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FXHW60 PHFO 111930
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
930 AM HST SUN MAY 11 2008

.SYNOPSIS...THE TRADE WINDS WILL GRADUALLY DIMINISH THROUGH
MONDAY...BUT WILL CONTINUE TO DELIVER A FEW CLOUDS AND SHOWERS TO
WINDWARD AREAS. WINDS WILL BECOME LIGHT AND VARIABLE ON TUESDAY...
AND PERSIST THROUGH FRIDAY...AS A RIDGE OF HIGH PRESSURE MOVES OVER
THE ISLANDS. THE LIGHT WINDS WILL MEAN MOSTLY CLEAR AND COOL NIGHTS
AND MORNINGS OVER THE ISLANDS...WITH CLOUDS AND A FEW SHOWERS
DEVELOPING OVER INTERIOR AREAS DURING THE AFTERNOONS. WITH THE LIGHT
WINDS...EXPECT HAZY CONDITIONS...AS VOLCANIC EMISSIONS FROM THE BIG
ISLAND STAGNATE OVER THE STATE.

&&

.DISCUSSION...CURRENTLY MODERATE TO LOCALLY FRESH TRADE WINDS ARE
BRINGING A FEW SHOWER-BEARING CLOUDS TO WINDWARD AREAS...WITH KAUAI
SEEING THE FEWEST SHOWERS SO FAR THIS MORNING. THE TRADES ARE BEING
SUPPORTED BY A 1029 MB HIGH FAR TO THE NORTHEAST...AND ITS
ASSOCIATED RIDGE THAT EXTENDS WESTWARD ALONG 30N. A COLD FRONT IS
FAR NORTHWEST OF THE ISLANDS...WORKING ITS WAY TOWARD THE EAST-
SOUTHEAST. MEANWHILE...THE UPPER ATMOSPHERE OVER THE ISLANDS
FEATURES A TROPICAL UPPER TROPOSPHERIC TROUGH /TUTT/ AXIS...WHICH
EXTENDS FROM 25N 140W TO 17N 180.

THE FRONT FAR TO THE NORTHWEST WILL MAKE LITTLE FURTHER HEADWAY
TOWARDS THE ISLANDS...INSTEAD WORKING EAST ALONG 30N...AS IT/S
PARENT LOW DOES A GYRE OVER THE ALEUTIAN ISLANDS OVER THE NEXT
SEVERAL DAYS. A LOW IS FORECAST TO DEVELOP IN THE NORTHWEST PACIFIC
LATER THIS AFTERNOON...AND DEVELOP FURTHER AS IT MOVES EASTWARD
ALONG 35N THROUGH TOMORROW. FROM TOMORROW THROUGH TUESDAY...
GFS/ECMWF/NOGAPS ARE FORECASTING EXPLOSIVE DEVELOPMENT OF THIS
LOW...AS IT MEETS THE /BOMB/ DEFINITION OF DROPPING MORE THAN 24 MB
IN 24 HOURS. AS THIS IS OCCURRING FAR NORTHWEST AND NORTH OF THE
ISLANDS...A FETCH OF STRONG NORTHWEST WINDS ALONG THE LOW/S WEST
SIDE WILL SEND LARGE NORTHWEST SWELLS TOWARD THE ISLANDS. NOT
UNUSUAL FOR MID-WINTER...BUT A LITTLE UNSEASONABLE FOR MID-MAY.

