Heavy Rain in Hawaii, June 2, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
315 AM HST MON JUN 2 2014

.SYNOPSIS...
A TROUGH PASSING NORTH OF THE ISLANDS WILL WEAKEN THE TRADE WINDS
TODAY...ESPECIALLY OVER KAUAI AND OAHU. THERE WILL BE A MIX OF NIGHT
AND MORNING TRADE WIND SHOWERS OVER WINDWARD AREAS...AND AFTERNOON
SHOWERS OVER INTERIOR AND LEEWARD AREAS THROUGH TONIGHT. TRADE WINDS
WILL STRENGTHEN STARTING TUESDAY...AND REMAIN BREEZY INTO NEXT
WEEK...WITH SHOWERS FOCUSED OVER WINDWARD AREAS.

&&

.DISCUSSION...
CURRENTLY...A 1034 MB SURFACE HIGH IS CENTERED ABOUT 2000 MILES TO
THE NNE...PROVIDING MODERATE E TO ESE WINDS TO THE ISLANDS...AS WE
LIE ON THE SW PERIPHERY OF THE HIGH/S CIRCULATION. LATEST SURFACE
ANALYSIS HAS A STALLED FRONT LOCATED ABOUT 300 MILES NW OF KAUAI...
WITH THE LOW LEVEL FLOW AT BUOY 51101 NW OF KAUAI WEAKENED AND
VEERED TO THE SE DUE TO IT/S PRESENCE. IN THIS REGIME...SHOWERS
HAVE BEEN MOVING IN OVER WINDWARD PORTIONS OF THE ISLANDS...BUT A
BATCH OF SHOWERY LOW CLOUDS THAT DEVELOPED TO THE LEE OF MOLOKAI AND
LANAI SUNDAY EVENING BROUGHT SOAKING RAIN TO SE OAHU OVERNIGHT. SOME
HEAVY RAIN CORES ARE SEEN ON LOCAL RADARS...HIGHLIGHTING THE MOIST
AND RELATIVELY UNSTABLE AIR MASS IN PLACE...THAT IS CONFIRMED BY
OVERNIGHT SOUNDINGS THAT SHOW UNUSUALLY HIGH PWAT NEAR 1.5 INCHES...
AND A LACK OF THE TYPICAL SUBSIDENCE INVERSION. WATER VAPOR IMAGERY
SHOWS A TROUGH ALOFT EXTENDING OVER THE ISLANDS FROM THE NNW...AND
IS THE PRIMARY CULPRIT BEHIND THE INSTABILITY.

THE FORECAST CALLS FOR THE HIGH TO THE NE TO MOVE/CHANGE LITTLE IN
THE SHORT TERM...THEN SLIDE S LATER THIS WEEK AND INTO NEXT WEEKEND
WITH LITTLE CHANGE IN CENTRAL PRESSURE. HOWEVER...THE FRONT TO THE
NW IS FORECAST TO TRANSITION TO A TROUGH AND DRIFT E TODAY...
LOOSENING THE PRESSURE GRADIENT NEAR THE ISLANDS IN THE PROCESS. THE
TROUGH WILL REMAIN IN PLACE INTO TUESDAY...AFTER WHICH TIME IT WILL
MOVE W AND DISSIPATE. AS THE TROUGH DEPARTS...THE LOCAL PRESSURE
GRADIENT WILL TIGHTEN...AND FRESH TO STRONG TRADE WINDS WILL
RETURN...THEN PERSISTING THROUGH THE FORECAST PERIOD. ALOFT...THE
ELONGATED N-S TROUGH NOW IN PLACE IS EXPECTED TO BREAK DOWN...AS A
CUT OFF LOW ALOFT DEVELOPS ABOUT 900 MILES TO THE ENE OF THE
ISLANDS. ALTHOUGH A TROUGH ALOFT IS EXPECTED TO EXTEND OVER THE
ISLANDS FROM THIS LOW...A GENERAL WARMING TREND IS EXPECTED IN THE
MID-LEVELS...LEADING TO A GRADUAL STABILIZATION OF THE ISLAND
ATMOSPHERE.

