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Hawaiian Islands Synoptic Discussion and Guidance

598
FXHW60 PHFO 291946
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
946 AM HST FRI AUG 29 2014

.SYNOPSIS...
LIGHT TRADE WINDS WILL PREVAIL ACROSS THE STATE TODAY THROUGH
THE WEEKEND AND INTO EARLY NEXT WEEK. SEABREEZES WILL DEVELOP
ACROSS MANY INTERIOR AND LEEWARD SECTIONS EACH AFTERNOON...
PRODUCING CLOUD BUILDUPS AND SOME SHOWERS...WHILE LAND BREEZES
BRING CLEARING AT NIGHT. STRONGER TRADES MAY RETURN TO THE
STATE AROUND THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
RADAR LOOPS DEPICT SCATTERED SHOWERS ALONG THE WINDWARD COASTS OF
THE BIG ISLAND AND EAST MAUI...WITH JUST ISOLATED SMALL SHOWERS
DOTTING THE WATERS ELSEWHERE AROUND THE STATE. RAIN GAUGE DATA
INDICATE LIGHT ACCUMULATIONS AT A FEW WINDWARD STATIONS DURING THE
PAST SIX HOURS...WITH MOST PLACES REMAINING DRY. EARLY MORNING
VISIBLE SATELLITE IMAGERY REVEALS A SMALL LOW CLOUD SWIRL...
APPARENTLY MARKING A WEAK LOW LEVEL TROUGH...CENTERED ABOUT 250
MILES EAST-NORTHEAST OF HILO AND MOVING SLOWLY TO THE SOUTHWEST.
REGIONAL SURFACE ANALYSIS DEPICTS AN EAST-WEST HIGH PRESSURE
RIDGE FAR TO OUR NORTH ALONG 40N...WITH A WEAK REMNANT LOW FROM
FORMER EAST PACIFIC TROPICAL CYCLONE LOWELL NEAR 30N 148W...AND
A MUCH LARGER REMNANT LOW FROM FORMER EAST PACIFIC TROPICAL
CYCLONE MARIE NEAR 29N 133W. THE 12Z SOUNDINGS AND MORE RECENT
88D VWP DATA INDICATE WEAKENING TRADES OVER THE STATE...WITH
NEAR NORMAL PWATS OF 1.3 TO 1.4 INCHES...AND HIGHER THAN NORMAL
INVERSIONS BASED AROUND 10K FEET. STABLE CONDITIONS REMAIN IN
PLACE ALOFT...WITH 500 MB TEMPS AROUND -2C...AND A MID/UPPER LEVEL
RIDGE CENTERED A FEW HUNDRED MILES SOUTHWEST OF THE BIG ISLAND.

IN THE NEAR TERM...WITH THE TRADES WEAKENING...EXPECT SEABREEZES
TO DEVELOP ACROSS MANY INTERIOR AND LEEWARD SECTIONS THIS
AFTERNOON. THIS SHOULD ENCOURAGE CLOUD BUILDUPS ALONG WITH
SCATTERED SHOWERS IN THESE AREAS. ISOLATED HEAVIER DOWNPOURS
WILL BE POSSIBLE WITH SLOW MOVING SHOWERS. OTHERWISE...SHOWERS
MAY CONTINUE TO BE ENHANCED ALONG THE WINDWARD COASTS OF MAUI
AND THE BIG ISLAND...AS AN AREA OF ENHANCED MOISTURE ASSOCIATED
WITH THE APPROACHING LOW LEVEL TROUGH IMPACTS THOSE AREAS. MAY
NEED TO NUDGE SHOWER COVERAGE UP FOR THOSE WINDWARD AREAS...
OTHERWISE THE EXISTING FORECAST APPEARS TO BE ON TRACK.

