Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Sat Apr 06 2024

Valid 00Z Sun Apr 07 2024 - 00Z Sun Apr 14 2024

Guidance still shows a good consensus for the forecast pattern
evolution through about Tuesday or early Wednesday.  Trades will
steadily trend lighter with time as high pressure north of the
state weakens and tracks into the eastern Pacific, while a front
approaching from the northwest will additionally help to weaken
the winds or at least lead to a more southeasterly component. 
Windward-focused showers, with a few possibly straying to leeward
areas, should be moderate as a weakness aloft could enhance
amounts but guidance shows precipitable water values staying
somewhat below normal.

Models and ensembles continue to diverge significantly for an
upper low expected to close off to the northwest or north of the
state by Wednesday-Thursday (and associated surface reflection),
with considerable differences for sensible weather effects across
the state depending on the solution.  As a starting point, there
is an overwhelming signal from the ECMWF/CMC, their means, and
12Z/00Z ECMWF-initialized machine learning models (MLs) that the
upper low should close off farther west than forecast by GFS/GEFS
runs thus far.  This suggests only a low probability of the
GFS/GEFS scenario of a rapid frontal passage that would minimize
rainfall as it passes through and a trailing push of drier air
coming in from the west behind it.  However there are still
significant differences among the remainder of guidance.  The past
couple ECMWF runs have adjusted west to the CMC that had been on
the western side of the envelope, while the 00Z CMCens mean is a
little east of the ECMWF/CMC while the 12Z ECens mean is between
the CMCens mean and GFS/GEFS.  Thus the ECens mean still shows a
decent drying trend, even if not to the degree of the GFS/GEFS. 
Meanwhile the MLs continue their initial theme from yesterday of
being in the western half of the spread, which currently places
them within the ECMWF/CMC/CMCens cluster.  Tilting preference a
little more in this direction, there would be potential for the
decelerating/stalling surface front to lift moisture northward and
produce enhanced rainfall over the western and possibly central
islands after midweek. 

Rausch