THEREFORE...THE EXPECTATION IS FOR WINDWARD SHOWERS TO REMAIN
RELATIVELY ACTIVE IN THE SHORT TERM...AS CLOUDS AND SHOWERS GET
PUSHED ALONG BY THE WEAKENING E TO SE FLOW. HOWEVER...THE LIGHT
WINDS WILL LIKELY ALLOW SEA BREEZES TO DRIVE THE FORMATION OF CLOUDS
AND SHOWERS OVER LEEWARD AND INTERIOR AREAS THIS AFTERNOON...WITH
THE CONTINUED INSTABILITY ALLOWING A FEW SHOWERS TO BECOME BRIEFLY
HEAVY. GRADUALLY STRENGTHENING TRADE WINDS BY TUESDAY AFTERNOON MAY
BE STRONG ENOUGH TO PRECLUDE LEEWARD SHOWER DEVELOPMENT ON THE
SMALLER ISLANDS...BUT SOME UNCERTAINTY SURROUNDS THAT FORECAST. BY
WEDNESDAY...BREEZY TRADE WINDS WILL BE IN PLACE...AND WILL PUSH A
FEW SHOWERY PATCHES OVER THE ISLANDS FROM THE E. BY THE END OF THE
WEEK...LATEST GUIDANCE SHOWS THE AIR MASS DRYING SOMEWHAT...WITH
FEWER TRADE SHOWERS EXPECTED IN A MORE STABLE ENVIRONMENT.

&&

.AVIATION...
VFR CONDITIONS WILL PREDOMINATE ACROSS THE ISLAND CHAIN THIS
MORNING...WITH BRIEF MVFR CONDITIONS OCCURRING OVER WINDWARD AND
MAUKA AREAS. ISOLATED MVFR CONDITIONS ARE LIKELY AT SOME OF THE
TERMINALS AS WELL...ESPECIALLY LIHUE...LANAI...KAILUA-KONA...AND
HILO.

WITH TRADE WINDS BACKING OFF TO SOME EXTENT AND BECOMING MORE
EAST-SOUTHEASTERLY LATER TODAY...LEEWARD CLOUDINESS AND SHOWERS ARE
POSSIBLE AS WELL.

&&

.MARINE...
TRADE WINDS WILL CONTINUE TO WEAKEN AND VEER TO THE SE TODAY...
ESPECIALLY NEAR KAUAI AND OAHU...WITH A MODERATE TO FRESH ESE FLOW
PERSISTING OVER NEAR SHORE WATERS E OF MAUI AND THE BIG ISLAND.
WINDS WILL BE AT THEIR LIGHTEST THIS AFTERNOON INTO TUESDAY...AND
WILL THEN INCREASE TUESDAY EVENING INTO WEDNESDAY...WITH SMALL CRAFT
ADVISORIES LIKELY NEEDED BY WEDNESDAY FOR THE WINDIER MARINE ZONES
AROUND MAUI AND THE BIG ISLAND. FRESH TO STRONG TRADE WINDS WILL
THEN PERSIST THROUGH THE REMAINDER OF THE FORECAST PERIOD.

NO SIGNIFICANT SWELLS ARE EXPECTED THROUGH THE FORECAST PERIOD.
SEASONABLY-SIZED SMALL SURF IS EXPECTED ALONG S FACING SHORES...
PRODUCED BY DISTANT LOWS IN THE S PACIFIC...WITH SHORT-PERIOD WIND
WAVES ALONG E FACING SHORES DRIVEN BY A TYPICAL FETCH OF TRADE WINDS
E OF THE ISLANDS.

&&

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

&&

DISCUSSION/MARINE...BIRCHARD
AVIATION...KINEL