High Surf in Hawaii, March 21 to 26, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
930 AM HST MON MAR 21 2011

.SYNOPSIS...
TRADE WINDS WILL INCREASE AND BECOME MORE GUSTY TUESDAY THROUGH
FRIDAY...FOCUSING SHOWERS OVER WINDWARD TERRAIN. A BRIEF INCREASE IN
SHOWER ACTIVITY IS EXPECTED WEDNESDAY NIGHT INTO THURSDAY. TRADES
WILL WEAKEN FRIDAY THROUGH THE BEGINNING OF THE FOLLOWING WEEK.
RAINFALL WILL STAY FOCUSED ON WINDWARD AND MOUNTAIN AREAS.

&&

.DISCUSSION...
GOES WV IMAGERY DEPICTS AN AMPLIFYING RIDGE OVER THE CENTRAL NPAC.
THIS WILL REINFORCE HIGH PRESSURE AT THE SURFACE PROVIDING A TRADE
WIND INCREASE LOCALLY. EASTERLY TRADES RAMP UP TO THE 15 TO 25 MPH
RANGE BECOMING LOCALLY GUSTY TO THE 30-40 MPH RANGE AGAIN TUE-FRI
WITH INTERMITTENT INCREASES IN REMNANT FRONTAL MOISTURE. A WIND
ADVISORY MAY BE REQUIRED SOMETIME IN THE SHORT TERM.

BLENDED TPW IMAGERY SUGGESTS MODEST BOUNDARY LAYER MOISTURE UPSTREAM
SUPPORTING MAINLY SCATTERED WINDWARD POPS WITH NOCTURNAL INCREASES
COVERAGE/FREQUENCY IN THE USUAL DIURNAL TRADE PATTERN. THE NEXT
NOTABLE INCREASE IN WINDWARD SHOWERS WILL COME WED NIGHT-EARLY THU.
BROAD CYCLONIC FLOW W OF THE STATE WILL CARRY VARIABLE AMOUNTS OF
THIN CIRRUS OVER THE STATE OVER THE NEXT SEVERAL DAYS. THIS SHOULD
STILL ALLOW FOR PLENTY OF SUN TO GET THROUGH.

GLOBAL GUIDANCE AND ENSEMBLES SUGGEST THE CENTRAL PACIFIC BLOCKING
RIDGE WILL BEGIN TO LOSE AMPLITUDE DURING THE SECOND HALF OF THE
WEEK AS POLAR JET GRADUALLY BECOMES MORE ZONAL. THE ASSOCIATED
SURFACE HIGH WILL WEAKEN IN RESPONSE...AS WILL THE TRADE WINDS
LOCALLY. MID/UPR LEVEL FLOW WILL BECOME INCREASINGLY CYCLONIC OVER
THE AREA DURING THE SECOND HALF OF THE WEEK AS ADJACENT RIDGING
WEAKENS AND RETROGRADES W. THE RESULTING MID LEVEL COOLING SHOULD
WEAKEN AND LIFT THE SUBSIDENCE INVERSION ALLOWING FOR BETTER SHOWER
COVERAGE ALONG WINDWARD TERRAIN AND ALONG THE BIG ISLAND KONA SLOPES
AT LEAST FRI-SUN...PERHAPS LONGER.

&&

.PREVIOUS DISCUSSION.../ISSUED 400 AM HST MON MORNING/
NO BIG SURPRISES OVERNIGHT. WHILE WINDS AT HALEAKALA AND NEAR SOUTH
POINT REMAINED ELEVATED EARLY LAST NIGHT...THEY DID BOTH DIE DOWN AS
THE NIGHT PROGRESSED. HAVE MODIFIED THE GRIDS TO REFLECT SLIGHTLY
LOWER WIND SPEEDS TODAY.

