973
FXHW01 KWNH 190757
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 AM EST SUN NOV 19 2023
VALID 00Z MON NOV 20 2023 - 00Z MON NOV 27 2023
TODAY'S MODELS AND ENSEMBLES SHOW A VARIABLE PATTERN OVER THE
COURSE OF THE PERIOD. A LEADING FRONT WILL ARRIVE SUNDAY,
BRINGING THE POTENTIAL FOR SOME LOCALLY MODERATE TO HEAVY RAINFALL
TO THE WESTERN ISLANDS AND SWITCHING BRISK SOUTHERLY WINDS TO
NORTHEASTERLY. RAPID DISSIPATION OF THE FRONT AND HIGH PRESSURE
TO THE NORTH/NORTHEAST WILL ALLOW FOR A RETURN OF MODERATE TRADES
AND WINDWARD/MOUNTAIN SHOWER FOCUS FROM TUESDAY INTO LATE WEEK.
THEN AN AMPLIFYING AND SHARPENING UPPER TROUGH SHOULD BRING IN
SECOND FRONT NEXT WEEKEND, WITH ANOTHER INCREASE OF RAINFALL AND A
WIND SHIFT FROM SOUTHEASTERLY TO NORTH-NORTHEASTERLY.
AS FOR DETAILS, YESTERDAY'S MAJORITY ECMWF CLUSTER HAS SINCE
TRENDED AT LEAST PARTIALLY IN THE GFS/GEFS DIRECTION FOR EVOLUTION
OF THE SUNDAY-MONDAY UPPER TROUGH AND WITH THE SURFACE FRONT'S
BAND OF ENHANCED MOISTURE SETTLING INTO APPROXIMATELY THE CENTRAL
ISLANDS BEFORE DISSIPATING AND/OR GETTING CARRIED WESTWARD IN THE
TRADES. THERE IS STILL SOME SPREAD FOR HOW MUCH ENHANCED MOISTURE
INITIALLY SOUTHEAST OF THE STATE MAY BRUSH THE BIG ISLAND AND
VICINITY BY TUESDAY-WEDNESDAY. NOW THE 00Z ECMWF SHOWS THE
GREATEST MOISTURE (A ROLE PLAYED BY THE 00Z GFS 24 HOURS AGO)
WHILE THE GFS AND THE ENSEMBLE MEANS KEEP THE MOISTURE MORE
SUPPRESSED TO VARYING DEGREES. AN AVERAGE OF THE GUIDANCE MINUS
THE ECMWF LOOKS REASONABLE FOR THIS ASPECT OF THE FORECAST.
MOISTURE SPECIFICS HAVE DECREASING PREDICTABILITY LATER IN THE
WEEK. BY NEXT WEEKEND, TYPICAL DETAIL DIFFERENCES WITH THE
APPROACHING UPPER TROUGH LEAD TO SOME TIMING SPREAD FOR THE FRONT
REACHING THE ISLANDS. HOWEVER THIS SPREAD IS FAIRLY MODEST FOR A
6-7 DAY FORECAST AND A COMPROMISE WOULD PROVIDE A REASONABLE
STARTING POINT FOR THE FORECAST.
RAUSCH
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