518
FXHW60 PHFO 220700
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
900 PM HST Sun Jun 21 2026

.SYNOPSIS...
Mostly dry and stable conditions with light to moderate trade
winds will prevail through Tuesday, with clouds and mainly light
showers favoring windward and mauka locations overnight through
the early morning hours. A few cloud buildups and light showers
are possible over leeward sections each afternoon where localized
sea breezes form. A modest increase in moisture associated with a
surface trough moving in from the east, combined with an upper-
level disturbance, will support increasing rainfall chances from
Tuesday into midweek. Trade winds will then strengthen into the
breezy category by Wednesday as the trough and upper disturbance
shift west of the area and the ridge strengthens north of the
islands.

&&

.DISCUSSION...
A relatively dry and stable trade wind pattern will persist
through Tuesday as a weak surface ridge remains positioned north
of the islands. Light to moderate easterly trades will continue,
with clouds and a few light showers primarily favoring windward
and mauka areas overnight through the morning hours. Afternoon
heating and localized sea breeze development may support a few
cloud buildups and brief showers over leeward and interior
sections each day, but rainfall amounts should remain limited
through Tuesday.

Conditions will begin to change late Tuesday as a surface trough
approaches from the east and moisture increases across the island
chain. Guidance remains in good agreement showing precipitable
water values rising to near 1.75 inches by Wednesday. At the same
time, an upper-level shortwave trough is forecast to dig southward
over the region, eventually cutting off and retrograding westward
across the islands through the middle part of the week. The
approach of this upper disturbance will lower mid- and upper-
level heights while helping to weaken and elevate the inversion.
The combination of slightly deeper moisture, reduced stability,
and enhanced large-scale lift associated with the upper trough
will support increasing shower coverage and rainfall potential
from late Tuesday through Thursday, particularly over windward and
mauka areas, though some showers may periodically spread into
leeward locations on the trades.

By late week into next weekend, both the surface trough and
upper-level disturbance are expected to shift west of the state.
In their wake, a strengthening subtropical ridge north of the
islands will support a return to a more typical breezy trade wind
pattern. Upper heights will gradually rise, the trade wind
inversion will strengthen and lower, and precipitable water values
are expected to decrease back toward climatological levels. As a
result, shower activity should trend downward, with rainfall
becoming focused once again over windward and mauka areas within
the prevailing trade flow.

&&

.AVIATION...
VFR conditions will prevail with limited showers through Monday.
Trade winds increase in strength over the next few days,
decreasing sea breeze coverage area. A passing low level trough
will drift from east to west across the island chain, increasing
shower trends from Tuesday afternoon through Wednesday.

No AIRMETs in effect.

&&

.MARINE...
A weak high pressure ridge will remain nearly stationary north of
the waters maintaining gentle to locally fresh trade winds over
the next several days. High pressure to the far north northeast
will strengthen by midweek as easterly trade winds gradually
strengthen. A low level trough moving in from the east Tuesday
through Wednesday will bring an increase in shower activity.

A series of small to moderate medium to long period south swells
will keep surf along south facing shores elevated through the
forecast period. Surf along east facing shores will remain small
due to the lack of trade winds energy upstream of the islands.
Surf along north facing shores will remain flat to tiny through
the forecast period with potentially tiny background energy
midweek into Thursday.

&&

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

&&

$$

DISCUSSION...Gibbs
AVIATION...Bohlin
MARINE...Shigesato