Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
808 AM EDT Mon May 15 2017

Valid 00Z Tue May 16 2017 - 00Z Tue May 23 2017

The subtropical ridge will remain dominant across the central
Pacific until Saturday, with a broad weakness in the ridge evident
across Hawai'i. Models show the potential for isolated shower
activity beneath this weakness, associated with the trades. 20-30
knot easterlies throughout the lower-levels will keep the deepest
moisture/highest precipitable water values south of Hawai'i
through this period, however. Over the weekend, a trough is
expected to begin amplifying to the north of the Hawai'ian
islands, pushing a cold front southward toward the archipelago and
becoming stationary north of the Islands by Sunday night into
Monday. Models show good consensus on the general evolution of
this trough and even with the timing of the  front. At this time,
the ECMWF suggests that the front will not be able to sufficiently
tap into the pool of deeper moisture well south of the Islands,
thus any shower activity would remain widely scattered even as the
front approaches. The GFS shows some modestly higher PW values
focused along the frontal boundary north of Hawai'i over the
weekend, but keeps the most widespread showers/heaviest QPF north
of the Islands through 00Z Tue.

Ryan