HAWAII EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 804 AM EDT TUE SEP 18 2012 VALID 00Z WED SEP 19 2012 - 00Z WED SEP 26 2012 EARLY MORNING RADAR IMAGERY SHOWED SHALLOW TRADE WIND SHOWERS...WITH INSTABILITY CAPPED AROUND 700 MB BY STABLE MID LEVEL AIR. SATELLITE IMAGERY...HOWEVER...REVEALED AN UPPER LEVEL TROUGH JUST NORTH OF THE ISLANDS...WITH PERHAPS A SMALL CLOSED LOW EVIDENT IN THE HIGH CLOUD PATTERN DUE NORTH OF MAUI. THIS TROUGH SHOULD BRING AT LEAST SOME LIFT/COOLING AND DESTABILIZATION OF THE MID LEVELS AS IT DRIFTS SSE ACROSS THE ISLANDS TODAY THROUGH WEDNESDAY. THIS MAY ENHANCE INSTABILITY JUST SLIGHTLY...LEADING TO HEAVIER RAIN RATES...WITH WINDWARD LOCATIONS STILL FAVORED FOR PRECIPITATION. THIS UPPER TROUGH IS FORECAST TO WEAKEN AS IT DIPS TO THE EAST OF THE ISLANDS. ATTENTION THEN TURNS TO THE MAIN BELT OF WESTERLIES ACROSS THE NORTHERN PACIFIC. A LONG WAVE TROUGH WILL GENERALLY REMAIN ESTABLISHED AND EXPAND ITS INFLUENCE ACROSS THE NORTH. ONE SIGNIFICANT SHORTWAVE WILL MIGRATE THROUGH THE GULF OF ALASKA EARLY IN THE WEEKEND...BRINGING A FRONT THAT WILL STALL NNW OF HAWAII...AND SUPPRESSING THE SURFACE HIGH OVER THE NORTHEAST PACIFIC. THIS WILL CAUSE LOW LEVEL WINDS TO VEER SLIGHTLY...AND TRADES TO SLACKEN A BIT...ALLOWING MORE INFLUENCE FROM SEA BREEZE ACTIVITY TO REGULATE DIURNAL SHOWERS. SOME INCREASE OF PRECIPITABLE WATER DURING THIS PERIOD WILL ALLOW FOR LOCALLY HEAVY DOWNPOURS...THOUGH GENERALLY WITH LITTLE ORGANIZATION. EXPECT A MORE SEASONAL ISLAND TRADES AND LIMITED WINDWARD SHOWER PATTERN MAY RETURN LATER IN THE WEEKEND INTO NEXT WEEK IN THE WAKE OF SYSTEM PASSAGE AS HIGH PRESSURE BRIDGES BACK TO THE NORTH OF THE STATE. BURKE