Flash Flood and Heavy Rain in Hawaii, April 6 to 9, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
409 PM HST TUE APR 6 2010

.SYNOPSIS...
LIGHT TRADE WINDS TODAY WILL INCREASE TO MODERATE TRADES ON
WEDNESDAY...AND THEN MODERATE TO FRESH WINDS THURSDAY AND INTO THE
WEEKEND. SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS WITH
INCREASED RAINFALL EXPECTED TONIGHT THROUGH THURSDAY.

&&

.DISCUSSION...
AFTERNOON RADAR IMAGERY SHOWS SCATTERED CONVECTIVE SHOWERS OVER
KAUAI...OAHU AND MOLOKAI...AS WELL AS SHOWERS MOVING INTO THE
WINDWARD BIG ISLAND. SOME OF THE CONVECTIVE SHOWERS HAVE PRODUCED
SOME BRIEF DOWNPOURS...AS THE SAINT STEPHENS GAGE SHOWED BY
PICKING UP 0.64 INCHES IN AN HOUR EARLIER THIS AFTERNOON. AS OF 2
PM...6-HOUR RAINFALL TOTALS PEAKED ON KAUAI AT HANALEI AND MOUNT
WAIALEALE GAGES WITH EACH RECEIVING A HALF INCH OF RAIN. ON
OAHU...A HEAVY SHOWER EARLIER THIS MORNING DROPPED ALMOST AN INCH
OF RAIN AT THE KAHUKU TRAINING GAGE. MAUI COUNTY HAS SEEN LITTLE
RAIN TODAY WHILE ON THE BIG ISLAND...GAGES FROM WAIAKEA TO
GLENWOOD HAVE AVERAGED A QUARTER OF AN INCH.

HIGH PRESSURE THAT HAS MAINTAINED THE TRADE WINDS OVER THE PAST
FEW DAYS HAS MOVED OFF TO THE EAST...WHILE A SURFACE TROUGH HAS MOVED
INTO POSITION WEST OF THE STATE...ALONG 170W. LIGHT TRADE WIND
FLOW TODAY ALLOWED WIDESPREAD SEA BREEZES ALONG THE LEEWARD
COASTS. AFTERNOON CONVECTIVE SHOWERS HAVE FORMED IN RESPONSE TO
THE SEA BREEZES WITH HELP FROM A DEEP MOIST LAYER THAT REACHES UP
TO 12 THOUSAND FEET. THESE SHOWERS ARE EXPECTED TO DIMINISH THIS
EVENING AS THE ISLANDS COOL.

THE AFOREMENTIONED SURFACE FEATURE TO THE WEST IS A REFLECTION OF
A MID/UPPER TROUGH. THE TROUGH ALOFT IS CURRENTLY LOCATED 700
MILES WNW OF KAUAI WITH AN ORIENTATION FROM NNE TO SSW. GLOBAL
MODELS BRING THIS TROUGH AND ASSOCIATED COLD POOL NEAR KAUAI
TONIGHT...CREATING A MODERATELY UNSTABLE ATMOSPHERE OVER THE
SMALLER ISLANDS TONIGHT THROUGH THURSDAY. THE GFS SHOWS
TEMPERATURES REACHING AS LOW AS -13 DEGREES C OVER KAUAI AND OAHU
DURING THIS PERIOD AND THE POSSIBILITY OF LOCALLY HEAVY SHOWERS
HAVE BEEN ADDED TO THE FORECAST FOR THOSE ISLANDS. WITHOUT ANY
FORESEEABLE LOW LEVEL FORCING...THE CHANCE OF THUNDERSTORMS SEEM
LESS LIKELY AT THIS TIME.

HIGH PRESSURE BUILDS NORTH OF THE STATE DURING THE SECOND HALF OF
THE WEEK INCREASING TRADE WINDS TO MODERATE TO FRESH LEVELS
WEDNESDAY...AND INTO THE WEEKEND. THE TROUGH ALOFT LINGERS JUST
NORTH OF THE STATE THROUGH THE END OF THE WEEK...BUT TEMPS ALOFT ARE
FORECAST TO WARM...ALLOWING A STABLE ATMOSPHERE TO RETURN BY
FRIDAY. OVER THE WEEKEND...TRADE WIND SHOWERS ARE EXPECTED TO
FOCUS OVER WINDWARD AND MAUKA AREAS.

&&

.MARINE...
SMALL SWELLS ENTERING THE AREA FROM AROUND THE COMPASS WITH THE
EXCEPTION OF THE WEST. SURF HEIGHTS WILL REMAIN WELL BELOW
ADVISORY LEVELS.

SMALL CRAFT ADVISORIES MAY BE NECESSARY THURSDAY IN THE WINDIER
ZONES AS TRADE WINDS INCREASE.

&&

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

&&

MORRISON