Heavy Rain in Hawaii, May 22, 2013

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST WED MAY 22 2013

CORRECTED TYPO

.SYNOPSIS...
A PAIR OF SURFACE TROUGHS TO OUR NORTH AND NORTHWEST WILL KEEP WINDS
LIGHT OVER THE STATE AGAIN TONIGHT. THESE TROUGHS WILL MOVE WEST AND
WEAKEN AS A SURFACE RIDGE BUILDS NORTH OF THE AREA. LIGHT TRADES
WILL BEGIN TO FILL IN ON THURSDAY...THEN STRENGTHEN THROUGH THE
WEEKEND.

&&

.DISCUSSION...
WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL LOW 800 MILES
NORTH-NORTHEAST OF THE STATE...WITH A TROUGH EXTENDING TO THE WEST
SOUTHWEST. AT THE SURFACE...TROUGHS ARE LOCATED WITHIN 300 MILES
NORTH AND NORTHWEST OF THE STATE...WITH A HIGH FARTHER TO THE
NORTHEAST. 00Z SOUNDINGS FROM HILO AND LIHUE SHOW INVERSIONS AROUND
9KFT...WITH PRECIPITABLE WATERS RANGING FROM 1.2 INCHES AT LIHUE TO
1.5 INCHES AT HILO. EARLY AFTERNOON MIMIC TOTAL PRECIPITABLE WATER
IMAGERY SHOWS A BAND OF MOISTURE CENTERED ACROSS THE ISLANDS...
EXTENDING IN A BAND TO THE NORTHEAST AND TO THE WEST OF THE STATE.
DRIER AIR IS LOCATED UPSTREAM FROM THE BIG ISLAND...AND ADDITIONAL
MOISTURE IS MOVING TOWARD KAUAI.

THE SURFACE TROUGHS TO THE NORTH AND NORTHWEST OF THE STATE WILL
KEEP THE GRADIENT WEAK ACROSS THE ISLANDS. THE LIGHT WINDS ALLOWED
WIDESPREAD SEA BREEZES TO FORM TODAY...AND LAND BREEZES ARE EXPECTED
AGAIN TONIGHT. SHOWERS THIS AFTERNOON WERE FOCUSED ACROSS INTERIOR
AND NORTHERN SECTIONS OF THE SMALLER ISLANDS...AS WELL AS THE
INTERIOR OF THE BIG ISLAND...AND THESE WILL LINGER INTO THE EVENING
BEFORE FADING WITH SUNSET. MOST ISLANDS STARTED OUT CLEAR THIS
MORNING...AND LAND BREEZES AGAIN WILL HELP TO CLEAR AREAS OUT AGAIN
TONIGHT. HOWEVER WITH GREATER MOISTURE AND CLOUDS EXPECTED OFFSHORE
THAT MAY HAVE AN IMPACT...ISLANDS ARE NOT GUARANTEED TO CLEAR OUT
AND IT IS WORTH KEEPING A CHANCE OF SHOWERS OVERNIGHT.

BY THURSDAY THE SURFACE TROUGH TO THE NORTHWEST WILL DISSIPATE BUT
THE TROUGH NORTH OF THE STATE WILL STILL PERSIST. THIS TROUGH WILL
LIMIT THE INFLUENCE OF THE HIGH TO THE NORTHEAST...BUT WE WILL START
TO SEE SOME SEMBLANCE OF TRADES RETURN. WINDS WILL BE LIGHT
INITIALLY...WHICH WILL ALLOW LINGERING SEA BREEZES ACROSS SHELTERED
LEEWARD SECTIONS. HOWEVER...CLOUDS AND SHOWERS SHOULD RETURN TO A
MORE TYPICAL TRADE WIND PATTERN. THE GFS AND ECMWF ARE BOTH SIMILAR
IN SHOWING THE TROUGH TO OUR NORTH GRADUALLY DIMINISHING THROUGH THE
END OF THE WEEK...WITH A SURFACE RIDGE BUILDING NORTH OF THE STATE
IN ITS PLACE. AS THIS RIDGE BUILDS IN...TRADE WINDS WILL STEADILY
STRENGTHEN THROUGH THE WEEKEND. WITH UPSTREAM MOISTURE EMBEDDED
WITHIN THE STRENGTHENING FLOW...TRADE WIND SHOWERS WILL BE SOMEWHAT
MORE ACTIVE THAN NORMAL.

&&

.AVIATION...
VFR CONDITIONS PREVAIL AT ALL TAF SITES THOUGH VOLCANIC EMISSIONS
MAY CAUSE SOME LOCAL MVFR CONDITIONS AT TIMES. DAYTIME HEATING HAS
CAUSED AN INCREASE IN CLOUD COVERAGE OVER LAND AREAS THIS AFTERNOON
WITH SOME LOCAL MVFR CONDITIONS POSSIBLE DUE TO LOW CLOUDS AND SHRA.
CLOUDS AND SHOWERS WILL LIKELY DIMINISH OVERNIGHT.

&&

.MARINE...
THE SOUTH SWELL REMAINS ELEVATED...BUT CONTINUES ITS DOWNWARD TREND.
SURF HEIGHTS ARE JUST BELOW ADVISORY LEVELS...AND HAVE LOWERED
ENOUGH FOR US TO DROP THE HIGH SURF ADVISORY FOR SOUTH FACING
SHORES. THE SOUTH SWELL WILL CONTINUE TO GRADUALLY DIMINISH THROUGH
THE WEEK. THE CURRENT NORTHWEST SWELL IS NEAR ITS PEAK AND WILL LAST
INTO THURSDAY BEFORE GRADUALLY DIMINISHING.

TRADE WINDS WILL STRENGTHEN THROUGH THE WEEK...AND ARE EXPECTED TO
REACH SMALL CRAFT ADVISORY LEVELS OVER THE WINDIER LOCATIONS NEAR
MAUI COUNTY AND THE BIG ISLAND BY THE WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 AM HST THURSDAY FOR BIG ISLAND SUMMITS.

&&

DISCUSSION/MARINE...BRAVENDER
AVIATION...BURKE