Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
244 AM EST Fri Jan 13 2023

Valid 00Z Sat Jan 14 2023 - 00Z Sat Jan 21 2023

Initially dry conditions should trend somewhat wetter with time,
but with some day-to-day variability plus greater uncertainty
after midweek in light of significant guidance differences for a
second front approaching the area.  Upper ridging will prevail
over the region into early next week though trade flow (which
could be light enough to allow for some land/sea influence on
showers) should bring a gradual increase of moisture, yielding
precipitable water values closer to climatology by around next
Tuesday or so.  Also by that time, a wavy front to the northwest
of the state may reach its closest point to the islands and keep
trade flow weak.

Guidance differences become more pronounced during the latter half
of the week as upstream shortwave energy further erodes the upper
ridge over the area.  The precise amplitude of this energy makes a
difference regarding whether a second front extends into the
islands, with an associated increase of rainfall over most of the
area, or stays just to the northwest which would likewise keep the
best rainfall chances over the northwestern islands--if even that
far east.  00Z/18Z GFS runs and most 00Z GEFS members show lower
upper heights versus nearly all of the 00Z CMCens/12Z ECens
members as well as the 00Z CMC/ECMWF.  Based on this distribution
of guidance, would at least favor keeping the front and its
moisture somewhat farther west than the GFS/GEFS.  As the 12Z
ECMWF mean holds the front farthest west (with highest upper
heights), the 00Z ECMWF/CMC/CMC mean seem to provide the best
intermediate starting point given the typical uncertainty for
forecasts at that time frame.

Rausch