FXHW60 PHFO 200636
AFDHFO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
830 PM HST FRI SEP 19 2008
.SYNOPSIS...
WEAK HIGH PRESSURE NORTH OF THE STATE WILL MAINTAIN GENTLE TRADE 
WINDS THROUGH SATURDAY. THE HIGH TO THE NORTH WILL STRENGTHEN 
SATURDAY NIGHT WITH MODERATE TRADES RETURNING TO THE REGION SUNDAY 
THROUGH EARLY NEXT WEEK. PRECIPITATION WILL TRANSITION BACK TO 
WINDWARD AND MOUNTAIN AREAS. A LOW ALOFT WILL MOVE OVER THE ISLANDS 
THIS WEEKEND AND LINGER THROUGH THE END OF NEXT WEEK.  
&&
.DISCUSSION...
LITTLE CHANGE IS EXPECTED ACROSS THE ISLANDS THROUGH SATURDAY 
AFTERNOON. A WEAK RIDGE NORTH OF THE STATE WILL KEEP THE ISLANDS 
FANNED BY GENTLE BREEZES. THE DIURNAL CYCLE OF NIGHT TIME LAND 
BREEZES UNDER CLEARING SKIES...AND AFTERNOON SEA BREEZES WITH 
INCREASING CLOUDS IS EXPECTED TO OCCUR FOR ONE MORE DAY. THE HIGH 
FAR TO THE NORTHEAST WILL BUILD SATURDAY AND ITS ASSOCIATED RIDGE 
WILL STRENGTHEN AND RETREAT NORTH BY SATURDAY NIGHT. THIS WILL LEAD 
TO AN INCREASE IN TRADE WINDS STATEWIDE BEGINNING SATURDAY NIGHT 
WITH MODERATE TRADE WINDS LASTING THROUGH THE EARLY PART OF NEXT 
WEEK.  
HEIGHTS ALOFT HAVE LOWERED A BIT AS AN UPPER TROUGH APPROACHES THE 
ISLANDS. AFTERNOON BALLOON SOUNDINGS FROM HILO AND LIHUE SHOWED 
COOLING IN THE MID LEVELS OVER THE ISLANDS AND HAS HELPED TO WEAKEN 
THE INVERSION. FORECAST MODEL SOUNDINGS INDICATE THAT THE COOLING 
ALOFT FROM THE APPROACHING LOW WILL KEEP THE INVERSION ELEVATED NEAR 
12000 FEET. THE GFS...ECMWF AND NOGAPS ALL AGREE THAT THE UPPER 
TROUGH WILL CLOSE OFF OVER THE HAWAIIAN ISLANDS ON TUESDAY. THE 
UPPER TROUGH IS EXPECTED TO LINGER OVER THE ISLANDS BUT WILL WEAKEN 
THROUGH THE END OF NEXT WEEK.
ALSO IN THE MIX IS A WEAK SURFACE TROUGH WELL EAST OF THE ISLANDS 
CURRENTLY NEAR 145W. THE MODELS BRING THIS SOURCE OF MOISTURE OVER 
THE STATE LATE SUNDAY AND MONDAY. IT IS DIFFICULT TO PINPOINT THE 
DETAILS...BUT WITH THE UPPER LOW OVERHEAD AND THE INCREASE IN LOW 
LEVEL MOISTURE...SOME LOCALLY HEAVY RAIN SHOWERS ARE POSSIBLE. THE 
CURRENT FORECAST HAS THIS IDEA PAINTED OVER WINDWARD AREAS AS WELL 
AS THE KONA DISTRICT UNDER THIS MOIST AND UNSTABLE ENVIRONMENT. THIS 
MAY NEED TO BE ADJUSTED AS WE PROGRESS TOWARDS THIS TIME PERIOD 
SINCE SOME OF THESE HEAVIER SHOWERS MAY SPREAD OVER TO LEEWARD 
SECTIONS AS WELL.  
FORECAST MODELS ARE SHOWING A FRONTAL BOUNDARY TO MOVE IN LATE NEXT 
WEEK. CONFIDENCE IS LOW AT THIS POINT WITH THIS FEATURE...BUT IF IT 
PANS OUT...THE RIDGE WILL BE PUSHED CLOSER TO THE ISLANDS AND THUS 
WEAKENING THE TRADE WINDS NEXT THURSDAY. FOR NOW...WILL STICK WITH 
A TYPICAL TRADE WIND REGIME WITH SHOWERS REMAINING FOCUSED OVER 
WINDWARD AND MOUNTAIN AREAS. 
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
ELAU