Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Sun Mar 15 2020

Valid 00Z Mon Mar 16 2020 - 00Z Mon Mar 23 2020

...Heavy rainfall threat during the first half of the week...

Today's models and ensembles continue to show similar ideas for
the overall pattern during the period.  Compact and sharply
amplifying energy aloft now near 180 longitude will close off an
upper low to the west-northwest of the region by around Sunday
night.  This Kona low will likely persist into Wednesday or early
Thursday and then open up/lift northward ahead of an approaching
mid-latitude trough/upper low.  As advertised in prior runs, flow
to the east of the upper low will bring abundant tropical moisture
into the region with bands of heavy rainfall and thunderstorms
during the first half of the week--most likely over the western
islands and to some degree central islands.  Over the past day not
much has changed with the guidance spread for the axis of heaviest
rainfall, as the GFS still tends to drift somewhat eastward of the
majority of other solutions (including the GEFS mean) for a time. 
Such details have low confidence multiple days out given
sensitivity to exact upper low position and shortwave impulses
flowing around the low.  Prefer an average of ideas from the 00Z
GFS/ECMWF and GEFS/ECMWF means, leaning away from the CMC that
ends up somewhat west of consensus for the upper low Tuesday
onward.

Later in the week expect the axis of deep moisture to become less
pronounced and drift northwestward as heights aloft rise, leading
to a lighter trend for rainfall.  In this time frame the GFS
appears somewhat more extreme with its lower heights aloft over
the state and corresponding higher rainfall versus most other
guidance.  The GEFS mean aligns much more closely with other
solutions that keep the deep moisture/rainfall farther west. 
Expect the drier trend to continue into next weekend as lower
precipitable water values move in from the east.

Consensus still shows brisk to strong southeasterly winds
developing over the main islands by Monday and persisting into
midweek in response to the tight gradient between the Kona low and
high pressure to the east.  Even if the axis of heaviest rainfall
does not reach the Big Island, terrain enhancement along windward
slopes may enhance totals.  Departure of the Kona low should allow
for some weakening of easterly-southeasterly winds late week into
the weekend but still holding at moderate strength.

Rausch