THU. WIND SPEEDS ARE EXPECTED TO
GENERALLY BE 10 KT OR LESS THROUGH THE PERIOD. THE DIRECTION WILL
BE MAINLY EASTERLY OR SE DURING THE AFTERNOON AND EVE HOURS. THE
LATE NIGHT AND MORNING LAND BREEZE WILL DISRUPT THE FLOW TO MORE
OF AN OFFSHORE DIRECTION.

SEAS WILL BE MAINLY 2 FT. A 8 TO 9 SECOND SE SWELL WILL BE
PRESENT...PERHAPS SLIGHTLY STRONGER MID WEEK AS COMPARED TO LATE
WEEK.  WINDS AND SEAS MAY BE HIGHER IN PERSISTENT THUNDERSTORMS.

&&

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

&&

$$

SYNOPSIS...MJC
NEAR TERM...MBB
SHORT TERM...MJC
LONG TERM...RJD
AVIATION...SGL
MARINE...MJC/RJD/MBB


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