Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
706 AM EST Wed Dec 17 2014

Valid 00Z Thu Dec 18 2014 - 00Z Thu Dec 25 2014

The surface high initially to the northeast of the islands will be
quickly replaced by another immediately upstream, which may lead
to a brief/modest freshening of trades around Thu.  GFS/ECMWF runs
agree upon somewhat lower precipitable water values around Fri-Sat
so primarily windward-focused showers should be lightest around
that time.  Continued eastward progression of high pressure and
the approach of a strong cold front will likely turn trades more
from the southeast during the weekend.  Guidance is still showing
some question marks by the Mon-Wed time frame, but one improvement
in the spread is that the 00z ECMWF has trended away from the
prior two runs that had closed off a very anomalously
deep/southward upper low just west of the islands leading to some
500mb heights that were 4-6 standard deviations below normal. 
Based on the 00z UKMET through 00z Tue as well as the 00z-06z
parallel GFS runs, the current best cluster of solutions is slower
than the operational 00z-06z GFS and corresponding GEFS means. 
The parallel GFS runs may bring their associated surface low a
little far west/southwest for a time but overall some compromise
among the 00z ECMWF mean and more closed aloft 00z ECMWF/00z-06z
parallel GFS looks best at this time given the
amplitude/sharpening of the large scale pattern.  Such a solution
would bring the cold front through the islands from west to east
during late Sun-Tue, with strengthening winds taking on a more
northerly component after passage of the front.

Rausch