Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 051100
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
700 AM EDT TUE MAY 5 2015

.SYNOPSIS...
HIGH PRESSURE CENTERED OFFSHORE FROM CAPE HATTERAS WILL CONTINUE
TO EXTEND INTO THE AREA THROUGH THE MID-WEEK PERIOD...AND PROVIDING
SEASONABLE WEATHER FOR THIS TIME OF THE YEAR. A COASTAL LOW IS
EXPECTED TO FORM IN THE BAHAMAS DURING THE MID-WEEK PERIOD...AND
MEANDER ALONG OR OFF THE SOUTHEAST U.S. COAST BY THURSDAY AND
CONTINUING THROUGH THE UPCOMING WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 630 AM TUESDAY...BASICALLY LOOKING AT A PERSISTENCE TYPE
FORECAST FOR THE NEXT 24 HRS...USING THE PREVIOUS 12-24 HRS AS
GUIDANCE. RIDGING ALOFT TO PROVIDE SUBSIDENCE...THUS LIMITING THE
VERTICAL DEVELOPMENT OF ANY DIURNALLY DRIVEN CU. SYNOPTICALLY
DRIVEN ONSHORE WINDS WILL PERSIST ACROSS THE FA THIS PERIOD. THIS
DUE TO THE POSITIONING OF THE EAST-WEST ORIENTED SFC RIDGE AXIS
ACROSS THE NORTHERN PORTIONS OF FA. THIS AXIS EXTENDS FROM ITS
PARENT HIGHS CENTER WELL OFFSHORE AND EAST OF CAPE HATTERAS. THE
SEA BREEZE WILL DEVELOP BY MIDDAY AND LIKELY PROGRESS WELL INLAND
TO THE I-95 CORRIDOR BY THE EARLY TO MID EVENING HRS BEFORE
DISSIPATING. ENHANCED CU ALONG THIS BOUNDARY AS IT PUSHES INLAND
WILL STILL HAVE STRONG ENOUGH SUBSIDENCE ALOFT TO PREVENT ANY
CONVECTION FROM DEVELOPING. OTHER THAN DIURNALLY DRIVEN CU FOR SKY
CONDITIONS...THIN CIRRUS WILL OCCASIONALLY PASS OVER...MAINLY
ALONG THE IMMEDIATE COAST. AS FOR TEMPS...WILL AGAIN START OFF
WITH PERSISTENCE...THEN POSSIBLY ADD 1 TO 2 DEGREES FOR TODAYS
HIGHS AWAY FROM THE IMMEDIATE COAST...AND ADD 1 TO 2 DEGREES FOR
THE TONIGHTS LOWS ACROSS ALL LOCATIONS DUE TO THE CONTINUED MARINE
INFLUENCE AND ITS FURTHER PUSH INLAND.

A PERSISTENT EASTERLY 2 TO 3 FOOT...9 TO 10 SECOND PERIOD GROUND
SWELL...WILL CONTINUE TO BE THE PRIMARY DRIVER TO ENHANCE RIP
CURRENT OCCURRENCE ACROSS ALL BEACHES TODAY...ESPECIALLY IN THAT 4
HR WINDOW CENTERED AT LOW TIDE.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 3 AM TUESDAY...WED WILL PROBABLY BE THE LAST DAY OF PLEASANT
WEATHER ACROSS THE AREA...THOUGH THIS IS NOT CERTAIN. BERMUDA HIGH
AND WEAK 5H RIDGING WILL RETREAT/WEAKEN DURING THE DAY...ALLOWING
THE SYSTEM CONDENSING OFF THE SOUTHEAST COAST AN OPPORTUNITY TO
START DRIFTING NORTH. SUBSIDENCE UNDER THE WEAKENING 5H RIDGE SHOULD
BE STRONG ENOUGH TO KEEP SKIES SUNNY BUT EAST TO NORTHEAST FLOW WILL
KEEP TEMPS ALONG THE COAST NEAR TO SLIGHTLY BELOW CLIMO WHILE INLAND
AREAS SHOULD END UP ABOVE CLIMO.

