273  
FXHW01 KWNH 031218  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
718 AM EST SAT MAR 03 2018  
 
VALID 00Z SUN MAR 04 2018 - 00Z SUN MAR 11 2018  
 
THE RECENT PATTERN OF MOIST EAST-SOUTHEASTERLY LOW LEVEL FLOW  
ALONG WITH AN AXIS OF ENHANCED DEEP MOISTURE ORIENTED JUST WEST OF  
160W LONGITUDE WILL EXTEND BRIEFLY INTO THIS WEEKEND. SHORTWAVE  
IMPULSES AHEAD OF A LINGERING UPPER TROUGH/LOW TO THE WEST OF THE  
STATE MAY PROVIDE SOME MODEST ENHANCEMENT TO SHOWER ACTIVITY AS  
THEY PASS OVER THE AREA.  
 
THEN THE ESTABLISHMENT OF AN EAST-CENTRAL PACIFIC TROUGH ALOFT  
WILL BRING SIGNIFICANTLY LOWER PRECIPITABLE WATER VALUES TO THE  
AREA FROM THE NORTH. EXPECT THE DRIEST AIR TO BE BEHIND A FRONT  
THAT REACHES THE STATE DURING THE LATE MONDAY/TUESDAY TIME FRAME  
AND MAY BE ACCOMPANIED BY SOME SHOWERS. BEHIND THE FRONT, STRONG  
CENTRAL PACIFIC HIGH PRESSURE WILL SUPPORT BRISK TRADES FROM THE  
NORTHEAST INTO LATE WEEK. TOWARD THE LATTER HALF OF THE WEEK  
THERE HAS BEEN SOME DISCREPANCY REGARDING THE DEPTH/AMPLITUDE OF  
UPPER TROUGHING THAT EXTENDS SOUTHWEST OVER THE AREA. BY  
THURSDAY-FRIDAY THE GFS SHOWS A SOMEWHAT WEAKER TREND COMPARED TO  
YESTERDAY. THIS YIELDS IMPROVED AGREEMENT BETWEEN THE GFS/ECMWF  
AND THEIR MEANS--THE RECOMMENDED COMPROMISE--WHILE THE 00Z CMC/CMC  
MEAN MAY STILL BE SOMEWHAT UNDERDONE WITH THE UPPER TROUGH.  
 
BY SATURDAY GUIDANCE BEGINS TO CLUSTER INTO TWO CAMPS FOR THE  
EVOLVING RIDGE/TROUGH PACIFIC PATTERN ALOFT, THE SHARPER AND  
WESTWARD ECMWF/CMC PLUS THEIR MEANS VERSUS THE BROADER AND  
EASTWARD GFS/GEFS. THE MAIN DIFFERENCE FOR HAWAI'I IS THAT THE  
ECMWF CLUSTER WOULD WEAKEN THE SURFACE RIDGE NORTH OF THE ISLANDS  
SOMEWHAT THUS LEADING TO A SLACKENING OF TRADES RELATIVE TO THE  
GFS/GEFS. OFFSETTING CONSIDERATIONS SEEM TO FAVOR A COMPROMISE AT  
THIS POINT. AGREEABLE MULTI-DAY D+8 MEANS SHOW A STRONG CORE OF  
POSITIVE HEIGHT ANOMALIES SOUTH OF THE WESTERN ALEUTIANS, WITH  
TELECONNECTIONS SUGGESTING THE BROADER GFS/GEFS SCENARIO ALOFT.  
HOWEVER THE OVERALL EASTERN ASIA THROUGH PACIFIC AND WESTERN NORTH  
AMERICA EVOLUTION LOOKS QUITE AMPLIFIED WHICH MERITS INCORPORATING  
ECMWF ASPECTS AS WELL. EITHER WAY EXPECT A CONTINUATION OF  
WINDWARD-FOCUSED SHOWERS, IN THE LIGHTER HALF OF THE SPECTRUM  
GIVEN BELOW NORMAL PRECIPITABLE WATER VALUES BUT PERIODICALLY  
ENHANCED BY INDIVIDUAL SHORTWAVES WITHIN THE CYCLONIC FLOW ALOFT.  
 
RAUSCH  
 

 
 
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