Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 040635
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
835 PM HST TUE MAY 3 2016

.SYNOPSIS...
BREEZY TRADE WINDS WILL PERSIST ACROSS THE ISLAND CHAIN INTO
WEDNESDAY. LOW CLOUDS AND SHOWERS CARRIED BY THE TRADES WILL
FAVOR WINDWARD AND MAUKA SECTIONS. A COLD FRONT WILL APPROACH
KAUAI FROM THE NORTHWEST AND CAUSE OUR WINDS TO WEAKEN AND VEER
FROM THE SOUTHEAST ON THURSDAY AND FRIDAY. THIS WILL ALLOW SEA
BREEZE CONVERGENCE TO TRIGGER CLOUD BUILD UPS AND LOCALLY HEAVY
AFTERNOON SHOWERS ACROSS ISLAND INTERIORS. 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 1032 MB SURFACE HIGH LOCATED NEAR 37N 145W HAS A RIDGE EXTENDING
SOUTHWEST TO A POINT ABOUT 575 MILES NORTH OF LIHUE. THE TIGHT
PRESSURE GRADIENT SOUTH OF THESE FEATURES IS MAINTAINING LOCALLY
BREEZY TRADE WINDS ACROSS THE STATE. MID-LEVEL RIDGING IN THE
VICINITY OF THE ISLANDS IS PROVIDING STABLE ATMOSPHERIC CONDITIONS.
SATELLITE IMAGERY AND RADAR REFLECTIVITY DATA SHOW A NEARLY EAST
TO WEST ORIENTED BAND OF BROKEN LOW CLOUDS AND SCATTERED SHOWERS
ASSOCIATED WITH AN OLD FRONT IN THE VICINITY OF THE NORTHERN
ISLANDS...INCLUDING OAHU. MOST OF THESE CLOUDS AND SHOWERS HAVE
BEEN OVER THE WINDWARD SIDES OF THESE ISLANDS. HOWEVER...THE
GUSTY TRADE WINDS HAVE ALSO BEEN CARRYING SOME LIGHT SHOWERS OVER
TO LEEWARD SIDES OF THESE ISLANDS.

THIS BAND OF LOW CLOUDS AND SHOWERS IS EXPECTED TO SAG SLOWLY
SOUTHWARD OVER THE REST OF THE ISLAND CHAIN TONIGHT. AT THE SAME
TIME...THE SHOWERS ARE ALSO LIKELY TO INCREASE IN COVERAGE AS WE
HEAD INTO THE DIURNAL MAXIMUM LATER TONIGHT. THE BREEZY TRADES
KEEP THE SHOWERS MOVING ACROSS THE WINDWARD AND MAUKA AREAS...BUT
SOME OF THE SHOWERS WILL CONTINUE TO MOVE OVER TO LEEWARD SIDES
OF THE SMALLER ISLANDS.

THE TRADE WINDS ARE EXPECTED TO BEGIN TO WEAKEN FROM WEDNESDAY
AFTERNOON THROUGH WEDNESDAY NIGHT AS A COLD FRONT...WHICH IS
CURRENTLY NEAR MIDWAY ATOLL...APPROACHES KAUAI FROM THE NORTHWEST.
THIS WILL CAUSE THE SURFACE HIGH AND ITS ASSOCIATED RIDGE TO
WEAKEN...AND LOOSEN THE PRESSURE GRADIENT OVER THE STATE. AS A
RESULT...THE SURFACE WINDS WILL WEAKEN AND VEER OUT OF THE
SOUTHEAST FROM LATE WEDNESDAY NIGHT THROUGH FRIDAY. THIS WEAKER
WIND REGIME WILL ALLOW LOCAL AFTERNOON SEA BREEZE AND NIGHTTIME
LAND BREEZE CIRCULATIONS TO DEVELOP OVER LEEWARD AND INTERIOR
SECTIONS OF MOST ISLANDS. ENHANCED MOISTURE AND ATMOSPHERIC
INSTABILITY ARE ALSO EXPECTED ALONG AND AHEAD OF THE FRONT. THE
CONVERGENCE OF SEA BREEZES OVER THE ISLANDS WILL PRODUCE
CONVECTIVE AFTERNOON CLOUD BUILD UPS AND SCATTERED SHOWERS. SOME
OF THESE SHOWERS MAY PRODUCE LOCALLY HEAVY RAINFALL ON ALL ISLAND
INTERIORS BOTH THURSDAY AND FRIDAY AFTERNOONS.

