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Hawaiian Islands Synoptic Discussion and Guidance

005
FXHW60 PHFO 231958
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1000 AM HST WED APR 23 2014

.SYNOPSIS...
BREEZY AND GUSTY TRADE WINDS WILL CONTINUE INTO SATURDAY AS STRONG
RIDGING HOLDS SEVERAL HUNDRED MILES NORTH OF THE ISLANDS. MODEST
RAINFALL WILL REMAIN FOCUSED ACROSS WINDWARD SLOPES...THOUGH SOME
SHOWERS WILL BE BRIEFLY CARRIED TO LEEWARD AREAS ON THE TRADES. LOOK
FOR AN INCREASE IN SHOWER ACTIVITY AS A BAND OF MOISTURE MOVES
THROUGH THURSDAY NIGHT AND EARLY FRIDAY. TRADES WILL WEAKEN SUNDAY
AND MONDAY.

&&

.DISCUSSION...
THE ISLANDS WILL REMAIN LOCKED IN A BREEZY AND GUSTY TRADE WIND FLOW
INTO SATURDAY. SURFACE RIDGING CENTERED ABOUT 700 MILES NORTH OF THE
STATE BETWEEN 30N AND 35N WILL BE DRIVING THE FRESH TO STRONG
TRADES. IN SPITE OF THE RIDGE BEING CURRENTLY SPLIT BY A DISSIPATING
FRONT NORTH OF THE ISLANDS...THE PRESSURE GRADIENT OVER THE ISLANDS
REMAINS RATHER STRONG AND SIMILAR TO YESTERDAY/S VALUES. RECENT
AIRCRAFT DATA OUT OF HNL SHOW A RATHER LOW INVERSION BELOW 4000
FT...WHILE THE OVERNIGHT SOUNDINGS HAD THE INVERSION AROUND 5500 FT.
GIVEN THE LOW INVERSION...THERE WILL LIKELY BE A GOOD AMOUNT OF
GUSTS IN THE 30/S WITH LOCALIZED GUSTS OVER 40 MPH OVER AND TO THE
LEE OF ISLAND TERRAIN THIS AFTERNOON.

THE GUSTY TRADES COULD BE A NOTCH STRONGER ON THURSDAY AND FRIDAY. A
1029 MB SURFACE HIGH WILL PASS ALONG THE RIDGE DURING THIS TIME.
THE GFS AND ECMWF SHOW 850 MB WINDS...ROUGHLY AROUND 5000 FT...
CRANKING UP FROM THE CURRENT 25 KT INTO THE 30 TO 35 KT RANGE.
STRONG MID LEVEL RIDGING SHOULD MAINTAIN A LOW INVERSION HEIGHT...
BUT A COMPLICATING FACTOR WILL BE A SHOWER BAND EXPECTED TO MOVE
THROUGH THURSDAY NIGHT AND FRIDAY. IF THE INVERSION STAYS LOW AND
STRONG ON EITHER SIDE OF THE BAND...WE COULD SEE ADVISORY LEVEL WIND
GUSTS OVER AND DOWNWIND OF TERRAIN. TRADES WILL BE DOWN ONLY
SLIGHTLY ON SATURDAY AND WILL DROP OFF TO MODERATE LEVELS ON SUNDAY.

MODEST RAINFALL WILL BE FOCUSED ACROSS WINDWARD SLOPES WITH AN
UPTICK IN SHOWER ACTIVITY EXPECTED THURSDAY NIGHT AND FRIDAY. THE
CENTRAL ISLANDS WILL A BIT DRIER TODAY...SO THE FORECAST HAS BEEN
UPDATED TO REFLECT THAT. A SHALLOW BAND OF MOISTURE CURRENTLY ALONG
23N WILL SKIRT JUST NORTH OF KAUAI THROUGH TOMORROW THEN PASS OVER
THE ISLANDS THURSDAY NIGHT AND EARLY FRIDAY. ASIDE FROM THIS
FEATURE...NO OTHER ORGANIZED AREAS OF MOISTURE ARE CURRENTLY
FORECAST.

&&

.AVIATION...
LOW CLOUDS AND SHOWERS CARRIED BY THE MODERATE TRADE WINDS WILL
AFFECT MAINLY WINDWARD AND MOUNTAIN AREAS...THOUGH WINDS ARE STRONG
ENOUGH FOR SOME OF THESE SHOWERS TO REACH LEE AREAS OF THE SMALLER
ISLANDS. VFR CONDITIONS WILL PREVAIL FOR ALL SITES...THOUGH PASSING
LOW CLOUDS AND SHOWERS MAY BRING BRIEF MVFR CEILING OR EVEN IFR
CEILING CONDITIONS MAINLY FOR THE WINDWARD SITES.

AIRMET TANGO FOR MECHANICAL TURBULENCE TO THE LEE OF MOUNTAINS
CONTINUES DUE TO THE WINDS.

&&

.MARINE...
FRESH TO STRONG TRADE WINDS WILL HOLD INTO SATURDAY. A SMALL CRAFT
ADVISORY /SCA/ IS IN EFFECT THROUGH FRIDAY AFTERNOON FOR ALL
CHANNELS AND THE TYPICALLY WINDY WATERS AROUND THE BIG ISLAND AND
MAUI. THE SCA WILL LIKELY NEED TO BE EXTENDED INTO SATURDAY AND WILL
PROBABLY BE EXPANDED TO ALL WATERS FOR THURSDAY OR FRIDAY. THE SCA
WILL BE AT LEAST PARTIALLY SCALED DOWN BY SUNDAY AS TRADE WINDS
BEGIN TO DECLINE.

WITH THE ISLANDS SQUARELY PLACED IN A BELT OF TRADE WINDS...
WIND-DRIVEN SEAS OF 7 TO 8 FT AT 8 TO 9 SECONDS WILL PERSIST INTO
SATURDAY. THIS WILL RESULT IN ROUGH SURF JUST BELOW THE ADVISORY
LEVEL FOR EAST FACING SHORES. EXPECT A DECLINE ON SUNDAY.

A NORTHWEST SWELL WILL BE BUILDING TODAY. WAVEWATCH GUIDANCE
SUGGESTS A PEAK LATER TODAY AND TONIGHT IN THE DOUBLE OVERHEAD
RANGE...THOUGH ADVISORY LEVEL SURF REMAINS POSSIBLE FOR NORTH FACING
SHORES OF THE SMALLER ISLANDS. THE CURRENT TREND AT BUOY 51101 DOES
NOT SUPPORT SURF THAT LARGE...BUT WE WILL MONITOR THE BUOY CLOSELY
TODAY.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...

SMALL CRAFT ADVISORY UNTIL 6 PM HST FRIDAY FOR ALL CHANNELS...
MAALAEA BAY AND THE WATERS SOUTH OF THE BIG ISLAND.

&&

$$

DISCUSSION/MARINE...WROE
AVIATION...MBALLARD







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