Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Tue Sep 12 2023

Valid 00Z Wed Sep 13 2023 - 00Z Wed Sep 20 2023

The ongoing pattern of brisk trades with mostly light
windward-focused showers will transition after midweek. 
Models/ensembles continue to show trades becoming weaker late week
through the weekend due to a front creating a break in surface
high pressure to the north late this week, supporting dynamics
forming a weakness/upper low just north/northwest of the islands
this weekend, and also passage of a surface trough (a remnant
reflection of tropical cyclone Jova) during the weekend. 
Meanwhile guidance agrees that precipitable water values should
trend to above normal levels from late this week through at least
the weekend.  Upper ridging in place through Thursday or early
Friday may keep rainfall fairly light through that time but lower
heights aloft thereafter (to a somewhat greater degree in the
GFS/GEFS relative to other guidance) should contribute to higher
rainfall totals by the weekend.  Trades may be weak enough to
allow for some land/sea breeze influence on showers as well.  By
next Tuesday the trades may rebound somewhat as the possible upper
low moves away to the west and eastern Pacific high pressure
extends its influence farther southwestward.  At that time there
is some disagreement over available moisture, as the 00Z GFS/ECMWF
and 12Z ECens mean all show a band of drier air moving in from the
east but the 00Z GEFS mean has this drier band getting pinched off
by another area of moisture arriving from the east.  The majority
cluster suggests a trend back toward moderate trades and windward
focus of somewhat lighter showers by the end of the period.

Rausch