Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 050211
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
411 PM HST WED MAY 4 2016

.SYNOPSIS...
CLOUDY SKIES AND SHOWERS TO CONTINUE THROUGH AT LEAST THE EVENING
HOURS...AND POSSIBLY ALL NIGHT FOR WINDWARD AREAS OF OAHU AND
KAUAI. A COLD FRONT APPROACHING THE REGION FROM THE NORTHWEST WILL
CAUSE WINDS TO WEAKEN AND VEER FROM THE SOUTHEAST TONIGHT THROUGH
FRIDAY. THIS WILL ALLOW SEA BREEZE CONVERGENCE TO TRIGGER CLOUD
BUILD UPS AND LOCALLY HEAVY AFTERNOON SHOWERS ACROSS ISLAND
INTERIORS THURSDAY AND FRIDAY. THE FRONT IS EXPECTED TO WEAKEN TO
A SURFACE TROUGH AS IT REACHES KAUAI FRIDAY. LOCALLY BREEZY
NORTHEASTERLY TRADE WINDS WILL FILL IN BEHIND THIS TROUGH AS IT
MOVES ACROSS THE ISLAND CHAIN THIS WEEKEND.

&&

.DISCUSSION...
A 1031 MB SURFACE HIGH LOCATED NEAR 36N142W HAS A RIDGE EXTENDING
WEST SOUTHWEST TO A POINT ABOUT 450 MILES NORTH OF LIHUE...AND IS
SLOWLY MOVING AWAY TO THE NORTHEAST. MEANWHILE...A COLD FRONT
LOCATED ABOUT 900 MILES TO THE WEST NORTHWEST OF KAUAI IS
APPROACHING THE ISLANDS. THE MOVEMENT OF THESE TWO FEATURES WILL
CAUSE THE TRADES TO WEAKEN AND VEER SOUTHEAST TONIGHT.

CONDITIONS ALOFT ARE MOSTLY STABLE AT THIS TIME DUE TO MIDLEVEL
RIDGING. 00Z SOUNDINGS SHOW SLIGHTLY ELEVATED INVERSIONS OF AROUND
9000 FEET AT LIHUE AND HILO THIS AFTERNOON. THE SLIGHTLY HIGHER
INVERSIONS ARE THE RESULT OF A WEAK TROUGH AT THE UPPER LEVELS
JUST WEST OF THE STATE...WHICH WILL PASS BY TONIGHT. PRECIPITABLE
WATER VALUES ARE AROUND 1.2 TO 1.4 INCHES...AVERAGE TO SLIGHTLY
ABOVE AVERAGE FOR MAY. THE CURRENT SATELLITE IMAGERY AND RADAR
REFLECTIVITY DATA SHOW MOSTLY CLOUDY SKIES OVER MOST OF THE STATE
WITH NUMEROUS SHOWERS PASSING OVER THE SMALLER ISLANDS. MOST OF
THE SHOWERS ARE AFFECTING THE WINDWARD SIDES OF THE ISLANDS...BUT
MANY OF THEM ARE ALSO REACHING THE LEEWARD SIDES. THE BIG
ISLAND...WHILE CLOUDY...HAS SEEN LESS RAIN THAN THE OTHER ISLANDS.

EXPECT THE SHOWERS TO CONTINUE THROUGH AT LEAST THE EVENING
HOURS...AND POSSIBLY ALL NIGHT FOR WINDWARD AREAS OF OAHU AND
KAUAI. AS WE TRANSITION FROM TRADES TO A LIGHTER SOUTHEAST
FLOW...THE CLOUDS AND SHOWERS WILL BEGIN TO SHIFT OFF TO THE WEST
NORTHWEST AND MAY PROVIDE A BRIEF DRYING PERIOD THURSDAY MORNING.

AFTERNOON SEA BREEZE AND NIGHTTIME LAND BREEZE CIRCULATIONS WILL DEVELOP
OVER LEEWARD AND INTERIOR SECTIONS OF THE ISLANDS FOR THURSDAY AND
FRIDAY. ENHANCED MOISTURE VALUES AND SLIGHT ATMOSPHERIC INSTABILITY
ARE ALSO EXPECTED ALONG AND AHEAD OF THE APPROACHING FRONT. THE
CONVERGENCE OF LOCAL SEA BREEZE CIRCULATIONS OVER THE ISLANDS WILL
PRODUCE CONVECTIVE AFTERNOON CLOUD BUILD UPS AND SHOWERS. SOME
OF THESE SHOWERS MAY PRODUCE LOCALLY HEAVY RAINFALL OVER THE
ISLANDS ON THURSDAY AND FRIDAY AFTERNOONS. IN ADDITION TO THE
INTERIOR SECTIONS OF THE ISLANDS BEING THE MAIN AREA OF CONCERN
WITH THE AFTERNOON SHOWERS...LOCAL HIGH RESOLUTION MODELS PREDICT
THE CONVECTION TO CONCENTRATE ACROSS THE NORTHERN SIDES OF THE
ISLANDS THURSDAY...AND THEN SOUTHERN SIDES OF KAUAI AND OAHU
FRIDAY.

