Heavy Rain in Hawaii, August 1, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
531 PM HST FRI AUG 1 2014

.UPDATE...
OROGRAPHIC LIFTING ALONG WITH DEEP TROPICAL MOISTURE HAS SET OFF A
FEW THUNDERSTORMS LATE THIS AFTERNOON. HAVE ADDED ISOLATED
THUNDERSTORMS OVER THE LEEWARD BIG ISLAND THROUGH THE EVENING AND
THROUGH THE NIGHT OVER THE WINDWARD BIG ISLAND.

&&

.SYNOPSIS...
HIGH PRESSURE FAR NORTH OF THE STATE WILL KEEP TRADE WINDS BLOWING
INTO NEXT WEEK. ENHANCED MOISTURE MOVING FROM EAST TO WEST ACROSS
THE ISLANDS TONIGHT AND SATURDAY WILL RESULT IN AN INCREASE IN
SHOWERS WITH LOCALLY HEAVY RAINFALL POSSIBLE. DRIER AND MORE
STABLE WEATHER IS EXPECTED SUNDAY THROUGH WEDNESDAY. ANOTHER BOUT
OF WET WEATHER IS POSSIBLE LATE NEXT WEEK.

&&

.DISCUSSION...

CURRENT FRESH TRADE WINDS ARE PROPELLING CLOUDS AND SHOWERS INTO
THE WINDWARD SLOPES OF THE SMALLER ISLANDS. THE WINDWARD BIG
ISLAND HAS HAD SHOWERS THROUGHOUT THE DAY WITH MORE MOISTURE
EXPECTED TONIGHT AS THE REMNANT MOISTURE OF TROPICAL DEPRESSION
GENEVIEVE PASSES THROUGH THE AREA. EXPECT INCREASING HUMIDITY AND
MUGGY CONDITIONS AS THIS MOISTURE MOVES ACROSS THE STATE.

SHOWERS COVERAGE AND INTENSITY WILL INCREASE OVER THE REST OF THE STATE
TONIGHT AS THE MOISTURE MOVES WEST INTO THE SMALLER ISLANDS. THE
SATELLITE MIMIC TOTAL PRECIPITABLE WATER ESTIMATE SHOWS A SLUG OF
2 INCHES PLUS PRECIPITABLE WATER ALREADY OVER THE BIG ISLAND WITH
ITS LEADING EDGE MOVING INTO MAUI THIS EVENING. THE HILO SOUNDING
CONFIRMS THE HIGH PRECIPITABLE WATER VALUES...CHECKING IN AT 2.2
INCHES. WINDWARD BIG ISLAND SITES RECEIVED AN AVERAGE OF A 1/4
INCH EARLY THIS AFTERNOON WITH THE HIGHEST AMOUNTS NEAR A 1/2
INCH. MODERATE SHOWERS WILL CONTINUE THROUGH THE NIGHT OVER
WINDWARD BIG ISLAND AND MAUI AREAS. FOR MOLOKAI OAHU AND
KAUAI...SHOWERS WILL INCREASE THIS EVENING AND TONIGHT AS THE
ENHANCED MOISTURE MOVES FROM EAST TO WEST. THE MAJORITY OF
RAINFALL WILL OCCUR OVER THE WINDWARD SLOPES BUT LEEWARD LOCATIONS
WILL GET A FAIR AMOUNT OF SHOWERS AS WELL.

ALOFT... A WEAK UPPER TROUGH NW OF KAUAI IS EXPECTED TO LIFT AWAY
FROM THE STATE TONIGHT WITH RIDGING BUILDING OVER THE STATE.
WITHOUT THE UPPER LEVEL SUPPORT...THUNDERSTORMS ARE UNLIKELY.
HOWEVER...OROGRAPHIC LIFTING ALONG WITH THE DEEP MOISTURE HAS SET
OFF A FEW LATE AFTERNOON THUNDERSTORMS ON THE BIG ISLAND. HAVE
UPDATED THE FORECAST TO INCLUDE ISOLATED THUNDERSTORMS THROUGH THE
EVENING FOR LEEWARD BIG ISLAND AND THROUGH THE NIGHT FOR THE WINDWARD
BIG ISLAND.

