Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
809 AM EDT Wed Apr 19 2017

Valid 00Z Thu Apr 20 2017 - 00Z Thu Apr 27 2017

Today's guidance remains fairly similar and consistent with the
forecast evolution through next Wednesday.  Low level flow is now
in the process of becoming southeasterly then southerly as a cold
front approaches from the northwest.  This front will reach the
northwestern islands Thursday, stall over the central islands
Friday, and then begin to dissipate over the weekend.  An area of
moisture initially supporting some rainfall in the vicinity of the
Big Island will combine with moisture along the front to bring the
possibility of some locally moderate to heavy rainfall over the
central/northwestern islands from late this week into the weekend.
 There will be a drier trend for precipitable water values and
primarily windward focused rainfall later Sunday into early next
week.  Toward next Wednesday the GFS/ECMWF are suggesting that a
pocket of somewhat higher moisture may reach the islands from the
east/northeast.  At that time frame such features have low
predictability so will monitor future runs for consistency.  High
pressure behind the cold front will reach north of the islands by
Friday and reestablish moderate to brisk trades.  The high will
settle northeast of the state but still maintain enough of a ridge
to its west to maintain trades into midweek.

Rausch