Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 200643
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI SEP 19 2014

.SYNOPSIS...
LIGHT WINDS WILL MAINTAIN A PATTERN OF LOCAL NIGHTTIME LAND AND
AFTERNOON SEA BREEZE CIRCULATIONS THROUGH THIS WEEKEND. IN THIS
REGIME...EXPECT MOSTLY CLEAR NIGHTS AND MORNINGS...WITH CLOUD BUILDS
AND ISOLATED SHOWERS DEVELOPING OVER LEEWARD AND INTERIOR SECTIONS
EACH AFTERNOON. A RETURN OF LIGHT TO MODERATE TRADES IS EXPECTED
EARLY NEXT WEEK...WITH BRIEF PASSING SHOWERS FAVORING WINDWARD AND
MAUKA AREAS THROUGH MID-WEEK. THE TRADE WINDS MAY BECOME WETTER FROM
THURSDAY INTO NEXT WEEKEND...AS MOISTURE ASSOCIATED WITH A WEAKENING
FRONT ARRIVES OVER THE ISLANDS.

&&

.DISCUSSION...
THE WEAK PRESSURE GRADIENT CONTINUES ACROSS THE MAIN HAWAIIAN ISLAND
CHAIN TONIGHT. A WEAK NORTH TO SOUTH ORIENTED SURFACE TROUGH HAS
BEEN ANALYZED IN THE VICINITY OF THE KAUAI CHANNEL. THE WEAK WINDS
WEST OF THIS FEATURE WERE FROM THE NORTHEAST...AND FROM THE
SOUTHEAST TO THE EAST OF THE TROUGH AXIS. ELSEWHERE...A WEAK SURFACE
HIGH IS FAR NORTHEAST OF THE STATE NEAR 31N 139W...WHILE A WEAK
SURFACE RIDGE EXTENDS FROM A HIGH JUST ACROSS THE INTERNATIONAL DATE
LINE NEAR 31N 177E TO A POINT ABOUT 575 MILES NORTH NORTHWEST OF
LIHUE. AS A RESULT OF THIS SLACK GRADIENT...THE BACKGROUND FLOW
ACROSS THE ISLANDS REMAINS VERY WEAK. THIS IS ALLOWING ALTERNATING
LOCAL NIGHTTIME LAND BREEZE AND AFTERNOON SEA BREEZE CIRCULATIONS TO
DOMINATE THE WEATHER PATTERNS ACROSS THE INDIVIDUAL ISLANDS EACH DAY.

ALSO...A PAIR OF WEAK TROPICAL DISTURBANCES ARE EVIDENT SOUTH AND
SOUTHEAST OF THE BIG ISLAND. ALTHOUGH THESE FEATURES ARE NOT HAVING
A SIGNIFICANT IMPACT ON LOCAL WINDS...THESE SYSTEMS ARE A SOURCE OF
DEEP TROPICAL MOISTURE. THE OUTER FRINGES OF THIS MOISTURE ALREADY
ARRIVED OVER THE SOUTHEASTERN AND SOUTH INTERIOR OF THE BIG ISLAND
EARLIER TODAY. AS A RESULT...THE EARLY AFTERNOON SOUNDINGS SHOW A
MOIST AND RELATIVELY UNSTABLE AIR MASS IN PLACE. THE SOUTHEASTERN
AND WINDWARD PORTIONS OF THE BIG ISLAND AND ADJACENT WATERS WILL
CONTINUE TO HAVE A MORE ACTIVE SHOWER PATTERN THROUGH SATURDAY NIGHT
DUE TO THE PASSAGE OF THE TROPICAL DISTURBANCES TO THE SOUTH OF THE
AREA.

ALOFT...A WEAK MID-LEVEL TROUGH PASSING NORTH OF THE ISLANDS WILL
EVENTUALLY BE REPLACED BY MID-LEVEL RIDGING STARTING SUNDAY. THE
PRESSURE GRADIENT OVER THE ISLANDS WILL REMAIN WEAK THROUGH THIS
WEEKEND. THIS WILL MAINTAIN THE ALTERNATING LAND AND SEA BREEZE
CIRCULATION PATTERN THROUGH SUNDAY. THEREFORE...EXPECT GENERALLY
CLEAR SKIES EACH NIGHT AND MORNING...FOLLOWED BY CLOUD BUILD UPS
AND ISOLATED SHOWERS DEVELOPING BY LATE MORNING AND LINGERING
THROUGH THE EARLY EVENING HOURS. THE AFTERNOON CONVECTION COULD ALSO
FEATURE SOME ISOLATED HEAVY DOWNPOURS ON SATURDAY...BUT THESE MAY BE
A LITTLE LESS LIKELY ON SUNDAY.

