Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
711 AM EST Sun Jan 14 2018

Valid 00Z Mon Jan 15 2018 - 00Z Mon Jan 22 2018

A relatively weak flow pattern will be in place across Hawai'i
initially, with ridging centered east and west of the state, and a
more active mid-latitude flow pattern to the north of the state.
Over the next few days, models show good agreement that upper
ridging will migrate eastward across Hawai'i, with the surface
high centered north of the state. This will allow brisk low-level
east to east-northeast flow to resume (reaching the 20-30 kt range
by midweek), but will keep the deepest moisture suppressed south
of the state. Thus, expect a modest increase through midweek in
shower activity along windward terrain due to the increasing
low-level flow, but widespread precipitation is not anticipated
due to Pwats remaining well below 1 inch through much of the week.

By late in the week, a majority of the models/ensembles show a
weakness in the ridge developing west of Hawai'i as a piece of
energy separates from the higher latitude flow. This should result
in a gradual increase in Pwats across Hawai'i into the 1.0-1.2
inch range by the weekend, with values perhaps increasing further
by early next week. A cold front is shown by both the ECMWF and
GFS stalling north of Hawai'i by late next weekend. At this time
both models show the greatest moisture pooling along this front,
remaining north of Hawai'i along with most of the precipitation.
Even if that is the case, the gradually increasing moisture across
the state should yield a gradual increase in windward shower
activity through next weekend.

Ryan