Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 052340
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
740 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/...
AS OF 730 PM TUESDAY...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.

&&

.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...
NEAR TERM /THROUGH TONIGHT/...
AS OF 730 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.

&&

.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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