Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
830 AM EDT Tue Aug 29 2017

Valid 00Z Wed Aug 30 2017 - 00Z Wed Sep 06 2017

Latest models and ensembles are in good agreement through Friday
handling the main features affecting the Hawaiian islands...with
solutions diverging thereafter...primarily with respect to the
amplifying pattern in the polar stream. 

An area of moisture extending from a weak tropical wave will
interact with a weak mid-level shear axis to support some enhanced
shower activity across the state today. Trades should return to
near normal levels Wednesday into Thursday as high pressure builds
to the northeast in response to a strengthening upper ridge in the
eastern Pacific. This should favor more limited windward showers.

Later this week through the weekend,the GFS continues to dig a
stronger short wave trough southward from an amplified west
Pacific ridge. While this solution is plausible considering the
amplitude of the ridge, ensemble member solution spreads including
the GEFS and ECMWF ensembles instead support a more concensus
solution amplitude of the ECMWF, UKMET, Canadian.

An associated surface front will set up well northwest of the
islands by later this week and should result in trades weakening a
bit as well as veering around to a more southeasterly direction.
This will likely result in an increase in low level moisture, but
overall the models maintain slightly below average PWs, so not
expecting a large increase in shower activity through Saturday.
Into Sunday-Tuesday, a trough in the polar stream and have a
pretty well-defined surface front approaching the northwest part
of the island chain. As a result...trades should weaken
considerably, with winds turning more southerly. Increasing
tropical moisture should support the chance for diurnal
showers...particularly across the western part of the state where
a slow moving plume of high precipitable water develops.

Schichtel