THE HIGH PRESSURE NORTH OF THE ISLANDS IS IN THE PROCESS OF BEING
REPLACED BY ANOTHER HIGH...WHICH IS EXPECTED TO MOVE NORTH OF THE
STATE TODAY AND START TO BUILD AND SINK SOUTHWARD TUESDAY. HEADING
INTO THIS EVENING THE TRADES WILL ONCE AGAIN BE ON THE INCREASE AS
THE HIGH BUILDS NORTH OF THE ISLANDS.

SHOWER ACTIVITY WILL REMAIN ON THE DRIER SIDE OF NORMAL THIS
MORNING...BUT AN AREA OF MOISTURE ABOUT 100 MILES NORTHEAST OF THE
ISLANDS WILL RIGHT IN ON THE TRADES LATER TODAY...BRINGING AN
INCREASE IN SHOWERS TO THE WINDWARD AND MAUKA AREAS FOR TONIGHT AND
TOMORROW. ADDITIONAL BOUTS OF MOISTURE ARE EXPECTED TO RIDE IN ON
THE TRADES THROUGH THE END OF THE WEEK.

THE HIGH PRESSURE MENTIONED ABOVE WILL BE THE MAIN WEATHER PATTERN
THROUGH THE END OF THE WEEK...WITH LITTLE CHANGE THROUGH THURSDAY.
HEADING INTO FRIDAY...THE HIGH IS EXPECTED TO WEAKEN A BIT AND START
TO MOVE TO THE EAST...WHICH WILL HELP TO WEAKEN TRADES AS WE HEAD
INTO THE WEEKEND.

&&

.MARINE...
TRADE WINDS WILL BE STRENGTHENING AGAIN OVER THE NEXT 24 HR THEN
PERSIST THROUGH THE WEEK. THE SCA HAS BEEN EXTENDED THROUGH 6 PM
HST THU. AS THE TRADES INCREASE...SO WILL LOCALLY GENERATED
WINDSWELL. SURF ALONG WINDWARD SHORES SHOULD BE BACK TO ADVISORY
LEVELS OF 8 FT OR GREATER BY WED...SO A HIGH SURF ADVISORY FOR EAST
FACERS WILL LIKELY MAKE AN APPEARANCE WITH TOMORROWS AFTERNOON
FORECAST PACKAGE AND HANG AROUND THROUGH FRI.

CENTRAL PACIFIC RIDGING IS KEEPING THE JET STREAM ORIENTATION
UNFAVORABLE FOR NW SWELL. THIS WILL GRADUALLY CHANGE DURING THE
SECOND HALF OF THE WEEK ALLOWING FOR MODERATE NW SWELL ARRIVE AROUND
THE 30TH.

THE SOUTHERN HEMISPHERE CONTINUES TO AWAKEN FURTHER. IT WILL PROVIDE
A DECENT AMOUNT OF S-SW SWELL FOR THE LAST WEEK OF MARCH.

&&

.AVIATION...
HIGH PRESSURE CONSOLIDATING N OF THE ISLANDS WILL DRIVE BREEZY TRADE
WINDS ACROSS THE AREA THROUGH MUCH OF THE WEEK. AIRMET TANGO REMAINS
IN EFFECT FOR MODERATE...MECHANICALLY GENERATED...TURBULENCE ON
LEEWARD SIDES OF THE ISLANDS BELOW 9000 FEET. WILL LIKELY LOWER THE
MAX HEIGHT OF THIS LAYER TO NEAR 7000 FEET WITH THE NEXT AIRMET
ISSUANCE...AS LATEST OBS INDICATE A STRONG SUBSIDENCE INVERSION NEAR
6000 FEET.

AT THE TERMINALS...VFR CONDITIONS AND RELATIVELY DRY TRADES WILL
PREVAIL TODAY...WITH BRIEF MVFR CONDITIONS POSSIBLE AT WINDWARD
SITES TONIGHT AS A MOISTENING TRADE FLOW BRINGS BRIEF PASSING SHRA.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST THURSDAY FOR ALL HAWAIIAN WATERS.

&&

PUBLIC/MARINE...DEJESUS
AVIATION...BIRCHARD
PREVIOUS...MBALLARD