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Hawaiian Islands Synoptic Discussion and Guidance

247
FXHW60 PHFO 221335
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST SAT NOV 22 2014

.SYNOPSIS...
MODERATE TRADE WINDS WILL DIMINISH TODAY. 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 REPORTED WINDS
GRADUALLY BECOMING MORE SOUTHEASTERLY...BUT STILL REMAINING STRONG
ENOUGH TO REQUIRE EXTENDING THE SMALL CRAFT ADVISORY IN PLACES
AROUND THE BIG ISLAND. ALOFT...THE RIDGE LANGUISHING ACROSS THE
STATE FROM WEST TO EAST THINNED OUT BETWEEN SHALLOW TROUGHING TO
SOUTH...AND A DEEPENING LONG-WAVE TROUGH TO THE NORTH. A JET STREAM
ASSOCIATED WITH THE TROUGH TO THE SOUTH BROUGHT CIRRUS LAYERS FROM
THE ITCZ AS FAR NORTH AS MAUI COUNTY...AND CLOUD COVER WAS INCREASED
ACCORDINGLY. HOWEVER...THE MID-LEVEL RIDGE REMAINED STRONG ENOUGH TO
LIMIT THE INVERSION TO NEAR ITS USUAL HEIGHT.

LOWER CLOUD COVER CONSISTED MAINLY OF GENERALLY STABLE CLOUDS.
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. RAIN GAUGES REPORTED LITTLE ACCUMULATION THROUGH THE
NIGHT. ON THE OTHER HAND...RADAR DETECTED ENOUGH SHOWER ACTIVITY
OVER THE WATER SO THAT THE CURRENT POP GRIDS FOR LATER TODAY
NONETHELESS APPEARED PLAUSIBLE GIVEN THE PREDICTED BREAKDOWN OF THE
RIDGE ALOFT.

GUIDANCE STILL LARGELY AGREED THAT THE DEEPENING LONG-WAVE TROUGH
ALOFT TO THE NORTH WILL START TO DISPLACE THE MID-LEVEL RIDGE
TOWARD THE EAST...FINALLY 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 AND BECOME INCREASINGLY SOUTHEASTERLY.

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 ALONG NORTHEAST SLOPES 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 AGAIN WITH TIME.

&&

.MARINE...
ALTHOUGH WIND DIRECTION AROUND MAUI AND HAWAII COUNTIES BECAME MORE
SOUTHEASTERLY...SPEEDS DID NOT DIMINISH AS QUICKLY AS EXPECTED
EARLIER...EXCEPT IN THE PAILOLO CHANNEL AND MAALAEA BAY...WHERE MAUI
BLOCKED THE WIND FLOW. THUS...THE SMALL CRAFT ADVISORY WAS EXTENDED
THROUGH THE DAY TODAY FOR THE ALENUIHAHA CHANNEL AND WATERS SOUTH
THROUGH WEST OF THE BIG ISLAND. WIND SPEEDS SHOULD START TO DIMINISH
THIS EVENING...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 PM HST THIS EVENING FOR ALENUIHAHA
CHANNEL-BIG ISLAND LEEWARD WATERS-BIG ISLAND SOUTHEAST WATERS.

&&

$$

RYSHKO



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