Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 230201
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST FRI MAY 22 2015

.SYNOPSIS...
A WEAK COLD FRONT WILL MOVE OVER OAHU THIS EVENING...MAUI COUNTY
OVERNIGHT...AND WINDWARD BIG ISLAND SATURDAY AND SATURDAY
NIGHT...BEFORE DISSIPATING SOUTH OF THE BIG ISLAND ON SUNDAY. A
BRIEF PERIOD OF BREEZY NORTHEAST WINDS WILL ACCOMPANY THE FRONT...
THEREBY FOCUSING MOST OF ITS ASSOCIATED MOISTURE ALONG WINDWARD
SLOPES AND COASTS. AFTER THE FRONT PASSES...LIGHT TO MODERATE
NORTHEAST TO NORTH WINDS WILL PREVAIL INTO NEXT WEEK...WITH BRIEF
SHOWERS FAVORING WINDWARD AREAS...ESPECIALLY DURING NIGHTS AND
MORNINGS. HOWEVER...A CLOUD BAND MOVING OVER THE ISLANDS ON SUNDAY
MAY BRING A FEW EXTRA WINDWARD SHOWERS.

&&

.DISCUSSION...
A 100 TO 150 MILE WIDE...ENE-WSW ORIENTED....FRAGMENTED BAND OF
BROKEN TO OVERCAST SHOWERY LOW CLOUDS MARKS A SOMEWHAT UNSEASONABLE
COLD FRONT THAT IS MOVING SOUTH ACROSS THE ISLANDS THIS AFTERNOON.
RELATIVELY LIGHT WINDS AHEAD OF THE FRONT ALLOWED SEA BREEZES TO
DRIVE CLOUD AND SHOWER FORMATION OVER THE ISLANDS FROM OAHU TO
HAWAII THIS AFTERNOON...WITH NW STEERING FLOW PUSHING THE CLOUDS AND
SHOWERS TOWARD THE SE. WHILE N FACING SLOPES OF KAUAI HAVE RECEIVED
CLOSE TO AN INCH OF RAIN WITH THE FRONT SO FAR...E AND SE SIDES OF
OAHU HAVE RECEIVED BENEFICIAL RAINFALL DUE TO THE SEA BREEZE
CONVERGENCE.

THE LEADING EDGE OF THE FRAGMENTED CLOUD BAND IS APPROACHING OAHU
FROM THE N AT 3 PM...WITH THE BOUNDARY MOVING SOUTH AT SPEEDS
BETWEEN 10 AND 15 MPH. THE FRONT IS FORECAST TO MOVE OVER
OAHU AND MAUI COUNTY OVERNIGHT...AND THE BIG ISLAND ON SATURDAY
BEFORE FINALLY BREAKING APART SE OF THE BIG ISLAND ON SUNDAY. WINDS
ARE LIGHT AND VARIABLE AT THE SURFACE AHEAD OF THE FRONT...AND WILL
SWITCH TO THE NNE AFTER THE FRONT PASSES...AND THUS MOST OF THE
SHOWERS ASSOCIATED WITH THE BOUNDARY WILL FOCUS ALONG N AND E FACING
SLOPES AND COASTS. WITH MINIMAL SUPPORT FROM ALOFT...EXCESSIVE
RAINFALL IS NOT EXPECTED WITH THE FRONTAL PASSAGE.

AFTER THE FRONT PASSES...NE WINDS WILL EASE AND GENERALLY REMAIN
LIGHT TO MODERATE INTO THE MIDDLE OF NEXT WEEK. THE FRONT...AND
FOLLOWING NE WINDS...WILL USHER IN A SLIGHTLY DRIER AIR MASS...WITH
DEW POINTS DROPPING ABOUT 3-5 DEGREES F. THUS SLIGHTLY COOLER AND
CLEARER WEATHER IS EXPECTED ON SATURDAY...WITH THE POTENTIAL FOR A
FEW MORE WINDWARD SHOWERS ON SUNDAY.

