Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 300630
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI MAY 29 2015

.SYNOPSIS...
A LIGHT TO MODERATE TRADE WIND REGIME WILL PREVAIL THROUGH THE
WEEKEND. ONLY EXCEPTION WILL BE AROUND THE WIND ISLAND WHERE LIGHT
AND VARIABLE WINDS WILL CONTINUE THROUGH THE COUPLE OF DAYS. THE
TRADE WINDS WILL CONTINUE TO BRING CLOUDS AND SHOWERS OVER WINDWARD
AND MOUNTAIN AREAS...WITH HIGHER CHANCES OF RAIN OVER KAUAI AND
OAHU. SEA BREEZES WILL ALSO BRING AFTERNOON AND EARLY EVENING
PERIODS OF CLOUDS AND SHOWERS OVER LEEWARD AREAS...WITH GENERALLY
CLEAR SKIES DURING THE NIGHTS AND MORNINGS.

&&

.DISCUSSION...
WEAK PRESSURE GRADIENTS ACROSS THE AREA ARE KEEPING A LIGHT TO
MODERATE TRADE WIND REGIME...MAINLY FROM THE NE AROUND KAUAI AND
OAHU...TURNING MORE NORTHERLY NEAR THE BIG ISLAND. LATEST MODEL AND
SATELLITE DATA STILL SUGGEST THE PRESENCE OF A WEAK SFC TROUGH
EXTENDING NE FROM NEAR THE BIG ISLAND...WHICH IS ALSO KEEPING HIGHER
THAN NORMAL MOISTURE UPSTREAM AND AROUND THE ALOHA STATE.

MEANWHILE...LATEST WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL TROUGH
MOVING NE AND AWAY FROM THE ISLANDS...BUT STILL KEEPING GRADIENTS
ALOFT TIGHT ENOUGH TO GENERATE LOCALIZED STRONG WINDS OVER THE BIG
ISLAND SUMMITS. THE SUMMITS WILL CONTINUE TO BE MONITORED IN CASE AN
ADVISORY BECOMES NECESSARY...BUT WITH THE TROUGH ALOFT MOVING AWAY
THE SUMMIT WINDS SHOULD BEGIN RELAXING THIS EVENING.

THE THICK CLOUD COVER OVER THE WINDWARD BIG ISLAND COURTESY OF THE
EARLIER SEA BREEZE CONVECTION SHOULD GRADUALLY CLEAR OUT TONIGHT...
WHILE THE LIGHT TO MODERATE NE WINDS OVER THE OTHER ISLANDS WILL
KEEP PASSING SHOWERS AND CLOUDS OVER WINDWARD AND MOUNTAIN
AREAS...ESPECIALLY OAHU AND KAUAI. ON THE OTHER HAND...LAND BREEZES
SHOULD ALSO HELP IN CLEARING OUT MOST LEEWARD LOCATIONS OF THE
SMALLER ISLANDS DURING THE OVERNIGHT HOURS.

THE CURRENT LIGHT TO MODERATE TRADE WIND REGIME IS EXPECTED TO
PREVAIL THROUGH THE REST OF THE WEEKEND AS HIGH PRESSURE REMAINS
LOCATED TO THE NW OF THE ISLANDS. MEANWHILE...A BAND OF ENHANCED
MOISTURE AND CLOUDS CAN BE OBSERVED IN MODEL SOLUTIONS AND SATELLITE
DATA ALIGNED FROM E TO W ABOUT 100 MILES N OF THE ISLANDS. MODEL
GUIDANCE BRINGS THIS BAND CLOSER TO THE ALOHA STATE DURING THE
OVERNIGHT HOURS...REACHING KAUAI SAT MORNING. THE COMBINATION OF
THIS ENHANCED MOISTURE AND DEVELOPING SEA BREEZES COULD BRING ACTIVE
AFTERNOON AND EARLY EVENING SHOWER PERIODS OVER LEEWARD AREAS OF THE
SMALLER ISLANDS ON SAT AND AGAIN SUN.

PRESSURE GRADIENTS ACROSS THE AREA SHOULD REMAIN WEAK ENOUGH TO KEEP
THE TRADES GENERALLY LIGHT THROUGH AT LEAST THE FIRST HALF OF NEXT
WEEK. THE AFOREMENTIONED HIGH NW OF THE ISLANDS WILL GRADUALLY
MIGRATE E DURING THE NEXT SEVERAL DAYS...WHILE THE WEAKENING SFC
TROUGH NE OF THE BIG ISLAND OR ITS REMNANTS SEEM TO DRIFT W AND OVER
THE SMALLER ISLANDS. IN ADDITION...MODELS SHOW A SHARP MID-LEVEL
TROUGH MOVING W TO E ACROSS THE AREA DURING THE WEEKEND AND INTO
EARLY NEXT WEEK. THIS SYNOPTIC SCENARIO COULD FURTHER ENHANCE SHOWER
ACTIVITY IN ADDITION TO THE SEA BREEZE CONVECTION.

