Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 060745 CCA
AFDHFO

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE HONOLULU HI
859 PM HST THU MAR 5 2015

.SYNOPSIS...
BRISK...COOL NORTHERLY WINDS WILL PREVAIL THROUGH FRIDAY NIGHT
THANKS TO HIGH PRESSURE FAR TO THE NORTHWEST OF THE ISLANDS.
SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS DURING THE NIGHTS AND
MORNINGS...AND MAY BLOW OVER TO LEEWARD SECTIONS FROM TIME TO
TIME. THE WINDS WILL WEAKEN OVER THE WEEKEND AS A RIDGE OF HIGH
PRESSURE APPROACHES FROM THE NORTH. DEEPER MOISTURE SOUTH OF THE
BIG ISLAND MAY PUSH FAR ENOUGH NORTH TO INCREASE RAIN AGAIN OVER
THE BIG ISLAND ON SUNDAY...BUT THIS REMAINS UNCERTAIN.

&&

.DISCUSSION...
DEEP MOISTURE HAS BEEN SHUNTED SOUTH OF THE ISLANDS THANKS TO THE
GUSTY NNE WINDS ADVECTING COOL...DRIER AIR OVER THE STATE TODAY.
DESPITE THE DRIER AIR...STEEP LAPSE RATES IN THE BOUNDARY LAYER
ARE KEEPING NUMEROUS NARROW BANDS OF LOW-TOPPED SHOWERS GOING ON
AROUND THE ISLANDS THIS EVENING...AND THESE WILL BRING DECENT
RAINFALL TO SOME WINDWARD SHORES OVERNIGHT. WILL PROBABLY NEED TO
BOOST SOME WINDWARD AND MAUKA AREAS TO CATEGORICAL POPS OVERNIGHT
BASED ON RADAR. A FEW OF THE SHOWERS WILL BE ROBUST ENOUGH TO
DAMPEN SOME LEEWARD SPOTS FROM TIME TO TIME AS WELL. THESE SHOWERS
SHOULD FADE SOMEWHAT TOMORROW BY MID-MORNING.

NOT MUCH CHANGE IS SEEN FOR THE NEXT COUPLE OF DAYS. NNE WINDS WILL
BACK OFF A BIT AND BECOME MORE TYPICAL NE TRADES ON SATURDAY AS A
RIDGE PRESSES S TOWARD THE ISLANDS. THE BAND OF DEEPER MOISTURE
WILL REMAIN S OF THE ISLANDS THROUGH AT LEAST THE FIRST HALF OF
THE WEEKEND...SO THE LOCAL AIRMASS WILL BE ON THE DRY SIDE.
HOWEVER...OWING TO THE COOL TEMPERATURES ALOFT...THERE WILL BE
CONSIDERABLE NIGHT AND MORNING SHOWERS FOR WINDWARD AND MAUKA
AREAS...BUT THESE SHOULD DECREASE A BIT WHEN THE WINDS SUBSIDE.

THERE IS STILL SOME DISAGREEMENT ABOUT HOW FAR N THE LURKING BAND
OF DEEP MOISTURE TO OUR SOUTH SHIFTS N BY SUNDAY. A PASSING MID-
LEVEL SHORTWAVE AND UPPER LEVEL JET ENERGY WILL FAVOR ANOTHER
ROUND OF RAIN WITH THIS FEATURE AS THEY PASS NEAR THE ISLANDS...
BUT IT IS DIFFICULT TO SAY WHETHER THE RAIN WILL REACH THE BIG
ISLAND OR NOT. THE GOING FORECAST BRINGS SOME HIGHER POPS...INTO
THE LIKELY RANGE...FOR THE SOUTHERN AND KAU PORTIONS OF THE BIG
ISLAND ON SUNDAY AND THIS LOOKS VERY REASONABLE. WE WOULD NEED TO
BEEF THE POPS AND WX UP SOME MORE IF IT LOOKS LIKE THE BAND WILL
GET MUCH FARTHER N THAN THAT.

THIS PESKY BAND OF DEEP MOISTURE HANGS AROUND EVEN INTO THE
MIDDLE OF NEXT WEEK. EARLIER MODEL RUNS WERE TRYING TO SLOSH THIS
MOISTURE UP OVER THE ISLANDS BRING A VERY ACTIVE SLUG OF
PRECIPITATION ALONG A FRONTAL BOUNDARY OVER US...WITH LOW PRESSURE
DEVELOPING TO OUR N. THE MOST RECENT RUNS OF THE GFS...AND NOW THE
06/00 UTC ECMWF...NOW SEEM TO BE MUCH LESS EXCITED ABOUT THIS
SITUATION...WITH WEAKER CYCLOGENESIS FARTHER NORTH...AND MAINTAINING
THE STATUS QUO OVER THE STATE WITH ACTIVE WEATHER NOT TOO FAR SE OF
THE BIG ISLAND. WE WILL KEEP AN EYE ON THIS BUT FOR NOW THE
INDICATIONS ARE THAT THE WEATHER SHOULD REMAIN FAIRLY QUIET WELL
INTO NEXT WEEK.

