Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 280654
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
854 PM HST FRI FEB 27 2015

.SYNOPSIS...
A WEAK FRONT CURRENTLY NEAR MAUI WILL DRIFT SLOWLY EASTWARD
TONIGHT AND SATURDAY...DISRUPTING THE TRADE WIND FLOW AND ACTING
AS A FOCUS FOR ENHANCED SHOWERS ACROSS THE CENTRAL AND EASTERN
PARTS OF THE STATE. AN UPPER LEVEL TROUGH LINGERING OVER THE STATE
WILL MAINTAIN A CHANCE OF LOCALLY HEAVY SHOWERS NEAR THE FRONT...
MAINLY DURING THE AFTERNOON HOURS AS SEA BREEZES DRIVE CONVECTION.
DRIER WEATHER WILL PREVAIL ACROSS THE WESTERN PART OF THE STATE.
TRADE WINDS WILL REBUILD ON SUNDAY AND CONTINUE INTO NEXT WEEK...
WITH WET CONDITIONS DEVELOPING ACROSS WINDWARD AND MAUKA AREAS.

&&

.DISCUSSION...
HEAVY SHOWERS AND SCATTERED THUNDERSTORMS HAVE DEVELOPED ALONG
AND JUST OFFSHORE FROM THE HAMAUKUA COAST OF THE BIG ISLAND
DURING THE PAST FEW HOURS. MOST OF THE HEAVIEST RAIN HAS STAYED
OFFSHORE SO FAR...BUT HAVE UPDATED THE FORECASTS TO INCLUDE A
HEAVY RAIN MENTION AND SLIGHT CHANCE OF THUNDERSTORMS FOR THE
HAMAKUA COAST THROUGH THIS EVENING.

QUIET CONDITIONS PREVAIL ON THE OTHER ISLANDS...WITH ISOLATED
SHOWERS DOTTING THE COASTAL WATERS AROUND MAUI COUNTY AND OAHU.
SURFACE ANALYSIS DEPICTS A WEAK FRONT THROUGH THE CENTER OF THE
STATE...LIKELY LOCATED NEAR MAUI AT THIS TIME. NORTHERLY LOW LEVEL
WINDS HAVE SPREAD OVER KAUAI AND OAHU TO THE WEST OF THIS
BOUNDARY...WHILE LIGHT NE TO E WINDS PREVAIL TO THE EAST.
ALOFT...THE STATE LIES UNDER THE EXIT REGION OF A 100+ KT JET
STREAK OVER THE CENTRAL PACIFIC...AND IN THE SOUTHEAST QUADRANT OF
A MID LEVEL TROUGH. THE 00Z LIHUE SOUNDING MEASURED COLD 500 MB
TEMPS OF -13C...BUT A RATHER MEAGER PWAT OF ONLY 1.09 INCHES...AND
A VERY DRY PROFILE ABOVE 700 MB. THE 00Z HILO SOUNDING HAD COOLED
SIGNIFICANTLY AT 500 MB AS WELL TO -11C...AND HAD A SOMEWHAT
HIGHER PWAT OF 1.34 INCHES...BUT THERE WAS STILL A DRY AND FAIRLY
STABLE LAYER IN PLACE BETWEEN 800 MB AND 600 MB. MIMIC-TPW
SATELLITE IMAGERY SHOWS PATCHES OF HIGHER MOISTURE OVER THE STATE
WITH ESTIMATED PWATS UP TO 1.6 INCHES...BUT THE MAIN POOL OF DEEP
TROPICAL MOISTURE REMAINS CONFINED WELL TO THE SOUTH AND EAST.

