Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
711 AM EST Thu Jan 11 2018

Valid 00Z Fri Jan 12 2018 - 00Z Fri Jan 19 2018

Today's guidance still shows good agreement for the overall
forecast, with the primary differences involving precipitable
water values from the weekend through next week.  By Sunday the
00z GFS shows the greatest northward extent of an area of enhanced
moisture passing just south of the state, while the 00z GEFS mean
and 06z GFS are a compromise between the 00z GFS and drier 00z
ECMWF.  For the rest of the period the 00z ECMWF tends to be drier
than other solutions as well.  The 00z ECMWF represented a drier
adjustment from its previous run so the 00z GEFS/06z GFS or only a
modest compromise with the 00z ECMWF looks best at this time.

An upper low initially over the state will drift southeastward
with time.  This feature along with a pocket of moisture near the
Big Island will support the potential for some enhanced rainfall
in its vicinity into Friday.  Meanwhile from late week into the
weekend a weak ridge will replace a surface trough, with
relatively light winds likely allowing for sea breezes to
influence any light shower activity that develops.  Models/means
are consistent in showing the surface ridge axis shifting
northward by Monday leading to light-moderate trade flow and more
windward focus for showers.  Then fairly strong high pressure
crossing the central Pacific will tighten the pressure gradient by
Wednesday-Thursday and generate brisk/windy conditions with
potential for some rainfall to stray into leeward areas.

Rausch