ANOTHER PROLONGED EPISODE OF VERY STRONG WINDS FOR THE BIG ISLAND
SUMMITS APPEARS LIKELY AS STRONG LOW PRESSURE IN THE MID-LEVELS
OF THE ATMOSPHERE PRESSES SOUTH TOWARD THE ISLANDS THIS WEEKEND.
IN THE MEANTIME WINDS WILL LIKELY REMAIN NEAR ADVISORY LEVELS FOR
MAUNA LOA AND MAUNA KEA THROUGH ABOUT SATURDAY...THEN RATCHET UP
TO WARNING LEVELS FOR SUNDAY AND BEYOND. WILL BE ISSUING A WIND
ADVISORY SHORTLY FOR THE SUMMITS.

&&

.AVIATION...
PASSING LOW CLOUDS AND SHOWERS UNDER THE TRADE WINDS WILL BRING
ISOLATED MVFR CEILINGS AND BRIEF MTN OBSC OVER WINDWARD SLOPES.
OTHERWISE VFR CONDITIONS SHOULD PREVAIL FOR ALL SITES THROUGH
EARLY FRIDAY MORNING.

AN AIRMET TANGO FOR MOD LOW LEVEL TURB OVER LEEWARD KAUAI WILL
LIKELY REMAIN IN EFFECT AT LEAST UNTIL FRIDAY DUE TO THE TRADE
WINDS. IN FACT...THE CONDITION MAY SPREAD TO OTHER SMALLER ISLANDS
AS THE GUSTY WINDS CONTINUE.

&&

.MARINE...
A STRONG...LARGE 1040 MB HIGH ABOUT 1500 MILES NW OF KAUAI IS
KEEPING TRADES MORE NORTHERLY THAN USUAL AND IN THE FRESH TO
LOCALLY STRONG RANGE...WITH SMALL CRAFT ADVISORIES /SCA/ NEEDED
FOR THOSE AREAS WHERE THE NNE WINDS ARE ACCELERATED AROUND ISLAND
TERRAIN. SCA-LEVEL WINDS WILL PERSIST THROUGH FRI NIGHT BUT SHOULD
DROP ON SAT AS A NARROW RIDGE OF HIGH PRESSURE PUSHES S TOWARD THE
ISLANDS. ROUGH SEAS ARE ALSO RUNNING CLOSE TO SCA CRITERIA AS
WELL.

A COMPLEX OF LOW PRESSURE AREAS MILLING AROUND SOUTH OF ALASKA
THE LAST FEW DAYS CREATED A COUPLE OF FETCHES OF NW AND NNW WINDS
SOUTH OF THE ALEUTIANS. THESE WINDS WERE MAINLY BELOW GALE FORCE
BUT STILL ENOUGH TO BRING A COUPLE OF SMALL NW SWELLS TO THE
ISLANDS. THE CURRENT SMALL NW SWELL WILL BE WINDING DOWN AS WE
HEAD INTO THE WEEKEND WHILE THE FORERUNNERS OF ANOTHER ARRIVE ON
FRIDAY.

IN ADDITION...THE GUIDANCE SHOWS ANOTHER COMPLEX LOW DEVELOPING
ABOUT 1100 MILES NNE OF THE ISLANDS...ON SATURDAY...AND LINGERING
INTO NEXT WEEK. THIS ONE WILL HAVE A FETCH OF NORTHERLIES THAT MAY
REACH GALE FORCE...WHICH WILL SEND A LARGER SWELL THAT WILL LIKELY
REACH THE ISLANDS ABOUT SUNDAY. THE SWELL WILL AGAIN BE RATHER
SHORT FETCH OWING TO THE PROXIMITY OF THE LOW. IT WILL LIKELY BE
SUB-ADVISORY LEVEL FOR NORTH FACING SHORES...BUT SURF HEIGHTS
ALONG E FACING SHORES EXPOSED TO SUCH A SWELL MAY REACH ADVISORY
CRITERIA BY MONDAY AS WELL AS A POSSIBILITY FOR HARBOR SURGES FOR
KAHULUI AND HILO HARBORS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 AM HST SATURDAY FOR KAUAI NORTHWEST
WATERS-KAUAI LEEWARD WATERS-KAUAI CHANNEL-OAHU LEEWARD WATERS-
KAIWI CHANNEL-MAUI COUNTY LEEWARD WATERS-MAALAEA BAY-PAILOLO
CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND
SOUTHEAST WATERS.

WIND ADVISORY UNTIL 6 PM HST SATURDAY FOR THE SUMMITS OF MAUNA LOA
AND MAUNA KEA.

&&

$$
DISCUSSION/MARINE...R BALLARD
AVIATION...HUI






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