Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 121330
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST SAT JUL 12 2014

.SYNOPSIS...
TRADE WINDS WILL DIMINISH SLIGHTLY ON SUNDAY AND MONDAY AS A TROUGH
APPROACHES THE ISLANDS FROM THE SOUTHEAST. THE TROUGH WILL BRING
ENHANCED MOISTURE FROM SUNDAY INTO TUESDAY...WHICH WILL FUEL AN
INCREASE IN MAINLY WINDWARD SHOWERS...AND BRING MUGGY CONDITIONS.
MORE COMFORTABLE CONDITIONS WILL RETURN TOWARD THE MIDDLE OF NEXT
WEEK AS BREEZY TRADE WIND WEATHER RETURNS.

&&

.DISCUSSION...
CURRENTLY THE ISLANDS ARE WITHIN THE SUMMERTIME TRADE WIND BELT...
WITH MODERATE TO LOCALLY FRESH WINDS SUPPORTED BY HIGHS CENTERED FAR
NE AND NW OF THE ISLANDS...AND THEIR ASSOCIATED RIDGE ALONG 30N.
THIN HIGH CLOUDS ARE TRACKING EASTWARD WITHIN THE SUBTROPICAL JET
OVERHEAD...WITH A NEARBY MID AND UPPER LEVEL RIDGE SUPPORTING A
STRONG SUBSIDENCE INVERSION BASED BETWEEN 6 AND 7 KFT. LATEST
SATELLITE AND RADAR IMAGES SHOW DISORGANIZED PATCHES OF STABLE AND
SHOWERY LOW CLOUDS MOVING OVER THE ISLANDS WITH THE TRADES...AND A
FAIRLY TYPICAL TRADE WIND WEATHER PATTERN IS EXPECTED FOR MOST OF
THE WEEKEND...WITH BRIEF WINDWARD SHOWERS FAVORING NIGHTS AND
MORNINGS. LOOKING FURTHER AFIELD...A SURFACE TROUGH... WITH AN AXIS
ABOUT 600 MILES ESE OF THE BIG ISLAND...MARKS THE REMNANTS OF WHAT
ONCE WAS TROPICAL CYCLONE FAUSTO IN THE E PACIFIC. A SIGNIFICANT
SURGE IN PRECIPITABLE WATER VALUES IS SEEN IN THIS AREA ON LATEST
MIMIC IMAGERY...WITH THE LEADING EDGE LOCATED ABOUT 350 MILES SE OF
WINDWARD BIG ISLAND.

THE FORECAST CALLS FOR MOISTURE ASSOCIATED WITH THE TROUGH TO ARRIVE
OVER WINDWARD BIG ISLAND BY SUNDAY. THIS MOISTURE IS THEN EXPECTED
TO ADVECT WNW ACROSS THE ISLAND CHAIN THROUGH TUESDAY. WHILE THE
TROUGH WILL BE WEAKENING AS IT REACHES THE LONGITUDE OF THE
ISLANDS...IT IS NONETHELESS EXPECTED TO BRING A WARM AND MUGGY AIR
MASS OVER THE ISLANDS...WITH DEW POINTS CLIMBING TOWARD THE
MID-70S...AND WILL ALSO BRIEFLY WEAKEN AND TURN WINDS TO THE ESE AS
IT PASSES FROM LATE SUNDAY INTO TUESDAY. THERE IS LITTLE IN THE WAY
OF UPPER LEVEL SUPPORT ACCOMPANYING THIS MOISTURE...WITH A WEAK
MID-LEVEL HIGH EXPECTED TO REMAIN OVER THE ISLANDS. HOWEVER...WITH
THE SIGNIFICANT INCREASE IN MOISTURE THERE REMAINS THE POTENTIAL
FOR SOME HEAVY SHOWERS...MAINLY WINDWARD...AND ALONG SE FACING
SLOPES.

AS THE DISSIPATING SURFACE TROUGH PASSES W OF THE ISLANDS BY LATE
TUESDAY...IT/S ASSOCIATED MOISTURE SURGE WILL FOLLOW SUIT AS HIGH
PRESSURE STRENGTHENS FAR NNE OF THE ISLANDS. THEREFORE WE CAN EXPECT
A TREND TOWARD MORE COMFORTABLE...AND BREEZY...TRADE WIND WEATHER
BY THE MIDDLE OF NEXT WEEK.

VARYING AMOUNTS OF RELATIVELY THIN HIGH CLOUDS ARE EXPECTED TO
TRAVERSE ISLAND SKIES OVER THE NEXT SEVERAL DAYS...AS THE
SUBTROPICAL JET REMAINS NEARBY. WHILE THEY ARE NOT EXPECTED TO HAVE
A MAJOR IMPACT ON LOCAL WEATHER...ISLAND SUNRISES AND SUNSETS MAY BE
A LITTLE MORE COLORFUL DUE TO THEIR PRESENCE.

&&

.AVIATION...
STABLE TRADE WIND FLOW WILL PRODUCE SCATTERED SHOWERS AND ISOLATED
MVFR CIGS ALONG WINDWARD SLOPES THROUGH TODAY AND TONIGHT. VFR
CONDITIONS WILL PREVAIL AT THE TERMINALS AND ACROSS LEEWARD SECTIONS.

AIRMET TANGO CONTINUES FOR LOW LEVEL TURBULENCE S AND W OF THE
MOUNTAINS BELOW 7000 FEET. VAD WIND PROFILES AND THE 12Z LIHUE
SOUNDING SHOW MARGINAL LOW LEVEL WIND FIELDS TO SUPPORT AN AIRMET
AT THIS TIME. THESE WINDS ARE FORECAST TO GRADUALLY DECREASE
FURTHER...AND THE AIRMET WILL PROBABLY BE DROPPED LATER TODAY
OR TONIGHT.

&&

.MARINE...
A SMALL CRAFT ADVISORY /SCA/ FOR WINDIER ZONES AROUND MAUI AND THE
BIG ISLAND HAS BEEN EXTENDED THROUGH TONIGHT...AS A SLIGHT
TIGHTENING OF THE LOCAL PRESSURE GRADIENT IS POSSIBLE LATER TODAY
AS A LOW LEVEL TROUGH APPROACHES FROM THE SE. THE EXPECTATION IS
THAT WINDS WILL CERTAINLY BE BELOW SCA SPEEDS BY SUNDAY AS THE
PASSAGE OF THE WEAKENING TROUGH WILL LOOSEN THE LOCAL PRESSURE
GRADIENT.

A S SWELL ARRIVING TONIGHT AND GRADUALLY BUILDING SUNDAY WILL BRING
INCREASED SURF ALONG S FACING SHORES THROUGH TUESDAY...WITH
EXPECTATIONS THAT SURF WILL APPROACH BUT REMAIN BELOW ADVISORY
LEVELS. LATEST WW III GUIDANCE INDICATES ANOTHER PULSE OF S SWELL
WILL ARRIVE AROUND WEDNESDAY...SUPPORTING MODERATE SURF ALONG S
FACING SHORES INTO NEXT WEEKEND.

&&

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

&&

$$

DISCUSSION/MARINE...BIRCHARD
AVIATION...JACOBSON





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