Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 AM EST Thu Dec 12 2024

Valid 00Z Fri Dec 13 2024 - 00Z Fri Dec 20 2024

Latest guidance remains in good agreement with most aspects of the
forecast.  Strong trades continuing into Thursday should gradually
slacken some as a series of fronts will weaken the surface ridge
and push it south, possibly reaching the main islands by around
Tuesday or Wednesday.  As the surface pattern changes, primarily
windward/mountain shower focus will likely transition toward more
sea breeze influence by Tuesday-Wednesday.  Guidance still shows
the highest rainfall totals during Thursday-Friday when the Big
Island in particular will be on the northern fringe of enhanced
precipitable water values as an upper low retrogrades well south
of the state.  Moisture should decrease below climatological
values by the weekend, favoring much lighter showers.  With
typical differences in specifics, guidance maintains the idea that
some increase of moisture should move into the Big Island and
vicinity from the southeast by next Tuesday-Wednesday.  However
rainfall should remain fairly light given nearby strong upper
ridging.  By Thursday most solutions show a cold front and
associated moisture band reaching very close or into the main
islands.  Although the GFS/GEFS are a bit more amplified with the
supporting upper shortwave versus the ECMWF/CMC and their means
(leading to the GFS/GEFS front reaching farther south), some
machine learning models lean at least as far as the GFS scenario. 
An even compromise seems to provide a good starting point for a
specific forecast given typical predictability seven days out in
time.

Rausch