251
FXHW01 KWNH 140906
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
406 AM EST SUN DEC 14 2025
VALID 00Z MON 15 DEC 2025 - 00Z MON 22 DEC 2025
...HEAVY RAINS FOR THE WESTERN HAWAIIAN ISLANDS POSSIBLY INTO
MUCH OF THE WEEK...
A COLD FRONT CURRENTLY APPROACHING KAUAI WITH A NOTABLE MOISTURE
PLUME ALONG AND AHEAD OF IT WILL BE THE PRIMARY WEATHER MAKER IN
THE NEXT COUPLE OF DAYS. THE FRONT IS SUPPORTED BY AN UPPER LOW TO
THE NORTHWEST, PLACING THE FAVORABLE RIGHT ENTRANCE REGION OF THE
JET ATOP THE WESTERN ISLANDS. THESE INGREDIENTS WILL ALLOW FOR
POTENTIALLY HEAVY RAINFALL MOVING ACROSS KAUAI EARLY SUNDAY AND
INTO OAHU AND MOLOKAI AS THE DAY PROGRESSES, PER THE HREF. SHOWERS
AND ISOLATED THUNDERSTORMS WITH POTENTIALLY HEAVY RAIN RATES ARE
FORECAST TO STALL NEAR OAHU/MOLOKAI INTO SUNDAY NIGHT. ON MONDAY,
THE FIRST FRONT IS LIKELY TO GRADUALLY DISSIPATE, BUT THE MOISTURE
WILL REMAIN IN PLACE AND THEN ANOTHER MOISTURE PLUME WILL GET
RENEWED FARTHER WEST TOWARD KAUAI IN RESPONSE TO ANOTHER FRONT
THAT APPROACHES FROM THE NORTHWEST. THUS ANOTHER DAY OF LOCALLY
HEAVY RAINFALL IS LIKELY FOR THE WESTERN HALF OF THE STATE, AND A
FLOOD WATCH IS IN EFFECT THROUGH LATE MONDAY NIGHT.
THE UPPER AND SURFACE LOWS NORTHWEST OF HAWAII WILL BE SLOW TO
MOVE EAST INTO TUESDAY-WEDNESDAY. THIS SECOND FRONT ASSOCIATED
WITH THESE LOWS APPROACHING MAY ALLOW FOR THE PRIMARY MOISTURE
PLUME AND THUS MAIN RAIN BAND TO SET UP JUST WEST OF THE STATE
TUESDAY, BUT WITH SOME SCATTERED CONVECTION AHEAD OF IT POSSIBLE,
AS INSTABILITY INCREASES AS WELL (THERE ARE UNUSUALLY HIGH VALUES
FOR CAPE PER THE EXTREME FORECAST INDEX). THEN THE FRONT IS
FORECAST TO CONTINUE TO STALL OR SLOWLY MEANDER NEAR THE WESTERN
ISLANDS FOR MID TO LATE WEEK. THE EXACT POSITION OF THIS FRONT
DOES SHOW SOME MODEL SPREAD. LIKE YESTERDAY, THE 00Z GFS REMAINS
WEST OF THE 00Z ECMWF WITH THE FRONTAL POSITION, WITH THE GFS
NEAR/JUST WEST OF KAUAI WHILE THE ECMWF IS GENERALLY BETWEEN KAUAI
AND OAHU FOR MULTIPLE DAYS. THIS POSITIONING WILL HAVE A NOTABLE
IMPACT ON PLACEMENT OF HEAVY QPF, SO WILL CONTINUE TO MONITOR, BUT
OVERALL UNSETTLED WEATHER WILL CONTINUE THROUGH MUCH OF THE WEEK.
FINALLY BY LATE WEEK INTO NEXT WEEKEND, A MORE COMMON EASTERLY
TRADES PATTERN LOOKS TO GET ESTABLISHED AS HEIGHTS ALOFT RISE AND
SURFACE RIDGING STARTS TO INFLUENCE THE PATTERN.
TATE
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