Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
812 AM EDT Fri May 20 2016

Valid 00Z Sat May 21 2016 - 00Z Sat May 28 2016

The current Hawaii forecast appears in relatively good agreement
among the 20/00Z model guidance suite through Monday morning,
after which ensemble mean differences emerge with respect to a
large scale trough crossing the northern Pacific.  These
differences become significant by the middle of next week with the
00Z EC mean much farther east with the trough and the 00Z GEFS
mean to the west.  However, this should be sufficiently far enough
north of Hawaii to not have any significant effects.  The models
continue to support the idea of a broken ridge to the north of the
islands, with relatively good agreement in the surface pattern
near 20 degrees north.  

At the surface, easterly trade winds averaging 15 to 25 knots over
the open waters should prevail through the period with little in
the way of fluctuation owing to the persistence of the ridge to
the north and northeast.  Clouds and showers are likely over the
favored east-facing slopes.  A trough axis approaching 30 degrees
north early next week may allow the trade winds to veer slightly
to the ESE, but nothing noteworthy at this time.  Overall, a blend
of the 20/00Z deterministic GFS/ECMWF and their ensemble mean
solutions should maintain a stable medium range forecast for
Hawaii.

Hamrick