Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
810 AM EDT Tue Apr 18 2017

Valid 00Z Wed Apr 19 2017 - 00Z Wed Apr 26 2017

Latest models and ensemble means agree well for the expected
pattern over the next seven days.  Over the next couple days low
level flow will turn from easterly to southerly as high pressure
initially north of the islands moves quickly eastward and a strong
Pacific storm pushes a trailing cold front toward the state.  A
band of moisture along 18-20N latitude may promote some
enhancement of rainfall over windward terrain of the Big Island
early in the period.  Around Wednesday-Thursday this moisture will
lift northward and join the axis of moisture along the approaching
front.  The front should push into the northwestern islands
Thursday and settle over the central islands Friday.  While the
front will gradually weaken it should leave an axis of above
normal precipitable water values over the area during the weekend.
 After a period of locally moderate to heavy showers with the
enhanced moisture late this week and weekend, expect drier air to
move in from the east with lesser shower activity next
Monday-Tuesday.  Meanwhile expect trade flow of at least moderate
strength from Friday onward.  High pressure trailing the cold
front will build north of the state Friday.  Although the high
will move on into the eastern Pacific, it will continue to extend
a ridge far enough westward to maintain the moderate to brisk
trades over Hawai'i into next week.

Rausch