Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 280203
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST WED MAY 27 2015

.SYNOPSIS...
A SURFACE RIDGE BUILDING NORTH OF THE STATE WILL LEAD TO A WEAK
TRADE WIND PATTERN...BUT WILL STILL BE LIGHT ENOUGH FOR LOCALIZED
LAND AND SEA BREEZES THROUGH THE REST OF THE WEEK. A PERSISTENT
TROUGH NEAR THE BIG ISLAND WILL KEEP WINDS EVEN LIGHTER OVER THE
EASTERN HALF OF THE STATE. INCREASING MOISTURE WILL LEAD TO AN
INCREASINGLY CLOUDY AND SHOWERY WEATHER PATTERN...PARTICULARLY
DURING THE AFTERNOONS AND EARLY EVENINGS. PORTIONS OF KAUAI AND
WINDWARD BIG ISLAND WILL SEE THE MOST RAINFALL TONIGHT.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS A BROAD UPPER LEVEL TROUGH JUST EAST OF
THE STATE...ASSOCIATED WITH A LOW FAR TO THE NORTHEAST. AT THE
SURFACE...A COMPLEX LOW IS LOCATED FAR NORTHEAST OF THE STATE...
WITH A TROUGH THAT EXTENDS TO NEAR THE BIG ISLAND. WITHIN THE
TROUGH...SMALL SCALE LOWS CAN BE SEEN IN THE CLOUD FIELD JUST EAST
OF THE BIG ISLAND AND JUST OUTSIDE OF THE COASTAL WATERS SOUTH OF
THE BIG ISLAND. 00Z RAOBS SHOW INVERSIONS RANGING FROM 7KFT AT LIHUE
TO 11KFT AT HILO...WITH PRECIPITABLE WATERS OF 1.16 INCHES AND 1.51
INCHES RESPECTIVELY. EARLY AFTERNOON TOTAL PRECIPITABLE WATER
IMAGERY SHOWS THE LARGE AREA OF MOISTURE NEAR THE BIG ISLAND...WITH
ANOTHER BAND JUST APPROACHING KAUAI FROM THE NORTH.

THICKER CLOUDS AND SHOWERS WILL CONTINUE TO AFFECT WINDWARD AND
SOUTHEAST BIG ISLAND TONIGHT...ASSOCIATED WITH THE LOWS EMBEDDED
WITHIN THE TROUGH. SOUTHEAST BIG ISLAND SHOULD IMPROVE A BIT THIS
EVENING...BUT REMAINING AREAS MAY STAY SHOWERY THROUGH THE NIGHT.
CLOUDS ASSOCIATED WITH THE BAND OF MOISTURE SPREADING ACROSS KAUAI
ARE STARTING TO FILL IN. WITH STRONGER TRADES NEAR KAUAI...THIS
MOISTURE WILL FOCUS MOST SHOWER ACTIVITY ALONG WINDWARD AND MAUKA
AREAS. ELSEWHERE ACROSS THE STATE...INTERIOR CLOUDS AND SHOWERS THAT
FORMED ALONG SEA BREEZES WILL DIMINISH WITH SUNSET THIS EVENING.
THE GRADIENT REMAINS WE ENOUGH THAT LAND BREEZES WILL BE WIDESPREAD
ACROSS MAUI COUNTY...BUT WILL BE MORE LOCALIZED ACROSS OAHU. AN AREA
OF MID-LEVEL CLOUDS ALSO EXTENDS ACROSS MUCH OF MAUI
COUNTY...KEEPING SKIES CLOUDIER THAN WOULD OTHERWISE BE EXPECTED
TONIGHT.

A SURFACE RIDGE NORTH OF THE STATE WILL KEEP A WEAK TO MODERATE
BACKGROUND TRADE WIND FLOW THROUGH THE LAST HALF OF THE WORK WEEK.
THE GRADIENT WILL STRONGER NEAR KAUAI/OAHU...AND LIGHTEST ACROSS THE
EASTERN HALF OF THE STATE...CLOSER TO THE LINGERING SURFACE TROUGH.
SEA BREEZES AND LAND BREEZES MAY 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 CLOUDS AND SHOWERS DURING THE AFTERNOON AND
EARLY EVENING. AT UPPER LEVELS...THE TROUGH JUST TO THE EAST WILL
GRADUALLY SHIFT EASTWARD AND FLATTEN THROUGH THE END OF THE WEEK...
THOUGH GFS FORECAST SOUNDINGS SHOW INVERSIONS STEADILY WEAKENING AND
LIFTING. THIS IS IN PART DUE TO THE AIRMASS JUST NORTH OF THE
STATE...ASSOCIATED WITH THE FORMER FRONT THAT DISSIPATED EARLIER IN
THE WEEK. AN INCREASE IN PRECIPITABLE WATER AND DECREASE IN
MID-LEVEL TEMPERATURES WILL LEAD TO THE RISE IN INVERSION HEIGHTS...
WHICH MAY HELP TO ENHANCE RAINFALL CHANCES AND AMOUNTS LATE IN THE
WEEK.

