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Hawaiian Islands Synoptic Discussion and Guidance

829
FXHW60 PHFO 080158
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
358 PM HST TUE JUL 7 2015

.SYNOPSIS...
TRADE WINDS WILL GRADUALLY INCREASE THROUGH WEDNESDAY AS HIGH PRESSURE
BUILDS FAR NORTH OF THE STATE. LOW CLOUDS AND PASSING SHOWERS WILL
FAVOR WINDWARD AND MAUKA AREAS AND MAY REACH THE LEE AREAS OF THE
SMALLER ISLANDS AS THE WINDS STRENGTHEN. A DISTURBANCE EAST SOUTHEAST
OF THE STATE WILL LIKELY DEVELOP INTO A TROPICAL DEPRESSION IN THE
SHORT TERM AND MAY AFFECT HAWAII FRIDAY INTO THIS WEEKEND.

&&

.DISCUSSION...
TRADE WIND WEATHER CONTINUES ACROSS THE ISLANDS THIS AFTERNOON...WITH
PASSING LOW CLOUDS AND SHOWERS AFFECTING MAINLY WINDWARD AND MAUKA AREAS.
VISIBLE SATELLITE IMAGERY SHOWS AN AREA OF LOW CLOUDS WITH LIGHT TO
MODERATE SHOWERS IMPACTING THE WINDWARD PORTIONS OF MAUI COUNTY.
THESE CLOUDS WILL SPREAD WESTWARD TONIGHT AND BRING INCREASED
CLOUDINESS AND SHOWERS TO THE WINDWARD SIDES OF OAHU AND KAUAI
TONIGHT AND WEDNESDAY.

SUBTROPICAL HIGH PRESSURE FAR NORTH OF THE STATE IS DRIVING THE
TRADE WINDS ACROSS THE HAWAIIAN ISLANDS. ANTICIPATING THE HIGH
PRESSURE TO STRENGTHEN SLIGHTLY THROUGH WEDNESDAY AND MAINTAIN ON
THURSDAY. TRADE WINDS WILL STRENGTHEN TO FRESH BREEZES TONIGHT AND
TOMORROW AND COULD PUSH A FEW SHOWERS ONTO THE LEEWARD SIDES
OF THE SMALLER ISLANDS TONIGHT AND WEDNESDAY...BUT SHOULD REMAIN
LIGHT. MOST OF CLOUDS AND SHOWERS WILL FOCUS OVER THE WINDWARD
SLOPES UNDER THE TRADE WIND REGIME.

THE FORECAST GETS A BIT MORE COMPLICATED AFTER THURSDAY WITH SEVERAL
SCENARIOS THAT COULD DEVELOP DEPENDING UPON THE PROGRESSION OF
TROPICAL DISTURBANCE 96E LOCATED 1075 MILES EAST-SOUTHEAST OF THE
BIG ISLAND. 96E IS FORECAST TO DEVELOP INTO A TROPICAL DEPRESSION
IN THE SHORT TERM AND MOVE TOWARDS THE WEST-NORTHWEST THROUGH
THIS WEEKEND.

MODELS SHOW THIS FEATURE TRACKING PARALLEL AND NORTH OF THE ISLAND
CHAIN FROM FRIDAY THROUGH THE WEEKEND WHILE WEAKENING TO AN OPEN
TROPICAL WAVE. IF THIS SCENARIO PLAYS OUT...WE ANTICIPATE THE
TRADE WINDS QUICKLY WEAKENING LATE THURSDAY OR EARLY FRIDAY AS THE
LOW MOVES BETWEEN US AND THE SUBTROPICAL HIGH. 96E WILL ALSO PUSH
VERY MOIST TROPICAL AIR OVER HAWAII WHICH WILL MAKE CONDITIONS
VERY HUMID THIS WEEKEND. AFTERNOON HEAT INDICIES COULD PEAK AT
NEARLY 100 DEGREES IN SOME LOW LYING COASTAL AREAS THIS WEEKEND.
THE MOISTURE...AND INSTABILITY TRIGGERED BY 96E COULD RESULT IN
LOCALIZED ACTIVE SHOWERS AND THUNDERSTORMS. A MORE SOUTHERLY TRACK
OF THIS SYSTEM WILL BRING MORE WIND IMPACTS AND LESS
HUMIDITY...AND WE CANNOT BE COMPLETELY CONFIDENT WITH WHICH
SCENARIO WILL ACTUALLY PLAY OUT.

