High Surf Advisory 28, NWS Honolulu, HI

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HONOLULU HI
500 PM HST SAT JUN 4 2011

.UPDATE...
HAVE ISSUED A HIGH SURF ADVISORY FOR SOUTH FACING SHORES...AS RECENT
OBSERVATIONS FROM SOUTH SHORE OAHU SHOW SOLID SIZED SURF TRENDING
UPWARDS...AS DO BUOY OBSERVATIONS...WHICH SHOW INCREASING ENERGY AT
LONGER WAVELENGTHS.

&&

.SYNOPSIS...
A LOW ALOFT WILL KEEP THE ISLAND ATMOSPHERE UNSTABLE THROUGH
TONIGHT...WITH THUNDERSTORMS AND LOCALLY HEAVY RAINFALL STILL
POSSIBLE. WHILE THE THREAT OF THUNDERSTORMS WILL DIMINISH SOMEWHAT
ON SUNDAY AND MONDAY...DAYTIME HEATING COULD LEAD TO ISOLATED HEAVY
SHOWERS OVER LEEWARD AND INTERIOR PORTIONS OF THE ISLANDS...
ESPECIALLY OVER THE BIG ISLAND. WINDS WILL WEAKEN THROUGH SUNDAY...
AND REMAIN ON THE LIGHTER SIDE...BEFORE STRENGTHENING AROUND
MID-WEEK. UNSTABLE WEATHER COULD RETURN BY THE MIDDLE TO END OF THE
UPCOMING WEEK.

&&

.DISCUSSION...
CURRENTLY...WATER VAPOR IMAGERY HIGHLIGHTS AN ELONGATED N-S ORIENTED
TROUGH ALOFT NEAR AND N OF THE ISLANDS...WITH THE SHARP TROUGH AXIS
RUNNING THROUGH THE MIDDLE OF THE ISLAND CHAIN THIS AFTERNOON. WHILE
UNCLEAR FROM SATELLITE IMAGERY WHETHER OR NOT A CLOSED LOW ALOFT
STILL EXISTS...MODELS CONTINUE TO REASONABLY INITIALIZE WITH A DEEP
LAYER MID AND UPPER LEVEL LOW OVER THE ISLANDS. AT THE SURFACE...A
1029 MB SURFACE HIGH ABOUT 1100 MILES NNE OF THE ISLANDS CONTINUES
TO PROVIDE LIGHT TO MODERATE TRADE WINDS.

WHILE THE SHALLOWER SHOWERS ARE MOVING SMARTLY TOWARD THE WEST
WITHIN THE MODERATE TRADE WIND FLOW THAT DOMINATES THE LOW-LEVELS...
POSING LITTLE IN THE WAY OF A FLOOD THREAT...THE TALLER SHOWERS AND
THUNDERSTORMS ARE MOVING MORE SLOWLY...EVEN BECOMING STATIONARY...
DUE TO THE S AND SW WINDS ALOFT E OF THE TROUGH AXIS. WITH THIS IN
MIND...AND DUE TO THE FACT THAT RECENT HEAVY RAINS HAVE SOAKED
PORTIONS OF KAUAI AND OAHU...A FLASH FLOOD WATCH WAS ISSUED
THIS MORNING...AND REMAINS IN EFFECT FOR ALL ISLANDS THROUGH
TONIGHT.

THE FLOOD WATCH INCLUDES ALL ISLANDS DUE TO THE FACT THAT LATEST
MODEL GUIDANCE SWINGS SHORT WAVE TROUGHS THROUGH THE BASE OF THE
LONG WAVE TROUGH THROUGH TONIGHT...AS THE LOW ALOFT MOVES E. THIS
WOULD REDUCE THE THREAT OF HEAVY RAIN ON KAUAI LATER THIS EVENING...
BUT BRING AN INCREASING THREAT TO MAUI AND THE BIG ISLAND.
HOWEVER...RECENT THUNDERSTORMS ON KAUAI...AND THE AFTERNOON
SOUNDING...HIGHLIGHT THE INSTABILITY THAT REMAINS THERE...WITH A
SIMILAR STORY ON THE BIG ISLAND...SO THE FLASH FLOOD WATCH REMAINS
IN EFFECT STATEWIDE. WINTRY WEATHER HAS DEVELOPED OVER THE BIG
ISLAND SUMMITS...WITH ACCUMULATING SNOW AND HAIL AT THE SUMMITS AND
UPPER ELEVATIONS...ASSOCIATED WITH DEEP CONVECTION. LAYERED CLOUDS
OVERNIGHT COULD BRING ADDITIONAL SNOWFALL...AND A WINTER WEATHER
ADVISORY REMAINS IN EFFECT.

