Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
347 AM EDT Sun Sep 29 2024

Valid 00Z Mon Sep 30 2024 - 00Z Mon Oct 07 2024

Today's guidance continues to show moderate trades through most of
this coming week with windward/mountain focus for showers that
should be fairly light most of the time as precipitable water
values hover around or slightly below normal.  Upper ridging in
place through Wednesday should also help to temper rainfall
amounts.  Models/ensembles agree that the upper ridge will
collapse after midweek, with some type of cyclonic flow aloft
likely becoming more prevalent over and north/west of the main
islands late week into the weekend.  However there is no real
clustering among the dynamical/machine learning guidance for the
details including where a compact upper low may evolve (for
example, just northeast of the main islands in the 00Z GFS but
well west in the 00Z ECMWF).  For the purposes of a deterministic
forecast, the broader trough seen in the ensemble means is a
reasonable option while awaiting better agreement.  This upper
trough may help to weaken the trades somewhat around late week
into the weekend, while possibly increasing rainfall a bit (though
with guidance generally not too enthusiastic).

Rausch