Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 05/18/2026 04:32:00 PM UTC

                        
510
FXHW60 PHFO 180632
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
832 PM HST Sun May 17 2026

.SYNOPSIS...
A slightly unstable and somewhat wet trade wind flow will continue
over the next few days with brief downpours possible. An increasingly
stable, windy trade wind flow will develop during the second half
of this week.

&&

.SHORT TERM UPDATE...
Issued at 830 PM HST Sun May 17 2026

This evening, heavy showers that occurred earlier in the day across
portions of the state have largely diminished. Radar and satellite
imagery still shows a few lighter windward and mauka showers at this
time, which will likely continue throughout the night. The remainder
of the forecast remains on track, so no updates have been made this
evening.

&&

.PREV DISCUSSION...
Issued at 344 PM HST Sun May 17 2026

Scattered heavy showers developed over select areas across the
state today due to the higher than normal moisture values combined
with some afternoon day time heating. As we head into the late
afternoon and evening, the intensity of the showers should
generally decrease. The one exception is over windward Big Island
and possibly east Maui, where we are seeing frequent trade wind
showers. Hilo sounding showed over 2 inches of precipitable water
values this afternoon and a wet trade wind pattern could very well
continue for the Big Island through the middle of the week with
frequent showers over windward areas.

Overall, broad troughing aloft combined with higher than normal
precipitable water values and moderate easterly trade winds will
continue to produce brief downpours at times through the middle of
the week. Showers will generally favor windward areas during the
overnight and morning hours with scattered leeward showers
developing during the afternoons. Dewpoints will continue to
linger in the upper 60s to low 70s, which should make temperatures
feel warmer than normal.

Increased stability and stronger trade winds are expected by
Thursday. Latest global guidance from the GFS and ECMWF are in
good agreement with a strong high developing far north of the
state, which should result in windy conditions. Winds could very
well reach Wind Advisory thresholds Thursday into Friday for
select areas downstream of terrain. Drier conditions are also
expected during this time, but scattered showers should continue
to ride in with the windy trade winds especially during the night
and early morning hours.

&&

.AVIATION...
Issued at 830 PM HST Sun May 17 2026

Moderate to locally breezy trades expected for the next couple
days. Low cigs and SHRA should primarily impact windward and mauka
locations with some limited spillover to leeward areas. Isol IFR
and MVFR conds possible in heavier SHRA, otherwise VFR prevails.

AIRMET Sierra is in effect for mtn obsc for Kauai, Oahu, Maui and
windward sections of the Big Island.

&&

.MARINE...
Issued at 830 PM HST Sun May 17 2026

The pressure gradient back from a surface high centered 1,400 nm
northeast of the islands remains tight enough to support moderate
to locally fresh trades the next few days. This anchored high
will strengthen and expand past mid week. The resultant tightening
gradient will produce fresh to locally strong trades during the
later half of the week.

A small, medium period north northwest (320-330 degree) swell and
associated north-facing surf will continue to slowly decline through
early Monday morning. A small size, short to medium period north
northwest bump in swell late Monday will provide an additional
foot or two upon north-facing shore surf later in the day through
Tuesday.

The arrival of a couple of medium to long period south southwest
(200 degree) swells will maintain near summertime average surf
along southern facing shores through most of the week. Strengthening
trades later this week will keep short period, elevated wind wave
chop alive through the week.

Water levels peaking between 2.5 to 3.0 ft MLLW during high tides
the next couple of days will result in some minor overwash within
low lying coastal areas.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SHORT TERM UPDATE...Vaughan
DISCUSSION...Kino
AVIATION...Walsh
MARINE...Blood