Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
738 AM EST Thu Dec 15 2016

Valid 00Z Fri Dec 16 2016 - 00Z Fri Dec 23 2016

...Excessive rainfall threat this weekend into early next week...

The latest models and ensembles offer below normal forecast spread
and uncertainty for the upcoming active weather pattern for
Hawaii. Satellite imagery shows a mid-upper level trough now
digging to the north of the state and an approaching cold front
underneath. High surf advisories are already in effect for
portions of the islands. Amplifying flow aloft leads to closed low
development with slow passage over and just to the southwest of
the islands this weekend into early next week. This significant
low induces a well organized surface low to tap/pool deep tropical
moisture. This increase in low-level convergence combined with
strengthening lift will definitely increase the coverage of
showers over the region. This should be particularly the case
along the lingering frontal zone which stalls to the south of the
Big Island. Expect heavy rainfall potential to build back across
the state into early next week before a drying trend through
midweek. A heavy rain threat should focus especially hard over the
southern islands where closed low instability combines with an
influx of high precipitatble water air forecast to rise upwards of
1.75". Cooling aloft is sufficient to also support some wintery
weather over the highest summits.

Schichtel