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Hawaiian Islands Synoptic Discussion and Guidance

972
FXHW60 PHFO 221330
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 AM HST MON SEP 22 2014

.SYNOPSIS...
THE PREVAILING LIGHT WINDS WILL FINALLY SHIFT TO A MORE TYPICAL
TRADE WIND PATTERN STARTING TODAY...BRINGING SOME RELIEF FROM THE
HUMID AND MUGGY CONDITIONS OF THE LAST SEVERAL DAYS. AS THE TRADES
ESTABLISH...SHOWERS WILL BECOME MORE FOCUSED OVER WINDWARD AND
MOUNTAIN AREAS. A WETTER TRADE WIND PATTERN IS EXPECTED FOR THE
SECOND HALF OF THE WEEK.

&&

.DISCUSSION...
A TROPICAL DISTURBANCE A COUPLE HUNDRED MILES WSW OF KONA IS STILL
KEEPING ENHANCED LOW LEVEL MOISTURE AROUND THE BIG ISLAND AND
ADJACENT S AND W COASTAL WATERS. MEANWHILE...LATEST WATER VAPOR
SATELLITE DATA SHOWS AN UPPER LEVEL TROUGH ALIGNED FROM SW TO NE
NEAR THE ALENUIHAHA CHANNEL AND MAUI. THESE FEATURES ARE STILL
PROVIDING FAVORABLE ATMOSPHERIC CONDITIONS FOR PASSING SHOWERS TO
MOVE ACROSS THE BIG ISLAND...MAINLY OVER WINDWARD AREAS AND THE SE
SLOPES OF MAUNA LOA...THROUGH THE LATE MORNING HOURS.

THE PREVAILING LIGHT WIND REGIME WILL FINALLY BEGIN TO MODIFY AS A
STATIONARY SFC FRONTAL BOUNDARY ABOUT 400 MILES N OF KAUAI IS
REPLACED BY A BUILDING HIGH PRESSURE SYSTEM NW OF THE ALOHA STATE.
PRESSURE GRADIENTS WILL INCREASE ACROSS THE AREA WITH A RETURN TO A
MORE TYPICAL TRADE WIND FLOW DURING THE FIRST HALF OF THE WEEK. AS
THE TRADES BUILD UP...EXPECT A GRADUAL RELIEF FROM THE MUGGY AND
HUMID CONDITIONS OF THE LAST SEVERAL DAYS. THE TRADES WILL ALSO
SHIFT THE FOCUS OF SHOWER ACTIVITY BACK TO WINDWARD AND MOUNTAIN
AREAS.

LATEST GLOBAL MODEL SOLUTIONS SHOW A FRONTAL BOUNDARY APPROACHING
THE AREA FROM THE N...REACHING THE MAIN HAWAIIAN ISLANDS LATE WED
AND INTO THU. THIS FRONT WILL ALSO DRAG A BAND OF ENHANCED MOISTURE
WITH IT...BRINGING A RATHER WET TRADE PATTERN DURING THE SECOND HALF
OF THE WEEK. THE OVERALL TIMING AND DURATION OF THIS SCENARIO IS
STILL BEING EVALUATED...BUT IF THE MODELS ARE CORRECT THIS BAND OF
MOISTURE COULD LINGER ACROSS THE ISLANDS THROUGH AT LEAST SAT.
THUS...THERE IS A POSSIBILITY FOR EXTENDED PERIODS OF VERY WET
CONDITIONS ESPECIALLY OVER WINDWARD AND MOUNTAIN AREAS TO LAST
THROUGH THE WEEKEND. THE LATEST FORECAST PACKAGE HAS BEEN UPDATED TO
CARRY INCREASING POPS/RAIN ACTIVITY FROM THU THROUGH SAT.

&&

.AVIATION...
TRADE WINDS ARE EXPECTED TO BEGIN RETURNING TODAY. SHOWER ACTIVITY
WILL SHIFT FOCUS TO WINDWARD AND MAUKA AREAS...WITH A FEW CLOUDS
DEVELOPING OVER LEEWARD AREAS.

&&

.MARINE...
INCREASING TRADES COULD BRING WIND SPEEDS CLOSE TO SMALL CRAFT
ADVISORY LEVEL OVER THE TYPICALLY WINDIER WATERS AROUND THE BIG
ISLAND AND MAUI COUNTY STARTING TUESDAY.

SURF HEIGHTS ARE EXPECTED TO REMAIN NEAR BACKGROUND LEVELS THROUGH
MOST OF THE WEEK. A SLIGHTLY HIGHER SWELL IS EXPECTED FROM THE NNE
THURSDAY THROUGH SATURDAY. A MODERATE SSW IS DUE NEXT WEEKEND.

&&

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

&&

$$

REYNES






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