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Hawaiian Islands Synoptic Discussion and Guidance

117
FXHW60 PHFO 050617
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
817 PM HST WED MAY 4 2016

.SYNOPSIS...
MOISTURE FROM AN OLD FRONT AND LIGHT WINDS WILL RESULT IN A UNSETTLE
WEATHER PATTERN FOR THE NEXT FEW DAYS. THEN A LATE SEASON FRONT
IS EXPECTED TO MOVE DOWN THE ISLAND CHAIN LATE FRIDAY... STALLING
OVER THE EASTERN PART OF THE CHAIN LATE IN THE WEEKEND. DRIER
WEATHER WITH MODEST TRADES WILL RETURN TO THE REMAINING ISLANDS BY
SUNDAY.


&&

.DISCUSSION...
A COMPLICATED WEATHER PICTURE IS SETTING UP ACROSS THE MAIN
HAWAIIAN ISLANDS THIS EVENING. WILL TRY TO STRAIGHTEN IT OUT.

FIRSTLY...MOISTURE FROM AN OLD FRONT HAS DESCENDED ON TO THE MAIN
HAWAIIAN ISLANDS. THIS LARGE AREA OF MOISTURE HAS CLEARED MAUI
COUNTY AND THE BIG ISLAND...LEAVING THESE TWO ISLANDS RATHER DRY.
NOT SO FOR OAHU AND KAUAI COUNTIES WHERE IT HAS BEEN CLOUDY AND
SHOWERY FOR MOST IF NOT ALL OF TODAY.

AS THE TRADE WINDS VEER TO THE SOUTHEAST TONIGHT AND THURSDAY...IT
WILL PUSH AWAY THIS MOISTURE TO THE WEST AND NORTHWEST CLEARING
OAHU IN THE PROCESS AND THIN SOME OF THIS MOISTURE OVER KAUAI
COUNTY. THIS MOISTURE WILL LINGER AROUND KAUAI COUNTY INTO FRIDAY.
THIS CHANGE IN THE WINDS AND THE MOISTURE IS BEING KEPT OVER KAUAI
COUNTY...IS DUE TO A LATE SEASON FRONT PRESSING EASTWARD TOWARD
THE ISLANDS.

ON THURSDAY NIGHT AND FRIDAY...A POOL OF MOISTURE SITUATED A
COUPLE OF HUNDRED MILES NORTHEAST OF THE BIG ISLAND AND MAUI THIS
EVENING...WILL MOVE IN ON THESE ISLANDS WITH SHOWERY WEATHER FOR
ESPECIALLY THE WINDWARD AREAS. OAHU IS NOT EXPECTED TO BE AFFECTED
AT THIS TIME. AS FOR THE FRONT...THE FRONT IS EXPECTED TO MOVE
ACROSS KAUAI FRIDAY AFTERNOON. THE FRONT CONTINUES TO EASTWARD
REACHING OAHU SATURDAY MORNING...AND MAUI COUNTY IN THE AFTERNOON
AND EVENING. MODERATE TRADES WITH A DRIER AIR MASS AND MAY BE A
SLIGHTLY COOLER AIR MASS WILL EASE IN BEHIND THE FRONT AFFECTING
KAUAI OAHU AND MOLOKAI ON SUNDAY.

THE FRONT STALLS OVER EASTERN MAUI/NORTHERN BIG ISLAND SUNDAY...
LASTING INTO AT LEAST MONDAY. IT MAY SPREAD TO THE REST OF THE BIG
ISLAND LATE SUNDAY.

THERE IS NO UPPER LEVEL SUPPORT FOR THESE SHOWERS...LOW LEVEL
MOISTURE WILL BE CAPPED AT 10 TO 12K FEET. ALL MODELS ARE IN GOOD
AGREEMENT WITH THIS SCENARIO TAKING PLACE

&&

.AVIATION...
AREA OF LOW LEVEL MOISTURE REACHING THE ISLANDS EARLIER IS NOW
AFFECTING MAINLY THE WESTERN ISLANDS...BRINGING SOME SHRA AND OCNL
MVFR CEILING CONDITIONS....WHILE THERE IS A BREAK IN THE CLOUD
COVERAGE OVER WINDWARD MAUI AND BIG ISLAND. EXPECT THE CLOUD PATTERN
TO CONTINUE SHIFT WEST UNDER THE EASTERLY WINDS OVERNIGHT. THUS
CLEARING WILL EVENTUALLY SPREAD TO MOLOKAI...OAHU AND KAUAI AS THE
NIGHT PROGRESSES. AIRMET SIERRA FOR MTN OBSC ALONG THE WINDWARD
AREAS OF THE WESTERN ISLANDS WILL PROBABLY BE DROPPED OVERNIGHT...AS
CONDITIONS IMPROVE. THERE IS ANOTHER AREA OF LOW CLOUDS EAST OF THE
ISLANDS THIS EVENING...AND MAY YET BRING MORE MVFR CEILING
CONDITIONS TO THE ISLANDS THURSDAY.

OTHERWISE MAINLY VFR CONDITIONS ARE EXPECTED FOR REST OF AREA.

WINDS WILL CONTINUE TO TURN MORE SOUTHEASTERLY AS A SURFACE HIGH
PRESSURE RIDGE FROM THE NORTH MOVES CLOSER TO THE ISLANDS.

&&

.MARINE...
WE ARE EXPECTING A SMALL NORTHWEST BUMP PEAKING TONIGHT FOLLOW BY
A GRADUAL DROP THURSDAY. A REINFORCING NORTHWEST SWELL OF
MODERATE SIZE AND A MORE NORTH COMPONENT IS DUE IN FRIDAY EVENING
AND SATURDAY...LASTING INTO SUNDAY. THE SOUTH FACING SHORES WILL
SEE SOME WAVES AS WELL. A GOOD SIZE BUMP IS SLATED TO START
ROLLING IN THURSDAY WITH SURF HEIGHTS BUILDING TO NEAR ADVISORY
LEVEL FOR THE SOUTH FACING SHORES LATE FRIDAY AND CONTINUING INTO
SATURDAY. THIS SWELL SHOULD START FADING SUNDAY.

NO SMALL CRAFT ADVISORY IN EFFECT...AND NONE IS EXPECTED INTO THE
WEEKEND. WE WILL TAKE A LOOK AT THE NORTHEAST WINDS BEHIND THE
FRONT...BUT IT DOES NOT APPEAR TO BE SMALL CRAFT STRENGTH AT THIS
TIME.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

DISCUSSION/MARINE...LAU
AVIATION...HUI

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