BY TOMORROW AFTERNOON THE WEAKENING LOW/TROUGH ALOFT SHOULD BE NE OF
THE ISLANDS...WITH ASSOCIATED SHORT WAVE TROUGH AXES ALSO E OF THE
ISLANDS. AS THE LOW DEPARTS...WARMER AIR ALOFT WILL LIMIT THE THREAT
OF THUNDERSTORMS ON SUNDAY AND MONDAY...BUT WEAK MID-LEVEL TROUGHING
WILL PREVENT OUR TYPICAL STRONG SUBSIDENCE INVERSION FROM DEVELOPING.
BY WEDNESDAY...MODEL GUIDANCE DEPICTS ANOTHER MID-LEVEL LOW
DEVELOPING NEAR THE ISLANDS...AND ALTHOUGH MID-LEVEL TEMPS ARE NOT
FORECAST TO BE AS COLD AS THEY ARE WITH THE CURRENT LOW...RELATIVELY
UNSETTLED WEATHER WILL PREVAIL INTO NEXT WEEKEND.

THE SURFACE WINDS ARE ON THE DECLINE...WITH SURFACE PRESSURES DOWN
ABOUT 2 MB OVER THE PAST 24 HOURS. OVER THE ISLANDS...LIGHT TO
MODERATE TRADE WINDS WILL WEAKEN TO LIGHT SOUTHEASTERLIES ON SUNDAY
AND MONDAY...LIKELY LEADING TO WIDESPREAD AFTERNOON SEA BREEZES.
WINDS WILL REMAIN LIGHT UNTIL MID-WEEK OR SO...AS A FRONT MOVES SE
OVER WATERS FAR TO THE NW OF THE ISLANDS...AND ERODES THE PRESSURE
GRADIENT OVER THE STATE. WITH THE LIGHT E-SE WINDS ON THE LARGE
SCALE...CLOUDS AND SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS
DURING NIGHTS AND MORNINGS...SHIFTING TO LEEWARD AND INTERIOR AREAS
DURING AFTERNOONS AND EVENINGS...IN RESPONSE TO SEA BREEZE
CONVERGENCE. WHILE WIDESPREAD HEAVY RAIN IS NOT EXPECTED IN THIS
REGIME...THE LINGERING MODERATE INSTABILITY COULD HELP TO FUEL
ISOLATED POCKETS OF HEAVY RAIN...AND POSSIBLY A THUNDERSTORM OVER
THE BIG ISLAND SLOPES. THE THREAT OF MORE WIDESPREAD THUNDERSTORMS
COULD RETURN BY THE END OF THE WEEK AS ANOTHER LOW ALOFT DEVELOPS
NEAR AND OVER THE ISLANDS.

&&

.AVIATION...
THUNDERSTORMS IN THE AREA WILL CONTINUE TO BE AN ISSUE THROUGH
TONIGHT. THUNDERSTORMS AND SHOWERS WILL AT TIMES REDUCE VISIBILITIES
AND CEILINGS. SEE AVIATION PRODUCTS FOR MORE DETAILS.

&&

.MARINE...
A MARINE WEATHER STATEMENT IS IN EFFECT THROUGH TONIGHT...
HIGHLIGHTING THE HAZARDS TO MARINERS ASSOCIATED WITH
THUNDERSTORMS...INCLUDING WATERSPOUTS.

LONG PERIOD S SWELLS ARE EXPECTED TO BUILD TONIGHT AND SUNDAY...
BRINGING SURF HEIGHTS TO ADVISORY LEVELS OF AT LEAST 8 FEET ALONG S
FACING SHORES. AS IS TYPICAL WITH S SWELLS...THERE REMAINS A FAIR
AMOUNT OF UNCERTAINTY AS TO THE EVENTUAL WAVE HEIGHTS...BUT AN
ADVISORY HAS BEEN ISSUED BASED ON LATEST OBS. THIS SURF WILL
CONTINUE INTO MONDAY BEFORE DIMINISHING...BUT ANOTHER S SWELL
EXPECTED BY MIDWEEK WILL PUSH SURF TO NEAR ADVISORY LEVELS ONCE
AGAIN. ALTHOUGH A LITTLE SLOW TO ARRIVE...A LATE SEASON WNW SWELL
WILL PRODUCE A NOTICEABLE BUMP IN SURF HEIGHTS ALONG N AND W FACING
SHORES TONIGHT AND SUNDAY BEFORE DIMINISHING MONDAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH ALL ISLANDS THROUGH 6 AM HST SUNDAY.

WINTER WEATHER ADVISORY FOR BIG ISLAND SUMMITS THROUGH 6 AM HST
SUNDAY.

HIGH SURF ADVISORY FOR SOUTH FACING SHORES OF ALL ISLANDS FROM 6 AM
HST SUNDAY TO 6 PM HST MONDAY.

&&

BIRCHARD