OVER THE WEEKEND...A NEW SURFACE HIGH BUILDS NORTH OF THE STATE. THE
SURFACE PATTERN REMAINS RATHER COMPLEX TO OUR NORTH...BUT FEATURES A
SLIGHT STRENGTHENING OF THE GRADIENT OVER THE ISLANDS. WHILE WE GET
BACK TO A LIGHT TO MODERATE TRADE WIND BACKGROUND FLOW...WEAK
FEATURES EMBEDDED WITHIN THE FLOW MAY INTERRUPT THE GRADIENT ENOUGH
TO ALLOW LOCALIZED SEA BREEZES TO CONTINUE ACROSS SHELTERED LEEWARD
AREAS. THEREFORE WE TRANSITION TO HYBRID RAINFALL PATTERN...WITH
CLOUDS AND SHOWERS FOCUSED ACROSS WINDWARD AREAS AT NIGHT AND
MORNING AND ACROSS LEEWARD AREAS DURING THE AFTERNOON AND EVENING.

THE EXTENDED MODELS HAVE BEEN BACK AND FORTH WITH THE FORECAST FOR
NEXT WEEK. THE OVERNIGHT RUNS SHOWED THE SURFACE HIGH BREAKING
DOWN...WITH ANOTHER FRONT POTENTIALLY APPROACHING THE ISLANDS. BOTH
THE 12Z GFS AND ECMWF HAVE TRENDED TOWARD A WEAKER/SLOWER
SOLUTION FOR THE NEXT NORTHERN SYSTEM...SHOWING THE SUBTROPICAL
RIDGE MAINTAINING ITS STRENGTH NORTH OF THE STATE WITH A FRONT
TRYING TO PUSH INTO IT LATE IN THE WEEK. THERE REMAIN DIFFERENCES
BETWEEN THE MODELS...WITH THE ECMWF FARTHER SOUTH WITH THE RIDGE
THAN THE GFS...BUT OVERALL THEY FEATURE A SIMILAR PATTERN FOR HAWAII
WITH PERSISTENT LIGHT TO MODERATE TRADE WINDS.

&&

.AVIATION...
A TROUGH OF LOW PRESSURE OVER THE BIG ISLAND IS RESPONSIBLE FOR
PREVAILING MVFR AND TEMPORARY IFR CIGS/VSBYS AT PHTO...AND THESE
CONDITIONS WILL LIKELY PERSIST THROUGH MUCH OF THE NIGHT.
ELSEWHERE...A WEAK PRESSURE PATTERN IS IN PLACE...WHICH WILL ALLOW
SEA AND LAND BREEZES TO DOMINATE THE WEATHER PATTERN THROUGH
THURSDAY. CAN/T RULE OUT SOME BRIEF MVFR CIGS/VSBYS IN SHRA AT THE
OTHER TERMINALS THIS AFTERNOON...BUT PREDOMINANTLY VFR CONDITIONS
ARE EXPECTED.

AIRMET SIERRA IS IN EFFECT FOR EASTERN SECTIONS OF THE BIG ISLAND
DUE TO MOUNTAIN OBSCURATION...AND THESE CONDITIONS ARE LIKELY TO
PERSIST THROUGH MUCH OF THE NIGHT. MOUNTAIN OBSCURATION COULD ALSO
IMPACT PORTIONS OF THE OTHER ISLANDS LATE THIS AFTERNOON INTO THIS
EVENING AS SEA BREEZE SHOWERS DEVELOP...WITH INTERIOR LOCATIONS THE
MOST LIKELY TO BE AFFECTED.

&&

.MARINE...
THE CURRENT SOUTH SWELL WILL CONTINUE TO SUBSIDE...THOUGH A SERIES
OF SMALLER SOUTH SWELLS WILL MAINTAIN SURF ALONG SOUTH FACING SHORES
THROUGH THE REST OF THE WEEK. LATEST WAVEWATCH GUIDANCE CONTINUES TO
SHOW A SIGNIFICANT SOUTH SWELL REACHING US SATURDAY NIGHT AND
PEAKING LATE SUNDAY INTO MONDAY...WITH 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 POINTED TOWARD THE
STATE A COUPLE OF DAYS AGO.

&&

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

&&

$$

DISCUSSION/MARINE...BRAVENDER
AVIATION...JELSEMA





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