980  
FXHW01 KWNH 131204  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
704 AM EST SAT JAN 13 2018  
 
VALID 00Z SUN JAN 14 2018 - 00Z SUN JAN 21 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 NORTH-NORTHEASTERLY SURFACE  
FLOW 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  
(REACHING THE 20-30 KT RANGE BY MIDWEEK), BUT WILL KEEP THE  
DEEPEST MOISTURE SUPPRESSED SOUTH OF THE STATE. THUS, EXPECT A  
MODEST INCREASE EARLY TO MID 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 INTO THE WEEKEND (GFS AND ECMWF BOTH SHOW PWAT  
VALUES RISING TO 1.0-1.3 INCHES). THE RESULT SHOULD BE FURTHER  
ENHANCEMENT OF WINDWARD SHOWERS, WITH PERHAPS SOME LOCALLY HEAVY  
RAIN POSSIBLE BY LATE WEEK INTO THE WEEKEND.  
 
RYAN  
 

 
 
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