NWS Bulletins for NPAC - MKWC
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Hawaiian Islands Synoptic Discussion and Guidance
369
FXHW60 PHFO 211854
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
854 AM HST Tue Apr 21 2026
.SYNOPSIS...
A light land and sea breeze pattern will produce afternoon clouds
and spotty showers over land and partial clearing at night. Trade
winds will redevelop late Wednesday and strengthen Thursday and
Friday, focusing rainfall over windward and mauka areas.
&&
.SHORT TERM UPDATE...
Emergent sea breezes will at least produce interior clouds and a
few showers, except for the Big Island where greater coverage and
intensity of showers is likely. Isolated heavy rainfall is not out
of the question given the resident moist airmass characterized by
dewpoints in the 70s and PWAT values around 1.5". However, like
yesterday, high cirrus threatens to weaken sea breeze convergence
just enough to limit interior shower potential. Inherited chc/sct
PoPs look reasonable. Short term forecast unchanged.
&&
.PREV DISCUSSION...
Issued at 334 AM HST Tue Apr 21 2026
Light winds prevail as somewhat stable conditions develop. A
surface low sitting about 500 miles north of Oahu is producing a
very weak pressure gradient and resulting background winds over
the Hawaiian Islands, leading to light land breezes. While there
is no organized moisture around the state, dew points remain
elevated in the upper 60s to 70 F in places. This modestly high
moisture has kept overnight temperatures a few degrees warmer than
normal and has allowed for isolated showers overnight, though
nothing more than a few hundredths of an inch at most sites. Mid-
to upper-level ridging is building overhead from the west as an
upper-level trough moves east of the islands. This is reflected
in an inversion near 5000 ft on the Hilo sounding, while lingering
deeper moisture near Kauai kept the inversion suppressed on the
Lihue sounding.
A humid land and sea breeze regime will prevail over the next 24
hours or so. Isolated showers near the coasts will dissipate
during the early morning, followed by interior clouds and spotty
showers in the afternoon. While stability is slowly returning, a
briefly heavy shower is still possible in the afternoon and
evening.
Trades will slowly redevelop on Wednesday as the low to the north
drifts east and weakens. The combination of the building trades
and gradually increase stability will lessen chances for afternoon
showers.
Trade winds will strengthen Thursday and Friday and will persist
into early next week as surface high pressure becomes established
north of the islands. The moderate to locally breezy trades and
more stable conditions will push dew points back into the lower
60s, providing relief from the recent humidity. Showers will
become focused over windward slopes.
&&
.AVIATION...
Issued at 334 AM HST Tue Apr 21 2026
Light and variable winds continue across all terminals this
morning, triggering land-sea breezes which are expected to persist
through midweek. Onshore sea breezes will bring clouds and
possible light showers over island interiors this afternoon as
peak heating occurs, which may lead to periods of MVFR conditions.
Otherwise, VFR conditions prevail.
No AIRMETs in effect.
&&
.MARINE...
Issued at 334 AM HST Tue Apr 21 2026
A weak low north of the area extends a trough south toward the
islands, which will keep light to locally moderate east-southeast
flow in place across the local waters through early Wednesday.
Light wind flow should allow for afternoon sea breeze development
near the shores. During the latter half of the week, surface high
pressure building north of the area will bring a return of
moderate to locally strong northeasterly trade winds.
A small, medium-period, northwest swell build today, providing a small
bump to surf along north and west-facing shores. At least one other
northwest swell of similar size and period arrives late today which
will support elevated surf along west-facing shores through mid-week.
A moderate, medium-period north-northeast swell also arrives today
and peaks on Wednesday, bringing moderate surf to north-facing
shores, before slowly declining through the end of the week. East-
facing shores will see an increase in surf with wrap from the
north-northeasterly swell, despite below seasonal average trade
winds. Strengthening trades late this week will support closer to
seasonal average surf for east facing shores into the weekend.