EXPECTED TOTAL RAINFALL AMOUNTS TONIGHT THROUGH SATURDAY...
WINDWARD AREAS OF THE BIG ISLAND 1-3 INCHES WITH POCKETS OF HIGHER
AMOUNTS. WINDWARD AND MAUKA AREAS OF THE SMALLER ISLANDS WILL
RANGE FROM A 1/2 INCH TO 2 INCHES. LEEWARD AREAS ARE LOOKING AT A
1/2 INCH OR LESS.

SUNDAY THINGS WILL DRY OUT AND HUMIDITY WILL DECREASE AS DRIER AIR
MOVES IN FROM THE EAST. RIDGING ALOFT AND THE DRY CONDITIONS WILL
KEEP SHOWERS TO A MINIMUM. A STABLE TRADE WIND PATTERN IS
EXPECTED THROUGH MID- WEEK WITH HIGH PRESSURE ANCHORED TO THE
NORTH.

LATE NEXT WEEK STARTING THURSDAY... GLOBAL MODELS HAVE BEEN
CONSISTENTLY ADVECTING TROPICAL MOISTURE OVER THE STATE FROM THE
EAST... BRINGING MUGGY CONDITIONS AND INCREASING RAIN TO
THE ISLANDS. THIS MOISTURE IN THE MODEL FIELD COMES FROM WHAT IS NOW
TROPICAL STORM ISELLE. HOWEVER AT 6-7 DAYS OUT...THIS FORECAST IS
HIGHLY UNCERTAIN AND THE OFFICIAL FORECAST FOR THE EXTENDED PERIOD
HAS ONLY BEEN NUDGED TOWARD A WETTER FORECAST. STAY TUNED FOR
UPDATES AS THIS TIME PERIOD APPROACHES.

&&

.AVIATION...
AN AREA OF INCREASED MOISTURE SPREADING WEST ACROSS THE ISLANDS
WILL PROMPT US TO KEEP AIRMET SIERRA UP THROUGH THE NIGHT FOR
MOUNTAIN OBSCURATION AND EXPAND THE AFFECTED AREA TO INCLUDE
MOLOKAI. AIRMET TANGO FOR MODERATE TURBULENCE IMMEDIATELY LEE OF
THE ISLANDS WILL REMAIN IN EFFECT AS WELL...THANKS TO LOCALLY
STRONG TRADE WINDS. WINDWARD TERMINALS WILL SEE OCCASIONAL MVFR
CONDITIONS TONIGHT...BUT VFR WILL CONTINUE TO DOMINATE ELSEWHERE.

&&

.MARINE...
FRESH TRADE WINDS WILL CONTINUE AND A SMALL CRAFT ADVISORY REMAINS
FOR THE WINDIER AREAS AROUND THE BIG ISLAND AND MAUI.

INCREASING SSW SWELL IS EXPECTED TONIGHT AND SATURDAY WITH SURF
APPROACHING ADVISORY LEVELS ON SOUTH FACING SHORES. THIS SURF
EVENT WILL SLOWLY DECREASE SUNDAY THROUGH MONDAY. SURF WILL SEE A
SLIGHT BUMP ON WEST FACING SHORES AS WELL DUE TO THE SSW
DIRECTION. LOW END SOUTH SWELL WILL MAINTAIN BACKGROUND SURF ALONG
SOUTH SHORES TUESDAY AND WEDNESDAY. OTHERWISE...PREVAILING TRADE
WINDS WILL CONTINUE TO PRODUCE SHORT PERIOD SWELL AND CHOPPY NEAR
AVERAGE SURF ALONG EAST FACING SHORES THROUGH THE NEXT SEVERAL
DAYS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST SUNDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.

&&

MORRISON...UPDATE DISCUSSION AND MARINE
POWELL...AVIATION