329
FXHW01 KWNH 290748
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 AM EST MON DEC 29 2025
VALID 00Z TUE 30 DEC 2025 - 00Z TUE 06 JAN 2026
THROUGH MID-WEEK, THE UPPER-LEVEL RIDGE AND MORE STABLE
ENVIRONMENT THAT HAD DOMINATED THE CENTRAL PACIFIC WILL BEGIN TO
BREAK DOWN AS A SERIES OF SHORTWAVE TROUGHS BYPASS THE ISLANDS TO
THE NORTH. DURING THIS TIME A WEAKENING SURFACE FRONT IS EXPECTED
TO STALL AND DISSIPATE WEST OF KAUAI. THROUGH NYE, THE GFS AND
ECMWF ARE SIMILAR WITH THE WEAK INVERTED SHORTWAVE TROUGH
LINGERING NEAR OR JUST WEST OF THE ISLANDS. THIS WILL ALLOW FOR
MORE DIURNAL INSTABILITY WITH THE MODEST COOLING ALOFT, WITH THE
SOUTHEASTERLY VEERING LOW-LEVEL WINDS AND BOOST PWS TO ABOVE
NORMAL LEVELS (1.5 TO 1.75"). THUS THE WEEK WILL START OUT
UNSETTLED WITH GREATER COVERAGE OF DIURNAL SHOWERS (ENHANCED
LEEWARD CONVECTION).
BY NYD INTO EARLY NEXT WEEK, THE MORE TRADITIONAL NORTHEASTERLY
TRADES RETURN AS THE BROAD RIDGE BUILDS IN FROM THE WEST, LEADING
TO INCREASED LOWER TROPOSPHERIC SUBSIDENCE/DRYING AND THUS
STABILITY. BY THE END OF THE WEEKEND INTO EARLY NEXT WEEK, THERE
IS LOWER FORECAST CONFIDENCE, AS THE GLOBAL GUIDANCE DIFFERS IN
THE AMPLITUDE AND TIMING OF THE NEXT UPPER LEVEL TOUGH MOVING
ACROSS THE CENTRAL PACIFIC. THE GFS DEPICTS A DEEPER, MORE
AMPLIFIED TROUGH THAT IS ABLE TO TAP MORE TROPICAL MOISTURE (PWS
CLIMBING BACK TO 1.5+ INCHES), WHILE THE ECMWF SHOWS A SHALLOWER,
MORE PROGRESSIVE TROUGH PASSING NORTH OF THE ISLANDS. THUS THE GFS
WOULD FAVOR MORE WIDESPREAD SHOWERS BY EARLY NEXT WEEK COMPARED TO
THE ECMWF AND GLOBAL ENSEMBLE MEANS.
HURLEY
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