675
FXHW01 KWNH 150852
PMDHI

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
352 AM EST Mon Dec 15 2025

Valid 00Z Tue 16 Dec 2025 - 00Z Tue 23 Dec 2025

...Periods of heavy rain for the western Hawaiian Islands
possible much of the week...

A weakening cold front will continue to bring showers and
isolated thunderstorms today across Kauai and Oahu with locally
heavy rain rates and flash flooding possible. After a brief lull
Tuesday a second cold front will approach and stall near the
western islands from late Tuesday through Friday. While moisture
anomalies are not forecast to be quite as high with this front,
instability is forecast to increase by late Tuesday through
Wednesday (there are unusually high values for CAPE per the
Extreme Forecast Index), which suggests the potential for locally
heavy rainfall rates within convection. This, combined with the
multi-day nature of the event does indicate some flood potential.

Some model spread remains with where the front will stall, which
impacts where the heaviest rain will fall. The GFS and GEFS keep
the heaviest rainfall west of the state, although locally heavy
showers ahead of the front could still impact Kauai and Oahu. The
ECMWF and AIFS solution of a farther east front would bring a
more significant rainfall risk into Kauai, and possibly Oahu. We
will need to continue to monitor trends, but at this point we can
say the highest threat for additional heavy rain and possible
flooding from this second front is over Kauai, with a lower
threat the farther southeast you go (the Big Island should not see
a significant rainfall threat).

Finally by late Friday into the weekend a more common easterly
trades pattern looks to get established as heights aloft rise and
surface ridging starts to influence the pattern.

Chenard

$$