A SURFACE FRONT NORTH OF THE ISLANDS WILL MOVE SLOWLY SOUTH THIS
WEEKEND...BUT WILL STALL NORTH OF THE AREA SOMETIME ON SUNDAY. A
MODERATELY STRONG SURFACE HIGH PASSING FAR NORTH OF THE ISLANDS WILL
INCREASE THE PRESSURE GRADIENT OVER THE AREA EARLY NEXT WEEK. THIS
WILL ALLOW THE LOW-LEVEL TRADE WIND FLOW TO GRADUALLY RETURN
STARTING MONDAY. LIGHT TO MODERATE TRADE WINDS WILL LIKELY PERSIST
THROUGH THE REMAINDER OF THE WEEK. THE FORECAST MODELS SHOW A NEW
FRONT MOVING DOWN TOWARD THE AREA AROUND THURSDAY. THIS FEATURE
APPEARS TO BE DROPPING DOWN TOWARD THE ISLAND CHAIN AS AN EAST TO
WEST ORIENTED BAND OF CLOUDS AND SHOWERS. AS A RESULT...IT APPEARS
THIS FEATURE WILL IMPACT THE ISLANDS FROM THURSDAY INTO FRIDAY. MOST
OF THE MOISTURE WILL FOCUS OVER WINDWARD SECTIONS OF THE STATE...AND
IT WILL POSSIBLY LINGER INTO NEXT WEEKEND. THE SLIGHTLY STRONGER
TRADE WIND FLOW MAY TRANSPORT A FEW OF THESE SHOWERS OVER TO LEEWARD
AREAS ON THE SMALLER ISLANDS...ESPECIALLY NIGHTS AND MORNINGS.

NOTE THAT THE LIGHT WINDS WILL ALLOW VOG AND SMOKE FROM THE BIG
ISLAND/S ACTIVE VOLCANO/LAVA FLOWS TO POOL NEAR THE SURFACE OVER
PARTS OF THE BIG ISLAND DURING THE OVERNIGHT AND EARLY MORNING HOURS
THIS WEEKEND...BEFORE CLEARING BY MID-MORNING. STRONGER WINDS NEXT
WEEK WILL LIKELY PREVENT A STRONG GROUND-BASED INVERSION FROM
DEVELOPING...AND THE POOLING OF PARTICULATES NEAR THE SURFACE SHOULD
BE LESS PRONOUNCED.

AS NOTED IN THE PREVIOUS DISCUSSION...LOCAL SEA SURFACE TEMPERATURES
/SSTS/ ARE ANOMALOUSLY WARM FOR SEPTEMBER...WHICH IS CONTRIBUTING TO
THE ONGOING MUGGY CONDITIONS. SURFACE DEW POINTS REMAIN IN THE LOWER
70/S. THE SSTS ARE NOT EXPECTED TO CHANGE SIGNIFICANTLY IN THE NEAR
FUTURE. THEREFORE...EVEN THOUGH THE TRADE WINDS ARE EXPECTED TO
INCREASE NEXT WEEK...TEMPERATURES MAY COOL SLIGHTLY...BUT THE DEW
POINTS WILL LIKELY REMAIN RELATIVELY HIGH.

&&

.AVIATION...
WEAK NIGHTTIME LAND BREEZES AND A GENERAL CLEARING TREND WILL
CHARACTERIZE THE WEATHER OVERNIGHT FOR MOST ISLANDS. THE BIG ISLAND
HOWEVER WILL REMAIN UNDER THE INFLUENCE OF ENHANCED LOW LEVEL
MOISTURE AND UPPER LEVEL INSTABILITY. TEMPO MVFR IN PASSING SHOWERS
CAN BE EXPECTED THROUGH MIDDAY SATURDAY ALONG SOUTHERN AND EASTERN
COASTS AND LOWER SLOPES OF THE BIG ISLAND. ISOLATED MVFR SHOWERS
POSSIBLE REMAINING AREAS.

GENTLE AFTERNOON SEAS BREEZES WILL REDEVELOP SATURDAY AFTERNOON AND
PERSIST THROUGH EARLY EVENING. DIURNAL CONVECTION WILL BE FOCUSED
OVER INTERIOR PORTIONS OF ALL ISLANDS. VFR CONDS WILL NEVERTHELESS
PREVAIL ALL AREAS.

&&

.MARINE...
THERE HAS BEEN LITTLE TO NO CHANGE WITH RESPECT TO THE MARINE
FORECASTS...WITH WINDS AND SEAS REMAINING BELOW SMALL CRAFT ADVISORY
/SCA/ CRITERIA INTO EARLY NEXT WEEK. THERE IS A POSSIBILITY TRADE
WIND SPEEDS MAY REACH THE SCA THRESHOLD ACROSS THE WINDIER MARINE
ZONES ADJACENT TO THE ISLANDS OF MAUI AND HAWAII COUNTIES BY THE
MIDDLE OF NEXT WEEK.

SURF WILL LIKELY REMAIN BELOW THE HIGH SURF ADVISORY CRITERIA ALONG
ALL SHORES OF ALL ISLANDS THROUGH NEXT FRIDAY. HOWEVER...SMALL
SWELLS WILL PROVIDE SOME SURF. SMALL SWELLS FROM THE NORTHWEST...
NORTHEAST...EAST AND SOUTH ARE EXPECTED TO PROVIDE SMALL BACKGROUND
SURF ALONG MOST SHORELINES OF THE STATE THROUGH THIS WEEKEND. NEW
NORTH AND NORTHWEST SWELLS WILL ALSO AFFECT MOST ISLANDS ON
WEDNESDAY AND THURSDAY...WITH A NORTH NORTHEAST SWELL POSSIBLE
THURSDAY AND FRIDAY. TINY LONG-PERIOD SWELLS FROM THE SOUTH WILL
MAINTAIN SURF HEIGHTS NEAR OR BELOW SEASONAL AVERAGES ALONG SOUTH
FACING SHORES NEXT WEEK.

&&

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

&&

$$

DISCUSSION/MARINE...HOUSTON
AVIATION...BEDAL







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