High Surf in Hawaii, July 6 to 9, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST WED JUL 6 2011

.SYNOPSIS...
MODERATE TRADE WINDS WILL BECOME LOCALLY BREEZY BY FRIDAY AS HIGH
PRESSURE BUILDS NORTH OF THE STATE. RAINFALL WILL REMAIN LIGHT
THROUGH FRIDAY...AND LIMITED MAINLY TO WINDWARD SLOPES ALL DAY...AND
LEE SLOPES OF THE BIG ISLAND IN THE AFTERNOON. SHOWERS WILL SPREAD
ACROSS THE STATE FROM FRIDAY THROUGH THE WEEKEND.

&&

.DISCUSSION...
OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS REPORTED LIGHT TO
MODERATE TRADE WINDS BLOWING. RAINFALL INCREASED CONSIDERABLY OVER
THE PAST SIX HOURS...BUT REMAINED LIGHT...AND FOCUSED ALMOST
ENTIRELY WINDWARD. SOUNDING DATA REVEALED INVERSION HEIGHT AND
PRECIPITABLE WATER CONTENT NEAR TYPICAL VALUES. SATELLITE ESTIMATES
OF PRECIPITABLE WATER UPWIND OF THE STATE REMAINED LOW...BUT
PROBABLY INCORRECTLY SO. ALOFT...STRONG RIDGING PREVAILED TO THE
NORTH THROUGH NORTHEAST OF THE STATE...WHILE A WEAK LOW ALOFT
APPEARED TO THE EAST NEAR 135W.

GUIDANCE STILL CONCURS THAT THE RIDGING ALOFT WILL CONSOLIDATE TO
THE NORTH OF THE ISLANDS THROUGH ABOUT FRIDAY. THE SUBTROPICAL RIDGE
AT THE SURFACE WILL STRENGTHEN IN TANDEM...BUILDING UP THE TRADES TO
MODERATE LEVELS. ENHANCED OROGRAPHIC FORCING WILL BECOME MORE
EFFICIENT AT WRINGING OUT THE AVAILABLE MOISTURE ALONG WINDWARD
SLOPES...SO FURTHER INCREASES IN RAINFALL ARE EXPECTED...THOUGH
CONDITIONS PROBABLY WILL FALL SHORT OF WHAT MIGHT BE CALLED WET
TRADES...AT LEAST THROUGH FRIDAY.

BY THE WEEKEND PROPER...MODEL DIFFERENCES IN PREDICTING THE BEHAVIOR
OF THE MID-LEVEL LOW TO THE EAST COULD BECOME IMPORTANT. GENERALLY
SPEAKING...THE CONSOLIDATING MID-LEVEL HIGH TO THE NORTH WILL PERMIT
THE LOW CURRENTLY LOCATED NEAR 135W TO DRIFT WEST ALONG THE SOUTH
EDGE OF THE HIGH. SOLUTIONS CONTINUE TO DIFFER WITH RESPECT TO THE
SPEED OF THE LOW...HOW MUCH IT DEEPENS...HOW COLD ITS ASSOCIATED
COLD POOL BECOMES...AND HOW FAR WEST IT TRAVELS. IN SHORT...THE GFS
SOLUTIONS TEND TO STOP THE LOW NEAR 150W BY SATURDAY NIGHT...WHILE
THE ECMWF LETS IT REACH 155W...ESSENTIALLY PARKING THE FEATURE OVER
THE STATE BY SUNDAY MORNING.

IN PRACTICAL TERMS...BOTH SCENARIOS WOULD ENHANCE WINDWARD RAINFALL
BY PROVIDING LIFT...AND BOTH WOULD DIMINISH THE TRADES BY LATE IN
THE WEEKEND. THE CHIEF DIFFERENCE IS THAT THE ECMWF SOLUTION WOULD
REDUCE STABILITY TO THE POINT WHERE LOCALLY HEAVY RAIN...AND PERHAPS
EVEN THUNDERSTORMS...MIGHT BECOME POSSIBLE. THIS FAR INTO THE SUMMER
SEASON...IT DOES SEEM PRUDENT TO ERR ON THE SIDE OF CLIMATOLOGY...
AND YET...THIS HAS BEEN A YEAR FOR MID-LEVEL LOWS.

FOR NOW...WET TRADES OVERALL...WITH AFTERNOON LEE TOWERING CUMULI ON
THE BIG ISLAND...SHOULD SUFFICE FOR THE WEEKEND FORECAST. HOWEVER...
IT WILL BE ESSENTIAL TO MONITOR ADDITIONAL MODEL GUIDANCE ON THE
BEHAVIOR OF THE LOW FROM THE EAST.

&&

.MARINE...
STRENGTHENING WINDS HAVE BROUGHT SMALL CRAFT ADVISORY CONDITIONS TO
THE TYPICALLY WINDY CHANNELS AND WATERS AROUND THE BIG ISLAND AND
MAUI...AND THE AREA OF THE ADVISORY COULD SPREAD FURTHER BY THE
WEEKEND. ROUGH...WIND-DRIVEN...SHORT-PERIOD SURF WILL INCREASE ALONG
EAST-FACING SHORES...THOUGH WAVE HEIGHTS ARE NOT EXPECTED TO REACH
THAT ADVISORY LEVEL.

A PAIR OF SOUTH SWELLS WILL PRODUCE ELEVATED SURF ALONG SOUTH-FACING
SHORES THROUGH SATURDAY. EXPECT SOUTH SHORE SURF TO TOP THE 8-FOOT
ADVISORY LEVEL BY LATER THIS MORNING...AND REMAIN HIGH INTO THURSDAY
BEFORE DIMINISHING. A REINFORCING SOUTH SWELL WILL MAINTAIN HIGH
SURF INTO SATURDAY. FOR NOW...A HIGH SURF ADVISORY REMAINS IN EFFECT
FOR SOUTH-FACING SHORES OF ALL ISLANDS THROUGH THURSDAY...BUT LIKELY
WILL BE EXTENDED THROUGH SATURDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY FROM 6 AM THIS MORNING TO 6 PM HST THURSDAY
FOR SOUTH-FACING SHORES OF ALL ISLANDS.

SMALL CRAFT ADVISORY FROM 6 AM THIS MORNING TO 6 PM HST THURSDAY
FOR MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND
LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

&&

RYSHKO