Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
807 AM EDT Sat Apr 15 2017

Valid 00Z Sun Apr 16 2017 - 00Z Sun Apr 23 2017

The upper trough moves east of the islands today and drying aloft
occurs through early next week with layer relative humidity
dropping to below 50 percent.  With a low level ridge north of the
islands, showers are focused primarily in windward locations with
moderate trades.

On next Wed and Thu the next deep layer trough is forecast to
approach from the west, with a surface cold front gradually
weakening as it crosses the islands.   The GFS and ECMWF show
pockets of enhanced precipitable water, with the GFS consistently
showing around 1.5 inches in the western islands (ECMWF just
under, near 1.4 inches).  Pre-frontal convergence should produce
an uptick in shower coverage and amounts.  The models have come
into better agreement with good clustering of forecasts among the
gfs/ECMWF/ECMWF ensemble mean/Canadian global regarding the
evolution of the early week ridge and later week approach of the
front. 

Next weekend the majority of solutions show another low level
ridge building north of the islands and trade winds becoming
re-established over the region, albeit at less than normal speeds.

Petersen