534
FXHW01 KWNH 160908
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
408 AM EST TUE DEC 16 2025
VALID 00Z WED 17 DEC 2025 - 00Z WED 24 DEC 2025
...PERIODS OF HEAVY RAIN EXPECTED FOR THE WESTERN HAWAIIAN
ISLANDS FOR MUCH OF THE WEEK...
SHOWERS AND ISOLATED THUNDERSTORMS WILL CONTINUE INTO EARLY THIS
MORNING ACROSS NIIHAU AND KAUAI BRINGING LOCALLY HEAVY RAINFALL
AND A CONTINUED RISK OF FLASH FLOODING. THE COVERAGE AND
INTENSITY OF THIS RAINFALL SHOULD DECREASE DURING THE DAY,
HOWEVER ANOTHER COLD FRONT WILL APPROACH FROM THE NORTHWEST BY
TONIGHT. THIS FRONT IS FORECAST TO STALL NEAR THE WESTERN ISLANDS
BRINGING AND INCREASE IN MOISTURE AND A MULTI-DAY THREAT OF
LOCALLY HEAVY RAINFALL.
MODEL TRENDS HAVE BEEN TO STALL THE FRONT A BIT FARTHER EAST,
WHICH IS INCREASING CONFIDENCE IN A HEAVY RAINFALL THREAT OVER
KAUAI AND OAHU BY LATER TONIGHT INTO FRIDAY. THE GFS/GEFS REMAIN
A BIT WEAKER AND WEST WITH THE FRONT, BUT EVEN THESE SOLUTIONS
BRING A HEAVY RAINFALL RISK INTO THE AFOREMENTIONED ISLANDS. GIVEN
TRENDS, WOULD LEAN OUR MODEL PREFERENCE MORE TOWARDS THE ECMWF
AND AIFS, WHICH ARE WETTER SOLUTIONS FOR THESE ISLANDS. THE LOWER
RESOLUTION GLOBAL MODELS GENERALLY SUPPORT 1-3" OF RAINFALL, BUT
THE 00Z RRFS INDICATES UPWARDS OF 2-6" THROUGH FRIDAY. GIVEN THE
STALLING NATURE OF THE FRONT, ANOMALOUS MOISTURE AND SOME
INSTABILITY IN PLACE, WOULD INDEED EXPECT TO SEE AT LEAST
LOCALIZED RAINFALL TOTALS UP OVER 4", WITH SOME RISK OF FLASH
FLOODING OVER NIIHAU, KAUAI AND OAHU.
FINALLY BY LATE FRIDAY INTO THE WEEKEND THE FRONT SHOULD DISSIPATE
AND/OR LIFT NORTH OF THE ISLANDS WITH MORE COMMON EASTERLY TRADES
TAKING OVER. THIS SHOULD REDUCE THE RISK OF HEAVY RAINFALL,
ALTHOUGH LINGERING ABOVE NORMAL MOISTURE WILL LIKELY STILL RESULT
IN SOME CONTINUED LIGHTER SHOWERS THROUGH THE WEEKEND. THE
EASTERLY TRADE PATTERN SHOULD CONTINUE INTO EARLY NEXT WEEK,
ALTHOUGH AN INCREASE IN WIND SPEEDS SHOULD RESULT IN AN UPTICK IN
UPSLOPE RAIN SHOWERS ACROSS THE FAVORED EAST FACING TERRAIN.
CHENARD
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