Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
826 AM EDT Fri Apr 24 2015

Valid 00Z Sat Apr 25 2015 - 00Z Sat May 02 2015

Models and ensembles continue to reasonably agree in showing an
unusually deep and southward displaced closed upper low just
northwest of the islands. This is well depicted in water vapor
imagery. This feature reflects at the surface as a 1011 mb low
near 26N 170W and an associated frontal zone around 160-165W
longitude as per 06 UTC Ocean Prediction Center (OPC) analysis. A
slow approach over the next couple of days is helping turn low
level winds over the islands more southward allowing for deeper
moisture return. The heaviest associated band of heavy rainfall is
now just northwest of the northwestern islands where models and
blended precipitatble water loops show values in excess of 1.75".
The slow weekend ejection of the closed low just to the north of
the state will lead to entrainment into mid-higher latitude flow
Sunday/Monday. A focus of heavier rainfall will gradually work
into the islands by this weekend and linger next week with
trailing frontal approach and weakening/stalling into an airmass
with enhanced precipitable water values. A surface high reaching
the central Pacific to the north of the islands in the wake of
closed low ejection will meanwhile act to strengthen island trades
as well next week to enhance terrain rainfall focus.

Schichtel