OVERNIGHT...THE MOST ACTIVE WEATHER SHOULD REMAIN ACROSS THE
EASTERN HALF OF THE STATE...WITHIN THE HIGHER MOISTURE AND
INSTABILITY TO THE EAST OF THE WEAK FRONT. SHOWERS WILL PROBABLY
REMAIN RATHER SPOTTY...BUT CANNOT RULE OUT AT LEAST ISOLATED
HEAVY DOWNPOURS OVER MAUI COUNTY AND THE BIG ISLAND. DRIER
CONDITIONS SHOULD PREVAIL ACROSS OAHU...AND MAY NEED TO UPDATE THE
FORECASTS LATER ON TO LOWER RAIN CHANCES THERE IF CURRENT TRENDS
CONTINUE. DRY WEATHER WILL CONTINUE ON KAUAI... WHICH IS DEEPER
WITHIN THE DRY AND MORE STABLE AIRMASS TO THE WEST OF THE FRONT.

ON SATURDAY...THE WEAK FRONT/TROUGH WILL CONTINUE DRIFTING EAST
TO NEAR THE BIG ISLAND...WITH N/NE LOW LEVEL FLOW SPREADING ACROSS
MAUI COUNTY IN ITS WAKE. SOMEWHAT ENHANCED LOW LEVEL MOISTURE WILL
REMAIN POOLED ALONG AND TO THE EAST OF THE TROUGH...AND THE
ATMOSPHERE WILL REMAIN SOMEWHAT UNSTABLE ALOFT AS THE MID LEVEL
TROUGH AND THE UPPER LEVEL JET STREAM EXIT REGION MOVES ONLY
SLIGHTLY EASTWARD. AS A RESULT...A CHANCE FOR SPOTTY HEAVY SHOWERS
WILL PERSIST OVER THE BIG ISLAND AND POSSIBLY MAUI COUNTY AS WELL.
THE BEST CHANCES FOR HEAVY SHOWERS AND PERHAPS AN ISOLATED
THUNDERSTORM WOULD APPEAR TO BE OVER THE BIG ISLAND DURING THE
AFTERNOON HOURS. MODELS ARE TRENDING TO A DRIER SOLUTION FOR OAHU
ON SATURDAY...AND WILL CONSIDER REMOVING MENTION OF HEAVY RAINS
THERE WITH THE MORNING FORECAST PACKAGE. MAINLY DRY WEATHER WILL
CONTINUE ACROSS KAUAI.

A WET TRADE WIND PATTERN WILL LIKELY DEVELOP ON SUNDAY AND MONDAY
ACROSS MUCH OF THE STATE. BUILDING HIGH PRESSURE NORTH AND
NORTHEAST OF THE REGION WILL DRIVE INCREASING TRADE WINDS..AND
THE MODELS ARE BRINGING AN AREA OF ENHANCED MOISTURE INTO THE
STATE FROM THE EAST. A LINGERING MID/UPPER LEVEL TROUGH OVERHEAD
WILL MAINTAIN SOMEWHAT UNSTABLE CONDITIONS ALOFT WITH THE USUAL
MID LEVEL INVERSION LIKELY REMAINING ABSENT. EXPECT INCREASINGLY
WET CONDITIONS ACROSS WINDWARD SECTIONS FROM THE BIG ISLAND
THROUGH OAHU. DRIER CONDITIONS WILL LIKELY PREVAIL OVER KAUAI
AT LEAST THROUGH SUNDAY...WITH INCREASED MOISTURE AND WETTER
TRADES POSSIBLY REACHING THE GARDEN ISLE BY MONDAY.

A RATHER WET AND BREEZY TRADE WIND PATTERN APPEARS LIKELY TO
PERSIST ACROSS THE STATE THROUGH AT LEAST THE MIDDLE OF NEXT
WEEK. A SOMEWHAT DRIER AIRMASS MAY FILTER SOUTHWARD INTO THE
STATE BY THE END OF NEXT WEEK...WITH BREEZY TRADES CONTINUING.

