Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
205 AM EDT Sat Apr 04 2020

Valid 00Z Sun Apr 05 2020 - 00Z Sun Apr 12 2020

...Locally heavy rain possible next week...

A deep upper-level low initially centered near 32N/169W Saturday
morning is forecast to remain relatively stationary before
beginning a gradual northeastward movement Sun-Mon as it weakens
and interacts with a shortwave crossing the North Pacific. At
larger scales, model/ensemble consensus is relatively good for
this system. Models continue to indicate some potential for heavy
rainfall as the associated slow-moving cold front crosses Hawaii
and eventually stalls. The upper-level low will initially be
rather anomalous, with 500-hPa heights at least 4 standard
deviations below average, but guidance generally shows agreement
that the feature should become gradually less anomalous through
time as it moves east/northeast. The ECMWF and GFS both maximize
PWs in the 1.5-1.7 inch range along the slow-moving or possibly
stalled front across Hawaii next week. Low-level flow in the
vicinity of the front looks relatively weak, however, which may
serve to limit areal coverage of heavier rains. ECENS ensemble
precipitation probabilities show some signal for locally heavy
rains, primarily across the western/central Hawaiian islands
during the early to middle portion of next week. The GEFS was a
bit less enthusiastic, however. Nonetheless, given relatively good
moisture and the strong nature of the upper low north of the
state, would expect the potential for at least locally heavy rains
next week, especially during the Mon-Wed time frame. Model
consensus has improved on the idea that the front should stall
across Hawaii late next week, which would keep the potential for
scattered convection with locally heavy rains a possibility across
Hawaii through the end of the week.

Ryan