Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
813 AM EDT Fri Jun 26 2015

Valid 00Z Sat Jun 27 2015 - 00Z Sat Jul 04 2015

Especially in the ensemble means, the pattern aloft over the
central Pacific exhibits some degree of retrogression with
successive shortwaves ultimately pulling the mean trough initially
well north/northeast of the islands to a position more to the
northwest of the area.  Features amplifying within the mean trough
late weekend into next week will support a lowering of surface
pressures over and north of the islands in that time frame.  As a
result expect an initial pattern of moderate trades and generally
windward rainfall focus to trend toward somewhat lighter trades
and a mix of terrain and land/sea breeze influence on shower
activity.  By the latter half of next week there is reasonable
agreement that the southern periphery of eastern Pacific high
pressure should build westward, even in operational GFS/ECMWF runs
that disagree somewhat with the means for central Pacific flow
aloft.  This should support a return of more typical trade flow
and precipitation focus.

Prevailing precipitable water values should be in the 1.25-1.50
inch range.  GFS/ECMWF runs similarly indicate a brief increase
over the Big Island and vicinity associated with a tropical wave
around Mon night-Tue.  This seems reasonable based on 06z Fri
analyzed position around 134W.  The 00z ECMWF shows another wave
brushing the Big Island around Thu while GFS runs actually depict
a drying trend.  There is potential for a late week wave if the
upstream wave initially analyzed near 116W persists through the
next week but if eastern Pacific high pressure evolves as
currently forecast the second wave may well track somewhat farther
south than forecast by the ECMWF.

Rausch