Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
800 AM EDT Fri Jun 19 2015

Valid 00Z Sat Jun 20 2015 - 00Z Sat Jun 27 2015

Overall the latest guidance maintains better than average
agreement with the forecast through period, albeit with some
differences starting to arise late next week.  Flow around an
upper ridge to the northwest of the islands will bring a weak
front toward the area during the weekend into Mon.  This feature
should be accompanied by a modest and brief weakening of trades
that will likely be in the moderate range for the forecast period
as a whole.  Also in this time frame precipitable water values
should reach or exceed 1.50 inches over the northwestern islands,
which may provide some degree of enhancement to typically windward
shower activity.  Continued eastward elongation of central Pacific
surface high pressure behind the front should then encourage
resumption of trades at a strength similar to that seen near the
start of the forecast.

By next Thu-Fri the models and ensembles show a westward
rebuilding of the upper ridge which may lead to a downstream
trough developing well north of the islands.  As of day 7 Fri the
06z GFS/00z ECMWF are a little more amplified with the trough
versus most other models and the ensemble means, though still
within the full ensemble spread.  Those operational runs would
lead to somewhat more of an inverted surface trough over the
islands Fri relative to the currently preferred ensemble means.

Rausch