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Temp8.3 C
RH51 %
WindN 7 mph
RoadOpen
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Hawaiian Islands Synoptic Discussion and Guidance

633
FXHW60 PHFO 012021
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
1021 AM HST WED OCT 1 2014

.SYNOPSIS...
LOCALLY HEAVY RAINS WILL BE POSSIBLE ACROSS PARTS OF THE STATE
ONCE AGAIN THIS AFTERNOON...AS LIGHT WINDS COMBINE WITH A MOIST
AND MODERATELY UNSTABLE AIRMASS. A DRIER AND MORE STABLE AIRMASS
IS EXPECTED TO RETURN TO THE ISLANDS FROM TONIGHT THROUGH THE
END OF THE WEEK...THOUGH LIGHT WINDS AND MUGGY CONDITIONS WILL
CONTINUE AS A WEAK SURFACE HIGH PRESSURE RIDGE STAYS NEAR OR
JUST NORTH OF THE STATE.

&&

.DISCUSSION...
DRY CONDITIONS PREVAIL ACROSS THE MAIN HAWAIIAN ISLANDS THIS
MORNING...WITH RADAR ANIMATIONS AND RAIN GAUGE DATA SHOWING ONLY
ISOLATED VERY LIGHT AMOUNTS OVER LAND AREAS DURING THE PAST
SEVERAL HOURS. MOSTLY SUNNY SKIES PREVAIL ACROSS MOST OF THE
SMALLER ISLANDS...WHILE AREAS OF HIGH CLOUDINESS STREAM UP
FROM THE DEEP TROPICS ACROSS THE BIG ISLAND. SURFACE ANALYSIS
DEPICTS A RIDGE AXIS EXTENDING FROM THE NORTHEAST PACIFIC HIGH
SOUTHWESTWARD TO A COUPLE HUNDRED MILES NORTH OF KAUAI. ALOFT...
A MID/UPPER LEVEL LOW IS CENTERED NEAR 23N152W AND MOVING SLOWLY
EASTWARD...WITH A WEAK TROUGH EXTENDING WESTWARD ACROSS THE STATE.
THE 12Z LIHUE SOUNDING REMAINED QUITE MOIST AND UNSTABLE...WITH
A WELL ABOVE NORMAL PWAT OF 1.76 INCHES AND NO INVERSION PRESENT.
THE 12Z HILO SOUNDING WAS SOMEWHAT DRIER AND MORE STABLE...WITH
NEAR NORMAL PWAT OF 1.51 INCHES...AND A WEAK INVERSION DEVELOPING
NEAR 8000 FEET. MIMIC-TPW SATELLITE IMAGERY SHOWS A MOIST PLUME
LINGERING ACROSS THE CENTRAL AND WESTERN PARTS OF THE STATE...
WITH A SOMEWHAT DRIER AIRMASS MOVING SLOWLY WESTWARD INTO THE BIG
ISLAND.

FOR THE REST OF TODAY...A CONTINUED CONVECTIVE SEABREEZE PATTERN
ALONG WITH AMPLE MOISTURE IN PLACE SUGGESTS THE POTENTIAL FOR
LOCALLY HEAVY RAINS ONCE AGAIN THIS AFTERNOON ACROSS THE CENTRAL
AND WESTERN PORTIONS OF THE STATE. LOCALLY DERIVED MOISTURE-
STABILITY INDICES DO INDICATE SOME STABILIZATION OF THE
ENVIRONMENT DURING THE DAY...APPARENTLY DUE TO A COMBINATION OF
MODEST DRYING AND SOME MID LEVEL WARMING. WILL UPDATE THE FORECAST
GRIDS AND TEXT TO INCLUDE MENTION OF LOCALLY HEAVY RAINS FOR
LEEWARD AND SOME INTERIOR SECTIONS OF THE SMALLER ISLANDS. THE
POTENTIAL FOR HEAVY DOWNPOURS APPEARS TO BE MINIMAL ACROSS THE BIG
ISLAND...DUE TO THE DRIER AND MORE STABLE AIRMASS IN PLACE THERE...
AS WELL AS THE HIGH CLOUDINESS STREAMING OVERHEAD WHICH WILL
REDUCE INSOLATION. CANNOT RULE OUT A FEW THUNDERSTORMS ACROSS THE
SMALLER ISLANDS DURING THE AFTERNOON AS WELL...BUT FEEL THAT THE
PROBABILITY IS TOO LOW TO INCLUDE IN THE FORECAST AT THIS POINT.

