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Hawaiian Islands Synoptic Discussion and Guidance

799
FXHW60 PHFO 300651
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
851 PM HST WED OCT 29 2014

.SYNOPSIS...
MODERATE TO LOCALLY FRESH TRADE WINDS WILL CONTINUE TO FOCUS
CLOUDS AND SHOWERS ACROSS WINDWARD AND MOUNTAIN AREAS OVERNIGHT.
A FRONT WILL BRING AN INCREASE IN CLOUDS AND SHOWERS AS IT SLOWLY
MOVES SOUTHWARD ACROSS THE SMALLER ISLANDS THURSDAY AND THURSDAY
NIGHT. LOCALLY HEAVY DOWNPOURS WILL BE POSSIBLE DURING THIS TIME.
TRADE WINDS WILL INCREASE THURSDAY AS STRONG HIGH PRESSURE PASSES
FAR NORTH OF THE STATE. TRADE WINDS WILL DECREASE A NOTCH DURING
THE WEEKEND AS LINGERING MOISTURE FROM THE DISSIPATED FRONT CLEARS
THE STATE.

&&

.DISCUSSION...
SHOWER ACTIVITY HAS REMAINED FOCUSED ACROSS WINDWARD OAHU...
MOLOKAI AND MAUI DURING THE LAST FEW HOURS. SHOWERS HAVE BEEN
RATHER PERSISTENT IN THESE AREAS...BUT MOST OF THE SHOWERS HAVE
BEEN LIGHT TO MODERATE...WHICH COMBINED WITH QUICK MOVEMENT HAS
KEPT RAINFALL AMOUNTS FROM BECOMING TOO HEAVY IN ANY GIVEN
LOCATION. SURFACE ANALYSIS DEPICTS A WEAK FRONT ABOUT 150 MILES
NORTH OF KAUAI...WITH STRONG HIGH PRESSURE CENTERED ABOUT 1200
MILES TO THE NNW. THIS HIGH IS FORCING THE FRONT TO MOVE SLOWLY
SOUTHWARD TOWARD THE STATE. ALOFT...A LONGWAVE TROUGH IS LOCATED
BETWEEN 140W AND 150W....WITH WATER VAPOR IMAGERY INDICATING A
SHORTWAVE DROPPING SOUTHWARD ALONG 160W ALONG THE WEST SIDE OF
THE LARGER TROUGH. MIMIC-TPW IMAGERY INDICATES A STRIPE OF
ENHANCED MOISTURE ALONG THE FRONT...WITH ANOTHER AREA OF HIGHER
MOISTURE SHIFTING SOUTH AND WEST OF THE BIG ISLAND. THE 00Z HILO
SOUNDING REFLECTED THE ADDED MOISTURE PRESENT AT THAT TIME...WITH
A WEAK/ELEVATED INVERSION AND ABOVE NORMAL PWAT OF 1.66 INCHES.
THE 00Z LIHUE SOUNDING REFLECTED MORE TYPICAL CONDITIONS...WITH
A WELL DEFINED INVERSION BASED NEAR 6700 FEET AND BELOW NORMAL
PWAT OF 1.08 INCHES.

OVERNIGHT...SHORT-TERM SATELLITE/RADAR/MODEL TRENDS INDICATE THAT
SHOWER ACTIVITY SHOULD REMAIN ABUNDANT ACROSS WINDWARD AREAS IN
THE CENTRAL PARTS OF THE STATE...POSSIBLY INCREASING ACROSS KAUAI
AS WELL LATE TONIGHT. SOME OF THE SHOWERS WILL SPILL OVER INTO
FAVORED LEEWARD AREAS. SHOWERS SHOULD REMAIN SOMEWHAT MORE LIMITED
ACROSS THE WINDWARD BIG ISLAND. THE EXISTING FORECAST APPEARS TO
BE ON TRACK...AND NO UPDATES ARE PLANNED.

THURSDAY AND THURSDAY NIGHT...THE FRONT WILL MOVE SLOWLY SOUTHWARD
ACROSS THE SMALLER ISLANDS...AS THE STRONG SURFACE HIGH MOVES
EASTWARD WELL TO OUR NORTH. ALTHOUGH LOW LEVEL CONVERGENCE WILL BE
LACKING ALONG THIS FEATURE WITH INCREASING TRADE WIND FLOW IN
PLACE...ENHANCED MOISTURE ALONG WITH INCREASING INSTABILITY DUE TO
A DEVELOPING MID/UPPER LEVEL TROUGH OVERHEAD SHOULD ALLOW FOR SOME
OF THE SHOWERS TO BECOME LOCALLY HEAVY. THE BEST CHANCES FOR HEAVY
DOWNPOURS WOULD APPEAR TO BE ACROSS KAUAI AND OAHU THURSDAY
AFTERNOON AND THURSDAY NIGHT...POSSIBLY SPREADING INTO MAUI COUNTY
THURSDAY NIGHT. LOCALLY DERIVED MOISTURE-STABILITY INDICES
INDICATE THE POTENTIAL FOR ISOLATED THUNDERSTORMS AS WELL THURSDAY
AFTERNOON AND EVENING...MAINLY ACROSS NORTHERN AND WESTERN SECTIONS.
WILL CONSIDER ADDING ISOLATED THUNDER TO THE FORECAST FOR THE NEXT
REGULAR ISSUANCE THURSDAY MORNING.