THE FORECAST MODELS APPEAR TO AGREE THAT THE FRONT WILL WEAKEN TO
A SURFACE TROUGH AS IT REACHES KAUAI FRIDAY. AS THIS TROUGH MOVES
ACROSS THE ISLAND CHAIN...NORTHEASTERLY TRADES WILL SPREAD FROM
WEST TO EAST ACROSS THE STATE THIS WEEKEND. THESE NORTHEASTERLY
WINDS MAY BE LOCALLY BREEZY...ESPECIALLY OVER THE WESTERN END OF
THE STATE ON SATURDAY. THE WINDS WILL EVENTUALLY WEAKEN TO
MODERATE BREEZES FROM SUNDAY INTO NEXT WEEK. THE REMNANT MOISTURE
ASSOCIATED WITH THE FORMER FRONT/TROUGH WILL ALSO LIKELY PRODUCE
AN EXTENDED PERIOD OF WET TRADE WIND CONDITIONS FROM SUNDAY INTO
THE MIDDLE OF NEXT WEEK. BOTH THE LONG RANGE GFS AND ECMWF MODELS
INDICATE THE TRADES WILL FOCUS SHOWERS MAINLY OVER THE WINDWARD
SIDES OF THE ISLANDS FROM OAHU TO THE BIG ISLAND.

&&

.AVIATION...
A SURFACE RIDGE ABOUT 400 NM NORTH OF THE STATE WILL SHIFT SOUTHWARD
TONIGHT...CAUSING THE LOW LEVEL FLOW TO SHIFT OUT OF THE EAST-
SOUTHEAST OVERNIGHT AND THURSDAY. RADAR VAD WINDS AND AFTERNOON
SOUNDINGS HAVE SHOWN A DECREASE IN THE LOW LEVEL FLOW...ALONG WITH
SOME SIGNS OF THE ANTICIPATED SHIFTING FLOW BETWEEN 5000 TO 10000 FT
ACROSS THE WESTERN END OF THE STATE. AS A RESULT...AIRMET TANGO FOR
LOW LEVEL TURB WILL LIKELY BE CANCELED THIS AFTERNOON.

A BAND OF LOW LEVEL MOISTURE MOVING ALONG THE TRADE WIND FLOW IS
HUNG UP OVER THE SMALLER ISLANDS THIS AFTERNOON. THIS MOISTURE WILL
IS EXPECTED TO DIMINISH OVER MAUI COUNTY IN THE NEXT FEW HOURS...
CLEAR OAHU OVERNIGHT...BUT REMAIN FOCUSED NEAR KAUAI THROUGH MUCH OF
THE NIGHT. AIRMET SIERRA FOR MTN OBSC REMAINS IN PLACE FROM MAUI TO
KAUAI AT THIS TIME...AND IT WILL LIKELY BE DROPPED FOR MAUI AND
MOLOKAI LATER THIS AFTERNOON.

&&

.MARINE...
THE SMALL CRAFT ADVISORY /SCA/ HAS BEEN DROPPED FOR ALL ZONES FOR
TONIGHT AS WINDS ARE EXPECTED TO WEAKEN AND VEER OUT OF THE
SOUTHEAST TONIGHT THROUGH FRIDAY. THE FORECAST MODELS CONTINUE TO
SHOW INCREASING NORTHEASTERLY TRADE WINDS SPREADING FROM WEST TO
EAST OVER THE AREA THIS WEEKEND. THESE WINDS MAY BRIEFLY REACH THE
SCA CRITERIA NEAR KAUAI ON SATURDAY.

A SMALL WEST NORTHWEST SWELL HAS ARRIVED IN THE ISLANDS THIS
AFTERNOON AND IS EXPECTED TO PEAK TONIGHT...AND PERSIST THROUGH
FRIDAY. A REINFORCING NORTH NORTHWEST SWELL WILL ARRIVE SATURDAY
AND CONTINUE INTO EARLY NEXT WEEK. SMALL SOUTH SWELLS WILL
MAINTAIN BACKGROUND SURF ALONG SOUTH FACING SHORES THROUGH
THURSDAY. A LONG PERIOD SOUTH SWELL WILL ARRIVE FRIDAY AND PEAK
LATE SATURDAY ABOVE THE SEASONAL SOUTH SWELL AVERAGE...AND THEN
SLOWLY SUBSIDE INTO EARLY NEXT WEEK. WHILE SURF WILL BE
ELEVATED...SURF HEIGHTS ARE EXPECTED TO REMAIN JUST BELOW THE HIGH
SURF ADVISORY CRITERIA ALONG SOUTH FACING SHORES THIS WEEKEND.
ALONG EAST FACING SHORES...THE BREEZY TRADE WINDS WILL CONTINUE TO
PRODUCE CHOPPY SURF TODAY...THEN TAPER OFF THROUGH THE END OF THE
WEEK AS THE WINDS WEAKEN AND VEER OUT OF THE SOUTHEAST.


&&

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

&&

$$

DISCUSSION/MARINE...FOSTER
AVIATION...WROE



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