602
FXHW01 KWNH 170731
PMDHI
HAWAII EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
331 AM EDT SUN MAY 17 2026
VALID 00Z MON 18 MAY 2026 - 00Z MON 25 MAY 2026
THE UNSEASONABLY STRONG AND UNSTABLE UPPER-LEVEL CUTOFF LOW THAT
BROUGHT WIDESPREAD HEAVY RAINFALL AND LOCALIZED FLOODING TO THE
STATE OVER THE WEEKEND WILL CONTINUE TO DRIFT NORTHEASTWARD AWAY
FROM THE ISLANDS WHILE RAPIDLY WEAKENING. THE GFS, ECMWF AND THEIR
CORRESPONDING ENSEMBLES ARE IN GOOD OVERALL AGREEMENT WITH THE
TIMING OF THE TRANSITION TOWARDS A MORE STABLE REGIME AS HIGH
PRESSURE BUILDS IN FROM THE NORTH.
EARLY IN THE FORECAST PERIOD, THE BROAD AND RELATIVELY FLAT
MID/UPPER LEVEL TROUGH WILL LINGER THROUGH TUE, MAINTAINING MODEST
MID-LEVEL INSTABILITY. THIS COMBINED WITH THE SLIGHTLY VEERED
(SOUTHEASTERLY) LOW-LEVEL FLOW WILL MAINTAIN HIGHER PWAT VALUES
(1.5 TO 1.8") THROUGH EARLY TUE. AS A RESULT POPS WILL REMAIN
ELEVATED (GENERALLY 40-60%) MON AND EARLY TUE ACROSS WINDWARD SLOPES.
BY WED, DIURNAL ACTIVITY WILL BECOME MORE INFREQUENT AND ISOLATED
AS HIGH PRESSURE BUILDS IN FROM THE NORTH AND SURFACE WINDS BACK
TOWARDS THE MORE TYPICAL E-NE TRADE WIND PATTERN.
THE STABLE AND PERSISTENT E-NE TRADES WILL REMAIN LOCKED IN THU
THROUGH NEXT WEEKEND, AS THE BROAD 1028-1032 SURFACE HIGH
CENTERED WELL N-NE OF THE ISLANDS WILL MAINTAIN MODERATE TO
LOCALLY STRONG TRADES (15-25 MPH WITH HIGHER GUSTS). DEEP-
TROPOSPHERIC STABILITY AND SEASONABLY DRY AIRMASS (PWAT VALUES
NEAR 1.0") WILL PERSIST AS WELL, MAINTAINING POPS AT PREDICTABLE
CLIMATOLOGICAL AND DIURNAL NORMS (~15-35% OVER WINDWARD SLOPES,
LESS THAN 10% ACROSS LEEWARD AREAS).
HURLEY
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