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Hawaiian Islands Synoptic Discussion and Guidance

817
FXHW60 PHFO 251333
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST FRI JUL 25 2014

.SYNOPSIS...
THE TRADE WINDS WILL BECOME MODERATE TODAY AND SATURDAY. WINDWARD
SHOWERS WILL CONTINUE THROUGH THE NEXT SEVERAL DAYS...MAINLY AT
NIGHT AND DURING THE MORNING HOURS. A SLIGHT INCREASE IN SHOWER
ACTIVITY IS EXPECTED DURING THE WEEKEND...WITH TRADES REGAINING
STRENGTH LATE SUNDAY AND INTO EARLY NEXT WEEK.

&&

.DISCUSSION...
THE STRONG SFC HIGH PRESSURE LOCATED FAR NNE OF THE MAIN HAWAIIAN
ISLANDS WILL RELAX A LITTLE TODAY AS A WEAK TROUGH PASSES JUST TO
THE N OF THE ISLAND CHAIN AND CONTINUES TO MIGRATE E THROUGH THE
WEEKEND. THIS WILL BRING A WEAKENING OF THE TRADES DURING THE NEXT
COUPLE OF DAYS. SHOWERS ARE STILL FAVORING WINDWARD AND MAUKA...BUT
LATEST RADAR DATA SHOW A SIGNIFICANT REDUCTION IN SHOWER/RAINFALL
COVERAGE ACROSS THE ISLANDS COMPARED TO PREVIOUS NIGHTS. MIMIC AND
MODEL MOISTURE ANALYSES DEPICT A DRYER AIRMASS UPSTREAM OF THE
ISLANDS...WITH PWATS STEADILY DECREASING TO AROUND 1 TO 1.3 INCHES.
12Z SOUNDINGS DEPICT STRONG INVERSIONS AROUND 6 THOUSAND
FEET...WHICH SHOULD MAKE VERTICAL DEVELOPMENT OF SHOWERS RATHER
DIFFICULT. A MID/UPPER LEVEL HIGH JUST SW OF THE ISLANDS IS ALSO
SUPPORTING AN ASSOCIATED RIDGE...WHICH IS EXTENDING THROUGH THE
ISLAND CHAIN. THIS SYNOPTIC SETUP SHOULD RESULT IN RELATIVELY BENIGN
WEATHER CONDITIONS ACROSS THE ALOHA STATE AT LEAST THROUGH EARLY
SATURDAY.

MEANWHILE...MODELS SHOW AN AREA OF ENHANCED TROPICAL MOISTURE
GRADUALLY APPROACHING THE MAIN HAWAIIAN ISLANDS AND POSSIBLY
BRINGING A SLIGHT INCREASE IN SHOWERS BY LATE SAT. ALSO...A LOW
PRESSURE SYSTEM WILL PASS FAR S OF THE ALOHA STATE HEADING W WHICH
COULD TIGHTEN PRESSURE GRADIENTS ACROSS THE ISLANDS. THIS MAY BRING
INCREASING TRADES LATE IN THE WEEKEND AND INTO EARLY NEXT WEEK.

BY THE MIDDLE OF NEXT WEEK...MODELS SHOW POTENTIAL FOR YET ANOTHER
SURGE OF TROPICAL MOISTURE APPROACHING THE ALOHA STATE FROM THE
SE...AROUND THE WED/THU TIMEFRAME. THIS MOISTURE WILL HELP IN
SIGNIFICANTLY ENHANCING TRADE WIND SHOWERS ACROSS THE ISLAND CHAIN
ONCE MORE.

&&

.AVIATION...
VFR CONDITIONS WILL DOMINATE OVER MOST AREAS TODAY. WINDWARD SLOPES
WILL SEE ISOL MVFR CIGS AS SMALL POCKETS OF MOISTURE RIDE IN ON THE
TRADE WIND FLOW. RADAR VAD WIND PROFILES SHOW THAT LOW LEVEL WINDS
ARE DOWN SLIGHTLY IN THE 15 TO 20 KT RANGE. AS A RESULT...AIRMET
TANGO FOR LOW LEVEL TURB WILL LIKELY BE CANCELLED BEFORE SUNRISE.

&&

.MARINE...
THE SMALL CRAFT ADVISORY FOR FOR THE TYPICALLY WINDIER WATERS AROUND
THE BIG ISLAND AND MAUI HAS BEEN CANCELLED. WINDS ARE EXPECTED TO
AGAIN INCREASE LATE SUNDAY AND INTO EARLY NEXT WEEK AS A DEVELOPING
SYSTEM PASSING WELL SOUTH OF THE STATE HELPS TO TIGHTEN THE PRESSURE
GRADIENT.

NO SIGNIFICANT SWELLS ARE EXPECTED THROUGH THE NEXT SEVERAL DAYS.
SMALL LONG-PERIOD BACKGROUND SWELL FROM THE SSW AND SHORT-PERIOD
SWELL FROM THE SE REPRESENT THE SWELL SOURCES FROM THE SOUTHERN
HEMISPHERE...WHILE SHORT PERIOD WIND WAVES FROM THE EAST REPRESENT
THE ONLY SOURCE OF SWELL FROM THE NORTHERN HEMISPHERE.

&&

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

&&

$$

DISCUSSION/MARINE...REYNES
AVIATION...WROE





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