LATEST MODEL GUIDANCE SUGGEST THE RETURN OF A FAIRLY SEASONABLE
TRADE WIND PATTERN FOR THE MIDDLE AND LATTER PART OF NEXT WEEK.

&&

.AVIATION...
AN AREA OF LOW CLOUDS AND A FEW EMBEDDED SHOWERS CONTINUES TO
ADVANCE TOWARDS KAUAI FROM THE NORTH. IT IS EXPECTED TO REACH THE
ISLAND AROUND 09Z. IT IS UNCERTAIN AT THIS TIME IF AN AIRMET SIERRA
FOR MTN OBSCURATION IS NEEDED...BUT WE WILL BE MONITORING THE
SITUATION CLOSELY.

OTHERWISE WE ARE EXPECTING VFR CONDITIONS THROUGH THE OVERNIGHT
HOURS. AS OF 7 PM HST...THE HEAVY LOW CLOUDS COVERING THE WINDWARD
DISTRICTS OF THE BIG ISLAND AND THE WINDWARD SIDE OF MAUI WILL
CONTINUE TO DISSIPATE THROUGH THE NEXT COUPLE OF HOURS.
THEREAFTER...THE NORTHERLY FLOW WILL BE STRONG ENOUGH TO DRIVE A
STRAY SHOWER OR TWO ONTO THE WINDWARD MTN AREAS OF THE SMALLER
ISLANDS...BRINGING BRIEF MVFR CEILINGS TO THESE MTN AREAS. NO
RESTRICTION TO VIS IS EXPECTED WITH THESE SHOWERS. A SLIGHT
DIFFERENT SITUATION FOR THE KONA COAST WHERE SOME LOW CLOUDS WILL
PERSIST THROUGH MOST OF THE NIGHT WITH A STRAY SHOWER OVER THE
ADJACENT WATERS. EXPECT MVFR CEILING AND VIS WITH THESE SHOWERS.
&&

.MARINE...
A RELATIVELY SMALL LONG-PERIOD S SWELL WILL PERSIST THROUGH
SATURDAY...WITH SURF BELOW ADVISORY LEVELS. A LONGER-PERIOD SSW
SWELL EXPECTED SUNDAY WILL PRODUCE ADVISORY-LEVEL SURF ALONG
S FACING SHORES INTO TUESDAY...WITH PEAK OPEN OCEAN SWELL HEIGHTS
NEAR 5 FEET. THIS SWELL MAY CAUSE SURGES IN HARBORS EXPOSED TO THE
S...AND BREAKING WAVES IN AND NEAR S-FACING CHANNEL ENTRANCES.
MARINERS AND BEACHGOERS SHOULD BE ALERT TO THE FACT THAT THIS IS
LIKELY TO BE THE LARGEST S SWELL OF THE SEASON THUS FAR. EXTREME
TIDAL CHANGES WILL ALSO LEAD TO LOCALLY STRONG CURRENTS. ALTHOUGH A
LITTLE TOO EARLY TO ISSUE A HIGH SURF ADVISORY...A MARINE WEATHER
STATEMENT HAS BEEN ISSUED TO HELP INCREASE AWARENESS. ADDITIONALLY...
THE OAHU SURF DISCUSSION /SRDHFO/ HAS BEEN UPDATED AND CONTAINS MORE
INFO.

OTHERWISE...SMALL AND RELATIVELY SHORT-PERIOD WNW SWELLS WILL
ARRIVE OVER THE NEXT COUPLE OF DAYS...SUPPORTING SMALL SURF ALONG N
FACING SHORES. WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL
CRAFT ADVISORY /SCA/ LEVELS THROUGH THE WEEKEND...AND INTO EARLY
NEXT WEEK...AFTER WHICH STRONGER TRADE WINDS MAY NECESSITATE A SCA
ISSUANCE IN THE WINDIER MARINE ZONES AROUND MAUI AND THE BIG ISLAND.


&&

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

&&

$$

SYNOPSIS/DISCUSSION...REYNES
MARINE...BIRCHARD
AVIATION...LAU





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