THE FORECAST MODELS APPEAR TO AGREE THAT THE FRONT WILL WEAKEN TO
A SURFACE TROUGH AS IT REACHES KAUAI FRIDAY. AS THIS TROUGH MOVES
FROM 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...
HIGH PRESSURE NE OF STATE WILL MAINTAIN MODERATE TO BREEZY TRADES
ACROSS THE ISLANDS. WINDS WILL STAY STRONG ENOUGH SUCH THAT
AIRMET TANGO FOR MECHANICAL TURBULENCE OVER THE IMMEDIATE LEE
AREAS OF THE MOUNTAINS WILL CONTINUE AT LEAST THROUGH EARLY
WEDNESDAY MORNING.

AN ALMOST EAST TO WEST ORIENTED BAND OF SHOWERY LOW CLOUDS IS
AFFECTING MAINLY OAHU THIS EVENING...BRINGING OCNL MVFR CEILING AND
SHRA TO THE WINDWARD AREAS OF THAT ISLAND. AS THIS BAND IS EXPECTED
TO LINGER THROUGH REST OF THE EVENING INTO EARLY WEDNESDAY
MORNING...EXPECT THE AIRMET SIERRA FOR MOUNTAIN OBSCURATION TO
CONTINUE FOR THE NORTH THROUGH EAST PARTS OF OAHU. FURTHERMORE...
THIS BAND MAY MEANDER...RESULTING IN SOME OF THE CLOUDS REACHING
THE WINDWARD AREAS OF THE OTHER ISLANDS AS WELL. THEREFORE THERE
IS A CHANCE THAT THE AREAL COVERAGE OF THIS AIRMET MAY NEED TO BE
EXPANDED.

OTHERWISE...MAINLY VFR CONDITIONS ARE EXPECTED FOR REST OF THE
AREAS.

&&

.MARINE...
A SMALL CRAFT ADVISORY /SCA/ REMAINS POSTED FOR THE TYPICALLY
WINDY WATERS ADJACENT TO THE ISLANDS OF MAUI COUNTY AND THE BIG
ISLAND...INCLUDING THE KAIWI CHANNEL...THROUGH TONIGHT. SCA
CONDITIONS FOR ALL BUT THE KAIWI CHANNEL ARE LIKELY TO PERSIST ON
WEDNESDAY. THEREFORE...THE SCA IS BEING EXTENDED THROUGH WEDNESDAY
AFTERNOON. BY WEDNESDAY EVENING...THE WINDS ARE EXPECTED TO
DECREASE AND VEER OUT OF THE SOUTHEAST. THESE WEAKER WINDS WILL
PERSIST 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 LONG PERIOD WEST-NORTHWEST SWELL IS EXPECTED TO ARRIVE
LATER TONIGHT...AND CONTINUE THROUGH FRIDAY. A REINFORCING NORTH-
NORTHWEST SWELL WILL PERSIST THROUGH THE WEEKEND. SOUTH SWELLS
WILL MAINTAIN BACKGROUND SURF ALONG SOUTH FACING SHORES THROUGH
THURSDAY. A LONG PERIOD SOUTH SWELL WILL ARRIVE FRIDAY...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. ON THE EAST
FACING SHORES...THE BREEZY TRADE WINDS WILL CONTINUE TO PRODUCE
CHOPPY SURF THROUGH WEDNESDAY...THEN TAPER OFF THROUGH THE END OF
THE WEEK AS THE WINDS WEAKEN AND VEER OUT OF THE SOUTHEAST.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 PM HST WEDNESDAY EVENING FOR MAALAEA
BAY...THE WATERS SOUTH OF THE BIG ISLAND...AND THE PAILOLO AND
ALENUIHAHA CHANNELS.

SMALL CRAFT ADVISORY UNTIL 6 AM HST WEDNESDAY FOR THE KAIWI
CHANNEL

&&

$$

DISCUSSION/MARINE...HOUSTON
AVIATION...HUI


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