TRADE WINDS WILL BUILD BACK IN EARLY NEXT WEEK AS THE SYSTEM MOVES
AWAY FROM THE AREA.

&&

.AVIATION...
AIRMET TANGO FOR LOW LEVEL TURB REMAINS POSTED FOR ALL AREAS OVER
AND SOUTH THROUGH WEST OF THE TERRAIN. THE TRADES WILL REMAIN
MODERATE TO FRESH AND GUSTY THROUGH THE NEXT FEW PERIODS.

CLOUDS AND SHOWERS WILL FAVOR WINDWARD AND MOUNTAIN SLOPES. EXPECT
SOME SHOWERS TO BE ENHANCED...ESPECIALLY ALONG THE CENTRAL ISLAND
SLOPES AS A SWATH OF MOISTURE PUSHES WEST. THE ENHANCED MOISTURE
SHOULD REACH OAHU THIS EVENING AND KAUAI BY EARLY WEDNESDAY MORNING.
THUS FAR TODAY...MOST CIGS HAVE STAYED VFR AND A MOUNTAIN
OBSCURATION AIRMET HAS NOT BEEN NEEDED. THIS WILL BE MONITORED AS
THE MOISTURE SPREADS OVER THE CENTRAL ISLANDS...AND DIURNAL TRENDS
AIDE IN ENHANCING SHOWERS FURTHER. MVFR CONDITIONS ARE HIGHLY LIKELY
ALONG WINDWARD SLOPES OF MAUI MOLOKAI AND OAHU TONIGHT AND POSSIBLY
KAUAI WEDNESDAY MORNING. SOME SHOWERS WILL BLOW OVER INTO LEEWARD
AREAS...OTHERWISE EXPECT VFR CONDITIONS.


&&

.MARINE...
SURF ASSOCIATED WITH THE CURRENT SOUTHERLY SWELLS WILL REMAIN ABOVE
ADVISORY HEIGHTS THROUGH WEDNESDAY...THUS THE HIGH SURF ADVISORY FOR
SOUTH FACING SHORES CONTINUES. THE CURRENT SOUTHERLY SWELLS WILL
DECLINE ON THURSDAY. REINFORCING SOUTHWEST SWELLS ARE EXPECTED TO
BOOST SURF HEIGHTS AGAIN ALONG SOUTH FACING SHORES FROM FRIDAY
THROUGH THIS WEEKEND...THOUGH SURF HEIGHTS ALONG SOUTH FACING
SHORES ARE EXPECTED TO STAY BELOW ADVISORY LEVEL.

A SMALL CRAFT ADVISORY /SCA/ IS IN EFFECT THROUGH WEDNESDAY FOR
THE TYPICAL WINDY COASTAL ZONES AROUND MAUI COUNTY AND THE BIG
ISLAND DUE TO THE WINDS. THE SCA WILL LIKELY NEED TO BE EXTENDED INTO
THURSDAY AS THE PRESSURE GRADIENT ACROSS HAWAII TIGHTENS DUE TO
THE PRESENCE OF A TROPICAL DISTURBANCE NEARING THE HAWAIIAN
ISLANDS. LOW CONFIDENCE FOR WIND IMPACTS OF THIS DISTURBANCE FRIDAY
INTO THE WEEKEND.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST WEDNESDAY FOR SOUTH FACING
SHORES OF NIIHAU KAUAI OAHU MOLOKAI LANAI KAHOOLAWE MAUI AND BIG
ISLAND.

SMALL CRAFT ADVISORY UNTIL 6 PM HST WEDNESDAY FOR MAALAEA BAY-
PAILOLO CHANNEL-ALENUIHAHA CHANNEL-BIG ISLAND LEEWARD WATERS-BIG
ISLAND SOUTHEAST WATERS.


&&

$$

DISCUSSION/MARINE...FOSTER
AVIATION...EATON


Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office