Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
816 AM EDT Wed Apr 25 2018

Valid 00Z Thu Apr 26 2018 - 00Z Thu May 03 2018

High pressure well northwest of the state will support brisk
trades through at least tonight and perhaps into Thursday.  Then
expect the well-advertised pattern change as rapidly amplifying
central Pacific energy closes off a deep upper low by Friday,
likely positioned to the north of the area around 30-35N latitude
through the weekend with a gradual northeastward drift during the
first half of next week.  Corresponding to this evolution aloft,
trades will quickly weaken Thursday into Friday and turn
southeasterly as a surface front and potential leading trough form
over the western islands.  Today there is better guidance
agreement for upper low position into early next week, so likewise
agreement is now better for surface front progression (by way of a
faster GFS trend) with consensus saying the front will likely
reach just east of the Big Island by mid-late weekend.  The
front/trough will bring the potential for areas of locally heavy
rainfall from late week into the weekend followed by a drier trend
and northerly winds behind the front.

By next Tuesday-Wednesday the majority of guidance shows a
lingering northeast-southwest upper trough lingering to the north
as the upper low itself lifts northeastward.  The 06z GFS differs
from consensus with a more neutrally tilted upper trough in this
time frame.  The guidance majority indicates that with the
gradually rising heights aloft, the axis of deep moisture
(precipitable water values reaching at least 1.75-2.00 inches) may
return northward into the islands and increase potential for
another period of enhanced rainfall.  The lower probability 06z
GFS scenario would keep the moisture more suppressed.  Confidence
in any particular solution is not particularly high at this time
frame given typical days 5-7 verification and adjustments seen in
some guidance over the past 24 hours.

Rausch