Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
810 AM EDT Sat Sep 13 2014

Valid 00Z Sun Sep 14 2014 - 00Z Sun Sep 21 2014

The 13/00Z GFS/ECMWF guidance were in good agreement with the key
features in the Pacific through day 4. Across the north Pacific,
the northward displacement of the surface and upper-level ridge
culminates with an inland migration across the Alaska Panhandle
and into northwest Canada.

In the central Pacific, the western portion of the Subtropical
Ridge rebuilds and migrates eastward to a position near 35N
160W---then east southeastward to approximately 33N 142W by day 6.
The flatter Subtropical Ridge solution in the central Pacific
results from the 'reshuffling' of mid-latitude energy from the
southern Bering Sea to the Gulf of Alaska by forecast period's
end.

For Hawai'i, trades should be on the increase around Wednesday.
The  positioning of the Subtropical Ridge axis northeast of the
Islands will allow a brief poleward movement of the ITCZ and cloud
debris embedded within it. This day 4-6 'transition period'
carries one uncertainty--- that being a decaying mid-latitude
surface trough left behind by the current shortwave trough and
well-defined mid-level circulation invof 31N 148W. The 13/00Z
deterministic GFS/ECMWF have enough of the detail in the central
Pacific locked down to recommend a blend of both into day 6 to
handle the surface trough sagging southward---and adding a mix of
clouds and showers to the current persistent nature of the
sensible weather pattern.

Vojtesak