Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 040203
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
403 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...WITH AN INCREASE IN SHOWERS
LATER TONIGHT. A COLD FRONT WILL APPROACH KAUAI FROM THE
NORTHWEST AND CAUSE WINDS TO WEAKEN AND VEER FROM THE SOUTHEAST
ON THURSDAY AND FRIDAY. THIS WILL ALLOW SEA BREEZE CONVERGENCE TO
TRIGGER AFTERNOON SHOWERS ACROSS ISLAND INTERIORS. THE FRONT IS
EXPECTED TO WEAKEN AS IT REACHES KAUAI...WITH LOCALLY BREEZY
NORTHEASTERLY TRADE WINDS BUILDING BEHIND IT THIS WEEKEND. TRADE
WINDS WILL CONTINUE INTO NEXT WEEK AND WILL DRIVE PRIMARILY
WINDWARD AND MAUKA SHOWERS.

&&

.DISCUSSION...
A 1032 MB SURFACE HIGH IS LOCATED NEAR 36N147W. THE TIGHT
PRESSURE GRADIENT BETWEEN THE HIGH AND EQUATORIAL LOW SOUTH OF
HAWAII IS RESULTING IN MODERATE TO FRESH TRADE WINDS ACROSS THE
STATE. MID-LEVEL RIDGING IN THE VICINITY OF THE ISLANDS IS
PROVIDING STABLE ATMOSPHERIC CONDITIONS. 00Z SOUNDINGS SHOW
INVERSIONS IN PLACE OVER THE STATE AT 6000 FEET WITH PRECIPITABLE
WATER VALUES IN THE 1.1 TO 1.2 INCH RANGE. VISIBLE SATELLITE
IMAGERY AND RADAR REFLECTIVITY DATA SHOW SCATTERED TO LOCALLY
BROKEN LOW CLOUDS AND SCATTERED SHOWERS FROM AN OLD FRONT
STREAMING TOWARD MOST OF THE SMALLER ISLANDS LATE THIS AFTERNOON.
MOST OF THESE CLOUDS AND SHOWERS HAVE BEEN DIRECTED OVER THE
WINDWARD SIDES OF KAUAI AND OAHU TODAY.

ANTICIPATING THE SHOWER BAND TO SLOWLY SAG SOUTHWARD TONIGHT WITH
THE BREEZY TRADES KEEP THE SHOWERS MOVING ACROSS THE WINDWARD AND
MAUKA AREAS. THE SHOWERS ARE LIKELY TO INCREASE IN COVERAGE AS WE
HEAD INTO THE DIURNAL MAXIMUM LATE TONIGHT. SOME OF THE SHOWERS
WILL PASS OVER TO LEEWARD SIDES OF THE SMALLER ISLANDS.

THE TRADE WINDS WILL BEGIN TO WEAKEN WEDNESDAY AND WEDNESDAY
NIGHT AS A COLD FRONT APPROACHES FROM THE NORTHWEST. THE EARLIER
MENTIONED HIGH PRESSURE SYSTEM WILL MOVE AWAY...LOOSENING THE
PRESSURE GRADIENT OVER THE STATE. AS A RESULT...THE WIND FLOW
WEAKEN AND VEER OUT OF THE SOUTHEAST THURSDAY AND FRIDAY...AND
ALLOW DAYTIME SEA BREEZES AND NIGHTTIME LAND BREEZES TO DEVELOP
OVER LEEWARD AND INTERIOR SECTIONS. THE CONVERGENCE OF SEA
BREEZES OVER THE ISLANDS WILL PRODUCE CONVECTIVE AFTERNOON CLOUDS
AND SHOWERS. HAVE ADDED LOCALLY HEAVY RAIN TO THE FORECAST FOR ALL
ISLAND INTERIORS BOTH THURSDAY AND FRIDAY AFTERNOONS GIVEN THE
EXPECTED INCREASE IN MOISTURE AND INSTABILITY ALONG AND AHEAD OF
THE FRONT.

THE FRONT WILL WEAKEN AS IT REACHES KAUAI FRIDAY FOLLOWED BY
NORTHEASTERLY TRADES SPREADING FROM WEST TO EAST ACROSS THE ISLAND
CHAIN THIS WEEKEND. THESE NORTHEASTERLY WINDS MAY BE LOCALLY
BREEZY...ESPECIALLY OVER THE WESTERN END OF THE STATE ON
SATURDAY...THEN WEAKEN BACK TO MODERATE BREEZES NEXT WEEK. THE
REMNANT MOISTURE ASSOCIATED WITH THE WEAKENING FRONT WILL ALSO
PRODUCE AN EXTENDED PERIOD OF WET TRADE WIND SHOWERS FROM SUNDAY
INTO THE MIDDLE OF NEXT WEEK. BOTH THE LONG RANGE GFS AND ECMWF
MODELS INDICATE THE TRADES WILL FOCUS SHOWERS OVER THE WINDWARD
SIDES OF THE ISLANDS FROM OAHU TO THE BIG ISLAND.


&&

.AVIATION...
MODERATE TO BREEZY TRADES TO CONTINUE INTO WEDNESDAY DUE TO HIGH
PRESSURE NORTH OF THE ISLANDS. A BATCH OF SHOWERY LOW CLOUDS IS
MOVING OVER OAHU THIS AFTERNOON...AND WILL LIKELY MOVE OVER PARTS OF
KAUAI TONIGHT. WHILE VFR CONDITIONS ARE EXPECTED TO PREVAIL...SOME
MVFR CONDITIONS ARE POSSIBLE IN CLOUDS AND SHOWERS.

AIRMET SIERRA WAS POSTED THIS MORNING FOR NORTH THROUGH EAST PARTS
OF MOLOKAI AND OAHU AS THE CLOUDS AND SHOWERS MOVED OVER. ANTICIPATE
DROPPING MOLOKAI LATER THIS AFTERNOON FROM THE AIRMET...AND POSSIBLY
OAHU. KAUAI MAY NEED TO BE ADDED AS THE BAND MOVES IN TO THE GARDEN
ISLE.

AIRMET TANGO CONTINUES FOR MECHANICAL TURBULENCE TO THE LEE OF THE
MOUNTAINS. EXPECT THESE CONDITIONS TO CONTINUE THROUGH AT LEAST
TONIGHT WITH THE MODERATE TO BREEZY TRADE WINDS.


&&

.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 OR MOST OF THESE AREAS ARE LIKELY TO PERSIST
ON WEDNESDAY BEFORE WINDS DECREASE AND VEER OUT OF THE SOUTHEAST
STARTING WEDNESDAY NIGHT. FORECAST MODELS SHOW INCREASING
NORTHEASTERLY TRADE WINDS SPREADING FROM WEST TO EAST OVER THE
AREA THIS WEEKEND. THESE WINDS MAY REACH THE SCA CRITERIA NEAR
KAUAI ON SATURDAY.

A SMALL LONG PERIOD WEST NORTHWEST SWELL WILL 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...WE ARE EXPECTED TO
STAY BELOW THE HIGH SURF ADVISORY CRITERIA. ON THE EAST FACING
SHORES...THE BREEZY TRADE WINDS WILL CONTINUE TO PRODUCE CHOPPY
SURF THROUGH WEDNESDAY...THEN TAPER OFF AS THE WINDS WEAKEN.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY UNTIL 6 AM HST WEDNESDAY FOR KAIWI CHANNEL-
MAALAEA BAY-PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND
LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.


&&

$$

DISCUSSION/MARINE...FOSTER
AVIATION...M BALLARD


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