740  
FXHW01 KWNH 171213  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
712 AM EST SAT FEB 17 2018  
 
VALID 00Z SUN FEB 18 2018 - 00Z SUN FEB 25 2018  
 
MODELS/ENSEMBLE SUGGEST A BLOCKY PATTERN DEVELOPING ACROSS THE  
NORTH/CENTRAL PACIFIC OVER THE NEXT SEVERAL DAYS, WITH AN RIDGE  
AMPLIFYING SOUTH OF ALASKA AND PERSISTENT NEGATIVE HEIGHT  
ANOMALIES IN THE VICINITY OF HAWAI'I. EARLY IN THE PERIOD, THROUGH  
SUNDAY, A WEAKENING SURFACE BOUNDARY (EVIDENT ON CURRENT SATELLITE  
IMAGERY) IS FORECAST TO SLOWLY DRIFT WESTWARD ACROSS THE EASTERN  
HAWAI'IAN ISLANDS. AN UPPER LOW IS FORECAST BY ALL GUIDANCE TO  
CLOSE OFF IN THE VICINITY OF HAWAI'I BY LATE SUN, WITH THE LOW  
WEAKENING AND A SECOND UPPER LOW CLOSING OFF WEST OF THE ISLANDS  
BY WED-THU. LOW-LEVEL SOUTHERLY FLOW WILL CONTINUE TO TRANSPORT  
DEEP MOISTURE NORTHWARD ACROSS HAWAI'I, WITH PWATS OF 1.50-2.0  
INCHES THROUGH EARLY NEXT WEEK, ESPECIALLY ACROSS THE EASTERN  
ISLANDS. AS THE SECOND UPPER LOW DEVELOPS WEST OF HAWAI'I BY  
MIDWEEK, A BROADER REGION OF SOUTHERLY FLOW WILL SPREAD DEEPER  
MOISTURE ACROSS THE ENTIRE STATE. THE ECMWF HAS BACKED OFF THE  
SOLUTION IT SHOWED YESTERDAY IN WHICH A SURFACE LOW TRACKED ACROSS  
HAWAI'I DURING THE PERIOD. BOTH THE ECMWF AND THE GFS NOW SHOW  
SIMILAR SOLUTIONS IN TERMS OF THE UPPER LOW WEST OF THE STATE BY  
MIDWEEK, AND BROAD SOUTHERLY FLOW SPREADING DEEP MOISTURE NORTH  
ACROSS HAWAI'I. THUS, EXPECT PRECIPITATION TO INITIALLY BE MOST  
WIDESPREAD AND HEAVIEST ACROSS THE EASTERN ISLANDS THROUGH TUE-WED  
(IN THE VICINITY OF THE SURFACE BOUNDARY), BEFORE GRADUALLY  
EXPANDING WESTWARD BY LATER IN THE WEEK, WITH EVEN THE WESTERN  
ISLANDS SEEING NOTABLE INCREASES IN PRECIP CHANCES. IN TERMS OF  
SURFACE WINDS, FLOW WILL GENERALLY BE EAST-SOUTHEASTERLY THROUGH  
MUCH OF THE NEXT WEEK, GRADUALLY INCREASING INTO EARLY NEXT WEEK.  
 
RYAN  
 

 
 
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