FORECAST BECOMES QUITE UNCERTAIN AS EARLY AS WED NIGHT WITH SOME OF
THE GUIDANCE SHOWING PRECIP MOVING ONSHORE AFTER MIDNIGHT. HOWEVER
HAVE LITTLE TO NO CONFIDENCE IN ANY ONE SOLUTION GIVEN THE LACK OF
RUN TO RUN CONSISTENCY WITHIN THE GUIDANCE. THE GFS ENSEMBLES DO
FAVOR A WEAK SYSTEM MOVING INTO CENTRAL OR SOUTHERN SOUTH CAROLINA
LATE IN THE WEEK. THIS SOLUTION AT LEAST SEEMS PLAUSIBLE GIVEN THE
LACK OF STEERING FLOW AND THE PRESENCE OF THE DISPLACED BERMUDA HIGH
AND WEAK MID LEVEL RIDGING TO THE NORTH. DO NOT PLAN TO PULL
INHERITED SLIGHT CHC/LOW CHC POP ALONG THE COAST WED NIGHT BUT
REGION COULD VERY WELL REMAIN DRY. EITHER WAY PRECIP CHANCES SHOULD
START TO RAMP UP DURING THE SECOND HALF OF THE PERIOD AS ABUNDANT
LOW LEVEL MOISTURE IS SPREAD ONSHORE. CLOUD COVER AND NORTHEAST FLOW
WILL KEEP HIGHS NEAR TO BELOW CLIMO THU WITH LOWS RUNNING NEAR TO
ABOVE CLIMO THU NIGHT.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 3 AM TUESDAY...UNCERTAINTY ABOUNDS IN THE LONG TERM WITH THE
MEANDERING SYSTEM OFF THE SOUTHEAST COAST THE FEATURE OF NOTE. BY
THE START OF THE LONG TERM THE LOW SHOULD BE ACQUIRING AT LEAST SOME
TROPICAL CHARACTERISTICS...THOUGH WHERE IT WILL BE WHEN ITS ACQUIRING
THEM REMAINS A MYSTERY. WEAK STEERING FLOW ALOFT WILL KEEP THE LOWS
MOVEMENT ERRATIC WHICH ALSO MAKES THE STRUCTURE AND STRENGTH
FORECAST DIFFICULT. IF IT REMAINS IN THE VICINITY OF THE 80 DEGREE
SSTS OF THE GULF STREAM IT WILL HAVE LITTLE TO INHIBIT IT FROM
GAINING STRENGTH. OF COURSE OUTSIDE THE GULF STREAM SSTS ARE MUCH
COOLER...WITH SOME AREAS STILL IN THE 60S. THIS WOULD KEEP THE LOW
WEAK AND DISORGANIZED. THIS SOLUTION SEEMS TO BE WHAT THE GFS
ENSEMBLES HAVE BEEN KEYING ON AND WHAT THE LATEST GFS IS HINTING AT.

THESE RECENT DEVELOPMENTS COMBINED WITH THE 12Z ECMWF SOLUTION OF A
WEAKER MEANDERING LOW INSPIRES A HINT OF CONFIDENCE...THOUGH NOT
ENOUGH TO MAKE DRASTIC CHANGES TO THE FORECAST. REGARDLESS OF THE
EXACT LOCATION OF THE FEATURE THERE IS LIKELY TO BE A LOT OF LOW
LEVEL MOISTURE OVER THE SOUTHEAST THROUGH THE PERIOD GIVEN THE
PROLONGED ONSHORE FLOW. THERE WILL ALSO BE DAYTIME HEATING AND AN
OVERALL LACK OF STRONG DOWNWARD MOTION...EVEN IF THE LOW IS
DISPLACED WELL OFF THE COAST. THIS IS A RECIPE FOR AT LEAST SHOWERS
EVERYDAY WITH POTENTIAL FOR ISOLATED THUNDERSTORMS AS WELL. THE
INHERITED FORECAST FITS THIS QUITE WELL THOUGH DID BUMP UP POP OVER
THE WEEKEND BUT KEPT EVERYWHERE CONFINED TO LOW CHC RANGE.

WHAT IS LEFT OF THE LOW SHOULD DISSIPATE EARLY NEXT WEEK AHEAD OF
POTENTIAL SHORTWAVE TROUGH. AS HAS BEEN THE CASE RECENTLY THE
GFS/ECMWF ARE AT ODDS OVER THE EVOLUTION OF THE MID LEVEL PATTERN
NEXT WEEK. THE GFS HOLDS ONTO THE SOUTHWEST CUTOFF...EJECTING
SHORTWAVES ACROSS THE SOUTHERN CONUS. THE ECMWF STARTS TO FILL THE
CUTOFF AND LIFTS IT NORTHEAST...REACHING THE AREA AS THE PERIOD
ENDS. BOTH SOLUTIONS RESULT IN SOMEWHAT SIMILAR RESULTS...AT LEAST
CHC POP TO END THE PERIOD WITH TEMPS NEAR CLIMO.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AS OF 06Z...WILL LEAN TOWARD PERSISTENCE FOR THE 06Z FORECAST
ISSUANCE PERIOD. SFC RIDGE AXIS WILL EXTEND WEST ACROSS THE NC-SC
AREA FROM THE HIGHS CENTER WELL OFFSHORE FROM CAPE HATTERAS.
LOOKING AT ONSHORE FLOW ACROSS ALL TERMINALS THRU THIS PERIOD...
ENHANCED BY THE SEA BREEZE LATE THIS MORNING THRU EARLY-MID THIS
EVENING. ENOUGH MOISTURE IN THE LOW LEVELS TO PRODUCE DIURNALLY
DRIVEN FEW/SCT CU BUT NO PCPN EXPECTED DUE TO SUBSIDENCE ALOFT
LIMITING VERTICAL DEVELOPMENT.

