308  
FXHW01 KWNH 141226  
PMDHI  
 
HAWAII EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
725 AM EST TUE NOV 14 2017  
 
VALID 00Z WED NOV 15 2017 - 00Z WED NOV 22 2017  
 
FOR MUCH OF THE FORECAST PERIOD, HAWAI`I WILL BE ALONG THE  
SOUTHWESTERN FLANK OF A LONGWAVE TROUGH WHICH WILL CONTINUE TO  
RELOAD DURING THE WEEK. THE PATTERN SHOULD REMAIN RATHER  
CONSISTENT AS A MEAN UPPER RIDGE REMAINS A FIXTURE IN THE FORECAST  
IN THE VICINITY OF THE INTERNATIONAL DATELINE. WHILE MODELS AGREE  
ON THE TIMING/POSITION OF THE INITIAL LONGWAVE TROUGH, THEY DIFFER  
WITH THE DETAILS OF THE SECOND SYSTEM LATE IN THE WORK WEEK. BY  
FRIDAY, ENSEMBLE SPAGHETTI PLOTS SHOW IT IS ESSENTIALLY THE 00Z  
ECMWF/ECMWF ENSEMBLE MEAN VERSUS ALL OTHER MODELS. BY SATURDAY  
MORNING, MOST OF THE 00Z ECMWF ENSEMBLE SUITE SHOW A CLOSED LOW TO  
THE NORTH OF THE ISLAND CHAIN WHILE OTHER SOLUTIONS FAVOR A MORE  
EASTERN SCENARIO. THE FORMER CAMP WOULD FAVOR A RETROGRADING UPPER  
LOW WHICH IS IN STARK CONTRAST TO OTHER MODELS. THE ECMWF HAS  
SHOWN CONSISTENCY IN SUCH A FORECAST ALTHOUGH THE 00Z RUN IS EAST  
OF ITS PRECEDING CYCLE. WHILE THE ENSEMBLE MEANS DO DIFFER, IT IS  
NOT AS EXTREME AS THE OPERATIONAL ECMWF. WOULD SUGGEST AN ENSEMBLE  
MEANS BASED APPROACH TAKING A SPLIT BETWEEN THE 06Z GEFS/00Z ECMWF  
ENSEMBLE MEANS BY AS EARLY AS FRIDAY AS GUIDANCE QUICKLY DIVERGE.  
 
AT THE SURFACE, A PROMINENT RIDGE ACROSS THE CENTRAL PACIFIC WILL  
KEEP A RATHER TIGHT PRESSURE GRADIENT IN PLACE. A WEAKENING  
BOUNDARY TO THE SOUTH OF THE HAWAI`IAN ISLANDS WILL MAINTAIN A  
EAST-NORTHEASTERLY FLOW REGIME. FORECAST WINDS WILL BE IN THE 20  
TO 25 KNOT RANGE AT TIMES EARLY ON WITH A BRIEF SLACKENING  
POSSIBLE BEFORE THE NEXT SURFACE HIGH BUILDS TO THE NORTH. BY  
THURSDAY AFTERNOON, SOME OF THE GUIDANCE SHOW A 1044-MB RIDGE  
SETTING UP SOUTH OF THE ALEUTIANS WHICH WILL GRADUALLY HELP  
INTENSIFY THE LOCAL WIND FIELDS AGAIN. BY FRIDAY ONWARD, MODEL  
DIFFERENCES BECOME CHALLENGING AS THE 00Z ECMWF WOULD SUGGEST A  
CONVERGENCE ZONE ASSOCIATED WITH A FRONT SWEEPING THROUGH THE  
REGION. THUS, IT COULD EITHER BE WEAKENING EAST-NORTHEASTERLY FLOW  
AS DEPICTED BY MOST MODELS OR VARIABLE WINDS IN RESPONSE TO THE  
NEARBY SURFACE BOUNDARY. REGARDING PRECIPITATION, THE GENERAL  
EAST-NORTHEASTERLY WINDS WILL BRING SCATTERED SHOWERS THROUGH THE  
ISLAND CHAIN WITH AN EVENTUAL DECREASE IN COVERAGE AS PRECIPITABLE  
WATER VALUES DROP BY MID-WEEK. IF THE ECMWF VERIFIES, IT COULD  
BECOME QUITE WET LATE IN THE PERIOD AS MOISTURE INCREASES AHEAD OF  
THE MEANDERING UPPER LOW. HOWEVER, OTHER SOLUTIONS WOULD FAVOR  
SCATTERED SHOWERS, THUS SUPPORTING THE GENERAL DICHOTOMY HERE.  
 
RUBIN-OSTER  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page