Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
815 AM EDT Thu Apr 25 2019

Valid 00Z Fri Apr 26 2019 - 00Z Fri May 03 2019

Trades will trend weaker over the coming days as ridging at the
surface and aloft drifts eastward.  Thus expect an initial
windward focus for showers to trend toward at least some sea/land
breeze focus.  At the same time moisture will gradually increase,
with precipitable water values reaching above climatological
levels by Sunday-Monday.  This will occur as shortwave energy on
the southwestern periphery of a mid-latitude system brings a front
toward/into the area.  Guidance is not particularly enthusiastic
for heavy rainfall potential with this front but there may be at
least some enhancement of rainfall during the Sunday-Monday time
frame.  Consensus shows a drying trend with northeasterly trades
becoming established Tuesday-Thursday as the upper shortwave
continues eastward away from the state and surface high pressure
tracks well north of the islands.  Overall an average of latest
GFS/ECMWF runs and their ensemble means would provide a reasonable
starting point for the forecast, with most differences small
enough in scale to have fairly low predictability at extended time
frames.  One note is that toward Wednesday-Thursday this solution
would lean away from the 00Z GEFS mean which becomes slowest with
the departing shortwave aloft.

Rausch