EXTENDED OUTLOOK...MVFR/IFR CONDITIONS FOR A 2 TO 3 HR WINDOW FOR
BR AND POSSIBLY FG IN THE VICINITY OF DAWN EACH DAY. UNSETTLED
WEATHER THURSDAY NIGHT INTO THE WEEKEND FROM A SPORADIC MOVING
LOW OFF THE SE U.S. COAST.

&&

.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 630 AM TUESDAY...WILL BASICALLY USE A PERSISTENT TYPE
FORECAST FOR WINDS AND SIGNIFICANT SEAS BASED ON THE PREVIOUS 12
TO 24 HRS. MODELS BASICALLY INDICATE THE SFC RIDGE AXIS WILL
EXTEND WEST ACROSS THE AREA WATERS FROM THE HIGHS CENTER LOCATED
WELL OFFSHORE FROM CAPE HATTERAS. THIS WILL KEEP THE HIER ONSHORE
EASTERLY WINDS JUST SOUTH OF THE AREA WATERS...AND THE HIGHER SSW-
SW WINDS WELL NORTH OF THE AREA WATERS. THEREFORE WIND SPEEDS WILL
HANG AROUND 10 KT...EXCEPT THE NEAR SHORE WATERS DURING THIS
AFTERNOON AND EARLY EVENING COULD OBSERVE 10-15 KT OR POSSIBLY A
SOLID 15 KT DEPENDING ON THE STRENGTH OF THE INLAND PROGRESSING
SEA BREEZE.

SIGNIFICANT SEAS WILL MAINLY BE GOVERNED BY A 2 TO POSSIBLY 3 FOOT 9
SECOND EASTERLY GROUND SWELL. THE LONG FETCH ASSOCIATED WITH THE
EASTERLY ONSHORE FLOW SOUTH OF THE SFC HIGH CENTERED WELL OFFSHORE
FROM CAPE HATTERAS WILL PROVIDE THIS SWELL. WIND DRIVEN WAVES AT 3.5
TO 4.5 SECOND PERIODS ESPECIALLY NEARSHORE DUE TO THE SEA BREEZE
WILL PROVIDE SOME CHOP. NEVERTHELESS...THE EASTERLY GROUND SWELL
WILL REMAIN QUITE VISIBLE.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 3 AM TUESDAY...LIGHT NORTHEAST FLOW AT THE START OF THE
PERIOD WILL GRADUALLY INCREASE. THE MAGNITUDE OF THE INCREASE
REMAINS IN QUESTION AS CONFIDENCE IN THE EVOLUTION OF THE LOW
DEVELOPING NORTH OF THE BAHAMAS DURING THE PERIOD IS LOW. IT DOES
NOT APPEAR A FULL BLOWN TROPICAL SYSTEM WILL DEVELOP DURING THE
PERIOD BUT THE LOW IS EXPECTED TO EXPERIENCE AT LEAST SOME
STRENGTHENING. THE COMBINATION OF EXTENDED NORTHEAST FLOW AND
SPEEDS SOLIDLY IN THE 15 TO 20 KT RANGE LATER IN THE PERIOD WILL
PUSH SEAS OVER 6 FT AS EARLY AS THU AM AND HEADLINES ARE LIKELY TO
BE REQUIRED FOR AT LEAST THE SECOND HALF OF THE PERIOD.

LONG TERM /FRIDAY THROUGH SATURDAY/...
AS OF 3 AM TUESDAY...LOCATION AND STRENGTH OF THE LOW OFF THE
SOUTHEAST COAST REMAINS IN QUESTION...BUT ITS PRESENCE WILL AT THE
VERY LEAST LEAD TO CONTINUED NORTHEAST FLOW. SPEEDS COULD APPROACH
25 KT AT TIMES...FURTHER BUILDING SEAS WITHIN 20 NM. IT SEEMS
ALMOST CERTAIN THAT HEADLINES WILL BE REQUIRED FOR AT LEAST SOME
PORTION OF THE FORECAST PERIOD THOUGH THE NATURE OF THE HEADLINES
AND THEIR DURATION WILL DEPEND SOLELY ON THE EVOLUTION OF THE LOW
OFF THE SOUTHEAST COAST. CONFIDENCE IN ANY ONE SOLUTION IS LOW SO
DID NOT MAKE MUCH IN THE WAY OF CHANGES.

&&

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

&&

$$
SYNOPSIS...III
NEAR TERM...DCH
SHORT TERM...III
LONG TERM...III
AVIATION...DCH



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