Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Tue Jan 17 2023

Valid 00Z Wed Jan 18 2023 - 00Z Wed Jan 25 2023

Today's guidance agrees decently for the overall forecast through
the next seven days, with typical refinements over the past day
and some lingering spread by the latter half of the period.  Light
winds will prevail over most areas mid-late week, favoring
land/sea breeze influence on showers.  Any prevailing background
flow should be from the southeast and would most likely provide
some terrain focus over windward locations on the Big Island. 
Consensus still suggests a weak front may get close enough to the
northwestern islands to increase rainfall somewhat over that area
around Thursday.  This front should weaken/lift northward as winds
gradually strengthen and turn more southerly ahead of a stronger
front approaching from the west.  Models/ensembles still differ
somewhat on the exact eastward extent of this stronger front and
its accompanying heavier rain and potential thunderstorms during
the weekend, with the spread fairly typical for a forecast several
days out in time but still significant in terms of weather
specifics over individual islands.  The 00Z ECMWF/CMC/CMC mean
have the front stalling as it nears the northwestern islands while
the 00Z GFS and 00Z GEFS/12Z ECMWF means bring it at least into
the central islands.  By Monday there is better consensus today
that upper heights should rise with a ridge briefly building in
from the west/southwest, which should lead to the front
stalling/weakening near its early Sunday position with easterly
trades becoming more prevalent later Sunday onward.  Upper heights
should decline again on Tuesday as another trough passes by to the
northwest/north.  By then the 00Z GEFS/12Z ECMWF means become the
most amplified among the guidance with the renewed upper trough. 
The continued split in solutions for the exact frontal position
argues for a compromise approach in determining a specific
forecast.

Rausch