&&

.AVIATION...
A WEAK FRONT/SURFACE TROUGH IS ACTING AS A FOCUS FOR ENHANCED SHOWER
ACTIVITY AND TEMPO MVFR CONDS. THE FRONT IS CURRENTLY POSITIONED
OVER MAUI COUNTY AND IS FORECAST TO DRIFT SLOWLY EASTWARD...EVENTUALLY
DISSIPATING NORTHEAST OF THE BIG ISLAND ON SUNDAY. LOCALIZED HEAVY
SHOWERS AND POSSIBLE LIGHTING ARE ASSOCIATED WITH THIS FEATURE.

INCREASED SHOWER ACTIVITY AND TEMPO MVFR CONDS ARE EXPECTED ACROSS
MAUI COUNTY TONIGHT THROUGH TOMORROW. GRADUAL IMPROVEMENT IS EXPECTED
ON OAHU WHERE SHOWERY BUT VFR CONDS WILL PREDOMINATE. KAUAI...NOW
WELL BEHIND THE FRONTAL BOUNDARY...WILL SEE ONLY PATCHY VFR CLOUDS
AND ISOLATED SHOWERS.

ON THE BIG ISLAND...LIGHT LAND BREEZES OVERNIGHT WILL ENCOURAGE A
GENERAL CLEARING TREND THAT WILL LAST THROUGH MID MORNING. IN THE
AFTERNOON...SEA BREEZES WILL ENCOURAGE CUMULUS BUILD UPS AND
ISOLATED SHOWERS OVER THE ISLAND/S INTERIOR. TOWARDS EVENING...TEMPO
MVFR CONDS ARE EXPECTED TO DEVELOP ACROSS WINDWARD BIG ISLAND IN
RESPONSE TO THE APPROACHING FRONT/TROUGH AND THE REASSERTION OF
EASTERLY FLOW.

THE HIGH CLOUDS BETWEEN 13000 AND 25000 FT OAHU EASTWARD ARE
ASSOCIATED WITH A SLOW MOVING UPPER LEVEL TROUGH. THIS HIGH LEVEL
OVERCAST IS EXPECTED TO PERSIST ACROSS MOST OF THE STATE THROUGH
SATURDAY AND BEYOND. TEMPO LIGHT ICE WITHIN THIS LAYER.

&&

.MARINE...
NORTHERLY WINDS AROUND KAUAI AND BUILDING AROUND OAHU WILL RUN
NEAR 20 KTS TONIGHT AND SATURDAY...AND MAY APPROACH SMALL CRAFT
ADVISORY LEVELS AT TIMES. AS THE TROUGH OVER THE CENTRAL AND
EASTERN ISLANDS DISSIPATES...TRADE WINDS WILL RETURN STATE-WIDE
BY SUNDAY...POSSIBLY REACHING SCA STRENGTH IN THE CHANNELS.
STRONGER TRADES ARE LIKELY LATER IN THE WEEK.

EASTERLY SWELL AROUND 5 FT AND 10 SECONDS WILL REMAIN THE
DOMINANT SOURCE OF SEAS ACROSS MOST AREAS TONIGHT AND SATURDAY...
THOUGH FRESH NORTHERLY WINDS DEVELOPING AROUND KAUAI AND OAHU WILL
PRODUCE SOMEWHAT LARGER SEAS IN THOSE AREAS. SURF ALONG EAST
FACING SHORES WILL REMAIN BELOW HIGH SURF ADVISORY LEVELS AS THE
EAST SWELL GRADUALLY DECLINES DURING THE WEEKEND. SURF ALONG
NORTH FACING SHORES WILL REMAIN LOW THROUGH SUNDAY. A NORTH-
NORTHWEST SWELL WILL PUSH NORTH SHORE SURF CLOSE TO MINIMAL
ADVISORY LEVELS LATE SUNDAY NIGHT AND MONDAY. THIS SWELL WILL
PEAK MONDAY THEN FADE AWAY THROUGH MIDWEEK. SEE THE COLLABORATIVE
NEARSHORE SWELL AND WIND FORECAST /SRDHFO/ FOR MORE DETAILS.

&&

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

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...BEDAL






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