Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
733 AM EST Thu Nov 19 2015

Valid 00Z Fri Nov 20 2015 - 00Z Fri Nov 27 2015

The latest models and ensembles forecast that a series of impulses
will feed into a mean mid-level trough that will linger and be
periodically reinforced to the west-northwest and north of the
Hawaiian Islands over the next week. This will provoke an
associated and prolonged inverted surface pressure trough
response. Easterly trades will gain a southeasterly then southerly
component during the week. This will support elevated precipitable
water values pooling to around 1.50-2.00 inches or about +1.5 to
+3.0 sigma. QPF from the models/ensembles remains a mess with lots
of spread over the region. However, heavier to locally excessive
rains should focus both on the northwestern islands closer to the
surface convergence zone, but also down to the Big Island as prone
to locally heavy and terrain enhanced downpours given extent of
pooling moisture. This is a wet pattern and a flash flood watch
has already been issued by the NWS forecast office in Honolulu for
portions of the Big Island today.

Schichtel