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Hawaiian Islands Synoptic Discussion and Guidance

388
FXHW60 PHFO 230136
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST TUE JUL 22 2014

.SYNOPSIS...
THE MOIST AND HUMID AIR MASS LINGERING OVER THE ISLANDS THIS
AFTERNOON WILL BE GRADUALLY USHERED WEST OF THE STATE TONIGHT AND
EARLY WEDNESDAY BY BUILDING TRADE WINDS. A DRIER...LESS HUMID...AND
RATHER STABLE AIR MASS WILL BECOME ESTABLISHED ON WEDNESDAY...AS
LOCALLY BREEZY TRADE WINDS FOCUS MODEST SHOWERS ACROSS WINDWARD
SLOPES.

&&

.DISCUSSION...
TRADE WINDS ARE BACK...BUT IT WILL TAKE A LITTLE TIME TO GET RID OF
THE HUMID AIR MASS LINGERING OVER THE ISLANDS. ISLAND OBSERVING
STATIONS SHOWED A SHARP RETURN OF THE TRADES THROUGH THE DAY...
REACHING KAUAI THIS AFTERNOON. EVEN THOUGH THE TRADE WINDS MAKE IT
FEEL A BIT LESS HUMID...DEW POINTS ARE STILL STUBBORNLY RUNNING IN
THE LOW TO MID 70/S. UNDER THESE MOIST CONDITIONS...MODEST SHOWERS
HAVE BEEN FALLING OVER WINDWARD SLOPES...WHILE A FEW SPOTTY HEAVY
SHOWERS BRIEFLY FLARED ON OAHU AND KAUAI. IN FACT...A BRIEF
THUNDERSTORM RECENTLY FIRED OFF ON THE MIDDLE SLOPES OF MAUNA LOA.
THE WANING INSTABILITY RESPONSIBLE FOR THIS CONVECTION IS A RAPIDLY
WEAKENING UPPER LEVEL TROUGH A FEW HUNDRED MILES NORTHWEST OF KAUAI.

THE HUMID AIR MASS WILL BE GRADUALLY PUSHED OFF TO THE WEST TONIGHT
BY THE STRENGTHENING TRADE WINDS...AND MID LEVEL RIDGING WILL BRING
INCREASED STABILITY. THE TRADE WINDS WILL INCREASE AS A WEAK SURFACE
TROUGH NORTHWEST OF KAUAI FILLS AND DRIFTS WESTWARD...ALLOWING A
1032 MB SURFACE HIGH ROUGHLY 1400 MILES TO OUR NORTH TO TAKE OVER.
MID TO UPPER LEVEL RIDGING MOVING IN FROM THE EAST WILL PRODUCE
INCREASINGLY STABLE CONDITIONS. THIS PROCESS IS ALREADY UNDERWAY...
AS A DEVELOPING INVERSION AROUND 6000 FT CAN BE SEE IN THE AFTERNOON
SOUNDINGS.

A STABLE AND LOCALLY BREEZY TRADE WIND FLOW WILL BE ESTABLISHED ON
WEDNESDAY. DEW POINTS TEMPERATURES WILL DROP AROUND 5 DEGREES...
BRINGING RELIEF FROM RECENT HUMID CONDITIONS. MODEST SHOWERS WILL BE
FOCUSED ACROSS WINDWARD SLOPES ALONG WITH AFTERNOON CLOUDS AND
SHOWERS ON THE KONA SLOPES.

IN THE LONG TERM...TRADES WILL DROP SLIGHTLY HEADING INTO THE
WEEKEND. FORECAST MODELS HAVE BEEN SHOWING A SMALL AREA OF DEEPER
MOISTURE PASSING OVER THE ISLANDS DURING THE SECOND HALF OF THE
WEEKEND. UNCERTAINTY REMAINS A BIT HIGH...BUT A BOOST IN MAINLY
WINDWARD RAINFALL IS LIKELY. THE RIDGE ALOFT WILL BE WEAKENED BY AN
UPPER LEVEL TROUGH PASSING BY TO THE NORTH...BUT SOMEWHAT STABLE
CONDITIONS LOOK TO HANG ON.

&&

.MARINE...
TRADE WINDS WILL GRADUALLY STRENGTHEN THROUGH TOMORROW...AND A
SMALL CRAFT ADVISORY /SCA/ IS IN PLACE FOR THE TYPICALLY WINDY
WATERS AROUND THE BIG ISLAND AND MAUI. FRESH TO LOCALLY STRONG TRADE
WINDS WILL PEAK WEDNESDAY AFTERNOON AND THURSDAY...FOLLOWED BY A
SLIGHT DECLINE ON FRIDAY AND SATURDAY TO BORDER LINE SCA LEVELS
ACROSS THE TYPICALLY WINDY AREAS.

NO SIGNIFICANT SWELLS ARE SEEN FOR THE UPCOMING WEEK. THE BIGGEST
SURF WILL FROM TRADE WIND SWELL ALONG EAST FACING SHORES. SEE THE
COLLABORATIVE NEARSHORE SWELL AND WIND FORECAST FOR OAHU /SRDHFO/
FOR MORE DETAILS.

&&

.AVIATION...
WITH SUNSET...THE AFTERNOON CONVECTION ALONG THE KONA SLOPES OF THE
BIG ISLAND SHOULD START TO SUBSIDE. OVERNIGHT...VFR WILL PREVAIL
WITH BRIEF MVFR CONDITIONS IN PASSING SHOWERS...MAINLY FOR WINDWARD
AND MAUKA AREAS.

REPORTS FROM THE LOCAL METAR STATIONS AND THE VAD WIND PROFILES SHOW
THE RETURN OF THE TRADE WINDS. VAD WIND PROFILES ARE REPORTING
10-15 KT WITH OCCASIONAL 20 KT WINDS. THE AFTERNOON SOUNDINGS FROM
LIHUE AND HILO BOTH HAVE A LOW LEVEL INVERSION BETWEEN 6 AND 7 KFT.
THE TRADE WINDS WILL CONTINUE THROUGH THE PERIOD WITH STRENGTHENING
EXPECTED TOMORROW. AN AIRMET FOR LOW LEVEL TURB WILL LIKELY BE
POSTED FOR AREAS IN THE LEE OF THE TERRAIN AT THAT TIME.

THE AIRMET SIERRA FOR TEMPO MOUNTAIN OBSCURATION WILL REMAIN POSTED
OVER N THRU E SECTIONS OF ALL ISLANDS...AS THE REMAINING ENHANCED
MOISTURE RIDES IN ON THE TRADES THIS EVENING AND OVERNIGHT. MUCH
DRIER AIR IS EXPECTED OVER THE ISLANDS TOMORROW.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
SMALL CRAFT ADVISORY THROUGH 6 PM HST THURSDAY FOR THE PAILOLO
AND ALENUIHAHA CHANNELS...MAALAEA BAY AND WATERS SOUTH OF THE BIG
ISLAND.

&&

$$

PUBLIC AND MARINE...WROE
AVIATION...EATON



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