Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
805 AM EDT Thu Oct 08 2015

Valid 00Z Fri Oct 09 2015 - 00Z Fri Oct 16 2015

A weak elongated surface ridge north of the state will support
light to moderate trades through the weekend.  Initially light
shower activity may be enhanced to some degree from Fri night into
the weekend as a band of greater deep moisture crosses the state
from southeast to northwest.  Both GFS and ECMWF runs indicate
precipitable water maxima of at least 2-2.25 inches in this band,
with best opportunity for increased rainfall over portions of the
Big Island.

By the first half of next week there is general agreement on a
sharpening/amplifying trough aloft to the northwest/north of the
state with its southern periphery likely brushing the islands. 
However differences persist on the exact amplitude and position of
the trough axis.  At the moment would give less weight to the 00z
GEFS mean as it holds the trough axis farther westward than other
guidance.  Compared to yesterday it appears that some models have
shifted in terms of their relative amplitude/progression, arguing
for a compromise approach between the more progressive and open
00z ECMWF and amplified/closed GFS runs.  Note the 00z ECMWF mean
also suggests somewhat slower timing than the operational ECMWF
run.  The resulting surface trough/front reaching the state will
likely disrupt the trades for a period of time with trailing high
pressure supporting establishment of northeasterly winds over the
islands by next Thu.  The western islands should see the earliest
onset of northeasterly winds.  On average guidance is not
particularly enthusiastic about enhanced rainfall with this system
early-mid week.  However activity will be sensitive to exact
amplitude/timing of the trough aloft with any trends toward the
slow GEFS mean leading to higher amounts.

Rausch