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Hawaiian Islands Synoptic Discussion and Guidance

500
FXHW60 PHFO 220549
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI NOV 21 2014

.SYNOPSIS...
MODERATE TRADE WINDS WILL DIMINISH ON SATURDAY. SHOWERS WILL BE
LIMITED MAINLY TO WINDWARD SLOPES...ESPECIALLY OVER THE BIG ISLAND.
A FRONT WILL BRING MODEST RAIN AND STRONGER...NORTHERLY WINDS TO
MOST OF THE STATE FROM SUNDAY NIGHT INTO TUESDAY. THE WINDS THEN
WILL WEAKEN AND BECOME NORTHEASTERLY AGAIN AS THE COOL AND DRY AIR
MASS MOISTENS GRADUALLY INTO FRIDAY.

&&

.DISCUSSION...
OBSERVATIONS AROUND THE MAIN HAWAIIAN ISLANDS CONTINUED TO REPORT
MODERATE TO LOCALLY STRONG TRADE WINDS...AND ANOTHER TIMELY
SATELLITE SCATTEROMETER PASS SUPPORTED KEEPING THE SMALL CRAFT
ADVISORY IN PLACE AROUND MAUI AND HAWAII COUNTIES AT LEAST THROUGH
TONIGHT. ALOFT...A FLAT BUT VERY BROAD AND STRONG RIDGE EXTENDED
ACROSS THE STATE FROM WEST TO EAST...KEEPING THE INVERSION HEIGHT
VERY MUCH ON THE LOW SIDE OF AVERAGE.

CLOUD COVER CONSISTED MAINLY OF GENERALLY STABLE LOW CLOUDS...WITH
SOME CIRRUS MOVING NORTH OUT OF THE ITCZ. VARIOUS MEASURES OF
PRECIPITABLE WATER DEPICTED A RELATIVELY DRY AIR MASS UPWIND OF MOST
OF THE STATE...EXCEPTING ONLY SOUTH SLOPES OF THE BIG ISLAND.
UNSURPRISINGLY...RAINFALL ACROSS THE STATE WAS SPARSE. SHOWERS
LIKELY WILL BECOME SOMEWHAT MORE ACTIVE OVERNIGHT...AND THE CIRRUS
COVER SHOULD LIMIT COOLING...THUS REDUCING LAND BREEZES. HOWEVER...
THE CURRENT POPS AND RELATED FIELDS MAY BE A LITTLE TOO WET. THIS
QUESTION WILL REQUIRE CONTINUED ATTENTION.

BY SATURDAY...GUIDANCE STILL LARGELY AGREED THAT A DEEPENING
LONG-WAVE TROUGH ALOFT WILL DISPLACE THE MID-LEVEL RIDGE TOWARD THE
EAST...SUPPORTING THE APPROACH AT THE SURFACE OF THE FRONT CURRENTLY
CROSSING 30N NEAR 170W. AS THE SURFACE RIDGE RETREATS TO THE
SOUTHEAST AHEAD OF THE FRONT...THE TRADE WINDS WILL DIMINISH
LOCALLY...BECOMING SOUTHEASTERLY IN PLACES BY SUNDAY.

THE FRONT ITSELF SHOULD REACH KAUAI BY SUNDAY NIGHT...BUT SOLUTION
CONSENSUS PREDICTED THE SUPPORTING MID-LEVEL TROUGH TO FOCUS MAINLY
TO THE EAST OF THE STATE. THUS...MOST DEVELOPMENT ALONG THE FRONT
SHOULD REMAIN NORTHEAST OF THE ISLANDS...LEAVING ONLY A FAIRLY
SHALLOW BOUNDARY TO MOVE DOWN THE STATE FROM SUNDAY NIGHT INTO
TUESDAY. SOME RAIN WILL ACCOMPANY THE FRONT...MAINLY OVER THE
SMALLER ISLANDS. THE BIG ISLAND MORE LIKELY WILL EXPERIENCE A LESS
ORGANIZED INCREASE IN SHOWERS FROM THE FRONTAL REMNANTS MOVING
ASHORE ON TUESDAY AND TUESDAY NIGHT. MODERATE TO STRONG NORTHERLY
WINDS IN THE COOLER AND DRIER AIR MASS BEHIND THE FRONT MAY BE MORE
SIGNIFICANT THAN THE FRONT ITSELF.

FROM WEDNESDAY INTO THE LATTER HALF OF THE WEEK...THE SUBTROPICAL
RIDGE WILL REESTABLISH ITSELF NORTH OF THE STATE GRADUALLY...
RETURNING LOCAL WINDS TO A MORE FAMILIAR NORTHEASTERLY DIRECTION...
THOUGH WIND SPEEDS WILL DROP OFF SIGNIFICANTLY UNTIL THE RIDGE
SHIFTS FAR ENOUGH NORTH. THE COOL AND DRY AIR MASS WILL MODIFY IN
PLACE...ALLOWING WINDWARD SHOWERS TO INCREASE WITH TIME AGAIN.

&&

.AVIATION...
EXPECT VFR CONDITIONS OVERNIGHT.

GUIDANCE INDICATE OCNL MODERATE TURBC BTN FL340 AND FL400 FOR THE
OVERNIGHT HOURS. THERE IS AN AIRMET TANGO OUT WHICH WILL BE
EXTENDED FOR THE REST OF TONIGHT. THE AIRMET COULD BE EXTENDED
BEYOND 16Z.

LOW CLOUDS RIDING IN WITH THE TRADES WILL AFFECT PRIMARILY THE
WINDWARD AND MTN AREAS OF ALL ISLANDS. THESE CLOUDS CONTAIN BRIEF
MVFR CEILINGS...AND THE EMBEDDED SHOWERS WILL REDUCE VIS TO AROUND
5 MILES.

&&

.MARINE...
A SMALL CRAFT ADVISORY REMAINED IN EFFECT FOR TYPICALLY WINDY WATERS
AROUND MAUI AND HAWAII COUNTIES. WINDS SHOULD DIMINISH STARTING ON
SATURDAY...BUT WILL STRENGTHEN AGAIN BEHIND THE FRONT EARLY NEXT
WEEK...LIKELY REACHING THE THRESHOLD FOR AN ADVISORY AGAIN.

A SERIES OF NORTHWEST SWELLS WILL ARRIVE DURING THE NEXT SEVERAL
DAYS. THE LARGEST SURF IS EXPECTED BETWEEN SUNDAY AND TUESDAY...
WHEN HEIGHTS MAY EXCEED ADVISORY LEVELS AT TIMES. TRADE WINDS WILL
CONTINUE TO PRODUCE SHORT-PERIOD CHOPPY SURF ALONG EAST-FACING
SHORES.

&&

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

&&

$$

SYNOPSIS/DISCUSSION/MARINE...RYSHKO
AVIATION...LAU



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