Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
718 AM EST Sat Mar 03 2018

Valid 00Z Sun Mar 04 2018 - 00Z Sun Mar 11 2018

The recent pattern of moist east-southeasterly low level flow
along with an axis of enhanced deep moisture oriented just west of
160W longitude will extend briefly into this weekend.  Shortwave
impulses ahead of a lingering upper trough/low to the west of the
state may provide some modest enhancement to shower activity as
they pass over the area.

Then the establishment of an east-central Pacific trough aloft
will bring significantly lower precipitable water values to the
area from the north.  Expect the driest air to be behind a front
that reaches the state during the late Monday/Tuesday time frame
and may be accompanied by some showers.  Behind the front, strong
central Pacific high pressure will support brisk trades from the
northeast into late week.  Toward the latter half of the week
there has been some discrepancy regarding the depth/amplitude of
upper troughing that extends southwest over the area.  By
Thursday-Friday the GFS shows a somewhat weaker trend compared to
yesterday.  This yields improved agreement between the GFS/ECMWF
and their means--the recommended compromise--while the 00z CMC/CMC
mean may still be somewhat underdone with the upper trough. 

By Saturday guidance begins to cluster into two camps for the
evolving ridge/trough Pacific pattern aloft, the sharper and
westward ECMWF/CMC plus their means versus the broader and
eastward GFS/GEFS.  The main difference for Hawai'i is that the
ECMWF cluster would weaken the surface ridge north of the islands
somewhat thus leading to a slackening of trades relative to the
GFS/GEFS.  Offsetting considerations seem to favor a compromise at
this point.  Agreeable multi-day D+8 means show a strong core of
positive height anomalies south of the western Aleutians, with
teleconnections suggesting the broader GFS/GEFS scenario aloft. 
However the overall eastern Asia through Pacific and western North
America evolution looks quite amplified which merits incorporating
ECMWF aspects as well.  Either way expect a continuation of
windward-focused showers, in the lighter half of the spectrum
given below normal precipitable water values but periodically
enhanced by individual shortwaves within the cyclonic flow aloft.

Rausch