Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 06/19/2026 04:42:00 PM UTC

                        
908
FXHW60 PHFO 190642
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
842 PM HST Thu Jun 18 2026

.SYNOPSIS...
A weak surface trough and its associated moisture plume over the
western end of the state will shift northwest through Friday,
bringing a slight uptick in shower activity as it passes through.
Otherwise, a lighter background flow will allow for a sea/land
breeze pattern to persist into the weekend with showers developing
over leeward and interior areas each afternoon, followed by
clearing at night. Then trade winds will gradually strengthen
through next week, shifting the shower focus to windward and mauka
areas.

&&

.SHORT TERM UPDATE...
A weak surface trough, currently located west of Oahu, edged slowly
northwestward today. Light flow allowed for diurnal coastal sea
breezes to form in the early afternoon. Moderate to heavy showers
developed along the Koolau range on Oahu over north Kauai with the
help of ample low level moisture and weak instability from the
trough. Southerly winds were noted in the 00Z Lihue sounding from
2500 ft to around 12000 feet. This helped push shower activity
that formed over the interior of the islands and mountains,
northward. Flood Advisories were needed for both central portions
of windward Oahu and far northern Kauai. Though shower intensity
on RADAR has been trending downward this evening, showers may
still continue close the trough tonight, mainly over Kauai and
Oahu. In the update, rainfall chances were upped slightly along
windward Oahu and north Kauai as left over weak boundaries, amble
low level moisture, and marginal instability exist. The rest of
forecast appeared on track.

&&

.PREV DISCUSSION...
Issued at 311 PM HST Thu Jun 18 2026
Radar and visible satellite imagery show a slightly veered east-
southeast flow steering clouds and isolated showers parallel to
the island chain this afternoon. The bulk of the clouds and
showers are remaining just east of the state and along a weakly
convergent boundary associated with the weak surface trough near
Kauai, but clouds and a few showers have also managed to develop
over leeward and interior areas of each island with the afternoon
sea breezes.

The surface trough will weaken further and gradually shift
northwest of the state through Friday, with moderate east-
southeast winds filling in behind it through Saturday. Winds will
briefly take on an east-northeasterly tilt on Sunday as a
front/trough approaches from the northwest. With wind speeds
gradually strengthening, a mix of windward and mauka showers with
isolated afternoon sea breeze leeward and interior showers can be
expected through the weekend. In addition, dew points are expected
to remain in the 70s for many locations through Saturday,
maintaining muggy conditions through much of the weekend.

Heading into next week, the subtropical high to the far northeast
will regain control and easterly trades will build to moderate to
breezy levels through midweek. This will usher in slightly lower
dew points, and combined with the breezier trades, some relief
from the mugginess. Model guidance suggests that an upper level
low will pinch off of the longwave trough to the far north and
approach the state from the northeast mid to late-week, possibly
providing some enhancement to windward and mauka showers as
batches of moisture move through.

&&

.AVIATION...

A departing surface trough continues to make for windward showers
across Kauai and Oahu this evening. A weakened trade wind pattern
remains in place, leading to land/sea breezes across most sites,
however a return to steady trades over the next several days is
expected. VFR conditions are broadly expected to prevail, however
windward sites may see periods of MVFR under occasional shower
activity.

AIRMET Sierra remains in effect for Kauai through Maui County due
to mountain obscuration from showers. Conditions are improving
for Maui County as of this TAF issuance, but mtn obsc may linger
longer for Kauai and Oahu as this system remains within the
vicinity of the islands.


&&

.MARINE...
Issued at 311 PM HST Thu Jun 18 2026
Light to moderate trades will hold for the next few days as a
weak surface ridge remains to the north and a broad surface trough
continues to move west over the island chain the next few days.
The weak trough is currently located between Oahu and Kauai waters
and is producing some scattered showers over the coastal and
offshore waters. Scattered showers will generally decrease over
the coastal waters by Friday. Trades may increase slightly over
the weekend as the trough dissipates, with more pronounced
strengthening early next week as the ridge strengthens to the
north.

A moderate, long period south swell is peaking at advisory levels
this afternoon, thus a High Surf Advisory remains in effect for
all south facing shores through early Friday morning. This swell
should drop below advisory levels by Friday as the swell gradually
fades late tonight into the weekend. A series of smaller south-
southwest swells will fill in Sunday into the first half of next
week and will maintain surf near seasonal averages through next
week.

Tiny surf will prevail on north and east shores through most of
the coming week. A slight increase in east shore surf is expected
around next Tuesday or Wednesday as trade winds build across the
region.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Friday for Big Island South-
Big Island Southeast-East Honolulu-Ewa Plain-Honolulu Metro-
Kahoolawe-Kauai South-Kauai Southwest-Kona-Lanai Leeward-Lanai
South-Maui Central Valley South-Maui Leeward West-Molokai
Leeward South-Niihau-South Haleakala-South Maui/Upcountry-
Waianae Coast.


&&

$$

SHORT TERM UPDATE...Thomas
DISCUSSION...Farris
AVIATION...Evans
MARINE...Almanza