157
FXHW01 KWNH 170905
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
405 AM EST WED DEC 17 2025
VALID 00Z THU 18 DEC 2025 - 00Z THU 25 DEC 2025
...PERIODS OF HEAVY RAIN EXPECTED FOR THE WESTERN HAWAIIAN
ISLANDS TODAY INTO FRIDAY...
A COLD FRONT IS FORECAST TO STALL NEAR THE WESTERN ISLANDS TODAY
INTO FRIDAY BRINGING AN INCREASE IN MOISTURE AND A MULTI-DAY
THREAT OF LOCALLY HEAVY RAINFALL. INSTABILITY IS GREATEST TODAY,
WITH A GRADUAL DECREASING TREND NOTED BY TONIGHT INTO THURSDAY AS
CLOUD COVER AND SHOWER ACTIVITY INCREASE IN CONVERAGE.
NONETHELESS, THE COMBINATION OF ANOMALOUS MOISTURE AND SOME
INSTABILITY, THE STALLING FRONT, AND UPPER DIVERGENCE SOUTH OF THE
UPPER JET, SHOULD SUPPORT PERIODS OF HIGHER RAINFALL RATES. THE
POSITION OF THE FRONT AND MOISTURE AXIS SUPPORTS THE GREATEST
HEAVY RAINFALL RISK ACROSS NIIHAU, KAUAI AND OAHU, WITH LIGHTER
RAIN SHOWERS FARTHER SOUTHEAST.
BOTH THE 00Z RRFS AND HREF INDICATE TOTAL RAINFALL TOTALS OF 2-6"
IN SPOTS, WITH HOURLY RAINFALL RATES UPWARDS OF 1"/HR POSSIBLE.
THIS RAINFALL WILL LIKELY BRING SOME RISK OF FLASH FLOODING TO
NIIHAU, KAUAI AND OAHU, WITH THE RISK PEAKING TODAY INTO TONIGHT,
BUT CONTINUING TO SOME EXTENT INTO THURSDAY AND FRIDAY.
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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