Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
726 AM EST Thu Nov 30 2017

Valid 00Z Fri Dec 01 2017 - 00Z Fri Dec 08 2017

...A Heavy Precipitation Threat...

Surface high pressure bridging to the north of the state is acting
to reinforce a pattern supporting breezy/windy trades through the
weekend. Deep tropical moisture with precipitatble water values
near 2" has lifted into the state as a mid-upper level shortwave
trough and associated height falls digs over and just to the north
then northeast of the state. This is inducing lead inverted
surface troughing through the state whose southeastward veered
trades on its east side are advecting deep tropical moisture to
fuel locally heavy rainfall.

A flash flood warning is currently in effect in Kauai. Flash flood
watches remain in effect over the Big Island and Maui and a winter
storm advisory is also in effect for the summits of Mauna Loa and
Mauna Kea for lingering snow. High surf and small craft advisories
are also in effect. The heavy precipitation threat will diminish
over the weekend with lead frontal passage.

A second and more amplified mid-upper level shortwave trough
passage along/north of the state into Tuesday and Wednesday and
associated frontal track will further filter drier air across the
state in a pattern with disrupted trades. Model and ensemble
forecast spread and uncertainty is about at average levels
overall. The most notable mass field differences are evident in
the Tuesday to Thursday timeframe and concern the amplitude of the
this feature. The NAVGEM is the least ampified. The Canadian is
the most amplified and actually carves out a separated southern
stream closed low just to the northeast of the state
Wednesday-next Thursday that could offer a more significant
weather threat renewal. The GFS and ECMWF are closer to the center
of the forecast envelope and have the most ensemble support.
Prefer a solution closer to the GFS/ECMWF, but will continue to
monitor upstream  mid-upper ridge amplitude over the west-central
Pacific for future signs of potentially deeper downstream energy
digging toward the islands next week.

Schichtel