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Hawaiian Islands Synoptic Discussion and Guidance

104
FXHW60 PHFO 020338
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
538 PM HST WED OCT 1 2014

.UPDATE...
HAVE UPDATED THE FORECASTS TO REMOVE MENTION OF LOCALLY HEAVY
RAIN...AS MOST ACTIVITY HAS SHIFTED OFFSHORE AND RAINFALL RATES
HAVE DECREASED CONSIDERABLY FROM THOSE OBSERVED EARLIER IN THE
AFTERNOON. REMAINING LEEWARD SHOWER ACTIVITY SHOULD CONTINUE TO
DIMINISH THIS EVENING WITH THE LOSS OF DAYTIME HEATING.

&&

.SYNOPSIS...
A DRIER AND MORE STABLE AIRMASS WILL RETURN TO THE ISLANDS FROM
TONIGHT THROUGH THE END OF THE WEEK. LIGHT WINDS AND MUGGY
CONDITIONS WILL CONTINUE AS A WEAK SURFACE HIGH PRESSURE RIDGE
STAYS NEAR OR JUST NORTH OF THE STATE.

&&

.PREV DISCUSSION.../ISSUED 350 PM HST WED OCT 1 2014/

HEAVY DOWNPOURS HAVE DEVELOPED ACROSS PARTS OF CENTRAL OAHU
DURING THE LAST FEW HOURS...WITH GAUGES AND RADAR ESTIMATES
SHOWING RAINFALL RATES OF OVER 4 INCHES PER HOUR NEAR MILILANI
DURING THE PAST COUPLE OF HOURS. ISOLATED HEAVIER SHOWERS HAVE
RECENTLY DEVELOPED OVER PARTS OF KAUAI AS WELL. THE EASTERN HALF
OF THE STATE REMAINS MUCH QUIETER...WITH JUST ISOLATED LIGHTER
SHOWERS OVER PARTS OF LEEWARD MAUI COUNTY...AND ALMOST NO SHOWER
ACTIVITY OVER 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 24N152W AND MOVING SLOWLY EASTWARD...WITH A WEAK
TROUGH EXTENDING WESTWARD ACROSS THE STATE. THE 00Z LIHUE SOUNDING
REMAINED RATHER MOIST AND UNSTABLE IN THE LOW LEVELS....WITH AN
ABOVE NORMAL PWAT OF 1.68 INCHES. SOME DRYING AND WARMING HAS
OCCURRED IN THE PAST 12 HOURS ABOVE 700 MB. THE 00Z HILO SOUNDING
CONTINUED TO BE DRIER AND MORE STABLE...WITH NEAR NORMAL PWAT OF
1.48 INCHES...AND A STRENGTHENING INVERSION BASED NEAR 7500 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.

IN THE NEAR TERM...LOCALLY HEAVY DOWNPOURS WILL REMAIN POSSIBLE
ACROSS OAHU AND KAUAI THROUGH THE NEXT COUPLE OF HOURS...AS SLOW
MOVING CONVECTION CONTINUES TO FIRE ALONG SEABREEZE BOUNDARIES.
THIS ACTIVITY SHOULD DIMINISH EARLY THIS EVENING AS DAYTIME
HEATING IS LOST. LATER 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 SHOULD
DEVELOP...AS A WEAK LOW LEVEL RIDGE NUDGES WESTWARD TO OUR NORTH.
WOULD STILL EXPECT SEABREEZES TO DEVELOP ACROSS SOME INTERIOR AND
LEEWARD AREAS THURSDAY AND FRIDAY AFTERNOONS...BUT THEY WILL
PROBABLY NOT BE 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. 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. DEVELOPING LIGHT SOUTHEAST
BACKGROUND FLOW MAY ALLOW AREAS OF VOLCANIC HAZE TO SPREAD
NORTHWESTWARD OVER SOME OF THE SMALLER ISLANDS DURING THIS TIME.

&&

.AVIATION...
VFR CONDITIONS PREVAIL AT MOST OF THE TAF SITES WITH THE EXCEPTION
OF PHNY WHICH IS EXPERIENCING MVFR CONDITIONS TO TO LOW CIGS. SOME
MVFR CONDITIONS ARE LIKELY OCCURRING OVER INTERIOR PORTIONS OF
KAUAI...OAHU AND MOLOKAI DUE TO SHRA. EXPECT IMPROVING CONDITIONS
LATER THIS EVENING AND ON THROUGH THE OVERNIGHT HOURS.

&&

.MARINE...
AFTERNOON 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
APPEARS TO HAVE PEAKED EARLIER TODAY AND WILL GRADUALLY SUBSIDE
THROUGH THE NEXT COUPLE OF DAYS...WITH SURF REMAINING BELOW
ADVISORY LEVELS ACROSS NORTH AND WEST FACING SHORES. A SERIES OF
MODERATE NORTHWEST SWELLS WILL ARRIVE DURING THE WEEKEND AND INTO
EARLY NEXT WEEK...WITH SURF ALSO 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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