Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
819 AM EDT Mon May 22 2017

Valid 00Z Tue May 23 2017 - 00Z Tue May 30 2017

A frontal boundary will wash out north of the Islands tonight into
early Tuesday, while a broad weakness in the upper ridge centered
well west of Hawai'i remains overhead. Scattered shower activity
may affect the northern Islands by Wednesday as the remnants of
the front drift southward. Models are in general agreement on a
pattern change by late in the week, as the upper level ridge
retreats westward, and heights quickly fall across Hawai'i as a
full latitude trough deepens generally along 150-160W. The UKMET
and ECMWF are a bit more aggressive with lowering heights across
the Islands Friday and Saturday relative to the GFS and GEM
global. The breakdown of the surface ridge over the North Pacific
will result in a weakening of the trades Thursday and Friday, with
surface easterlies weakening to 5-10 knots by Friday. Precipitable
water values will begin to increase across the southern Islands by
early next week as a surface ridge reestablishes itself off the
west coast of the U.S. mainland, drawing moisture north around the
western periphery.

Ryan