Weather Service Report


242 
FXHW60 PHFO 300828
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 BIG ISLAND WHERE LIGHT 
AND VARIABLE WINDS WILL CONTINUE THROUGH THE NEXT 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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