Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
814 AM EDT Sun Apr 23 2017

Valid 00Z Mon Apr 24 2017 - 00Z Mon May 01 2017

A surface ridge extending west-southwest from eastern Pacific high
pressure will maintain trades of at least moderate strength into
midweek, possibly weakening a bit into early Monday and then
becoming a little stronger Monday-Tuesday night.  Generally
windward focused shower activity should trend lighter early in the
week as precipitable water values decline to around an inch.  With
differences in specifics most guidance shows a modest increase in
moisture around midweek.

Broadly speaking the models and ensembles are gradually trending
toward a more common evolution for the amplifying upper trough
expected to reach the state by around Friday-Saturday.  This upper
trough will bring a surface front into the area and likely support
a period of more unsettled weather with potential for some locally
enhanced rainfall through the weekend.  Best guidance agreement
now exists into Thursday, through 00z of the 28th, with widening
spread of solutions thereafter.  Latest GFS runs have moderated
the more extreme aspects of forecasts from the past couple days
but may still be a little deep with a compact upper low that
closes off just north of 30N by Saturday and a little fast with
the part of the upper trough that crosses the state
Friday-Saturday.  The 00z GEFS mean agrees better with the 00z
ECMWF/ECMWF MEAN in keeping the axis of moisture along the front
somewhat westward of 00z/06z GFS runs, so would recommend those
solutions at this time.  Meanwhile the front will separate brisk
northeasterly winds over the northwestern islands from
southeasterly winds over the Big Island.

Rausch