THE FRONT WILL THEN GRADUALLY DISSIPATE ACROSS THE STATE FRIDAY
THROUGH SATURDAY...WITH THE MID/UPPER TROUGH LINGERING NEAR OR
JUST TO THE SOUTHWEST OF THE AREA. FRESH TRADE WINDS WILL CONTINUE
TO DRIVE SHOWERS INTO WINDWARD AREAS...CARRYING OVER INTO SOME
LEEWARD SECTIONS. A FEW HEAVIER DOWNPOURS WILL REMAIN POSSIBLE AS
WELL DUE TO LINGERING INSTABILITY ALOFT...BUT RAPID SHOWER MOTIONS
SHOULD KEEP MOST RAINFALL AMOUNTS FROM BECOMING EXCESSIVE.

TRADES SHOULD DECREASE SOMEWHAT FROM SUNDAY INTO EARLY NEXT WEEK...
AS THE SURFACE HIGH SHIFTS FURTHER TO THE EAST AND ANOTHER COLD
FRONT MOVES SLOWLY SOUTHEAST TOWARD THE STATE. GENERALLY WOULD
EXPECT A TYPICAL TRADE WIND WEATHER PATTERN TO PREVAIL...ALTHOUGH
SOME OF THE MODELS CONTINUE TO ENTRAIN DEEPER TROPICAL MOISTURE
NORTHWESTWARD ACROSS THE STATE AHEAD OF THE APPROACHING FRONT
EARLY NEXT WEEK...WHICH COULD RESULT IN HIGHER RAIN CHANCES. THE
FRONT MAY EVENTUALLY REACH THE WESTERN END OF THE STATE BY NEXT
WEDNESDAY OR THURSDAY...BUT THE MODELS REMAIN UNCLEAR AT THOSE
TIME RANGES.

&&

.AVIATION...
AN AREA OF BROKEN LOW CLOUDS WITH EMBEDDED SHOWERS WILL BE AFFECTING
PRIMARILY THE CENTRAL ISLANDS DURING THE OVERNIGHT HOURS...
ESPECIALLY THE WINDWARD AND MOUNTAIN AREAS. THESE SHOWERS BEING
GUIDED IN BY THE TRADES CONTAINS MVFR CONDS...AND MAYBE AN ISOLATED
SHOWER OR TWO WITH BRIEF IFR CONDS. ALSO...A FEW OF THESE SHOWERS
WILL VENTURE FURTHER DOWNWIND INTO THE LEEWARD ZONES OF THE SMALLER
ISLANDS. THERE ARE SOME CLOUDS OVER WINDWARD BIG ISLAND BUT THEY
APPEARS TO BE AT THE MID LEVELS ABV 080. ALTHOUGH LEEWARD BIG ISLAND
IS CURRENTLY SHOWER FREE...AN ISOL SHOWER MAY QUICKLY DEVELOP ALONG
THE SHORELINE LATER THIS EVENING. A FEW OF THE SHOWERS AFFECTING
OAHU WILL LIKELY DRIFT OVER TO KAUAI LATER THIS EVENING.

NO AIRMET FOR MTN OBSCURATION AT THE MOMENT BUT WILL BE MONITORED
CLOSELY. LIKEWISE FOR LO LVL TURB WHERE THE TRADE WINDS ARE
EXPECTED TO STRENGTHEN THROUGH 301600 UTC.

&&

.MARINE...
THE EXPECTED NORTH SWELL IS ARRIVING INTO THE HAWAIIAN COASTAL
WATERS THIS EVENING...AS DEPICTED BY INCREASING WAVE HEIGHTS AND
PERIODS AT THE CDIP MOKAPU POINT BUOY. THIS SWELL IS EXPECTED TO
PEAK ON THURSDAY...WITH ANOTHER REINFORCING NORTH SWELL ARRIVING
THURSDAY NIGHT INTO FRIDAY. THESE SWELLS...IN COMBINATION WITH
STRONG TRADE WINDS EXPECTED TO BUILD LATE TONIGHT THROUGH THURSDAY
NIGHT...WILL BRING HAZARDOUS SURF CONDITIONS TO EAST FACING SHORES
OF THE STATE THROUGH EARLY SATURDAY MORNING. A HIGH SURF ADVISORY
REMAINS IN EFFECT FOR EAST FACING SHORES. NORTH FACING SHORES WILL
ALSO SEE A BOOST TO SURF OVER THE NEXT FEW DAYS...BUT SURF HEIGHTS
WILL REMAIN BELOW ADVISORY CRITERIA THERE. SURF ALONG THE SOUTH
FACING SHORES WILL REMAIN SMALL THROUGH MONDAY...WITH A SLIGHT BUMP
TUESDAY AS A NEW LONG PERIOD SWELL ARRIVES. ANOTHER SMALL NORTHWEST
SWELL WILL ARRIVE TUESDAY AS WELL.

A SMALL CRAFT ADVISORY /SCA/ IS IN EFFECT FOR THE TYPICALLY WINDY
ZONES AROUND MAUI COUNTY AND BIG ISLAND OVERNIGHT. INCREASING
WINDS AND SEAS WILL SPREAD SCA CONDITIONS TO MOST OTHER MARINE
ZONES ON THURSDAY...CONTINUING THROUGH FRIDAY NIGHT AND POSSIBLY
INTO SATURDAY. WINDS AND SWELL WILL BEGIN TO TAPER OFF DURING THE
WEEKEND.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SATURDAY FOR EAST FACING SHORES
OF KAUAI OAHU MOLOKAI MAUI AND BIG ISLAND.

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

SMALL CRAFT ADVISORY FROM 6 AM THURSDAY TO 6 AM HST SATURDAY FOR
KAUAI NORTHWEST WATERS-KAUAI WINDWARD WATERS-KAUAI LEEWARD
WATERS-KAUAI CHANNEL-OAHU WINDWARD WATERS-KAIWI CHANNEL-MAUI
COUNTY WINDWARD WATERS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...LAU




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