762
FXHW01 KWNH 190745
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 AM EST FRI DEC 19 2025
VALID 00Z SAT 20 DEC 2025 - 00Z SAT 27 DEC 2025
AT THE START OF THE PERIOD, THE ISLANDS WILL REMAIN ALONG THE
LEADING EDGE OF A BROAD UPPER TROUGH CENTERED OVER THE CENTRAL
PACIFIC. AN UPPER LOW TO THE NORTH WILL CONTINUE TO WEAKEN AND
LIFT TO THE NORTHEAST THROUGH SATURDAY. AN AXIS OF DEEPER
MOISTURE, CHARACTERIZED BY ABOVE-NORMAL PRECIPITABLE WATER (PW)
ANOMALIES CENTERED NEAR THE AXIS OF AN OLD FRONTAL BOUNDARY, WILL
LINGER ACROSS THE ISLANDS. SOUTHERLY FLOW ALONG THE WESTERN
PERIPHERY OF A SURFACE HIGH EAST OF THE ISLANDS WILL DIRECT A
REINFORCING PLUME OF DEEPER MOISTURE ACROSS THE CENTRAL ISLANDS
LATE FRIDAY INTO SATURDAY, SUPPORTING SHOWERS WITH THE POTENTIAL
FOR HEAVY RAINFALL RATES EARLY IN THE PERIOD. HREF GUIDANCE
INDICATES GREATER THAN 50 PERCENT PROBABILITIES FOR
ACCUMULATIONS EXCEEDING 2 INCHES ACROSS PORTIONS OF OAHU,
MOLOKAI, LANAI, AND MAUI FROM 00Z SATURDAY TO 00Z SUNDAY.
THE SYNOPTIC PATTERN WILL SHIFT BY SUNDAY AS AN UPPER RIDGE BEGINS
TO BUILD ACROSS THE ISLANDS, REMAINING LARGELY IN PLACE THROUGH
MUCH OF THE WEEK BEFORE SHIFTING EAST LATE IN THE PERIOD. SURFACE
HIGH PRESSURE BUILDING IN FROM THE NORTH WILL SUPPORT INCREASING
EASTERLY TRADE WINDS THROUGH MID-WEEK. WINDS ARE EXPECTED TO VEER
MORE TO THE SOUTHEAST OR SOUTH LATE IN THE WEEK AS THE SURFACE
HIGH SHIFTS FURTHER EAST. WHILE THE GFS CONTINUES TO SHOW
POSITIVE PW ANOMALIES THROUGH THE FORECAST PERIOD, THE ECMWF AND
CANADIAN MODELS SUGGEST DRIER AIR SPREADING INTO THE ISLANDS FROM
THE EAST LATER IN THE WEEK.
PEREIRA
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