Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
359 AM EDT Fri Apr 05 2024

Valid 00Z Sat Apr 06 2024 - 00Z Sat Apr 13 2024

Guidance continues to agree well for the forecast pattern from
late this week through about the middle of next week.  Strong high
pressure initially over the mid-latitude Pacific will support
strong trades from Friday into the weekend.  With time the high
will slowly weaken and move eastward while a front approaches from
the northwest.  This evolution will steadily weaken the trades,
with winds likely taking on a more southeasterly component by next
Wednesday.  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.

By Wednesday-Thursday, operational models and the 00Z CMCens/12Z
ECens means all suggest that an upper low should close off within
an amplifying upper trough to the northwest/north of the state
(00Z GEFS mean keeping an open trough), with this feature
persisting into Friday.  Associated low pressure would have a
front extending to its south.  Guidance diverges significantly for
the eventual longitude of this system, with important implications
for weather over the state.  Among the 00Z solutions the GFS is on
the eastern side of the envelope, leading to rapid frontal passage
and lighter precipitation.  On the other hand, the CMC keeps the
upper low northwest of the state through Friday, ultimately
leading to the surface front helping to focus heavy rainfall over
or near the state.  The ECMWF/ECens mean and CMCens mean are
between these extremes, suggesting a brief increase of
moisture/rainfall before drier air moves in from the northwest on
Friday.  Interestingly, most of the recent runs of
ECMWF-initialized machine learning models lean to the slower half
of the spread between the ECMWF and CMC.  Based on the full array
of guidance currently available, a solution closest to the 00Z
ECMWF seems to be the best starting point albeit with low
confidence.

Rausch