Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 231405
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
405 AM HST SAT MAY 23 2015

.SYNOPSIS...
A WEAK COLD FRONT WILL MOVE SOUTH OF MAUI COUNTY THIS MORNING...
THEN ACROSS THE BIG ISLAND LATER TODAY AND TONIGHT...BEFORE
DISSIPATING SOUTH OF THE BIG ISLAND ON SUNDAY. MODERATE NORTH TO
NORTHEAST WINDS WILL PREVAIL BEHIND THE FRONT FROM TODAY THROUGH
SUNDAY...WITH SHOWER ACTIVITY FOCUSED MAINLY ON WINDWARD COASTS
AND SLOPES. A CLOUD BAND MOVING OVER THE ISLANDS FROM THE NORTH
ON SUNDAY MAY ENHANCE THE WINDWARD SHOWERS SOMEWHAT. LIGHTER
NORTHEAST WINDS ARE EXPECTED FOR MONDAY...WITH LIGHT BACKGROUND
FLOW AND A RETURN TO A LAND AND SEA BREEZE PATTERN FORECAST FOR
TUESDAY THROUGH THURSDAY.

&&

.DISCUSSION...
AN INCREASINGLY DIFFUSE COLD FRONT LIES ACROSS MAUI COUNTY
CURRENTLY...WITH SHOWER ACTIVITY ALONG AND AHEAD OF THE FRONT
AFFECTING WINDWARD MAUI AND APPROACHING THE HAMAKUA COAST OF THE
BIG ISLAND. PERSISTENT MODERATE TO OCCASIONALLY HEAVY RAINS
ANCHORED ON THE NORTH/NORTHEAST FACING SLOPES REQUIRED SEVERAL
FLOOD ADVISORIES TO BE ISSUED DURING THE NIGHT...WITH SEVERAL
STREAM GAUGES ON MOLOKAI AND MAUI EARLIER SHOWING MODEST WATER
LEVEL RISES. DRIER NORTHERLY FLOW PREVAILS ACROSS OAHU AND KAUAI
BEHIND THE FRONT. SURFACE ANALYSIS DEPICTS THE AFOREMENTIONED
FRONT STRETCHING SW FROM A LOW CENTERED ABOUT 900 MILES NNE OF
PHNL...WITH A 1026 MB HIGH CENTERED ABOUT 1000 MILES NW OF KAUAI.
AN UNSEASONABLY DEEP TROUGH ALOFT IS LOCATED OVER THE CENTRAL
PACIFIC...SUPPORTING THE UNUSUAL MOVEMENT OF THE SURFACE FRONT
SOUTHWARD ACROSS THE MAIN HAWAIIAN ISLANDS IN LATE MAY. MIMIC-TPW
SATELLITE IMAGERY DEPICTS A NARROW BAND OF ENHANCED MOISTURE ALONG
THE FRONT...WITH ESTIMATED PWATS UP TO 1.5 INCHES. THE 12Z LIHUE
SOUNDING REFLECTED THE DRIER AIRMASS BEHIND THE FRONT...WITH THE
INVERSION DOWN TO 5K FEET AND PWAT OF 0.99 INCHES. THERE HAS BEEN
LITTLE AIRMASS CHANGE DURING THE PAST 12 HOURS AT HILO AHEAD OF
THE FRONT...WITH THE INVERSION STILL AROUND 9K FEET AND PWAT OF
1.28 INCHES.

FOR TODAY...EXPECT THE WEAK FRONT TO CONTINUE MOVING SOUTHWARD
FROM MAUI ACROSS THE BIG ISLAND. SHOWERS WILL MAINLY AFFECT
WINDWARD AREAS...ALTHOUGH THE DEEPER MOISTURE ALONG THE FRONT
WILL PROBABLY ALLOW SCATTERED SHOWERS TO DEVELOP ALONG THE KONA
COAST DURING THE AFTERNOON. DRIER NNE FLOW WILL PREVAIL ACROSS
KAUAI AND OAHU...WITH IMPROVING CONDITIONS SPREADING INTO MAUI
COUNTY DURING THE DAY. A SLIGHTLY DRIER AND COOLER AIR MASS HAS
SPREAD INTO THE WESTERN END OF THE STATE BEHIND THE FRONT...WITH
DEW POINTS HAVING ALREADY DROPPED INTO THE LOWER 60S. HIGH TEMPS
SHOULD BE A COUPLE OF DEGREES COOLER THIS WEEKEND THAN THEY HAVE
BEEN RECENTLY FOR MOST AREAS.

