Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
720 AM EST Mon Dec 07 2015

Valid 00Z Tue Dec 08 2015 - 00Z Tue Dec 15 2015

For much of the week, an elongated upper ridge will extend across
the subtropics maintaining the primary storm track well north of
the Hawai`ian island chain. By early Friday, models agree the
ridge will gain amplitude east of the islands as a longwave trough
tracks toward 30N/170W. This is the point where the consistency
between the guidance breaks down as the 06Z GFS attempts to peel
off a closed low. The 06Z GFS indicates this feature would be just
north of Kauai by 13/0000Z. However, there are no other
deterministic models nor ensemble solutions highlighting such a
scenario. Of note, the 00Z GFS exhibited this behavior as well.
Except for these GFS runs, models agree a longwave ridge will take
hold of the region through the weekend and into early next week.

At the surface, high pressure to the north and east should
maintain a steady period of moderate trade winds. The parent
surface high is expected to further strengthen late in the work
week which will support an enhancement in the east-southeasterly
flow as sustained winds may approach 30 knots. This uptick in the
trade wind strength is forecast to subside as the surface ridge
migrates eastward. Given the 06Z/00Z GFS solutions were the
outlier here, its scenario will be dismissed. Regarding
precipitation, the threat does not look particularly organized as
the guidance shows scattered activity moving through the islands.
Precipitable waters are rather low in the 0.50 to 0.75 inch range
before spiking to above an inch as the trades enhance. This could
potentially lead to heavier rainfall where convection can
organize, particularly in the orographically favored locations.


Rubin-Oster