THE FRONT ASSOCIATED WITH THIS STRONG LOW WILL ADVANCE TOWARD THE
ISLANDS FROM THE NORTHWEST STARTING ON TUESDAY...WITH THE RIDGE TO
OUR NORTH SUBSEQUENTLY WEAKENING AND MOVING SOUTH. THE RIDGE IS
EXPECTED TO MOVE TO A POSITION JUST NORTH OF KAUAI ON TUESDAY...
AND TO THE BIG ISLAND BY WEDNESDAY...WHERE IT WILL REMAIN THROUGH
THURSDAY. THE FRONT WILL BE NEAR KAUAI ON THURSDAY...AND THEN STALL
AND GRADUALLY DISSIPATE THROUGH SUNDAY. WHETHER OR NOT IT DIRECTLY
AFFECTS WEATHER ON KAUAI REMAINS TO BE SEEN...BUT THE FRONT/S CLOSE
PROXIMITY WARRANTS THE SLIGHTLY HIGHER POPS CURRENTLY IN THE
FORECAST FOR KAUAI AND SURROUNDING WATERS. THESE POPS MAY NEED TO
BE TRENDED UPWARD AS THE WEEK UNFOLDS. HIGH PRESSURE WILL SLOWLY
REBUILD TO THE NORTHEAST AS THE FRONT DISSIPATES...WITH TRADE WINDS
WORKING THEIR WAY BACK INTO THE FORECAST NEXT WEEKEND.

UNDER THE LIGHT WIND REGIME...LAND AND SEA BREEZE CIRCULATIONS WILL
DOMINATE ON THE SCALE OF THE ISLANDS...WITH A FEW SHOWERS DEVELOPING
OVER INTERIOR AREAS DURING THE AFTERNOONS AND EVENINGS. A FEW
SHOWERS MAY ALSO DEVELOP NEAR KAUAI IN THE WEAKLY CONVERGENT
SOUTHWEST FLOW AHEAD OF THE APPROACHING FRONT...BUT THE UPPER AIR
PATTERN DOES NOT LOOK TO BE CONDUCIVE TO SUPPORT HEAVY SHOWERS.
THEREFORE...THE FORECAST PROBLEM OF THE UPCOMING WEEK APPEARS TO BE
AIR QUALITY...ESPECIALLY ON THE BIG ISLAND...AS THE INCREASINGLY
STAGNANT FLOW ALLOWS VOLCANIC EMISSIONS FROM THE BIG ISLAND TO POOL
OVER THE ISLANDS...MAKING FOR HAZY CONDITIONS.

&&

.MARINE...MORNING QUIKSCAT PASS SUPPORTS CONTINUATION OF THE SMALL
CRAFT ADVISORY /SCA/...WITH 25 KT OBSERVED SOUTH OF THE BIG ISLAND
AND IN THE ALENUIHAHA CHANNEL. STILL EXPECT THE SCA TO BE TERMINATED
FOR ALL WATERS BY THIS EVENING AS THE TRADES TREND DOWN.

NORTHWEST SWELL WILL SLOWLY BUILD ON WEDNESDAY...THEN MORE STEADILY
ON THURSDAY...WITH OPEN OCEAN SWELL HEIGHTS FORECAST TO PEAK NEAR 10
FEET IN HAWAIIAN WATERS LATE THURSDAY. THIS WILL LIKELY BRING
ADVISORY LEVEL SURF TO NORTH AND WEST FACING SHORES OF MOST
ISLANDS...BUT THE RESPONSIBLE LOW HAS YET TO DEVELOP...SO THE
FORECAST WILL CONTINUE TO NEED FINE-TUNING.

&&

.AVIATION...THE WASHINGTON VOLCANIC ASH ADVISORY CENTER /VAAC/ HAS
DISCONTINUED ADVISORIES FOR EMISSIONS FROM HALEMAUMAU...STATING THAT
THE PLUME CONTAINS MOSTLY STEAM AND GASES...BASED ON INFO FROM
HAWAII VOLCANO OBSERVATORY THAT NOTES MINUSCULE ASH IN COLLECTOR
PLATES UNDER PLUME. WE HAVE THEREFORE TERMINATED VOLCANIC ASH SIGMET
SERIES VICTOR.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY THROUGH TODAY FOR THE PAILOLO AND ALENUIHAHA
CHANNELS...MAALAEA BAY...AND WATERS SOUTH OF THE BIG ISLAND.

&&

$$

BIRCHARD

NWS HFO Office Area Forecast Discussion