Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
816 AM EDT Sat Mar 23 2019

Valid 00Z Sun Mar 24 2019 - 00Z Sun Mar 31 2019

Models and ensembles continue to agree well for the overall
pattern evolution over the next week while offering some spread
for the exact amplitude of upper features.

Moderate to brisk trades will persist into early next week due to
surface high pressure to the north of the state.  The high will
accelerate eastward after early Tuesday, leading to weaker trade
flow into midweek.  A band of moisture associated with a weak
front initially stalled near 25N latitude should gradually push
west-southwest toward the northwestern main islands over the
coming days while a modest upper trough evolves over and
north/east of the area.  As of early Tuesday the GFS/ECMWF and
their ensemble means have converged reasonably well for amplitude
of this trough while the CMC and its ensembles remain flatter.

Guidance still shows an amplifying upper trough passing by just to
the north during the mid-late week time frame, followed by
upstream shortwave energy that may serve to pull the overall mean
trough axis a little westward.  There is a general consensus that
the leading upper trough will push a front into the main islands
around Wednesday night-Thursday.  Then the trailing energy would
cause the front to stall over the islands, with the front (or its
associated band of moisture if the front itself dissipates)
possibly lifting back to the northwest slightly by
Friday-Saturday.  Operational GFS runs are still in the more
amplified part of the full guidance envelope, a bit more so for
the trailing upper energy.  The 06Z GFS has trended less amplified
than the 00Z run for the latter feature to provide more support
for an intermediate solution.

Precipitable water values should remain near to below climatology
with showers tending to be relatively light/scattered and focused
over windward/mauka areas into early next week.  Lighter trades by
midweek may promote a period of sea/land breeze focus.  The late
week front may not bring precipitable water values much higher
than normal so rainfall should still be on the lighter side of the
spectrum late in the forecast period.

Rausch