Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Sat Dec 04 2021

Valid 00Z Sun Dec 05 2021 - 00Z Sun Dec 12 2021

Active weather will continue over Hawaii through this weekend and
well into next week. First, a cold front currently moving through
the state will continue to track southward Saturday before
stalling, which will help to focus moisture especially over the
Big Island and Maui. The enhanced moisture should lead to
increased coverage of showers for those areas. Meanwhile, drier
dew points and gusty northwesterly winds are occurring and
forecast behind the cold front. The highest elevations of the Big
Island have Blizzard Warnings issued by NWS Honolulu given the
moisture in place with the stalled front and windy conditions.
Meanwhile, there is a Flood Watch in place for most of the rest of
the state lasting through early next week.

By Sunday into Monday, an upper low is expected to reform around
25N/165W, while an upper high resides well east of the state, and
a surface low and high generally reflect the positions of the
upper-level features. This pattern will lead to mean southerly
flow across Hawaii through much of the period, directing deep
tropical moisture northward from the ITCZ. Model guidance agrees
that precipitable water values will be over the 95th percentile
(with the ECMWF showing periods above the 99th percentile) around
Monday-Wednesday, with the axis of highest PWs drifting slowly
east to west across the state as a couple of surface troughs could
focus the moisture. Heavy rainfall should follow this pattern and
several inches of rain can be expected, along with flooding/flash
flooding potential. By the latter part of next week, the upper low
is forecast to drift westward while an upper high encroaches
toward Hawaii, eventually lessening heavy rain chances.

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