Heavy Rain in Hawaii, March 31, 2014

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1001 AM HST MON MAR 31 2014

.SYNOPSIS...
TRADE WINDS WILL PREVAIL THROUGH THE UPCOMING WEEK...BECOMING BREEZY
WEDNESDAY...THEN DIMINISHING OVER THE WEEKEND. THE ISLAND ATMOSPHERE
WILL BE SOMEWHAT UNSTABLE THROUGH WEDNESDAY... ALLOWING PASSING
SHOWERS TO BECOME BRIEFLY HEAVY. IN ADDITION...THUNDERSTORMS WILL
BE POSSIBLE OVER THE BIG ISLAND SLOPES THE NEXT COUPLE OF
AFTERNOONS. A DRIER TRADE WIND WEATHER REGIME WILL PREVAIL FOR THE
SECOND HALF OF THE WEEK BEFORE SHOWERS PICK UP AGAIN OVER THE
WEEKEND.

&&

.DISCUSSION...
MODERATE TRADE WINDS ARE PUSHING ENHANCED SHOWERS INTO WINDWARD
ISLAND SLOPES TODAY WITH SOME SHOWERS REACHING LEEWARD
LOCATIONS OF THE SMALLER ISLANDS. AN UPPER TROUGH E OF THE BIG
ISLAND CONTINUES TO BRING SOME ATMOSPHERIC INSTABILITY... AND
TRADE SHOWERS NORMALLY CAPPED AT 6 TO 8 THOUSAND FEET ARE REACHING
UP TO 20 THOUSAND FEET IN HEIGHT. THE ADDED VERTICAL CLOUD EXTENT
IS ALLOWING FOR SOME AREAS TO SEE BRIEF DOWNPOURS AS THE SHOWERS
PASS OVERHEAD. AFTERNOON LAND HEATING ADDED TO THE UPPER LOW/S
INSTABILITY WILL BRING A CHANCE OF THUNDERSTORMS THIS AFTERNOON
OVER THE BIG ISLAND SLOPES AND THE LEEWARD SLOPES OF HALEAKALA.

THE UPPER TROUGH WILL LINGER E OF THE BIG ISLAND THROUGH
WEDNESDAY. TRADE SHOWERS WILL REMAINED ENHANCED AND THE POTENTIAL
FOR AFTERNOON THUNDERSTORMS OVER THE BIG ISLAND SLOPES WILL
REMAIN. THURSDAY...WEAK RIDGING ALOFT WILL PUSH IN FROM THE WEST
AND SHOWER INTENSITY AND COVERAGE IS EXPECTED TO DIMINISH FOR THE
SECOND HALF OF THE WEEK.

HIGH PRESSURE FAR NNE OF THE STATE IS PROVIDING MODERATE TO FRESH
TRADE WINDS ACROSS THE STATE TODAY. THE HIGH WILL DRIFT SLOWLY
SOUTH AS AN EASTWARD MOVING HIGH REINFORCES IT TUESDAY. AN UPTICK
IN TRADES IS EXPECTED TUESDAY NIGHT AS THE N-S PRESSURE GRADIENT
INCREASES OVER THE ISLANDS. TRADES WILL REMAIN FRESH TO LOCALLY
STRONG UNTIL NEXT WEEKEND AS THE HIGH REMAINS IN PLACE. AN
APPROACHING FRONT WILL WEAKEN WINDS OVER THE WEEKEND. BOTH ECMWF
AND GFS ARE SHOWING RUN TO RUN INCONSISTENCY WITH THIS FEATURE.
MODEL SOLUTIONS ARE FLUCTUATING BETWEEN A STRONG FRONT AND A WEAK
SHEARLINE PASSING OVER THE STATE. CURRENT FORECAST OPTS FOR THE
SHEARLINE SOLUTION AS MODELS ARE TRENDING IN THAT DIRECTION. WITH
THAT IN MIND...WEAKENING WINDS ARE EXPECTED SATURDAY AND INCREASING
SHOWERS WILL REMAIN FOCUSED OVER WINDWARD SLOPES. WINDS ARE
EXPECTED TO TURN OUT OF THE NE SUNDAY AND STRENGTHEN FROM W TO E
ACROSS THE ISLANDS AS A NEW HIGH BUILDS NW OF THE ISLANDS.

&&

.AVIATION...
INSTABILITY ASSOCIATED WITH THE TROUGH ALOFT NEAR THE AREA WILL
MAINTAIN SHOWERY WEATHER...ESPECIALLY OVER WINDWARD AREAS...SO
AIRMET SIERRA FOR MTN OBSC WILL LIKELY CONTINUE TODAY. AIRMET TANGO
FOR TURB ALOFT WILL ALSO CONTINUE DUE TO A JET STREAM OVER THE AREA.

&&

.MARINE...
NO MARINE ADVISORIES ARE CURRENTLY IN EFFECT...AND SURF LOOKS TO
REMAIN BELOW ADVISORY LEVELS ALONG N...W AND S FACING SHORES THROUGH
THE WEEK. A SMALL N SWELL AND A SHORT-PERIOD ENE WIND SWELL WILL
DIMINISH TODAY...WITH A MODERATE NW SWELL EXPECTED TO BUILD
WEDNESDAY NIGHT AND PEAK BELOW ADVISORY LEVELS THURSDAY. A STORM
FORCE LOW E OF JAPAN THIS MORNING IS EXPECTED TO DEVELOP A CAPTURED
FETCH THAT GENERATES A WNW SWELL THAT ARRIVES BY THE END OF THE
WEEK...WITH PEAK SURF HEIGHTS NEAR ADVISORY LEVELS ALONG N AND W
FACING SHORES SATURDAY. A PULSE OF SWELL FROM THE S IS ALSO
EXPECTED FROM WEDNESDAY THROUGH FRIDAY.

SMALL CRAFT ADVISORY /SCA/ WINDS ARE EXPECTED TO BEGIN IN THE WINDY
ZONES AROUND MAUI AND THE BIG ISLAND TUESDAY NIGHT...WITH THE
POTENTIAL FOR SCA WINDS/SEAS TO SPREAD TO MOST OTHER ZONES FROM
WEDNESDAY THROUGH SATURDAY AS A LONG FETCH OF FRESH TRADE WINDS
EXTENDS E FROM THE ISLANDS. THIS FETCH COULD RESULT IN SURF ALONG
E FACING SHORES REACHING ADVISORY LEVELS AROUND THE MIDDLE OF THE
WEEK.

&&

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

&&

MORRISON...DISCUSSION AND MARINE
DONALDSON...AVIATION