285  
FXHW01 KWNH 281226  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
725 AM EST WED FEB 28 2018  
 
VALID 00Z THU MAR 01 2018 - 00Z THU MAR 08 2018  
 
TO COMMENCE THE FORECAST PERIOD, A BROAD UPPER TROUGH CENTERED  
JUST EAST OF THE INTERNATIONAL DATELINE WILL ALLOW A SERIES OF  
WEAK PERTURBATIONS TO LIFT NORTHEASTWARD TOWARD THE HAWAI`IAN  
ISLAND CHAIN. THIS PARTICULAR SETUP WILL FOCUS A STEADY PERIOD OF  
STRONG LOW-LEVEL EAST-SOUTHEASTERLY FLOW WITH SUSTAINED WINDS IN  
THE 25 TO 30 KNOT RANGE AT TIMES. A BROAD AREA OF SHOWERS SHOULD  
ACCOMPANY THIS REGIME WITH PRECIPITABLE WATER VALUES LIKELY  
EXCEEDING 1.50 INCHES. HOWEVER, THE FOCUS OF THIS ACTIVITY SHOULD  
DRIFT WESTWARD IN TIME AS THE NORTH/SOUTH ORIENTED INVERTED TROUGH  
IS EXPECTED TO RETROGRADE IN TIME. CONSEQUENTLY, THE SURFACE WINDS  
WILL TURN MORE EASTERLY WHILE WEAKENING IN TIME GIVEN A REDUCTION  
IN THE SYNOPTIC-SCALE PRESSURE GRADIENTS. SOME LINGERING CHANCES  
FOR SHOWERS WILL CONTINUE ALTHOUGH THE MORE CONCENTRATED ACTIVITY  
IS FORECAST TO STAY WEST OF THE ISLANDS.  
 
TOWARD THE CONCLUSION OF THE WORK WEEK, THIS ELONGATED TROUGH AXIS  
SHOULD EVOLVE INTO MORE A CLOSED OFF FEATURE WHILE LIFTING  
NORTH-NORTHWESTWARD INTO THE MID-LATITUDES. BY EARLY NEXT WEEK,  
THE PATTERN SHIFTS TOWARD AN OMEGA BLOCK WITH AN UPPER RIDGE  
CENTERED OVER THE MIDDLE OF THE PACIFIC. THE CORRESPONDING  
NEGATIVE HEIGHT ANOMALY SHOULD DOMINATE GENERALLY EAST OF 150W  
LONGITUDE. THIS WILL EVENTUALLY PLACE THE WESTERN EXTENT OF THE  
MEAN POSITIVELY-TILTED LONGWAVE TROUGH OVER HAWAI`I. WHILE MODEL  
SPREAD BEGAN ON THE LOWER END, THERE ARE A SERIES OF DETAIL  
DIFFERENCES WITHIN THIS BAND OF HEIGHT FALLS WHICH SUGGESTS A MORE  
ENSEMBLE-BASED APPROACH FOR MUCH OF NEXT WEEK. AT THIS POINT,  
THERE IS THE GREATEST OVERLAP BETWEEN THE 06Z GEFS/00Z ECMWF  
ENSEMBLE MEANS. WITH THIS SHIFT IN THE PATTERN, THE PREVAILING  
SURFACE WINDS WILL TURN MORE EAST-NORTHEASTERLY BY LATE SUNDAY AS  
LOW PRESSURE FORMS NORTHEAST OF THE ISLAND CHAIN. THIS IS FORECAST  
TO CONTINUE THROUGH MUCH OF THE WEEK WITH WINDS PICKING UP AT  
TIMES GIVEN THE 1040-MB ANTICYCLONE POSITIONED OVER THE CENTRAL  
PACIFIC. ULTIMATELY IT WILL BE A DRIER PERIOD GIVEN THE INFLUX OF  
LOWER PRECIPITABLE WATER AIR INTO THE REGION.  
 
RUBIN-OSTER  
 

 
 
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