Drought in Hawaii, August 1 to 31, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
805 PM HST TUE JUL 31 2012

.SYNOPSIS...
HIGH PRESSURE TO THE NORTH WILL MAINTAIN MODERATE TO FRESH TRADE
WINDS THROUGH THE WEEKEND. SHOWERS WILL FAVOR WINDWARD AND MAUKA
AREAS DURING NIGHTS AND MORNINGS. LEEWARD SIDES OF THE SMALLER
ISLANDS WILL BE DRY...WITH A FEW AFTERNOON SHOWERS OVER THE KONA
SLOPES.

&&

.DISCUSSION...
A RELATIVELY QUIET NIGHT IS EXPECTED WITH MODERATE TO LOCALLY FRESH
TRADE WINDS DELIVERING PASSING CLOUDS...AND A FEW SHOWERS...THAT
WILL FOCUS OVER WINDWARD AREAS. CLOUDS ARE CURRENTLY IN GREATER
ABUNDANCE UPSTREAM OF KAUAI AND THE BIG ISLAND...WITH FEWER LOW
CLOUDS UPSTREAM OF MAUI COUNTY AND OAHU. RADAR DETECTS JUST A FEW
SMALL SHOWERS MOVING INTO WINDWARD AREAS...BUT MOST OF THE RADAR
RETURNS THIS EVENING ARE OVER LEEWARD WATERS...AND ARE FROM
NON-METEOROLOGICAL TARGETS. WILL BE UPDATING THE FORECAST TO FINE
TUNE THE OVERNIGHT FORECAST...BUT NO SIGNIFICANT CHANGES ARE
EXPECTED TO THE OVERALL FORECAST PHILOSOPHY PRESENTED BY THE DAY
SHIFT.

&&

.PREV DISCUSSION ISSUED 400 PM HST...
THIS BEING SUMMER...THE SUBTROPICAL HIGH/RIDGE IS PARKED NORTH OF
30N...WHILE THE NEAR-EQUATORIAL TROUGH IS LOCATED...WELL...NEAR THE
EQUATOR. THE ISLANDS...SITUATED BETWEEN THE TWO ARE IN THE MIDDLE OF
THE TRADE WIND BELT. THIS WILL BE THE CASE THROUGH THE FIRST HALF OF
AUGUST AND PROBABLY BEYOND.

WIND SPEED AND PRECIPITATION VARY DEPENDING ON WHAT IS GOING ON
ALOFT OVER OR NEAR THE ISLANDS...AND ON LOW LEVEL FEATURES SUCH AS
SCREAMING EAGLES...TROUGHS...ETC MOVING ALONG IN THE TRADES. ONE
SUCH FEATURE...A TROUGH...PASSED SOUTH OF HAWAII YESTERDAY AND LAST
NIGHT. MOISTURE AND A MODICUM OF INSTABILITY IN THE NORTHERN FRINGES
OF THE TROUGH...ALONG WITH THE SEA BREEZE CONTRIBUTED TO THE SETTING
OFF OF SHOWERS AND A FEW THUNDERSTORMS OVER THE KONA SLOPES
YESTERDAY AFTERNOON.

PRECIPITABLE WATER DERIVED FROM SATELLITE IMAGERY IS DECREASING AS
THE TROUGH DEPARTS TO THE WEST. THERE REMAINED...HOWEVER...ENOUGH
MOISTURE AND INSTABILITY TO ONCE AGAIN SET OFF SOME SHOWERS AND A
SMALL THUNDERSTORM OR TWO. IT SHOULD BE A LOT DRYER AND MORE STABLE
TOMORROW...SO THUNDERSTORMS ARE NOT FORECAST. JUST THE USUAL
AFTERNOON SHOWER ALONG THE SEA BREEZE FRONT..

THE PRESSURE GRADIENT BETWEEN THE TRANSIENT TROUGH TO THE SOUTH AND
THE HIGH TO THE NORTH ALSO TIGHTENED...RESULTING IN A BOOST IN THE
TRADES. WITH THE TROUGH MOVING AWAY...SURFACE PRESSURES OVER THE
PAST 24 HOURS UNDERSTANDABLY ROSE. WITH THIS TREND EXPECTED TO
CONTINUE...ALBEIT SLOWLY...THE PRESSURE GRADIENT WILL SLACKEN AND
THE TRADE WINDS WILL DIMINISH THROUGH WEDNESDAY NIGHT. AFTER
THAT...MODERATE TRADE WINDS WITH BRIEF MAINLY WINDWARD AND MAUKA
SHOWERS ARE FORECAST INTO NEXT WEEK.

&&

.AVIATION...
VFR CONDITIONS WILL PREVAIL AT MOST TAF SITES THROUGH THE FORECAST
PERIOD...WITH BRIEF MVFR EXCEPTIONS EXPECTED AT PHLI AND PHTO.

AIRMET TANGO IS POSTED FOR LOW LEVEL TURB BELOW 090 TO THE S AND W
OF THE MT OF ALL ISLANDS...DUE TO MODERATELY STRONG TRADE WINDS.
LITTLE CHANGE IN WIND SPEED IS EXPECTED OVER THE NEXT 24 HOURS.
AIRMET SIERRA FOR MT OBSCURATION IS IN EFFECT DUE TO CIGS FOR
WINDWARD PORTIONS OF THE BIG ISLAND.

&&

.MARINE...
A MODERATE SOUTH SWELL WILL PERSIST THROUGH WEDNESDAY. TRADE WINDS
WILL CONTINUE TO PRODUCE SHORT PERIOD CHOPPY SURF ALONG EAST FACING
SHORES. NO OTHER SIGNIFICANT SWELLS ARE EXPECTED.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY THROUGH 6 PM HST WEDNESDAY FOR THE PAILOLO AND
ALENUIHAHA CHANNELS...MAALAEA BAY...AND WATERS SOUTH OF THE BIG
ISLAND.

&&

BIRCHARD