Heavy Rain in Hawaii, May 28 to 29, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST TUE MAY 28 2013

.SYNOPSIS... LIGHT TRADES WINDS WILL PREVAIL FOR THE NEXT FEW DAYS
AS THE HIGH PRESSURE RIDGE NORTH OF THE STATE WEAKENS. AN UPPER
LEVEL LOW NEAR THE ISLANDS TODAY WILL HELP TO ENHANCE THE
SHOWERS...ESPECIALLY OVER MAUI COUNTY AND THE BIG ISLAND. TRADE
WINDS ARE EXPECTED TO INCREASE BY THE WEEKEND AS A STRONG SURFACE
HIGH REBUILDS FAR NORTHEAST.

&&

.DISCUSSION...
TRADE WINDS CONTINUE TO DECREASE OVER THE ISLANDS EARLY THIS MORNING
AS THE HIGH PRESSURE RIDGE NORTH OF THE ISLANDS WEAKENS AHEAD OF AN
ADVANCING SURFACE TROUGH FROM THE NORTHWEST. AT THE UPPER LEVEL...A
LOW IS JUST NORTHEAST OF THE BIG ISLAND WITH ITS ASSOCIATED TROUGH
EXTENDING WESTWARD OVER THE STATE. EARLY MORNING SOUNDINGS FROM
LIHUE AND HILO SHOWED THE AIR MASS REMAINS SLIGHTLY UNSTABLE...WITH
RATHER DEEP LOW LEVEL MOISTURE EXTENDING TO NEAR 16K FEET ON THE
HILO SOUNDING. PARTIAL CLEARING HAS OCCURRED OVER THE BIG ISLAND IN
THE PAST COUPLE OF HOURS...THOUGH THERE ARE STILL PLENTY OF CLOUDS
IN THE VICINITY TO PROVIDE MORE SHOWERS. ANOTHER AREA OF CLOUDS IS
PASSING OVER OAHU AT THIS TIME...BRINGING LOCALIZED MODERATE RAIN TO
A FEW WINDWARD AND MOUNTAIN LOCATIONS IN THE PAST HOUR. RADAR DATA
INDICATE MORE SCATTERED SHOWERS ARE IN THE ISLAND VICINITY AT
TIME...AND SOME OF THESE SHOWERS ARE POSSIBLY HEAVY. THUS MORE
PASSING CLOUDS AND SHOWERS WILL AFFECT THE ISLANDS TODAY.

TRADE WINDS WILL REMAIN LIGHT OVER THE ISLANDS FOR THE NEXT FEW DAYS
AS THE SURFACE RIDGE TO THE NORTH BREAKS DOWN. WINDS MAY BECOME
LIGHT ENOUGH TO ALLOW LAND AND SEA BREEZES TO DEVELOP AT TIMES. AS
LIGHT TRADE WINDS ARE EXPECTED TO PERSIST...THE WEATHER PATTERN WILL
BE CONVECTIVE TRADE WIND TYPE...WITH CLOUDS AND SHOWERS STILL FAVOR
WINDWARD AND MOUNTAIN AREAS...WHILE AFTERNOON CONVECTION MAY DEVELOP
OVER THE SMALLER ISLANDS AND BE DISPLACED TOWARDS THE WESTERN SIDE.
THE UPPER LEVEL LOW NORTHEAST OF THE BIG ISLAND WILL PASS NEAR THE
STATE TODAY...AND THEN LIFT NORTH BY EARLY WEDNESDAY. THE CLOSE
PROXIMITY OF THIS UPPER LOW WITH ITS ASSOCIATED TROUGH WILL BRING AN
ENHANCEMENT TO THE TRADE WINDS SHOWERS AT LEAST THROUGH TODAY.

THE ADVANCING SURFACE TROUGH IS EXPECTED TO LIFT NORTH BY THE LATER
PART OF THE WEEK. MEANWHILE...A STRONG HIGH WILL REBUILD FAR
NORTHEAST OF THE ISLANDS. THIS COMBINATION WILL ALLOW THE RETURN OF
STRONGER TRADE WINDS TO THE STATE TOWARDS THE WEEKEND. WINDS MAY
BECOME LOCALLY BREEZY BY THE LATER PART OF THE WEEKEND. AN UPPER
LEVEL TROUGH MAY LINGER JUST WEST OF THE ISLANDS...AND MAY ONCE
AGAIN PROVIDE ENHANCEMENT TO THE TRADE WIND SHOWERS...ESPECIALLY
OVER THE WESTERN ISLANDS.

&&

.AVIATION...
AIRMET SIERRA IS IN EFFECT FOR MTN OBSC OVER WINDWARD AND MAUKA
AREAS OF OAHU MOLOKAI MAUI AND BIG ISLAND DUE TO MVFR CIGS AND SHRA.
UPSTREAM CLOUDS LOOK TO CONTINUE FILTERING THROUGH THE MORNING.
CLOUD TOP WARMING AND DAYTIME MIXING OF CURRENT CLOUDS MAY BE
COUNTERACTED BY DEVELOPMENT OF NEW SHOWERS CAUSED THE INSTABILITY
OVER THE ISLANDS TODAY. HARD TO SAY WHEN AIRMET SIERRA WILL BE
DROPPED...BUT WILL KEEP IT GOING AS LONG AS MTN OBSC PERSIST. VFR
CONDITIONS WILL PREVAIL ELSEWHERE AROUND THE STATE...WITH ISOL MVFR
COND AND BRIEF MTN OBSC.

AIRMET ZULU HAS ALSO BEEN ISSUED FOR LIGHT ICING NEAR THE CLOUD
TOPS AROUND THE BIG ISLAND.

&&

.MARINE...
THE CURRENT FORECAST DOES NOT SHOW SMALL CRAFT ADVISORY /SCA/
CONDITIONS OVER THE HAWAIIAN COASTAL WATERS THROUGH THE END OF THE
WORK WEEK. THE FORECAST MODELS SUGGEST THE WINDS WILL INCREASE TO
SCA SPEEDS OVER THE TYPICALLY WINDY WATERS ADJACENT TO THE ISLANDS
OF MAUI COUNTY AND THE BIG ISLAND THIS WEEKEND.

SMALL SWELLS ORIGINATING FROM THE SOUTHERN HEMISPHERE WILL CONTINUE
TO MAINTAIN BACKGROUND SURF ALONG SOUTH FACING SHORES OF THE ISLANDS
THIS WEEK. A NEW LONG PERIOD SOUTHWEST SWELL ARRIVING LATE SATURDAY
MAY PRODUCE A SMALL BUMP IN SURF HEIGHTS ALONG SOUTH FACING SHORES
OF THE ALOHA STATE STARTING SUNDAY. ELSEWHERE...A MODERATE EASTERLY
TRADE SWELL WILL SLOWLY SUBSIDE THROUGH MID-WEEK AS THE TRADE WINDS
WEAKEN. EXPECT THE TRADE WIND GENERATED SWELL TO INCREASE SURF
HEIGHTS ALONG EAST FACING SHORES OF MOST ISLANDS AGAIN THIS WEEKEND
AS THE TRADES STRENGTHEN.

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

MARINE...HOUSTON
AVIATION...FOSTER
DISCUSSION...HUI