Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
815 AM EDT Fri May 22 2015

Valid 00Z Sat May 23 2015 - 00Z Sat May 30 2015

There are some lingering detail differences with aspects of
evolution at the surface and aloft to the northeast of the
islands.  An upper low forming to the northeast of the islands
over the next 24 hours will eject eastward by early next week as
energy immediately upstream falls into the longer term mean trough
position.  Then this trough will begin to move eastward in
response to upstream flow.  Associated low pressure will push a
front across the state early in the period, with the front
lingering near or southeast of the Big Island for a number of days
as one or more surface low centers wobble around to the northeast.


Around the middle of next week the 00z ECMWF extends the upper
trough somewhat southwestward, and the surface low westward,
compared to most other guidance.  Also by mid-late week the 06z
GFS does not build the trailing high quite as far eastward as the
majority of other solutions.  Thus would ultimately recommend a
compromise among remaining guidance in that time frame. 

Frontal passage will bring a lengthy period of northerly to
northeasterly winds.  For most the period, precipitable water
values should be in the 1-1.25 inch range with rainfall along and
behind the front generally light to moderate in intensity. 
Greatest focus should be over windward terrain though winds may be
light enough for brief intervals that land/sea breeze boundaries
may have some influence on activity.  Late next week there is some
developing spread regarding moisture levels with the 00z ECMWF and
to a lesser extent 06z GFS showing higher PWATs moving in from the
east/southeast relative to the 00z GFS.  Predictability at this
time frame is fairly low, favoring an average solution while
awaiting any definitive trends.

Rausch