High Surf in Hawaii, May 1 to 2, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST WED APR 30 2008

.SYNOPSIS...
HIGH PRESSURE WILL DOMINATE NORTHEAST OF THE STATE...MAINTAINING
TRADE WINDS THROUGH THE COMING WEEK. SHOWERS WILL FAVOR WINDWARD AND
MAUKA AREAS. AN UPPER LOW WILL DEVELOP WEST OF THE STATE EARLY NEXT
WEEK...WHICH WILL DESTABILIZE THE AIRMASS AND LEAD TO GREATER SHOWER
COVERAGE.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS THE STATE LOCATED BETWEEN A UPPER LEVEL
TROUGH TO THE WEST AND A RIDGE TO THE EAST. AT THE SURFACE...HIGH
PRESSURE IS LOCATED NORTHEAST OF THE STATE WITH TRADE WINDS
REMAINING RATHER GUSTY TODAY. THE 00Z SOUNDINGS FROM HILO AND LIHUE
SHOW A STRENGTHENING AND LOWERING SUBSIDENCE INVERSION...ESPECIALLY
AT LIHUE. THE STABLE AIRMASS HAS LIMITED RAINFALL...WITH HYDRONET
GAGES ACROSS MAINLY WINDWARD SECTIONS REPORTING AT MOST A FEW
HUNDREDTHS OF AN INCH OVER THE PAST 12 HOURS.

THE STABLE AIRMASS WILL GIVE WAY TO INCREASING SHOWERS BY THIS
WEEKEND. THE UPPER RIDGE EAST OF THE STATE WILL SHIFT NORTHWARD...AS
AN EXTRATROPICAL LOW DEVELOPS FAR TO OUR NORTHWEST. 00Z GFS FORECAST
SOUNDINGS SHOW INVERSION HEIGHTS BEGINNING TO CLIMB BY THURSDAY
NIGHT. LOW LEVEL MOISTURE FIELDS ALSO SHOW AN INCREASE IN MOISTURE
BY THURSDAY NIGHT/FRIDAY. THE CURRENT FORECAST HAS THIS IN HAND...
WITH POPS BELOW NORMAL FOR TONIGHT/THURSDAY THEN SLOWLY INCREASING
AS WE HEAD THROUGH THE WEEKEND. WINDS HAVE BEEN PETTY GUSTY ACROSS
LAND TODAY...WITH SMALL CRAFT CONDITIONS FOR ALL THE COASTAL WATERS.
THE SURFACE GRADIENT ACROSS THE STATE RELAXES SOMEWHAT AS THE
SUBTROPICAL HIGH WEAKENS AHEAD OF THE DEVELOPING NORTH PACIFIC
SYSTEM. TRADE WINDS WILL DROP OFF TO MORE MODERATE LEVELS BY THE END
OF THE WEEK.

THE GFS AND ECMWF CONTINUE TO OFFER DIFFERENT SOLUTIONS FOR THE
EXTENDED...BUT ARE SHOWING FEWER SIGNIFICANT CHANGES COMPARED TO THE
RUNS FROM A FEW DAYS AGO. THE GFS CONTINUES TO SHOW AN UPPER LOW
DEVELOPING WEST OF THE STATE EARLY NEXT WEEK. THE ECMWF HAD BEEN
WEAKER WITH THIS SOLUTION...BUT THE 12Z RUN NOW TRIES TO DEVELOP A
LOW OVER/TO THE EAST OF HAWAII LATER DURING THE MIDDLE OF NEXT WEEK.
THE ECMWF STILL SHOWS AN INVERTED SURFACE TROUGH NORTH OF THE STATE
MONDAY/TUESDAY...SIMILAR TO THE GFS SOLUTION. THE CURRENT FORECAST
KEEPS TRADES GOING DURING THIS PERIOD...ALTHOUGH WITH MORE OF A DUE
EASTERLY COMPONENT DUE TO THE SURFACE TROUGH NORTHWEST OF THE STATE.
THE UPPER LEVEL LOW AND INCREASING MOISTURE/CONVECTIVE DEPTH WILL
LEAD TO MORE OF A WET TRADE PATTERN...WITH GREATER SHOWER COVERAGE
AND RAINFALL RATES BUT STILL MAINLY FOCUSED ACROSS WINDWARD AND
MAUKA AREAS.

&&

MARINE...
WINDS AT EXPOSED COASTAL LOCATIONS SUCH AS KAHOOLAWE AND SOUTH POINT
ARE STILL RATHER STRONG. THE 00Z/30 HIGH RESOLUTION WRF FROM THE
UNIVERSITY OF HAWAII SHOWS WINDS SLOWLY SUBSIDING DURING THE DAY
TOMORROW. WILL EXTEND THE CURRENT SMALL CRAFT ADVISORY FOR THE
COASTAL WATERS INTO THURSDAY MORNING...AND FOR THE REMAINING
CHANNELS AND WATERS SOUTH OF THE BIG ISLAND THROUGH THE DAY.

THE HIGH SURF ADVISORY CONTINUES FOR SOUTH FACING SHORES. A POWERFUL
STORM EAST OF NEW ZEALAND LAST WEEK PRODUCED A LARGE SOUTH SWELL
WHICH CONTINUES TO IMPACT SOUTH FACING SHORELINES. THE KILO NALU
BUOY CONTINUES TO REPORT 3 FT SEAS WITH A 17 SECOND PERIOD.
WAVEWATCH III GUIDANCE SHOWS THE PERIOD SLOWLY DROPPING THROUGH THE
WEEK. SURF ALONG SOUTH FACING SHORES SHOULD REMAIN AT ADVISORY
LEVELS THROUGH THE DAY THURSDAY BEFORE SLOWLY LOWERING THROUGH THE
WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THURSDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-OAHU SOUTH SHORE-WAIANAE COAST-MOLOKAI
LEEWARD-LANAI MAKAI-KAHOOLAWE-MAUI LEEWARD WEST-MAUI CENTRAL
VALLEY-LEEWARD HALEAKALA-KONA-SOUTH BIG ISLAND-BIG ISLAND NORTH
AND EAST.

SMALL CRAFT ADVISORY UNTIL 6 PM HST THURSDAY FOR KAUAI CHANNEL-
KAIWI CHANNEL-MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG
ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

SMALL CRAFT ADVISORY UNTIL 10 AM HST THURSDAY FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-OAHU
WINDWARD WATERS-OAHU LEEWARD WATERS-MAUI COUNTY WINDWARD WATERS-
MAUI COUNTY LEEWARD WATERS-BIG ISLAND WINDWARD WATERS.

&&

BRAVENDER