327  
FXHW01 KWNH 041218  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
717 AM EST SUN MAR 04 2018  
 
VALID 00Z MON MAR 05 2018 - 00Z MON MAR 12 2018  
 
AN UPPER TROUGH/EMBEDDED LOW CURRENTLY SETTLING OVER THE  
EAST-CENTRAL PACIFIC WILL BEGIN THE LONGER-TERM DRIER TREND THAT  
HAS BEEN ADVERTISED BY GUIDANCE. PRECIPITABLE WATER VALUES WILL  
DECREASE FAIRLY SLOWLY OVER THE NEXT COUPLE DAYS AHEAD OF A  
WEAKENING FRONT WHICH MAY BE ACCOMPANIED BY SOME POCKETS OF  
MODERATELY ENHANCED RAINFALL. THEN EXPECT A PUSH OF DRIER AIR  
(PWATS POSSIBLY DECREASING BELOW 0.75 INCH AT SOME LOCATIONS) THAT  
SHOULD REACH AT LEAST AS FAR SOUTH AS THE NORTHWESTERN/CENTRAL  
ISLANDS. MODELS/ENSEMBLES STILL SHOW SOUTHWESTWARD ELONGATION OF  
UPPER TROUGHING BEHIND THE INITIAL EAST-CENTRAL PACIFIC TROUGH BUT  
TODAY'S SOLUTIONS INDICATE A FARTHER NORTHWEST AXIS. AS A RESULT  
THE MOISTURE GRADIENT ENDS UP BEING CLOSER TO THE BIG ISLAND THAN  
SEEN IN CONTINUITY. THE 00Z GFS COULD BE A LITTLE TIGHT WITH ITS  
GRADIENT HOWEVER AS THE 06Z GFS HAS WEAKENED THE CORE OF UPPER  
ENERGY A BIT IN FAVOR OF THE 00Z ECMWF WHILE THE ENSEMBLE MEANS  
ARE A LITTLE WEAKER YET.  
 
CONTINUING FROM YESTERDAY, GFS TO A MODEST DEGREE GEFS SOLUTIONS  
MAINTAIN A SOMEWHAT BROADER/EASTWARD DEPICTION OF THE AMPLIFIED  
PACIFIC PATTERN ALOFT BY NEXT WEEKEND VERSUS THE ECMWF/CMC AND  
THEIR MEANS. THE MAIN EFFECT OF THIS DIFFERENCE ON HAWAI'I IS  
THAT WESTERN PACIFIC HIGH PRESSURE THAT MERGES WITH AN INITIAL  
CENTRAL PACIFIC HIGH EXTENDS FARTHER SOUTHEASTWARD ESPECIALLY IN  
THE 00Z/06Z GFS, LEADING TO STRONGER TRADES. THE 00Z GEFS MEAN  
OFFERS SOMEWHAT OF A COMPROMISE. THE AMPLIFIED NATURE OF THE  
OVERALL PATTERN SEEMS TO FAVOR LEANING SOMEWHAT TOWARD THE ECMWF  
CLUSTER AND TO SOME EXTENT GEFS MEAN BUT TELECONNECTIONS RELATIVE  
TO THE STRONG CORE OF POSITIVE HEIGHT ANOMALIES SOUTH OF THE  
ALEUTIANS BY LATE IN THE PERIOD LEAVE THE DOOR OPEN TO SOME  
BROADENING OF THE PATTERN. EITHER WAY EXPECT A FARTHER  
SOUTHEASTWARD PUSH OF LOWER PWATS NEXT WEEKEND.  
 
FLOW AROUND CENTRAL PACIFIC HIGH PRESSURE AND EVENTUAL MERGING  
WESTERN PACIFIC HIGH WILL SUPPORT NORTHEASTERLY TRADES THROUGH THE  
PERIOD--THOUGH SUBJECT TO UNCERTAINTY IN STRENGTH BY NEXT WEEKEND  
AS NOTED ABOVE. WHAT RAINFALL OCCURS SHOULD BE MOST FAVORED OVER  
WINDWARD TERRAIN AND THE BIG ISLAND WHICH WILL TEND TO SEE HIGHER  
PWATS RELATIVE TO OTHER PARTS OF THE STATE FROM MIDWEEK ONWARD.  
 
RAUSCH  
 

 
 
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