HAWAII EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 824 AM EDT SAT APR 06 2013 VALID 00Z SUN APR 07 2013 - 00Z SUN APR 14 2013 TRANQUIL WEATHER PATTERN EXPECTED FOR HAWAI'I--MUCH OF THIS FORECAST PERIOD. LITTLE CHANGE FROM PREVIOUS FORECASTS THROUGH AT LEAST DAY 5 (THURSDAY) WITH ISOLATED MAUKA SHOWERS AND MODERATE/BRISK TRADES EXPECTED THROUGH THIS WEEKEND. BROAD MID- TO UPPER-LEVEL RIDGING NORTHEAST OF THE THE ISLANDS WILL CONTINUE TO HOLD FIRM BETWEEN THE MAINLAND AND THE BIG HAWAII...ANCHORING INVOF 30N 145W THROUGH NEXT FRIDAY. IF THERE IS A TREND IN THE 6/00Z ECMWF/GFS PACKAGES...IT IS TO DELAY THE IMPACTS OF LONG WAVE TROUGH DEVELOPMENT IN THE CENTRAL PACIFIC INVOF 35N 170W-175W UNTIL NEXT FRIDAY/SATURDAY (DAYS 6/7) WHEN EXPECTED HEIGHT FALLS AND RAINFALL POTENTIAL ACROSS KAUAI INCREASE. TIL THEN...A BLEND OF THE EC/GEFS ENSEMBLE MEANS WOULD REASONABLY HANDLE A 'PERSISTENCE' FORECAST BASED ON THE FLOW PATTERN ALOFT AND IN THE LOWER LEVELS OF THE ATMOSPHERE. THE 6/00Z DETERMINISTIC GFS/ECMWF HAVE COME INTO BETTER FOCUS WITH THE AMPLIFYING TROUGH AXIS OVER SOUTHWEST ALASKA AND THE CENTRAL PACIFIC. PART OF THE FORECAST CHALLENGE HAS BEEN TO DETERMINE WHETHER OR NOT THERE WOULD BE SOME PHASING OF AN UPPER TROUGH IN THE MID LATITUDE AND SUBTROPICAL CENTRAL PACIFIC. IN THE GULF OF ALASKA...THE SOLUTION IS STABILIZING...AND CALLS FOR THE BULK OF THE COLD AIR AND TROUGHING TO SLOWLY MIGRATE THROUGH THE EASTERN GULF OF ALASKA AND INTO SOUTHWEST CANADA. IN TURN AND IN RESPONSE...THE STABLE RIDGE BETWEEN THE MAINLAND AND HAWAI'I SLOWLY MIGRATES SOUTHWESTWARD...RATHER THAN NORTHEASTWARD IN MORE OF A BLOCKY CONFIGURATION RATHER THAN A PROGRESSIVE PATTERN. THUS...THE PROGRESSION OF THE SUBTROPICAL PORTION OF THE TROUGH CONTINUES TO SLOW DOWN...BUT THE TROUGH AMPLIFICATION CONTINUES ALONG THE DATELINE WITH LITTLE TO NO PHASING UPSTREAM ALONG 40N 150W/160W WITH THE NORTHERN STREAM. THE 6/00Z DETERMINISTIC GFS/ECMWF SEEM TO AGREE THAT NEXT FRIDAY AFTERNOON INTO EARLY SATURDAY MORNING (LOCAL TIME)...THIS TROUGH WILL BE ON KAUAI'S DOORSTEP AND ORGANIZED RAINFALL POTENTIAL WILL BE ON THE INCREASE (13/00Z TO 13/18Z TIME FRAME). VOJTESAK