Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
820 AM EDT Thu Apr 23 2015

Valid 00Z Fri Apr 24 2015 - 00Z Fri May 01 2015

The models and ensembles reasonably agree in showing an unusually
deep and southward displaced closed upper low developing to the
northwest of the islands. This is well depicted in water vapor
imagery. This feature reflects at the surface as a frontal zone
around 165W longitude,and slow approach over the next couple of
days will help 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 by early next week. A
focus of heavier rainfall will gradually work into the islands by
this weekend and linger through midweek 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 through
early-mid next week to enhance terrain rainfall focus.

Schichtel