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Hawaiian Islands Synoptic Discussion and Guidance

797
FXHW60 PHFO 020203
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 PM HST MON SEP 1 2014

.SYNOPSIS...
LIGHT WINDS WILL ALLOW LAND BREEZES TO DEVELOP LATER TONIGHT AS THE
LAND COOLS...RESULTING IN CLEARING SKIES OVERNIGHT. SLIGHTLY
STRONGER TRADES ARE EXPECTED TO BUILD IN THE NEXT FEW DAYS AS A HIGH
PRESSURE RIDGE EXTENDS NORTH OF THE ISLANDS. WITH THE STRENGTHENING
TRADES...EXPECT THE CLOUDS AND SHOWERS TO BE FOCUSED MORE OVER THE
WINDWARD SLOPES.

&&

.DISCUSSION...
AFTERNOON CONVECTION BUILT OVER THE ISLAND THIS AFTERNOON AS
EXPECTED...WITH LOCALIZED SHOWERS...RATHER HEAVY OVER WINDWARD OAHU
IN THE PAST HOUR. A FEW GAGES REPORTED ALMOST HALF AN INCH OF RAIN
IN THE PAST FIFTEEN MINUTES. THEREFORE HAVE ISSUED A FLOOD ADVISORY
FOR WINDWARD OAHU AT TIME. EXPECT THE CONVECTION TO PEAK IN THE NEXT
FEW HOURS...THEN SLOWLY DISSIPATES AFTER SUNSET. SEA BREEZES PRETTY
MUCH DOMINATE THE ISLAND WIND FLOW THIS AFTERNOON...AS SYNOPTIC
BACKGROUND WINDS REMAIN LIGHT EAST SOUTHEASTERLY. AFTERNOON LIHUE
AND HILO SOUNDINGS ARE NOT THAT MUCH DIFFERENT...COMPARED TO
YESTERDAYS...EXCEPT FOR THE LOWER LOW LEVEL MOISTURE DEPTH. AIR MASS
REMAINS MARGINALLY UNSTABLE...WITH NEAR NORMAL MOISTURE AS INDICATED
BY THE SOUNDINGS. AS THE EVENING FALLS...EXPECT A SLOW CLEARING OF
SKIES OVER THE ISLANDS...WITH LAND BREEZES DEVELOPING OVERNIGHT.

EVEN THOUGH A SURFACE TROUGH WILL PERSIST FAR NORTHWEST OF THE
ISLANDS THROUGH EARLY PART OF THIS WEEK...FORECAST MODELS CONTINUE
TO INDICATE A SURFACE HIGH PRESSURE RIDGE WILL DEVELOP NORTH OF THE
STATE IN THE COMING DAYS. THIS WILL ALLOW STRONGER TRADES TO RETURN
TO THE ISLANDS. IN FACT...THE ISLANDS ARE EXPECTED TO SEE THESE
TRADE WINDS BEGINNING TUESDAY. AS THIS RIDGE WILL NOT BE TOO
STRONG...THE SURFACE PRESSURE GRADIENT ACROSS THE ISLANDS WILL
REMAIN SOMEWHAT SLACK AND THUS THE BUILDING TRADE WINDS WILL BE
MODEST AT MOST. THEREFORE...MAY SEE A HYBRID TRADE WIND AND
CONVECTIVE WEATHER PATTERN OVER THE ISLANDS THROUGH THIS WEEK...WITH
CLOUDS AND SHOWERS EMBEDDED IN THE TRADE WINDS TO AFFECT WINDWARD
AREAS...WHILE AFTERNOON CLOUDS WITH POSSIBLE A FEW SHOWERS WILL
BUILD OVER THE LEE AREAS. THE MODELS STILL SHOW A DECREASE IN LOW
LEVEL MOISTURE ACROSS THE STATE BY WEDNESDAY. THIS MAY LEAD TO
LIMITED PRECIPITATION FOR THE ISLANDS.

MODEL RUNS ALSO CONTINUE TO SHOW HIGHER LOW LEVEL MOISTURE EMBEDDED
IN THE TRADE WIND FLOW REACHING THE ISLANDS TOWARDS THE WEEKEND.
THIS MOISTURE APPEARS TO BE LOOSELY ASSOCIATED WITH THE REMNANT OF
MARIE. THEREFORE...EXPECT AN UPTICK IN THE SHOWERS UNDER THE LIGHT
TO MODERATE TRADE WINDS FOR THE STATE BY THE WEEKEND.

&&

.AVIATION...
SEABREEZE DEVELOPMENT HAS ALLOWED FOR CLOUD BUILDUPS AND SHOWERS TO
FORM OVER THE ISLANDS. WITH SUNSET...THESE CLOUDS AND SHOWERS WILL
SCATTER OUT AND OVERNIGHT THE ISLANDS SHOULD REMAIN FAIRLY QUIET.
WINDWARD AND MOUNTAIN AREAS MAY EXPERIENCE ISOL MVFR CONDITIONS AS
WEAK TRADE WIND FLOW BEGINS TO COME BACK. THERE ARE NO AIRMETS IN
EFFECT.

&&

.MARINE...
LATEST READINGS FROM NEAR SHORE BUOY JUST SOUTHWEST OF OAHU SHOWED
A SLOW DOWNWARD TREND...AS EXPECTED. LOOK FOR THE ELEVATED SURF FOR
SOUTH FACING SHORES TO SLOWLY SUBSIDE THROUGH REST OF THE DAY INTO
TUESDAY.

A VERY LONG PERIOD SOUTH SWELL...20-25 SECONDS...IS DUE TO ARRIVE
EARLY TUESDAY...THEN BUILDING THROUGH WEDNESDAY. THIS SWELL WILL
LIKELY PRODUCE ADVISORY LEVEL SURF WEDNESDAY INTO THURSDAY.

WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS
AT LEAST FOR THE NEXT SEVERAL DAYS.

&&

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

&&

$$

AVIATION...EATON
REST...HUI



Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office