Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
828 AM EDT Thu Sep 25 2014

Valid 00Z Fri Sep 26 2014 - 00Z Fri Oct 03 2014

In a similar fashion as described yesterday, an amplified
mid-latitude pattern will be featured north of the Hawaiian
Islands with a 594-dm ridge initially centered over 30N/165W. A
west-to-east oriented ridge should remain sprawled over the
latitude encompassing the islands throughout the forecast period
with any meaningful height falls displaced well to the north. By
30/1200Z...the last several runs of the 06Z GFS/GEFS mean remain a
pair of the more aggressive solutions digging a longwave trof east
of 170W. Compared to other deterministic/ensemble guidance and
considering modest upstream mid-upper level ridge amplitude, this
appears to be more of an outlying solution. Would recommend
staying away from the 06Z GFS/GEFS mean during the latter half of
the period.  The compatable ECMWF/ECMWF ensembles offer better WPC
continuity.

At the surface, a dome of high pressure is forecast to slide
eastward along roughly 30-35N over the next few days. In response
to the increasing pressure gradient, the east-northeasterly trade
winds should pick up in intensity. Some models depict 20 to 25
knots of low-level flow at times from late Thursday until
Saturday. Gradually the trades are expected to gradually weaken
from late in the weekend into the early/middle part of next week.
Overall, precipitation should be a little more active, especially
over favored windward terrain, during the Thursday through
Saturday time frame given the increase in the trades as an
enhanced plume of moisture funnels over Hawaii. Once the trades
begin to weaken, expect a return to the more usual windward
showers and enhanced convection across the favored upslope terrain.

Schichtel