THE LOW WITH WITH WHICH THE FRONT IS ASSOCIATED IS CURRENTLY ABOUT
750 MILES NNE OF THE ISLANDS...AND MOVING NE...BUT THE FORWARD
MOTION OF THE LOW IS EXPECTED TO HALT TONIGHT. THE LOW IS THEN
EXPECTED TO MOVE S AND WEAKEN THROUGH THE WEEKEND...AS HIGH PRESSURE
BUILDS FAR NW OF THE AREA. THIS WILL KEEP A RELATIVELY COOL NE WIND
FLOW OVER THE AREA. SHALLOW BANDS OF MOISTURE ROTATING AROUND THE
LOW WILL BRING SHOWERS THAT WILL FAVOR THE N AND E FACING
SLOPES...BUT THE ATMOSPHERE WILL REMAIN RELATIVELY STABLE THROUGH
THE PERIOD. GFS CONTINUES TO INDICATE THAT ONE SUCH WEAK BAND WILL
MOVE OVER THE ISLANDS SUNDAY AND SUNDAY EVENING. THE FLOW WILL
BECOME QUITE LIGHT AT TIMES...ESPECIALLY AS WE APPROACH THE MIDDLE
PART OF NEXT WEEK...WHICH WILL LIKELY ALLOW LAND AND SEA BREEZES TO
DOMINATE THE ISLAND WIND/WEATHER. THE LOW WILL EXIT TO THE NE BY THE
SECOND HALF OF NEXT THE WEEK ALLOWING THE RETURN OF LIGHT TO
MODERATE TRADE WINDS BY THE END OF THE WEEK.

&&

.AVIATION...
THE WEAKENING COLD FRONT IS SLOWING MOVING OVER KAUAI AS OF 02Z.
PREVAILING MVFR WITH TEMPO IFR IS LIKELY AT PHLI UNTIL LATER THIS
EVENING WHEN THE FRONT MOVES TOWARDS OAHU. THE FRONT IS EXPECTED TO
BE NEAR OAHU AROUND 06Z. AS THE FRONT MOVES OVER OAHU...PHJR AND
PHNL ARE LIKELY TO SEE POSSIBLE PERIODS OF ISOL TO TEMPO MVFR IN
SELECT SHOWERS. A SIMILAR SCENARIO IS EXPECTED AT MAUI COUNTY
TERMINALS...ESPECIALLY THOSE IN WINDWARD AREAS...AFTER 10Z AS THE
FRONT CONTINUES TO MOVE DOWN THE ISLAND CHAIN. MODERATE NORTH TO
NORTHEAST WINDS WILL FILL IN BEHIND THE FRONT.

THE FRONT...OR WHAT IS LEFT OF IT...IS NOT FORECAST TO REACH THE
BIG ISLAND UNTIL SATURDAY AFTERNOON. WINDS ON THE BIG ISLAND WILL
REMAIN LIGHT AND VARIABLE ALLOWING FOR LAND BREEZES TO FORM TONIGHT.
THE LAND BREEZES WILL HELP CLEAR OUT THE CLOUDS THAT BUILT UP THIS
AFTERNOON OVER THE LOWER SLOPES. VFR WILL PREVAIL.

MOST SIGNIFICANT UPPER LEVEL TURB WILL REMAIN NORTH OF THE ISLANDS
NEAR THE CENTER OF THE DEEP LOW AT 32N 151W. AIRMET TANGO OVER THE
ISLANDS HAS BEEN CANCELLED...HOWEVER ISOL LIGHT TO MODERATE TURB
MAY OCCUR OVER AND NEAR THE ISLANDS AS THE UPPER LEVEL TROUGH
EXTENDING FROM THE LOW MOVES EAST.

&&

.MARINE...
HI-RES GUIDANCE INDICATES THAT A BRIEF SURGE IN NE WINDS IN THE
WAKE OF THE FRONTAL PASSAGE WILL BRING A PERIOD OF NEAR 25 KT WINDS
TO KAUAI LEEWARD WATERS TONIGHT AND SATURDAY...AND RECENT
OBSERVATIONS AT PHBK INDICATE 20 KT SUSTAINED WINDS...WHICH IS A
LITTLE HIGHER THAN THE GUIDANCE. THUS...A SHORT-LIVED SCA HAS BEEN
POSTED FOR THAT ZONE THROUGH SATURDAY. OTHERWISE AND ELSEWHERE...
WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA INTO THE
MIDDLE OF NEXT WEEK.

AN EXTENDED RUN OF S SWELL...GENERATED BY SEVERAL LOWS IN THE DEEP S
PACIFIC OVER THE LAST WEEK...WILL BRING SOMEWHAT ELEVATED SURF TO S
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 S FACING SHORES. 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. THE OAHU
SURF DISCUSSION /SRDHFO/ HAS BEEN UPDATED AND CONTAINS DETAILS ON
THE SOURCES OF THE SWELLS...AND

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST SATURDAY FOR KAUAI LEEWARD
WATERS.

&&

$$

DISCUSSION/MARINE...BIRCHARD
AVIATION...EATON




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