Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 281329
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
329 AM HST THU MAY 28 2015

.SYNOPSIS...
A SURFACE RIDGE BUILDING NORTHWEST OF THE STATE WILL BRING GENTLE
TO MODERATE TRADE WINDS ACROSS THE WESTERN ISLANDS TODAY THROUGH
FRIDAY...BUT WINDS WILL REMAIN LIGHT ENOUGH TO ALLOW LOCALIZED
LAND AND SEA BREEZES. A PERSISTENT TROUGH LINGERING NEAR THE BIG
ISLAND WILL MAINTAIN LIGHTER WINDS WITH WIDESPREAD SEA BREEZES
OVER THE EASTERN HALF OF THE STATE. ABUNDANT MOISTURE LINGERING
AROUND THE STATE WILL PROVIDE A RATHER CLOUDY AND SHOWERY WEATHER
PATTERN AT TIMES. TRADE WINDS SHOULD INCREASE SOMEWHAT ACROSS THE
STATE DURING THE WEEKEND...BUT LINGERING MOISTURE WILL KEEP
SHOWERS ACTIVE ESPECIALLY ACROSS WINDWARD AND MAUKA AREAS.

&&

.DISCUSSION...
A HIGHLY ANOMALOUS WEATHER PATTERN PREVAILS OVER THE NORTH PACIFIC
OCEAN...WITH A LARGE VERTICALLY STACKED LOW PRESSURE AREA AT THE
SURFACE AND ALOFT SITTING NEAR THE POSITION WHERE THE NORTHEAST
PACIFIC SURFACE HIGH USUALLY RESIDES AT THIS TIME OF YEAR. A
COMPLEX SURFACE TROUGH EXTENDS SOUTH AND WEST FROM THIS LOW TO
NEAR THE BIG ISLAND...WITH A PERSISTENT SMALL-SCALE CIRCULATION
WITHIN THIS TROUGH EVIDENT IN SATELLITE/RADAR DATA JUST TO THE
SOUTHEAST OF THE BIG ISLAND. ABUNDANT CLOUDINESS ASSOCIATED WITH
THE TROUGH CONTINUES TO BLANKET THE BIG ISLAND AND MOST OF MAUI
COUNTY. FURTHER TO THE WEST...A RIDGE EXTENDING EASTWARD FROM HIGH
PRESSURE CENTERED OUT NEAR THE INTERNATIONAL DATELINE IS PROVIDING
GENTLE TO MODERATE NORTHEAST FLOW OVER THE WESTERN END OF THE
STATE. MIMIC-TPW SATELLITE IMAGERY DEPICTS A LARGE AREA OF
ENHANCED MOISTURE AROUND AND EAST OF THE BIG ISLAND...WITH ANOTHER
SMALLER POCKET OF ENHANCED MOISTURE NEAR AND WEST OF KAUAI. A
SOMEWHAT DRIER AIRMASS PREVAILS IN BETWEEN...BUT ESTIMATED PWATS
ARE ABOVE NORMAL EVEN IN THAT AREA. THE 12Z SOUNDINGS FOUND ABOVE
NORMAL PWATS AROUND 1.45 INCHES AT BOTH LIHUE AND HILO...WITH
THE INVERSION HEIGHTS RANGING FROM NEAR 9KFT AT LIHUE TO 6KFT
AT HILO.

ONLY SUBTLE CHANGES ARE FORECAST IN THE PATTERN FOR TODAY THROUGH
FRIDAY. MODEL CONSENSUS INDICATES THAT GENERALLY ABOVE NORMAL
MOISTURE WILL LINGER ACROSS THE STATE THROUGH THE PERIOD...DUE TO
A COMBINATION OF THE TROUGH TO OUR EAST AND MOISTURE DRIFTING
SOUTHWARD FROM A DISSIPATED FRONT. THE DEEP LOW TO OUR NE WILL
SHIFT SLOWLY EASTWARD AND WEAKEN...WITH A WEAK SFC TROUGH SLOWLY
FILLING NEAR THE BIG ISLAND...WHILE HIGH PRESSURE WILL REMAIN FAR
TO OUR WNW NEAR THE DATELINE. THE RESULTING PRESSURE GRADIENT WILL
BE STRONGER NEAR KAUAI/OAHU...AND WEAKER ACROSS THE EASTERN HALF
OF THE STATE. SEA BREEZES AND LAND BREEZES WILL BE MORE LOCALIZED
NEAR KAUAI/OAHU THAN FARTHER EAST...BUT WILL STILL CONTRIBUTE TO
ISLAND-SCALE EFFECTS. ENHANCED CONVERGENCE ALONG THE LEEWARD SEA
BREEZES WILL CONTRIBUTE TO INTERIOR/LEEWARD CLOUDS AND SHOWERS
DURING THE AFTERNOONS AND EARLY EVENINGS...WHILE THE TRADES WILL
PRODUCE SOME WINDWARD SHOWERS AS WELL ESPECIALLY OVER KAUAI AND
OAHU. MORE WIDESPREAD CLOUDINESS AND SHOWERS MAY LINGER OVER THE
BIG ISLAND THROUGH TODAY DUE TO THE PROXIMITY OF THE SFC
TROUGH...BUT CONDITIONS SHOULD SLOWLY IMPROVE TONIGHT AND FRIDAY
AS THE TROUGH GRADUALLY WEAKENS.

