259
FXHW60 PHFO 210630
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI NOV 20 2009
SYNOPSIS
TRADE WINDS WILL CONTINUE THROUGH THE WEEKEND AS HIGH PRESSURE
REMAINS FAR NORTH OF THE ISLANDS. SHOWERS WILL BE FOCUSED MAINLY
ON WINDWARD AND MOUNTAIN SLOPES...WITH A FEW SHOWERS LEEWARD.
TRADES WILL WEAKEN SLIGHTLY EARLY NEXT WEEK.
DISCUSSION
RAINFALL HAS BEEN SPARSE ACROSS THE STATE TODAY WITH THE HAWAII
RAIN GAGE NETWORK ONLY SHOWING LIGHT TO MODERATE RAINFALL ON THE
WINDWARD SIDE OF THE BIG ISLAND. GAGES ALONG THE NORTHEAST LOWER
SLOPES OF THE BIG ISLAND RANGED BETWEEN A TENTH TO A HALF INCH
OVER THE 12-HOUR PERIOD FROM 5 AM TO 5 PM. SOME OF THE HIGHER
ELEVATIONS ON WINDWARD MAUI ALSO RECEIVED SIMILAR TOTALS WHILE THE
REST OF THE STATE STAYED DRY. THE DRY WEATHER IS EXPECTED TO
CONTINUE TONIGHT...AND THE POP GRIDS HAVE BEEN SUMMARILY DECREASED
ACROSS THE STATE TO REPRESENT A DRY TRADE WEATHER REGIME OF SCATTERED
SHOWERS AND CLOUDY SKIES OVER WINDWARD AREAS...WITH MOSTLY CLEAR
SKIES AND A SMALL CHANCE OF SHOWERS OVER LEEWARD LOCATIONS.
BOTH AFTERNOON SOUNDING FROM LIHUE AND HILO DEPICT THE DRY
ATMOSPHERE WITH PRECIPITABLE WATER VALUES NEAR ONE INCH...WHICH IS
IN STARK CONTRAST TO THE TWO INCH PW VALUES DURING LAST WEEKEND/S
FLOOD EVENT. PW VALUES ARE EXPECTED TO SLOWLY INCREASE OVER THE
WEEKEND AND A MORE CLIMATOLOGICAL TRADE WIND WEATHER PATTERN
SHOULD RESULT...IN OTHER WORDS...INCREASING SHOWERS TO NORMAL
AMOUNTS.
A 1028 MB HIGH PRESSURE FAR NORTH OF THE STATE IS MAINTAINING THE
FRESH TO STRONG TRADE WINDS ACROSS THE ISLANDS. STORM SYSTEMS
RACING ACROSS THE NORTH PACIFIC ARE FORECAST TO PUSH THE HIGH TOWARD
THE EAST AND ITS ASSOCIATED SURFACE RIDGE SOUTH OVER THE
WEEKEND AND NEXT WEEK... THEREBY RELAXING THE PRESSURE GRADIENT OVER
THE STATE AND DECREASING THE TRADE WINDS INTO THE MODERATE TO
FRESH RANGE EARLY NEXT WEEK.
THE GFS AND ECMWF BOTH SHOW A WEAK COLD FRONT APPROACHING KAUAI
TUESDAY NIGHT AND WEDNESDAY...BUT NEVER REACHING THE GARDEN ISLE.
THE MODELS DO SHOW TROPICAL MOISTURE BEING DRAWN UP FROM THE SOUTH
IN RESPONSE TO THE FRONT...INCREASING PW VALUES NEAR THE BIG
ISLAND TUESDAY NIGHT...AND THEN MAUI COUNTY AND OAHU ON WEDNESDAY.
THIS SCENARIO WOULD BRING INCREASING SHOWERS TO WINDWARD AREAS OF
THOSE ISLANDS. HOWEVER...PREVIOUS MODEL RUNS HAD SHOWN A SURFACE
TROUGH OR EVEN A WEAK SURFACE LOW ACCOMPANYING THIS MOISTURE...SO
THE MODELS HAVE BEEN TRENDING TOWARD A WEAKER FEATURE OVER THE
PAST FEW DAYS. THE WEAKENING TREND DOES NOT BODE MUCH CONFIDENCE
IN THIS FEATURE...SO THE FORECAST REMAINS WITH CLIMO TRADE WIND
WEATHER.
MARINE
A LARGE NORTHWEST SWELL IS EXPECTED TO BEGIN FILLING IN SATURDAY
NIGHT...LIKELY REACHING ADVISORY LEVELS SUNDAY AND MONDAY THEN
SLOWLY LOWERING INTO TUESDAY. A LARGER NORTHWEST SWELL IS EXPECTED
TO FILL IN TUESDAY NIGHT...AND PEAK LATE WEDNESDAY OR WEDNESDAY
NIGHT.
HFO WATCHES/WARNINGS/ADVISORIES
SMALL CRAFT ADVISORY UNTIL 5 PM HST SUNDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.
SMALL CRAFT ADVISORY UNTIL 6 AM HST SATURDAY FOR KAUAI CHANNEL-
KAIWI CHANNEL.
MORRISON
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