874
FXHW01 KWNH 100759
PMDHI

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 AM EST Fri Jan 10 2025

Valid 00Z Sat Jan 11 2025 - 00Z Sat Jan 18 2025

Guidance agrees upon moderate to brisk trade flow from late this
week into the start of next week, favoring windward/mountain
rainfall focus, though with a potential interruption in trades
around Tuesday as a front approaches.  Meanwhile initial elongated
shortwave energy crossing the islands should soon form a closed
low just south of the Big Island, lingering until it starts to
depart eastward next Monday.  This upper low should promote
periods of enhanced rainfall especially over the eastern side of
the Big Island, though differences exist for how much moisture may
increase (ECMWF/ECens mean precipitable water values higher than
the GFS/GEFS with a compromise being a reasonable starting point).
 Expect showers to trend lighter Tuesday-Wednesday with an upper
ridge building in and PWATs declining somewhat.  After midweek,
central Pacific upper troughing may extend toward the region and
push a cold front into the main islands.  Dynamical and machine
learning (ML) models differ with details of the upper trough, but
at least with a relative majority of guidance suggesting that the
upper trough should be more amplified than the 00Z GFS.  At the
surface this corresponds to the associated cold front pushing
farther east/southeast into the islands versus that GFS run.  A
non-GFS composite would be preferred for this part of the
forecast.  A band of enhanced rainfall will be possible with this
late week front, but specifics will be sensitive to finer scale
details that have low predictability a week out in time.

Rausch





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