082  
FXHW01 KWNH 121204  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
704 AM EST FRI JAN 12 2018  
 
VALID 00Z SAT JAN 13 2018 - 00Z SAT JAN 20 2018  
 
A RELATIVELY WEAK FLOW PATTERN WILL BE IN PLACE ACROSS HAWAI'I  
INITIALLY, WITH RIDGING CENTERED EAST AND WEST OF THE STATE, AND A  
MORE ACTIVE MID-LATITUDE FLOW PATTERN TO THE NORTH OF THE STATE.  
THIS SETUP WILL PREVENT LOW-LEVEL TRADES FROM TAKING HOLD AT LEAST  
INTO EARLY NEXT WEEK, WITH VERY LIGHT NORTHERLY SURFACE LOW  
INSTEAD. THIS FLOW WILL KEEP DRY AIR ACROSS THE STATE THROUGH THE  
WEEKEND, WITH PWATS NEAR OR JUST BELOW 1 INCH, AND VERY LITTLE IN  
THE WAY OF SHOWER ACTIVITY. BY EARLY NEXT WEEK, MODELS SHOW GOOD  
AGREEMENT THAT UPPER RIDGING WILL MIGRATE EASTWARD ACROSS HAWAI'I,  
WITH THE SURFACE HIGH CENTERED NORTH OF THE STATE. THIS WILL ALLOW  
BRISK LOW-LEVEL EAST TO EAST-NORTHEAST FLOW TO RESUME (INTO THE  
20-30 KT RANGE), BUT WILL KEEP THE DEEPEST MOISTURE SUPPRESSED  
SOUTH OF THE STATE. THUS, EXPECT A MODEST INCREASE EARLY NEXT WEEK  
IN SHOWER ACTIVITY ALONG WINDWARD TERRAIN DUE TO THE INCREASING  
LOW-LEVEL FLOW, BUT WIDESPREAD PRECIPITATION IS NOT ANTICIPATED.  
 
BY LATE NEXT WEEK, A MAJORITY OF THE MODELS/ENSEMBLES SHOW A  
WEAKNESS IN THE RIDGE DEVELOPING WEST OF HAWAI'I AS A PIECE OF  
ENERGY SEPARATES FROM THE HIGHER LATITUDE FLOW AND DRIFTS SOUTH.  
THE EFFECTS OF THIS FEATURE ON HAWAI'I APPEAR RATHER LIMITED AT  
THIS TIME, PRIMARILY JUST A GRADUAL INCREASE IN MOISTURE THROUGH  
LATE IN THE WEEK (GFS AND ECMWF BOTH SHOW PWAT VALUES RISING TO  
1.2-1.3 INCHES). THE RESULT SHOULD BE FURTHER ENHANCEMENT OF  
WINDWARD SHOWERS, WITH PERHAPS SOME LOCALLY HEAVY RAIN POSSIBLE BY  
LATE NEXT WEEK.  
 
RYAN  
 

 
 
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