Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
201 AM EDT Sun Apr 05 2020

Valid 00Z Mon Apr 06 2020 - 00Z Mon Apr 13 2020

...Locally heavy rain possible this week...

A deep upper-level low well north of Hawaii is forecast to drift
eastward through midweek. An associated surface cold front is
forecast to reach the western Hawaiian islands late Mon, and then
move east across the state Tue-Wed as it gradually weakens,
perhaps dissipating by Fri or Sat. Overall model/ensemble
consensus surrounding these features is relatively good among the
ECMWF/GFS/UKMET. Models continue to show PWs in the 1.5-1.7 inch
range spreading northward along the front, which should result in
the potential for at least localized heavy rainfall. One
inhibiting factor to more widespread heavy rains will be
relatively weak low-level flow in the vicinity of the front.
Ensemble guidance suggests the best probabilities for locally
heavy rains will occur across the western/central islands late Mon
into Tue as the front arrives. As the front weakens after that,
probabilities drop off, but fairly deep moisture in the vicinity
of the front should allow for isolated heavy rains through late in
the week even as far east as the Big Island as the front gradually
washes out. Models/ensemble show some degree of consensus that
another upper low may cut off north of Hawaii next weekend,
perhaps a bit closer to the state than the previous one. At this
time, models show the second upper low taking a moving in a more
easterly direction more quickly, which would keep the majority of
the deep moisture plume east of Hawaii. Another implication of
this somewhat repetitive synoptic setup is the relative lack of
much in the way of trades, which should largely remain south of
Hawaii through much of the upcoming week, with low-level flow
remaining consistently light and variable.


Ryan