THE PARENT LOW OF THE FRONT WILL MOVE SOUTH AND WEAKEN THROUGH THE
WEEKEND...AS HIGH PRESSURE BUILDS FAR NW OF THE AREA. THIS WILL
KEEP A RELATIVELY COOL MODERATE N/NE WIND FLOW OVER THE STATE
TONIGHT AND SUNDAY. SHALLOW BANDS OF MOISTURE ROTATING AROUND THE
LOW WILL BRING SHOWERS MAINLY ACROSS THE NORTH AND EAST FACING
SLOPES...BUT THE ATMOSPHERE WILL REMAIN RELATIVELY STABLE THROUGH
THE PERIOD. GFS CONTINUES TO INDICATE THAT A WEAK BAND OF ENHANCED
MOISTURE WILL MOVE ACROSS THE STATE SUNDAY INTO SUNDAY EVENING.
LIGHT NE FLOW SHOULD HOLD THROUGH MONDAY...BUT THEN IS FORECAST TO
WEAKEN FURTHER TUESDAY THROUGH THURSDAY AS LOW PRESSURE LINGERS
FAR TO OUR NORTH AND HIGH PRESSURE WEAKENS TO OUR NORTHWEST. THIS
WILL LIKELY ALLOW LAND AND SEA BREEZES TO DOMINATE THE LOCAL
WEATHER REGIME ONCE AGAIN....WITH AFTERNOON CLOUDS AND SHOWERS
ACROSS THE INTERIOR/LEEWARD AREAS OF THE ISLANDS. THE LOW SHOULD
FINALLY EXIT TO THE NE TOWARD THE END OF NEXT WEEK...ALLOWING A
WEAK HIGH PRESSURE RIDGE TO BUILD TO OUR NORTH...AND BRINGING
LIGHT TO MODERATE TRADES BACK ACROSS THE STATE.

&&

.AVIATION...
A WEAKENING COLD FRONT ACROSS MAUI COUNTY WILL SHIFT SOUTHEASTWARD
AND INTO THE BIG ISLAND THIS MORNING...AND PUSH SOUTH OF STATE
TONIGHT. TEMPORARY MVFR CIGS/VSBYS WILL BE POSSIBLE AT THE TERMINALS
AS THE FRONT MOVES THROUGH...WITH IMPROVING CONDITIONS EXPECTED
BEHIND THE FRONT.

AIRMET SIERRA IS IN EFFECT FOR MOUNTAIN OBSCURATION ACROSS MOLOKAI
LANAI AND MAUI...AND THESE CONDITIONS SHOULD IMPROVE AROUND
DAYBREAK. AN AIRMET MAY BE NEEDED ACROSS THE BIG ISLAND LATER THIS
MORNING FOR MOUNTAIN OBSCURATION AS WELL.

&&

.MARINE...
THE FRIDAY EVENING ASCAT PASS FOUND AREAS OF 20 KT WINDS ACROSS
THE WESTERN HAWAIIAN COASTAL WATERS...BEHIND THE ADVANCING COLD
FRONT. A SMALL CRAFT ADVISORY /SCA/ REMAINS IN EFFECT FOR THE
LEEWARD KAUAI COASTAL WATERS THROUGH TODAY...WITH 25 KT WINDS
POSSIBLE MAINLY ACROSS THE KAULAKAHI CHANNEL. MODERATE TO FRESH
N/NE FLOW IS EXPECTED TO SPREAD SOUTHWARD THROUGH THE REMAINDER OF
THE COASTAL WATERS AROUND THE BIG ISLAND TODAY...AND PREVAIL
STATEWIDE TONIGHT AND SUNDAY. WINDS ARE FORECAST TO REMAIN BELOW
SCA LEVELS AT THIS POINT...BUT MAY COME CLOSE IN SOME AREAS
EXPOSED TO THE NNE WIND DIRECTION. WINDS WILL THEN WEAKEN ONCE
AGAIN MONDAY...BECOMING LIGHT WITH AFTERNOON SEABREEZES LIKELY
DEVELOPING TUESDAY AND WEDNESDAY.

AN EXTENDED RUN OF SOUTH SWELL...GENERATED BY SEVERAL LOWS IN THE DEEP
SOUTH PACIFIC OVER THE LAST WEEK...WILL BRING SOMEWHAT ELEVATED SURF
TO SOUTH FACING SHORES FOR THE NEXT WEEK. SURF HEIGHTS ARE EXPECTED TO
REMAIN BELOW ADVISORY LEVELS FOR THE BULK OF THE TIME...BUT
OVERLAPPING SWELLS FROM SUNDAY INTO TUESDAY COULD BRING SURF TO
NEAR ADVISORY-LEVELS ALONG EXPOSED SOUTH FACING SHORES. A
MODERATE NNE SWELL IS EXPECTED TO ARRIVE ON SUNDAY AND LINGER
THROUGH MONDAY...BUT RELATIVELY SHORT SWELL PERIODS SHOULD RESULT
IN SURF WELL BELOW ADVISORY LEVELS ON NORTH FACING SHORES.
OTHERWISE...A COUPLE OF SMALL SWELLS FROM THE NNW AND WNW ARE
EXPECTED OVER THE WEEKEND AND EARLY NEXT WEEK...WITH RESULTANT
SURF WELL BELOW ADVISORY LEVELS. SEE THE LATEST OAHU SURF
DISCUSSION /SRDHFO/ FOR MORE DETAILS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL NOON HST TODAY FOR BIG ISLAND SUMMITS.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THIS EVENING FOR KAUAI
LEEWARD WATERS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...JELSEMA






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