DURING THE WEEKEND AND INTO EARLY NEXT WEEK...THE MID/UPPER
TROUGH TO OUR NE AND E WILL FINALLY WEAKEN AND MOVE FURTHER
AWAY...ALLOWING A MORE ZONAL FLOW PATTERN ALOFT TO DEVELOP OVER
THE CENTRAL PACIFIC. A SFC HIGH BUILDING TO OUR NORTH WILL BRING
GENTLE TO MODERATE TRADES BACK ACROSS THE ENTIRE STATE. A SOMEWHAT
MORE TYPICAL TRADE WIND WEATHER PATTERN SHOULD RETURN WITH CLOUDS
AND SHOWERS FOCUSED MAINLY ACROSS WINDWARD/MAUKA AREAS...BUT
CONTINUED ABOVE NORMAL MOISTURE AND HIGH INVERSIONS WILL PROBABLY
ALLOW FOR MORE SHOWERS AND CLOUDS LEEWARD AND INTERIOR ALONG
LOCAL SEA BREEZES THAN WOULD USUALLY BE THE CASE.

THE LATEST AVAILABLE GFS AND ECMWF RUNS HAVE COME INTO BETTER
AGREEMENT THROUGH THE MIDDLE OF NEXT WEEK. THE GFS HAS CONTINUED
TO TREND TOWARD THE CONSISTENT ECMWF SOLUTION...MAINTAINING A
RIDGE OF HIGH PRESSURE NORTH OF THE AREA AND MODERATE TRADE WINDS
OVER THE ISLANDS. WITH EARLY JUNE CLIMATOLOGY FAVORING THE RECENT
MODEL TRENDS...HAVE STEERED THE EXTENDED FORECAST IN THAT
DIRECTION.

&&

.AVIATION...
A TROUGH OF LOW PRESSURE OVER THE BIG ISLAND CONTINUES TO PRODUCE
WIDESPREAD CLOUDINESS AND SCATTERED SHOWERS THERE. AREAS OF MVFR
AND LOCAL IFR WILL REMAIN POSSIBLE ACROSS WINDWARD SECTIONS
TODAY...AND AIRMET SIERRA FOR MOUNTAIN OBSCURATION IS POSTED.
A WEAK PRESSURE PATTERN IS IN PLACE FROM THE BIG ISLAND THROUGH
OAHU...WHICH WILL ALLOW SEA AND LAND BREEZES TO DOMINATE THE
WEATHER PATTERN AGAIN TODAY. CANNOT RULE OUT SOME BRIEF MVFR
CIGS/VSBYS IN SHRA...BUT PREDOMINANTLY VFR CONDITIONS ARE
EXPECTED.

&&

.MARINE...
THE WEDNESDAY EVENING ASCAT PASS FOUND TRADE WINDS A BIT STRONGER
THAN EXPECTED AROUND KAUAI AND OAHU...WITH AREAS OF WINDS NEAR 20
KT ESTIMATED AROUND AND WEST OF KAUAI. IT APPEARS THAT WINDS DROP
OFF ABRUPTLY FURTHER TO THE EAST AROUND MAUI COUNTY. WINDS AND
SEAS ARE FORECAST TO REMAIN BELOW SMALL CRAFT ADVISORY /SCA/
LEVELS THROUGHOUT THE HAWAIIAN COASTAL WATERS DURING THE REST OF
THIS WEEK AND THROUGH THE WEEKEND.

THE CURRENT SOUTH SWELL WILL CONTINUE TO SUBSIDE TODAY...ALTHOUGH
A SERIES OF SMALLER SOUTH SWELLS WILL MAINTAIN SMALL TO MODERATE
SURF ALONG SOUTH FACING SHORES THROUGH THE REST OF THE WEEK.
LATEST WAVEWATCH GUIDANCE CONTINUES TO SHOW A SIGNIFICANT SOUTH
SWELL ARRIVING SATURDAY NIGHT...THEN PEAKING LATE SUNDAY INTO
MONDAY...WITH RESULTING SURF LIKELY REACHING ADVISORY LEVELS FOR
SOUTH FACING SHORES. THIS SWELL WAS PRODUCED BY A STRONG GALE LOW
EAST OF NEW ZEALAND WITH A LONG FETCH AIMED TOWARD HAWAII A FEW
DAYS AGO. DATA FROM THE AUNUU BUOY NEAR AMERICAN SAMOA SHOWS THIS
SWELL INCREASING DURING THE NIGHT...WITH HEIGHTS AND PERIODS
RUNNING NEAR WAVEWATCH GUIDANCE THUS FAR.

OTHERWISE...SURF WILL REMAIN WELL BELOW ADVISORY LEVELS THROUGH
THE NEXT SEVERAL DAYS WITH ONLY SMALL SWELLS EXPECTED.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

JACOBSON






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