HAWAII EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 759 AM EDT THU SEP 27 2012 VALID 00Z FRI SEP 28 2012 - 00Z FRI OCT 05 2012 CONSENSUS OF MODELS IS THAT A SIGNIFICANT TROUGH AMPLIFIES TO THE NORTHWEST OF THE HAWAIIAN ISLANDS THIS WEEKEND INTO EARLY NEXT WEEK. SOME OF THE MODELS...INCLUDING THE 06Z GFS...HOLD THE TROUGH TO THE NORTHWEST OF THE ISLANDS WHILE SOME OTHERS BEGIN TO LIFT IT NORTHEASTWARD. GIVEN THE STRENGTH OF THE UPPER RIDGE OVER THE WESTERN PACIFIC...TEND TO FAVOR THE SOLUTIONS THAT KEEPS THE TROUGH IN PLACE RATHER THAN LIFTING IT NORTHEASTWARD. EVEN THE 00Z ECMWF LEAVES A SIGNIFICANT PORTION OF THE TROUGH TO THE NORTHWEST OF THE ISLANDS EARLY NEXT WEEK. NET EFFECT OF THE DIGGING TROUGH IS TO DISRUPT THE MODERATE TRADE REGIME...CAUSING THE SURFACE FLOW TO WEAKEN AND SHIFT TO A WEAK SOUTHEASTERLY FLOW. THIS SHOULD INCREASE THE MOISTURE ACROSS THE ISLAND CHAIN AS IT STILL APPEARS THAT THE FRONT ASSOCIATED WITH THE TROUGH WILL REMAIN NORTHWEST OF THE ISLANDS. THIS CHAIN OF EVENTS APPEARS TO INCREASE THE CHANCES OF HEAVY DOWNPOURS LATER THIS WEEKEND AND EARLY NEXT WEEK. WHAT MAKES THIS FORECAST PARTICULARLY COMPLEX ARE THAT THERE ARE A COUPLE OF TROPICAL CYCLONES OVER THE WEST PACIFIC THAT THE MODELS ARE ALL OVER THE PLACE WITH THEIR EVOLUTION ACROSS THE PACIFIC...BUT MAY INFLUENCE THE STRENGTH OF THE UPPER RIDGE WEST OF HAWAII AND HOW THEY MAY ULTIMATELY INFLUENCE HOW THE DEEP TROUGH EVOLVES OVER THE CENTRAL PACIFIC. KOCIN