793
FXHW60 PHFO 041330
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST SAT JUL 4 2009
SYNOPSIS
TRADE WINDS WILL GRADUALLY INCREASE ACROSS THE STATE THROUGH THE
WEEKEND AS HIGH PRESSURE STRENGTHENS TO OUR NORTH. CLOUDS AND
SHOWERS WILL FAVOR WINDWARD AND MAUKA AREAS...WITH ONLY LIGHT TOTAL
RAINFALL AMOUNTS EXPECTED.
DISCUSSION
WATER VAPOR IMAGERY SHOWS AN UPPER LOW NORTHEAST OF THE ISLANDS...
WITH A TROUGH EXTENDING SOUTHWESTWARD ACROSS THE STATE. THIS TROUGH
HAS HELPED TO WEAKEN INVERSION HEIGHTS...BUT 12Z SOUNDINGS FROM HILO
AND LIHUE SHOW THE INVERSIONS STRENGTHENING AT AROUND 6-8KFT. THE
HILO SOUNDING HAS WARMED UP TO 5C BETWEEN 800MB AND 500MB...A SIGN
THAT THE UPPER TROUGH IS ALREADY BEGINNING TO MOVE WESTWARD. THE
POES AMSU TOTAL PRECIPITABLE WATER SENSOR SHOWS DRIER AREAS UPSTREAM
TO THE EAST NORTHEAST OF THE STATE. IT ALSO SHOWS A LARGER AREA OF
HIGH PW/S MOVING TOWARD THE BIG ISLAND FROM THE SOUTHEAST...WHICH
APPEARS TO BE ASSOCIATED WITH HIGH-LEVEL MOISTURE/CLOUDS ON THE EAST
SIDE OF THE UPPER TROUGH.
THE GFS AND ECMWF ARE PRETTY SIMILAR SHOWING THE UPPER TROUGH
CONTINUING TO MOVE WESTWARD ACROSS THE STATE...AS AN UPPER LEVEL
HIGH BUILDS IN FROM THE EAST. AS HEIGHTS BUILDS...THE SURFACE HIGH
FAR NORTH OF THE STATE WILL STRENGTHEN AND BECOME MORE OF A DOMINANT
FEATURE ACROSS THE CENTRAL PACIFIC. BY TUESDAY/WEDNESDAY...IT TAKES
ON A POSITION NORTHEAST OF THE STATE THAT IS MORE TYPICAL OF THE
SUMMERTIME SEASON.
SURFACE PRESSURES ACROSS THE STATE HAVE SHOWN STEADY 1-1.5MB
PRESSURE RISES THROUGH THE NIGHT. TRADE WINDS WILL CONTINUE TO
INCREASE THROUGH EARLY NEXT WEEK...AND REMAIN AT MODERATE TO FRESH
LEVELS THROUGH THE END OF THE WEEK. THE GFS SHOWS AN INCREASING
AMOUNT OF LOW-LEVEL MOISTURE GETTING PICKED UP IN THE TRADE FLOW.
HOWEVER...INVERSION HEIGHTS WILL STRENGTHEN AND LOWER UNDER THE
BUILDING MID/UPPER LEVEL RIDGE...KEEPING RAINFALL AMOUNTS LIMITED.
FIRE WEATHER
LIMITED RAINFALL FROM THE DRIER TRADE WIND PATTERN WILL CONTINUE
OVER THE HOLIDAY WEEKEND. MINIMUM RELATIVE HUMIDITY VALUES TODAY
WILL BE SIMILAR TO OR SLIGHTLY HIGHER THAN FRIDAY...THANKS TO AN
AREA OF CLOUDS/MOISTURE MOVING ACROSS THE STATE. RH VALUES WILL BE
AROUND 50 ACROSS LEEWARD SECTIONS...ABOVE THE RED FLAG THRESHOLD OF
45 PERCENT. WIND SPEEDS AND THE KBDI ALSO REMAIN BELOW CRITICAL
VALUES.
MARINE
WAVE HEIGHTS AT THE KILO NALU BUOY HAVE CONTINUED TO SLOWLY LOWER
THROUGH THE NIGHT. 06Z WAVEWATCH III SHOWS THIS DIMINISHING TREND
CONTINUING THROUGH THE WEEKEND. SURF ALONG SOUTH FACING SHORES WILL
REMAIN BELOW ADVISORY LEVELS ON SATURDAY...AND DIMINISH FURTHER
SUNDAY AND MONDAY.
AS THE SURFACE HIGH BUILDS ACROSS THE EASTERN PACIFIC THROUGH EARLY
NEXT WEEK...THE BROAD FETCH OF STRONGER WINDS WILL GENERATE A
MODERATE SHORT PERIOD EASTERLY TRADE SWELL. THIS SWELL WILL BE
GREATEST MID/LATE WEEK. WITH THE STRONGER PRESSURE GRADIENT...WINDS
MAY ALSO REACH SMALL CRAFT LEVELS BY MID-WEEK...INITIALLY ACROSS THE
WINDIER CHANNELS.
AVIATION
A MORE TYPICAL TRADE WIND CLOUD/SHOWER PATTERN IS EXPECTED TODAY.
VFR CONDITIONS WILL AGAIN BE THE RULE...WITH THE TYPICAL EXCEPTION
OF MVFR AT PHNY DUE TO THE HIGHER ELEVATION OF THE AIRPORT. SHOWERS
MAY DROP CEILINGS DOWN TO MVFR ACROSS WINDWARD SECTIONS...BUT THEY
WILL BE BRIEF AND PASSING.
HFO WATCHES/WARNINGS/ADVISORIES
NONE.
BRAVENDER
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