Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
813 AM EDT Sun Sep 15 2019

Valid 00Z Mon Sep 16 2019 - 00Z Mon Sep 23 2019

Through about Thursday guidance shows a drier period with
primarily windward focus for any showers that occur.  Expect
trades to strengthen somewhat as an upper low initially
north-northwest of the main islands moves away and low pressure
possibly develops west of 165W longitude.  Meanwhile an upper
ridge will move toward and across the region from east to west.

Models and ensembles continue to disagree over details of the
Friday-Sunday period.  The one common theme is a trend toward
wetter conditions but with differences aloft leading to various
moisture sources and rainfall intensity.  ECMWF-based guidance
continues to be fastest with energy aloft moving northeast to
southwest, reaching west of the state after early Saturday and
resulting in earlier establishment of moist flow from the south
and noticeably heavier rainfall.  In fact the 00Z ECMWF even
brings a surface low to the eastern islands by early Sunday.  The
00Z CMC's details aloft differ but its upper pattern ends up being
fairly similar to the ECMWF/ECMWF mean by Sunday.  ECMWF mean runs
are somewhat less aggressive with the precipitable water increase
than recent operational runs though.  Slower GFS/GEFS timing with
the upper energy would initially lead to an area of moisture
reaching the area from the north/northeast and it would take until
Sunday for moisture to start moving in from the southeast.  With
no clear trends in either cluster from yesterday, and the ECMWF
mean thus far being somewhat subdued compared to the operational
runs, preference would be for a compromise between the GFS/GEFS
cluster and the ECMWF mean.

Rausch