503  
FXHW01 KWNH 181214  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
713 AM EST SUN FEB 18 2018  
 
VALID 00Z MON FEB 19 2018 - 00Z MON FEB 26 2018  
 
A WET PATTERN APPEARS SET TO CONTINUE ACROSS HAWAI'I THROUGH THE  
NEXT WEEK. A SURFACE BOUNDARY CONTINUES TO LINGER ACROSS THE STATE  
EARLY THIS MORNING, WHICH ALONG WITH RELATIVELY HIGH PWATS  
(1.25-1.50 INCH RANGE) IS PRODUCING AREAS OF DEEP CONVECTION WITH  
HEAVY RAINFALL. THE LARGE SCALE PATTERN ACROSS THE CENTRAL PACIFIC  
IS NOT EXPECTED TO CHANGE APPRECIABLY OVER THE NEXT WEEK. WELL TO  
THE NORTH OF HAWAI'I, A BLOCKING RIDGE IS EXPECTED TO WEAKEN  
SLIGHTLY, BUT WILL REMAIN PREVALENT. SOUTH OF THE RIDGE, THE  
PATTERN WILL FAVOR THE DEVELOPMENT AND PERSISTENCE OF UPPER-LEVEL  
LOWS. THE FIRST SUCH UPPER LOW IS SHOWN BY ALL MODELS TO DEVELOP  
TONIGHT INTO MONDAY, CENTERED JUST NORTH OF HAWAI'I. THIS FEATURE  
APPEARS RELATIVELY TRANSIENT, WITH MOST GUIDANCE SHOWING IT  
DISSIPATING BY MID-WEEK AS ANOTHER, DEEPER UPPER LOW DEVELOPS  
FARTHER TO THE WEST. MODELS SHOW A GENERAL CONSENSUS THAT THE  
SURFACE BOUNDARY OVER THE STATE THIS MORNING WILL GRADUALLY DRIFT  
WESTWARD AND WEAKEN AS THE INITIAL UPPER LOW WEAKENS. AS THIS  
SECOND UPPER LOW DEVELOPS BY LATE IN THE WEEK, A RIDGE AXIS IS  
FORECAST TO DEVELOP JUST EAST OF HAWAI'I. THE COMBINATION OF THESE  
TO FEATURES WILL KEEP DEEP SOUTHERLY/SOUTHWESTERLY FLOW IN PLACE  
AND WILL CONTINUE TO SUPPLY THE REGION WITH ABUNDANT MOISTURE TO  
SUPPORT CONVECTION, WHILE SURFACE FLOW REMAINS EAST-SOUTHEASTERLY  
DUE TO A STRONG SURFACE HIGH WELL NORTHEAST OF HAWAI'I. SURFACE  
ESE FLOW SHOULD GRADUALLY STRENGTHEN THROUGH THE WEEK AND INTO  
NEXT WEEKEND AS THE AFOREMENTIONED SURFACE HIGH DRIFTS SOUTHWARD,  
STRENGTHENING THE PRESSURE GRADIENT ACROSS THE CENTRAL PACIFIC.  
 
BOTH THE ECMWF AND THE GFS SUGGEST A BRIEF LULL IN CONVECTIVE  
ACTIVITY BY TUE AS THE INITIAL UPPER LOW WEAKENS AND THE SURFACE  
BOUNDARY DRIFTS WEST OF THE STATE. BUT A RESUMPTION IN THE  
POTENTIAL FOR CONVECTION AND HEAVY RAINFALL SHOWN FROM THU ONWARD  
AS THE UPPER LOW TAKES HOLD FARTHER WEST, AND DEEPER MOISTURE ONCE  
AGAIN BEGINS TO STREAM ACROSS HAWAI'I EAST OF THE LOW.  
 
RYAN  
 

 
 
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