Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
740 AM EST Mon Dec 18 2017

Valid 00Z Tue Dec 19 2017 - 00Z Tue Dec 26 2017

...Heavy rain threat Wednesday into Thursday...

An upper low that has been retrograding north of Hawaii for the
past few days is forecast to weaken while gradually lifting
northeastward away from the Islands.  An upper-level trough from
the higher latitudes will quickly approach the Islands from the
northwest, and will help develop a cold front a head of the
trough.  Models indicate a decent amount of moisture ahead of the
front, which should move from west to east across the Islands from
Wednesday into Thursday.  The GFS shows a faster eastward motion
of the moisture compared with the ECMWF.  A compromise between the
two should yield a good starting point for the timing of the
precipitation.  Dry air will then filter into the Islands behind
the front through the weekend into Monday of next week under brisk
northwesterly then northerly winds.  Meanwhile, models indicate
the potential of a tropical/subtropical cyclone passing a few
hundred miles east of the Islands late this week following the
passage of the cold front.

Kong