Surf will continue to be small along south facing shores through
the period.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM UPDATE...JVC
DISCUSSION...Wroe
AVIATION...Pierce
MARINE...Quesada
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office
Narrow the Menu List
Select Time Limit: 12 hours | 24 hours | 48 hours | 72 hours | No time limit
Select Product Type: All | Routine Bulletins/FCSTS | Warnings/Watches/Advisories | HAWN Weather | Tropical | Marine | Aviation | Daily Obs | Special
Hawaiian Islands Synoptic Discussion and Guidance
369
FXHW60 PHFO 211854
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
854 AM HST Tue Apr 21 2026
.SYNOPSIS...
A light land and sea breeze pattern will produce afternoon clouds
and spotty showers over land and partial clearing at night. Trade
winds will redevelop late Wednesday and strengthen Thursday and
Friday, focusing rainfall over windward and mauka areas.
&&
.SHORT TERM UPDATE...
Emergent sea breezes will at least produce interior clouds and a
few showers, except for the Big Island where greater coverage and
intensity of showers is likely. Isolated heavy rainfall is not out
of the question given the resident moist airmass characterized by
dewpoints in the 70s and PWAT values around 1.5". However, like
yesterday, high cirrus threatens to weaken sea breeze convergence
just enough to limit interior shower potential. Inherited chc/sct
PoPs look reasonable. Short term forecast unchanged.
&&
.PREV DISCUSSION...
Issued at 334 AM HST Tue Apr 21 2026
Light winds prevail as somewhat stable conditions develop. A
surface low sitting about 500 miles north of Oahu is producing a
very weak pressure gradient and resulting background winds over
the Hawaiian Islands, leading to light land breezes. While there
is no organized moisture around the state, dew points remain
elevated in the upper 60s to 70 F in places. This modestly high
moisture has kept overnight temperatures a few degrees warmer than
normal and has allowed for isolated showers overnight, though
nothing more than a few hundredths of an inch at most sites. Mid-
to upper-level ridging is building overhead from the west as an
upper-level trough moves east of the islands. This is reflected
in an inversion near 5000 ft on the Hilo sounding, while lingering
deeper moisture near Kauai kept the inversion suppressed on the
Lihue sounding.
A humid land and sea breeze regime will prevail over the next 24
hours or so. Isolated showers near the coasts will dissipate
during the early morning, followed by interior clouds and spotty
showers in the afternoon. While stability is slowly returning, a
briefly heavy shower is still possible in the afternoon and
evening.
Trades will slowly redevelop on Wednesday as the low to the north
drifts east and weakens. The combination of the building trades
and gradually increase stability will lessen chances for afternoon
showers.
Trade winds will strengthen Thursday and Friday and will persist
into early next week as surface high pressure becomes established
north of the islands. The moderate to locally breezy trades and
more stable conditions will push dew points back into the lower
60s, providing relief from the recent humidity. Showers will
become focused over windward slopes.
&&
.AVIATION...
Issued at 334 AM HST Tue Apr 21 2026
Light and variable winds continue across all terminals this
morning, triggering land-sea breezes which are expected to persist
through midweek. Onshore sea breezes will bring clouds and
possible light showers over island interiors this afternoon as
peak heating occurs, which may lead to periods of MVFR conditions.
Otherwise, VFR conditions prevail.
No AIRMETs in effect.
&&
.MARINE...
Issued at 334 AM HST Tue Apr 21 2026
A weak low north of the area extends a trough south toward the
islands, which will keep light to locally moderate east-southeast
flow in place across the local waters through early Wednesday.
Light wind flow should allow for afternoon sea breeze development
near the shores. During the latter half of the week, surface high
pressure building north of the area will bring a return of
moderate to locally strong northeasterly trade winds.
A small, medium-period, northwest swell build today, providing a small
bump to surf along north and west-facing shores. At least one other
northwest swell of similar size and period arrives late today which
will support elevated surf along west-facing shores through mid-week.
A moderate, medium-period north-northeast swell also arrives today
and peaks on Wednesday, bringing moderate surf to north-facing
shores, before slowly declining through the end of the week. East-
facing shores will see an increase in surf with wrap from the
north-northeasterly swell, despite below seasonal average trade
winds. Strengthening trades late this week will support closer to
seasonal average surf for east facing shores into the weekend.
Surf will continue to be small along south facing shores through
the period.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM UPDATE...JVC
DISCUSSION...Wroe
AVIATION...Pierce
MARINE...Quesada
Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office