Drought in Hawaii, May 1 to 31, 2011

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE HONOLULU HI
835 PM HST SAT APR 30 2011

.SYNOPSIS...
LOW PRESSURE HIGH OVER THE ISLANDS WILL KEEP OUR WEATHER UNSETTLED.
THERE IS THEREFORE A CHANCE OF HEAVY SHOWERS OR THUNDERSTORMS
THROUGH EARLY NEXT WEEK. HIGH PRESSURE TO THE NORTH WILL PRODUCE
TRADE WINDS...BUT THE TROUGH ALOFT WILL KEEP THE WINDS GENTLE. A
HIGH PRESSURE RIDGE WILL BUILD TO THE NORTH...BRINGING STRONGER
TRADE WINDS STARTING WEDNESDAY.

&&

.DISCUSSION...
A SURFACE HIGH FAR TO THE NORTH WILL MOVE EAST AND STRENGTHEN OVER
THE NEXT FEW DAYS. NORMALLY SUCH A HIGH WOULD PRODUCE MODERATE TO
FRESH TRADE WINDS. IN THIS CASE HOWEVER...A SURFACE TROUGH...THE
REFLECTION OF A TROUGH ALOFT...IS WEDGED BETWEEN THE HIGH AND THE
ISLANDS RESULTING IN A RATHER FLAT PRESSURE GRADIENT AND LIGHT TRADE
WINDS. THE TROUGHS AT THE SURFACE AND ALOFT WILL NOT GOING TO GO
ANYWHERE SOON...SO THE TRADES WILL REMAIN LIGHT THROUGH TUESDAY.

THE TROUGH ALOFT ALSO HAS SOME PRETTY COOL TEMPERATURES...LIKE -13C
OVER KAUAI AND -11C OVER THE BIG ISLAND. THE RESULTANT STEEP
TEMPERATURE LAPSE RATE MAKES FOR RATHER UNSTABLE CONDITIONS. VARIOUS
STABILITY INDICES INCLUDING A LIFTED INDEX OF -7.3 AND A CAPE OF
2702 J/KG OVER KAUAI CONFIRM THE INSTABILITY...AS DO THE
THUNDERSTORMS JUST SOUTHWEST OF KAUAI. THE BALLOON SOUNDING OFF OF
HILO SHOWED SLIGHTLY MORE STABLE CONDITIONS THERE. THIS SEEMS
REASONABLE SINCE THAT END OF THE ISLAND CHAIN IS FARTHER AWAY FROM
THE UPPER TROUGH LOCATED WEST THROUGH NORTH OF KAUAI.

WATER VAPOR SATELLITE IMAGERY...WHICH DETECTS MOISTURE ABOVE 25
THOUSAND FEET...SHOWS AN UPPER LEVEL LOW FORMING IN THE SOUTHWEST
END THE UPPER LEVEL TROUGH AROUND 500 MILES WEST OF KAUAI. THE LOW
IS FORECAST TO MOVE OVER THE ISLANDS SUNDAY INTO TUESDAY...BRINGING
MORE INSTABILITY WITH IT. SATELLITE IMAGERY SHOWS AN AREA OF SHOWERY
LOW CLOUDS TO THE EAST AND HEADED IN OUR DIRECTION. COMPUTER MODELS
OF THE ATMOSPHERE PICKED UP ON CLOUDS AND KNOWS ABOUT THE UPPER LOW
MOVING OVERHEAD...SO THEY ARE PAINTING A BETTER CHANCE OF HEAVY
SHOWERS AND THUNDERSTORMS.

THE COLD TEMPERATURES ALOFT ALSO MAY LEAD TO SOME LATE SEASON SNOW
ON THE SUMMITS OF MAUNA KEA AND MAUNA LOA. WINTER WEATHER ADVISORIES
OR WARNINGS MAY BE NEEDED AS THE LOW ALOFT GETS CLOSER TO THE BIG
ISLAND OVER THE NEXT COUPLE OF DAYS.

DURING THE LATTER HALF OF NEXT WEEK THE LOW AND TROUGH ALOFT WILL
SETTLE OVER THE SOUTHEAST END OF THE ISLAND CHAIN AND AN UPPER
RIDGE WILL BUILD TO THE NORTHWEST AND NORTH. THE RIDGE ALOFT WILL
SUPPORT A BIGGER SURFACE HIGH TO THE NORTH RESULTING IN STRONGER
TRADE WINDS. THE EVER PRESENT TROUGH ALOFT AND ITS COLD TEMPERATURES
MAY MAKE FOR WET AND BREEZY TRADE WINDS STARTING WEDNESDAY NIGHT AND
LASTING INTO NEXT WEEKEND.

&&

.MARINE...
THE TRADE WINDS WILL LIKELY STRENGTHEN ENOUGH WEDNESDAY TO REQUIRE
SMALL CRAFT ADVISORIES FOR THE WINDY AREAS AROUND THE BIG ISLAND AND
MAUI. THE STRONGER TRADES ARE EXPECTED TO LAST THROUGH THE REST OF
THE WEEK...AND MAY PRODUCE ENOUGH ROUGH SURF ALONG EAST FACING
SHORES TO REQUIRE A HIGH SURF ADVISORY.

&&

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

&&

CRAIG