610
FXHW01 KWNH 180614
PMDHI

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
214 AM EDT Fri Apr 18 2025

Valid 00Z Sat 19 Apr 2025 - 00Z Sat 26 Apr 2025


...Heavy Rain/Runoff Threat for Hawaii...

Model and ensemble solutions seem reasonably well clustered
overall, bolstering forecast confidence in a favored composite
solution that should tend to mitigate lingering smaller scale
variances consistent with individual predictability. An upper
trough now atop Hawaii should remain overhead through late week.
At the surface, inverted troughing in place is disrupting the
trades. Winds are forecast to stay mainly weak in most areas and
allow for land and sea breezes. Meanwhile a weakening front will
stall to the west, ahead of which moisture will be drawn northward
atop the islands and increase shower coverage. Precipitable water
values could be near or over the 90th percentile for this time of
year, while the upper trough could allow for some instability to
form to support some thunderstorms in a wet pattern. Currently,
flood advisories are in effect for portions of the western and
central islands, with winter weather advisories for the cold Big
Island summits.

Over the weekend, the upper trough is forecast to weaken and pull
away, while Pacific surface high pressure develops well north and
allows for trades to gradually resume. This may be a somewhat wet
trade wind pattern through early next week as moisture lingers.
Then by around the middle of next week, another upper trough is
forecast to dig west of the state. This will once again cause the
mean flow to veer for southeasterly/southerly winds that may be
stronger this round. Moisture and showers are likely to increase
once again as well.

Schichtel