Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
820 AM EDT Tue Sep 23 2014

Valid 00Z Wed Sep 24 2014 - 00Z Wed Oct 01 2014

To begin the period, a 594-dm ridge is forecast to develop north
of the islands within a very amplified mid-latitude pattern. A
broad upper trof will gradually take shape by late in the work
week with height falls constrained to north of 30N. Overall, any
meaningful mid-latitude features will remain well north of Hawaii
as a west-to-east oriented ridge maintains its position across
15N-35N. 

A surface anticyclone north of the island chain will continue to
favor the usual east-northeast trade winds throughout the period.
Models agree that the trades should pick up in intensity during
the Thursday-Saturday time frame with the guidance suggesting
sustained winds of 20 to 25 knots. By Sunday onward, the trades
will slacken a bit as the surface high migrates eastward thereby
reducing the pressure gradient. With regard to precipitation, a
decaying frontal zone should begin to increase the threat of
showers by early Thursday. While convergence along the front will
weaken significantly, an enhanced precipitable water axis of 1.50
to 1.75 inches will reside over the region. The coverage of
rainfall will expand Thursday-Saturday in respond to the
increasing tropospheric moisture and enhancement in the trades.
The 06Z GFS/00Z CMC are a pair of the wetter solutions noted in
the guidance. Eventually a return to the usual windward showers
and terrain enhanced convection will take place from Sunday until
early next week.


Rubin-Oster