Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EST Fri Dec 18 2020

Valid 00Z Sat Dec 19 2020 - 00Z Sat Dec 26 2020

...Wet pattern to subside after the weekend...

Today's guidance is fairly similar for the general pattern
evolution through late next week.  Through this weekend there will
be the potential for locally heavy showers and thunderstorms,
aided by an upper trough (with one or more embedded low centers)
hovering near the eastern islands along with an area of enhanced
deep moisture.  Precipitable water values may reach as high as
1.50-1.75 inches, especially over the Big Island/Maui where the
highest rainfall totals are most likely.  A shortwave dropping
down the eastern periphery of an upper ridge centered west of the
state will quickly push the moisture and upper trough away from
the islands after Sunday, ushering in a drier pattern.  Gradually
amplifying central Pacific flow aloft should encourage a front and
its accompanying band of light to moderate rain to approach/reach
the northwestern islands late in the week. 

Varying forms of surface ridging to the north and northeast of the
state will support trades over the next few days, likely strongest
early in the weekend and then trending weaker into early next
week.  This flow will support best rainfall focus over
windward/mauka areas.  Then the approaching front should interrupt
the trades for a time.  By late week anticipate winds turning
northeasterly over western areas once they are behind the front.  


Rausch