Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
830 AM EDT Mon Oct 30 2017

Valid 00Z Tue Oct 31 2017 - 00Z Tue Nov 07 2017

The overall synoptic-scale pattern will feature a rex block off to
the northeast of the Hawai`ian chain while broad longwave
troughing initially extends just east of the International
Dateline. Eventually a closed upper low is forecast to develop on
Tuesday in the proximity of 30N/170W with the cyclonic circulation
eventually getting lifted northward toward the north-central
Pacific. As this occurs, mid-level heights will continue to rise
downstream along the longitude spanning Hawai`i. By Thursday into
the weekend, models depict a 588-dm closed upper high forming. See
little change in this evolving pattern with the only model spread
being with surrounding features which pose no threats to the
region.

At the surface, the initial lighter winds across the islands will
gradually pick up in strength today as warm advection ensues in
response to lowering heights farther upstream. Precipitable water
values respond with modest rises as numbers exceed 2 inches over
the northern most islands including Kauai. This should increase
the threat for moderate to locally heavy rainfall over these
regions beginning Tuesday as the cold front approaches from the
northwest. By the following day, the heavier axis of precipitation
should begin to lift back toward the north as the parent feature
migrates further into the mid-latitudes. Eventually surface winds
will diminish as surface gradients begin to weaken. On Friday and
the days following, a robust surface ridge builds across the
northeast Pacific allowing for a return to moderate to
occasionally stronger trade winds. Many solutions show the winds
reaching the 25 to 30 knot range this weekend as the gradient
further tightens. This will be accompanied by the usual windward
showers although the coverage should decrease some by the end of
the period as overall moisture starts to come down.


Rubin-Oster