TONIGHT THROUGH FRIDAY...WOULD EXPECT A LESS ACTIVE WEATHER
PATTERN OVER THE STATE...AS A SOMEWHAT DRIER AIRMASS SPREADS IN
FROM THE EAST...AND MID LEVEL TEMPS CONTINUE TO WARM. MODELS
INDICATE THAT A WEAK TRADE WIND FLOW MAY DEVELOP...AS A WEAK LOW
LEVEL RIDGE NUDGES WESTWARD TO OUR NORTH. WOULD STILL EXPECT
SEABREEZES TO DEVELOP ACROSS SOME INTERIOR AND LEEWARD AREAS...
BUT THEY MAY NOT BE QUITE AS WIDESPREAD AS WE HAVE OBSERVED THE
PAST FEW DAYS. A HYBRID WEATHER PATTERN SEEMS LIKELY TO RESULT...
WITH LIMITED SHOWERS AND CLOUDS ACROSS WINDWARD AREAS DURING THE
NIGHTS AND EARLY MORNING...AND CLOUDS WITH SCATTERED SHOWERS
ACROSS LEEWARD AND INTERIOR IN THE AFTERNOONS. THE POTENTIAL FOR
HEAVY DOWNPOURS OR THUNDERSTORMS APPEARS TO BECOME VERY LOW AFTER
TODAY. WARM AND MUGGY CONDITIONS WILL CONTINUE...WITH ABOVE NORMAL
SEA SURFACE TEMPERATURES SURROUNDING THE ISLANDS CONTRIBUTING TO
RATHER HIGH DEWPOINTS.

DURING THE WEEKEND AND INTO EARLY NEXT WEEK...A COLD FRONT SEVERAL
HUNDRED MILES NORTHWEST OF THE STATE WILL SAG SLOWLY TO THE
SOUTHEAST...PUSHING THE SURFACE RIDGE OVER THE STATE AND ALLOWING
A WIDESPREAD SEABREEZE PATTERN TO PREVAIL ONCE AGAIN. SCATTERED
SHOWERS WILL DEVELOP MAINLY ACROSS INTERIOR AND LEEWARD AREAS EACH
AFTERNOON...WITH CLEARING EACH NIGHT AS LAND BREEZES TAKE OVER.
CONTINUED ABOVE NORMAL DEWPOINTS AND THE LACK OF TRADE WINDS WILL
MAINTAIN WARM AND MUGGY CONDITIONS.

&&

.AVIATION...
VFR CONDITIONS PREVAIL AT ALL TAF SITE SITES WITH THE EXCEPTION OF
PHNY WHICH IS EXPERIENCING MVFR CONDITIONS TO TO LOW CIGS. EXPECT
THESE CONDITIONS TO CONTINUE THROUGH THE DAY WITH SOME BRIEF MVFR
POSSIBLE IN PLACES THIS AFTERNOON AND EVENING DUE TO SHRA AND LOW
CIGS.

&&

.MARINE...
MORNING SURF OBSERVATIONS AND BUOY DATA INDICATE THAT THE
CURRENT SOUTH SWELL REMAINS HIGH ENOUGH TO MAINTAIN ADVISORY
LEVEL SURF ACROSS SOUTH FACING SHORES. THIS SWELL AND RESULTING
SURF WILL CONTINUE TONIGHT INTO THURSDAY...WITH SURF LIKELY TO
DECREASE BELOW ADVISORY LEVELS BY THURSDAY EVENING. NO OTHER
SIGNIFICANT SOUTH SWELLS ARE EXPECTED THROUGH THE WEEKEND. A
NORTHWEST SWELL WILL PEAK TODAY...WITH BELOW ADVISORY LEVEL SURF
RESULTING ACROSS NORTH AND WEST FACING SHORES. A SERIES OF
MODERATE NORTHWEST SWELLS WILL ARRIVE DURING THE WEEKEND AND INTO
EARLY NEXT WEEK...WITH SURF EXPECTED TO REMAIN BELOW ADVISORY
LEVELS.

WINDS AND SEAS WILL REMAIN WELL BELOW SMALL CRAFT ADVISORY LEVELS
THROUGH THE NEXT SEVERAL DAYS.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
HIGH SURF ADVISORY UNTIL 6 PM HST THURSDAY FOR SOUTH FACING SHORES
OF ALL ISLANDS.

&&

$$

DISCUSSION/MARINE...JACOBSON
AVIATION...BURKE




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