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Hawaii Extended Forecast Discussion
(Caution: Version displayed is not the latest version. - Issued 0750Z Mar 21, 2023)
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Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
350 AM EDT Tue Mar 21 2023

Valid 00Z Wed Mar 22 2023 - 00Z Wed Mar 29 2023

The models and ensemble means continue to converge with respect to
the forecast evolution through late this week.  An upper low
initially northwest of the main islands will track northeastward
over the coming days, taking along its associated surface low to a
position well north of the state by early Friday.  As this occurs,
expect southeasterly low level winds to prevail while a band of
moisture drifts into the western/central islands by mid-late week.
 Currently the guidance is split as to how organized the heavier
rainfall may be over the western islands around Wednesday-Thursday
(00Z ECMWF/UKMET more pronounced than the GFS/CMC).  Farther east,
windward locations should see the best rainfall focus.  Trends
over recent days have seen the previously western ECMWF/ECMWF
mean/UKMET solutions for the upper low/trough and moisture axis
adjust steadily eastward closer to the GEFS mean if not quite to
the GFS that has been on the eastern side of the envelope.

Consensus still shows a drier trend and a return to more typical
trades/windward shower focus for the weekend as the upper system
open up and weakens.  However, the next upper low forecast to
close off northwest of the state has trended farther east than
seen in previous days.  As a result the upper ridge that was
expected to build over the main islands during the weekend has
shifted a bit eastward in today's guidance.  Then by next
Monday-Tuesday the upper trough gets close enough that low level
winds may weaken some and gain a more southerly component
(especially over the western islands) as a surface trough
approaches from the west.  Currently the models and means show
better than average clustering for the upper system and surface
trough relative to typical 6-7 day forecasts.  At the moment the
models and means are not too enthusiastic about any meaningful
increase of moisture through Tuesday, but this will merit
monitoring over coming days.