THROUGH THE HOLIDAY WEEKEND...THE NORTHEAST PACIFIC HIGH WILL
REMAIN RATHER WEAK AND FAR TO THE NORTH...DUE TO A COMBINATION OF
THE FORMER TROPICAL CYCLONE REMNANT LOWS MOVING SLOWLY WESTWARD
ALONG 30N AND A WEAK COLD FRONT MOVING SLOWLY EASTWARD FROM THE
INTERNATIONAL DATELINE. THIS SYNOPTIC REGIME WILL ALLOW FOR LIGHT
TRADE WINDS TO CONTINUE ACROSS THE STATE...WITH A CONVECTIVE
SEABREEZE PATTERN AND ASSOCIATED CLOUDS/SHOWERS LIKELY TO DEVELOP
ACROSS INTERIOR AND LEEWARD AREAS EACH AFTERNOON. SOME CLOUDS AND
PASSING SHOWERS WILL LINGER OVER WINDWARD AREAS AS WELL...MOST
LIKELY OCCURRING DURING THE NIGHTS AND EARLY MORNINGS. LAND BREEZES
SHOULD CLEAR OUT THE REMAINDER OF THE SMALLER ISLANDS DURING THE
NIGHTTIME HOURS. NEARBY MID/UPPER LEVEL RIDGING SHOULD MAINTAIN A
FAIRLY STABLE REGIME OVER HAWAII...BUT THERE WILL BE A COUPLE OF
AREAS OF SOMEWHAT HIGHER MOISTURE (PWATS AROUND 1.5 INCHES) MOVING
THROUGH THE STATE DURING THE WEEKEND. ISOLATED HEAVIER DOWNPOURS
WILL BE POSSIBLE EACH AFTERNOON...WHEN SLOW MOVING SHOWERS WILL BE
MOST LIKELY TO DEVELOP ALONG THE SEABREEZES.

THE LIGHT TRADE WIND PATTERN SEEMS LIKELY TO CONTINUE THROUGH
ABOUT NEXT TUESDAY...AS THE EAST PACIFIC RIDGE REMAINS RELATIVELY
WEAK AND FAR TO THE NORTH. WOULD EXPECT A CONTINUED SEABREEZE/LAND
BREEZE PATTERN ACROSS LEEWARD/INTERIOR SECTIONS... WITH SOME
CLOUDS AND PASSING SHOWERS PERSISTING WINDWARD. MOST OF THE
GUIDANCE INDICATES TRADES INCREASING BACK TO MODERATE LEVELS
DURING THE MIDDLE AND LATER PART OF NEXT WEEK...WHICH WOULD BRING
A RETURN TO TYPICAL TRADE WIND WEATHER ACROSS THE STATE.

&&

.AVIATION...
A LIGHT TRADE WIND PATTERN MAY ALLOW FOR THE DEVELOPMENT OF
SEABREEZES THIS AFTERNOON...INTERIOR CLOUD BUILD UPS ARE LIKELY
WITH THIS OCCURRING. A REGION OF LOWER CLOUDS JUST NE OF MAUI AND
THE BIG ISLAND THIS MORNING HAS BECOME INCREASINGLY ISOLATED.
HOWEVER...PASSING CLOUDS AND SHOWERS...MAINLY ALONG WINDWARD BIG
ISLAND AND MAUI...CAN BE EXPECTED. OTHERWISE...VFR CONDITIONS WILL
PREVAIL. NO AIRMETS ARE EXPECTED AT THIS TIME.

&&

.MARINE...
THE ANTICIPATED LONG PERIOD EASTERLY SWELL ARRIVED AT THE CDIP
NEAR SHORE BUOYS NORTH OF OAHU AND MAUI DURING THE PREDAWN HOURS.
BARBERS POINT CDIP BUOY SHOWS SOUTH SWELL CONTINUING AS WELL.
EXPECT MARGINAL ADVISORY LEVEL SURF ON BOTH EAST AND SOUTH FACING
SHORES TODAY INTO TONIGHT. STRONG CURRENTS WILL DEVELOP IN SOME
AREAS DUE THE INTERACTION BETWEEN THE LONG PERIOD EAST AND SOUTH
SWELLS. THE SURF FROM BOTH SWELLS WILL SLOWLY DECLINE DURING THE
WEEKEND.

SMALL CRAFT ADVISORY CRITERIA WINDS OF 25 KT OR GREATER ARE NOT
EXPECTED THROUGH THE HOLIDAY WEEKEND. HOWEVER...THE LONG PERIOD
EASTERLY AND SOUTHERLY SWELL MENTIONED ABOVE COULD BRING CONFUSED
SEAS TO AREAS EXPOSED TO BOTH SWELLS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 AM HST SATURDAY FOR NIIHAU-KAUAI
WINDWARD-KAUAI LEEWARD-OAHU SOUTH SHORE-WAIANAE COAST-OAHU
KOOLAU-OLOMANA-MOLOKAI-LANAI MAKAI-KAHOOLAWE-MAUI WINDWARD WEST-
MAUI LEEWARD WEST-MAUI CENTRAL VALLEY-WINDWARD HALEAKALA-LEEWARD
HALEAKALA-KONA-SOUTH BIG ISLAND-BIG ISLAND NORTH AND EAST.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...EATON




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