High Surf in Hawaii, April 5 to 6, 2011

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1100 AM HST TUE APR 5 2011

.SYNOPSIS...
LIGHT TRADE WINDS WILL PREVAIL AS HIGH CLOUDS AND WINDWARD SHOWERS
INCREASE TODAY. MOISTURE MOVING UP FROM THE SOUTHEAST...TOGETHER
WITH A VERY COLD LOW IN THE MIDDLE ATMOSPHERE...WILL BRING
UNSETTLED WEATHER TO THE WHOLE STATE FROM TONIGHT INTO THURSDAY.
LIGHTER BUT MORE WIDESPREAD RAIN IS EXPECTED TO SET IN BY THE
WEEKEND...AND WILL LINGER INTO NEXT WEEK...AS THE TRADE WINDS RETURN.

&&

.DISCUSSION...
LIGHT TRADE WINDS CONTINUE ACROSS THE STATE THIS MORNING...WITH NOT
MUCH LOW CLOUDS IN THE ISLAND VICINITY. BUT THEN...IT DOES NOT TAKE
LONG FOR CLOUDS DEVELOPING OVER THE ISLANDS AS LATEST SATELLITE
IMAGERY ALREADY SHOWING SOME DEVELOPMENT AT THIS POINT. NOT MUCH
CHANGE IN FORECAST PHILOSOPHY AT THIS TIME...AS AN UPPER LEVEL LOW
PRESSURE SYSTEM IS STILL EXPECTED TO MOVE SOUTH NEAR THE WESTERN
ISLANDS IN THE NEXT COUPLE OF DAYS...BRINGING UNSETTLED WEATHER TO
THE ISLAND CHAIN.

AN UPPER LEVEL LOW...CURRENTLY LOCATED AT ABOUT 600 MILES NORTH OF
KAUAI IS SLOWLY MOVING SOUTH. AN ASSOCIATED SURFACE TROUGH HAS
DEVELOPED JUST NORTH OF THE WESTERN ISLANDS. AS THE UPPER LEVEL LOW
MOVES CLOSER TO THE ISLANDS THIS AFTERNOON...AIR MASS WILL BECOME
MORE
UNSTABLE...ALLOWING LOCALLY HEAVY SHOWERS AND EVEN THUNDERSTORMS TO
DEVELOP. IT WILL BE HARD PIN POINT EXACTLY WHERE THE CONVECTION WILL
BLOSSOM...THOUGH IT WILL NOT BE SURPRISED IF THE SHOWER ACTIVITIES
AS WELL AS DEEPER CONVECTION WILL BE INFLUENCED BY TOPOGRAPHY.

THUS EXPECT WORSENING WEATHER CONDITIONS OVER THE ISLANDS AS THE DAY
PROGRESSES...WITH INCREASING CHANCE OF SHOWERS AND THUNDERSTORMS.
THE COLD POOL OF AIR ASSOCIATED WITH THE UPPER LEVEL SYSTEM WILL
CERTAINLY BE COLD ENOUGH TO BRING WINTER WEATHER TO THE SUMMITS OF
THE BIG ISLAND. HENCE A WINTER WEATHER WATCH IS POSTED BEGINNING
THIS EVENING THROUGH LATE THURSDAY NIGHT. A FLASH FLOOD WATCH IS
ALSO POSTED FROM LATE TONIGHT THROUGH LATE THURSDAY NIGHT...AS THE
CONDITIONS BECOME FAVORABLE FOR FLOODING TO DEVELOP DUE TO LOCALLY
HEAVY SHOWERS.

LATEST FORECAST CHARTS ALSO INDICATE AN INCREASE IN MOISTURE OVER
THE ISLANDS WEDNESDAY...AS SURFACE WINDS TURN A LITTLE MORE
SOUTHEAST. LOOK FOR MORE WIDESPREAD SHOWERS WITH THE INCREASE
MOISTURE. AIR MASS WILL REMAIN UNSTABLE WITH AN INCREASING CHANCE OF
THUNDERSTORMS AS THE UPPER LEVEL SYSTEM PASSES WEST OF THE ISLANDS.

DO EXPECT THE UPPER LEVEL SYSTEM TO MOVE FAR SOUTHWEST ENOUGH BY
THURSDAY...WITH MORE STABLE WEATHER CONDITIONS TO RETURN TO THE
STATE. ON THE OTHER HAND...FORECAST CHARTS INDICATE QUITE A BIT OF
MOISTURE WILL LINGER IN THE ISLAND VICINITY...THUS WETTER WEATHER
WILL CONTINUE TO AFFECT THE STATE THROUGH REST OF THE WEEK INTO THE
WEEKEND.

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL AT MOST TERMINALS IN THE SHORT TERM...
WITH THE USUAL MVFR CEILINGS EXPECTED AT PHNY THROUGH MID-AFTERNOON.

A DEVELOPING UPPER LOW MOVING S NEAR THE ISLANDS WILL BRING
INCREASED POTENTIAL FOR THE DEVELOPMENT OF +SHRA/+TSRA OVER THE NEXT
24 HOURS...BUT CONFIDENCE AND COVERAGE IS LOW ENOUGH AT THE MOMENT
THAT NO AIRMETS ARE IN EFFECT.

&&

.MARINE...
A HIGH SURF ADVISORY REMAINS IN EFFECT FOR NORTH AND EAST FACING
SHORES OF KAUAI AND OAHU AS WELL AS NORTH FACING SHORES OF NIIHAU
DUE TO A LARGE NORTH NORTHWEST SWELL. THIS CURRENT SWELL IS
EXPECTED TO PEAK TODAY THEN DECREASING EARLY WEDNESDAY. ANOTHER
MODERATE SIZED NORTHWEST SWELL WILL ARRIVE THURSDAY AND FRIDAY AND
MAY APPROACH ADVISORY LEVELS ON THE NORTH SHORE. THERE WILL ALSO BE
A SERIES OF SOUTH SWELL THROUGH THE WEEKEND...LIKELY REACHING
OVERHEAD FOR SOME FOCAL AREAS.

A SMALL CRAFT ADVISORY CONTINUES FOR KAUAI COASTAL WATERS...OAHU
WINDWARD WATERS AND KAIWI CHANNEL UNTIL EARLY WEDNESDAY MORNING DUE
TO THE ELEVATED COMBINED SEAS WITH THE LARGE SWELL.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM LATE TONIGHT THROUGH LATE THURSDAY NIGHT
FOR ALL HAWAIIAN ISLANDS.

WINTER STORM WATCH BIG ISLAND SUMMITS FROM 6 PM HST THIS EVENING
THROUGH LATE THURSDAY NIGHT.

HIGH SURF ADVISORY NORTH AND EAST FACING SHORES OF KAUAI AND OAHU
AND FOR NORTH FACING SHORES OF NIIHAU UNTIL 6 AM HST WEDNESDAY.

SMALL CRAFT ADVISORY UNTIL 6 AM HST WEDNESDAY FOR KAUAI
NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD WATERS-KAUAI
CHANNEL-OAHU WINDWARD WATERS-KAIWI CHANNEL.

&&

AVIATION...BIRCHARD
PUBLIC AND MARINE...HUI