Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
812 AM EDT Fri Mar 22 2019

Valid 00Z Sat Mar 23 2019 - 00Z Sat Mar 30 2019

Today's guidance agrees well for the overall forecast through the
next seven days.  There are some differences with the amplitude of
weak upper troughing early next week and then again with a deeper
trough that develops toward next Thursday-Friday.

Surface high pressure to the north of the state will support
moderate to brisk trades into early next week.  A weak front
stalled near 25N latitude into early Saturday may gradually push
south/southwest toward the main islands during the weekend and
early next week as a modest upper trough evolves to the north/east
of the area.  By early Tuesday there is a fair amount of spread
with the amplitude of this trough--GFS/GEFS ensembles the deepest
and CMC/CMC ensembles the weakest.  The ECMWF and ECMWF mean
represent a good intermediate solution at this time.

Trades will weaken from late Tuesday through midweek as high
pressure continues eastward.  At the same time an amplifying upper
trough over the central/east-central Pacific should bring a front
toward Kauai by early next Thursday.  The front will likely
continue southeastward thereafter.  The primary guidance
discrepancy in this time frame involves the latest GFS/FV3 GFS
runs depicting a more amplified upper trough than most other
guidance including the 00Z GEFS mean.  This leads the GFS to push
the front somewhat farther southeast than consensus.  Therefore
would recommend an average among the 00Z ECMWF and GEFS/ECMWF
means as the most reasonable starting point for this part of the
forecast.

During most of the period expect precipitable water values to
remain somewhat below climatology, with showers tending to be
relatively light/scattered and focused over windward/mauka areas
into early next week.  Trades may be light enough by midweek to
promote a period of sea/land breeze focus.  The late week front
may not bring precipitable water values much higher than normal
and then for only a brief time, so even with that boundary
rainfall should still be on the light side.

Rausch