055  
FXHW01 KWNH 131211  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
711 AM EST TUE FEB 13 2018  
 
VALID 00Z WED FEB 14 2018 - 00Z WED FEB 21 2018  
 
TODAY'S GUIDANCE CONTINUES TO SUGGEST THAT MEAN TROUGHING ALOFT  
WILL SUPPORT A LENGTHY PERIOD OF UNSETTLED WEATHER, ALONG WITH A  
PERSISTENT NORTH-SOUTH TROUGH AXIS AT THE SURFACE PREVENTING ANY  
SEMBLANCE OF TRADE FLOW.  
 
WITHIN THE OVERALL MEAN TROUGH ALOFT THE FIRST FEATURE OF INTEREST  
WILL BE A DEEP UPPER LOW NORTHWEST OF THE STATE. GUIDANCE  
CONSENSUS SHOWS THIS UPPER LOW TRACKING SOUTHEAST TO POSITION  
NORTH OF KAUAI BY THURSDAY FOLLOWED BY A RAPID TURN TO THE NORTH  
IN RESPONSE TO UPSTREAM FLOW. EXACT DETAILS VARY BY MODEL BUT IN  
PRINCIPLE THERE IS DECENT AGREEMENT THAT THIS EVOLUTION WILL  
LIKELY GENERATE ENHANCED FOCUS OF DEEP MOISTURE WITH AN AXIS OF  
HEAVY RAINFALL POTENTIAL DRIFTING FROM WEST TO EAST ACROSS THE  
ISLANDS DURING WEDNESDAY TO THURSDAY NIGHT.  
 
WITH THE NORTHWARD DEPARTURE OF THE UPPER LOW, THE AXIS OF  
GREATEST DEEP MOISTURE MAY STALL NEAR THE BIG ISLAND INTO THE LATE  
WEEK/WEEKEND TIME FRAME. THUS THE BIG ISLAND MAY CONTINUE TO SEE  
SOME RAINFALL WHILE WESTERN ISLANDS SEE A PERIOD OF RELATIVELY  
DRIER WEATHER. THEN OVER THE WEEKEND UPSTREAM ENERGY RELOADING  
THE MEAN UPPER TROUGH MAY PULL SOME MOISTURE BACK TO THE WEST  
LEADING TO ANOTHER PERIOD OF ENHANCED RAINFALL POTENTIAL. THERE  
IS SOMEWHAT MORE SPREAD FOR THE PRECISE EVOLUTION DURING THIS PART  
OF THE FORECAST VERSUS THE PRIOR EPISODE THOUGH. BY NEXT MONDAY  
MOST GUIDANCE INDICATES THAT THE TROUGH ENERGY WILL CLOSE OFF  
ANOTHER UPPER LOW NEAR THE ISLANDS. THE 00Z CMC TRACK ENDS UP  
SOUTH OF MOST OTHER SOLUTIONS WHILE THE 00Z/06Z GFS ARE DEEPER  
THAN OTHER MODELS/MEANS. LOOKING AT THE ENSEMBLES, AS MIGHT BE  
EXPECTED 00Z GEFS MEMBERS OFFER MORE SUPPORT FOR THE GFS DEPTH (ON  
A PERCENTAGE BASIS) THAN DO ECMWF MEMBERS. THIS FEATURE WILL  
LIKELY KEEP THE AREA FAIRLY UNSTABLE BUT AT LEAST PUSH THE AXIS OF  
HIGH PRECIPITABLE WATER VALUES FARTHER TO THE EAST AWAY FROM THE  
STATE.  
 
RAUSCH  
 

 
 
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