Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
206 AM EST Mon Dec 27 2021

Valid 00Z Tue Dec 28 2021 - 00Z Tue Jan 04 2022

An anomalously strong high pressure system will remain anchored in
the North Pacific between Hawaii and Alaska through at least the
middle of this week, but should finally weaken and shift southward
by next weekend. Meanwhile, a closed upper low meandering west of
Hawaii should also drop to the south as the overall amplified
upper pattern over the central Pacific begins to break down. Gusty
trade winds should continue through much of this week, with
showers tending to favor the typical windward facing terrain.
Models have shown better agreement in recent days on an upper
trough amplifying to the west of Hawaii by next weekend driving a
cold front towards the western islands. This should allow for a
shift in the trades to a more south/southeasterly direction
advecting a plume of deeper ITCZ moisture northward towards Hawaii
late this week and especially next weekend. Amidst lingering
uncertainties in the deterministic solutions with regards to
timing and placement of the upper trough and surface front, there
remains a decent signal in the guidance for widespread and
moderate to locally heavy rainfall across at least parts of the
island chain next weekend. Both the 00z GFS and ECMWF show
potential for several inches of rain for some areas, but
considerable uncertainty continues to keep confidence low in the
forecast specifics at this point.

Santorelli