Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 04/10/2026 12:14:00 PM UTC

                        
346
FXHW60 PHFO 100214
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
414 PM HST Thu Apr 9 2026

.SYNOPSIS...
An active weather pattern will persist through Friday as low
pressure strengthens northwest of the state. Deep tropical
moisture being drawn northward into the islands will support
periods of heavy rainfall, strong southerly winds, and isolated
strong to severe thunderstorms through Friday. Although some brief
improvement for portions of the state is possible by Saturday,
another active period appears possible from Sunday through early
next week.

&&

.DISCUSSION...
Issued at 413 PM HST Thu Apr 9 2026

This afternoon, a deepening surface low and deep upper trough
with embedded shortwave energy is located northwest of the state.
This feature is drawing deep tropical moisture northward towards
the main Hawaiian Islands, and has the potential to bring high-
impact weather to the state through Friday. The primary concerns
with this system are heavy rainfall capable of producing flash
flooding, strong southerly winds, and a few strong to severe
thunderstorms.

It is notable that the event`s heavy rainfall has been delayed to
some degree from what forecast guidance originally depicted.
Therefore, refinements to timing and QPF have been made to the
forecast with this afternoon`s updates based on the latest
observations and trends. Mid-afternoon satellite and radar imagery
shows that an initial band of rain with higher rainfall rates up
to 3 inches has finally arrived to Kauai as of press time. The
afternoon upper air sounding from Lihue shows that instability has
continued to gradually increase, and precipitable water values
are hovering right around 2.0 inches.

This evening into tonight, large-scale ascent and strengthening low-
level convergence will support favorable conditions for organized
heavy rainfall and isolated strong to severe thunderstorms
for Kauai, with flooding concerns significantly increasing as
rain rates become more intense, thunderstorms begin moving into
the western part of the state, and potential training occurs over
certain areas or basins. Tonight into early Friday morning, the
heavier shower bands are anticipated for Oahu, followed by a shift
in focus to the central and eastern islands later Friday.

In addition to the heavy rain and flood threat, strong
downsloping winds will continue to be a concern across the
western islands through early Friday, with strong gusts possible
in areas north and downwind of steep terrain. The stronger
southerly winds will shift farther east to mainly Maui County and
areas around the Big Island by Friday afternoon, though not
anticipating wind headlines for the lower elevations at this time.
Much lighter winds will prevail statewide this weekend.

Also of note, lava fountain episode 44 of the ongoing Kilauea
eruption began earlier today. An Ashfall Warning remains in effect
for Hawaii Volcanoes National Park and areas to the north and
northeast. Transport of ash, Pele`s hair, and other lightweight
tephra is possible to locations downwind of the eruption. See the
latest Ashfall Warning for details.

For the Big Island summits, gusty winds along with a wintry mix
supports the Winter Weather Advisory and High Wind Advisory into
Friday.

Although forecast confidence decreases somewhat beyond Friday,
some gradual or temporary improvement is anticipated this weekend
as upper heights rise and some drier air advances down the island
chain from the west. Guidance, however, shows another shortwave
dipping southeastward into the area late in the weekend, likely
supporting another active weather period across the state that may
extend through early next week.

&&

.AVIATION...
Issued at 413 PM HST Thu Apr 9 2026

Light to moderate showers have moved in from the SW through the
majority of the state. MVFR to VFR conditions have occurred from
Oahu to the Big Island, with heavier showers bringing MVFR to IFR
conditions to Kauai. The heavier showers will continue to move
through Kauai, and are accompanied by gustier S winds. These
winds will expand eastward along with the heavier band of showers,
primarily affecting Oahu and Kauai overnight. Maui County and the
Big Island will likely not receive heavier showers until
tomorrow. Expect MVFR conditions within preceding showers, and
periods of IFR within heavier showers.

Recently, Kilauea erupted producing an ash cloud reaching up to
15-20kft. This also prompted an ashfall warning for areas east and
southeast of the volcano, including Hilo. SIGMET series Quebec is
issued to cover the ash plume. Ashfall is currently in the PHTO
TAF, but the threat is expected to diminish shortly, as the plume
cloud continues to decrease in altitude.

AIRMET Sierra is in effect for mountain obscuration above 020 ft
for Kauai. This will likely need to be expanded later tonight, as
showers move west to east across the island chain.

AIRMET Tango remains in effect for moderate turbulence between
FL180 and FL360 across the entire islands, and for moderate
turbulence downwind of terrain for Oahu and Kauai.

AIRMET Zulu remains in effect for moderate icing between
140-FL200 as this ongoing weather pattern envelops the islands
with extensive cloud cover.


&&

.MARINE...
Issued at 413 PM HST Thu Apr 9 2026

South to southeast winds are expected to steadily increase
to strong to gale force speeds tonight as a low pressure system
develops just northwest of the state and lifts northward. A Gale
Warning remains in effect for the western half of the coastal
waters and the offshore waters for these strengthening winds.
Gales are expected to continue over the western half of the
coastal waters through the first half of the night, gradually
shifting eastward throughout the night and potentially lingering
near Oahu early on Friday. The likelihood of any significant
widespread gale force winds reaching further east (near Maui) has
decreased, and as a result, the Gale Watch for those waters has
been canceled. Instead, the Small Craft Advisory (SCA) has been
extended for most of the remaining waters through Friday evening.

As the low pressure system further deepens today into Friday, we
will likely see a greater coverage of thunderstorms and gusty
winds, especially tonight into Friday, where we could potentially
see severe thunderstorms over the coastal waters capable of
producing waterspouts and damaging winds. Very rough boating
conditions are also expected later today into Friday as seas
quickly rise in response to the strong to gale force winds. South
facing harbor entrances will also be greatly impacted due to rough
conditions.

Strong to gale force southerly winds are expected to quickly
develop today over the western half of the state tonight,
supporting a High Surf Advisory for Kauai County and Oahu. Large
disorganized surf is expected along south facing shores of Kauai
and Oahu through at least tonight, but may persist into the day on
Friday. The probability of high surf conditions for Maui on Friday
has decreased.

Along north facing shores, the current mid period northwest (320
degree) swell will steadily lower tonight and dissipate to background
levels on Friday. However a smaller short-period northwest swell
generated by the low developing just northwest of the islands
will fill in Friday night through early next week.

Surf along east facing shores could see an increase later this
week due to the strengthening southeasterly winds especially for
southeast exposures.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Friday afternoon for all Hawaiian islands.

High Surf Advisory until 6 AM HST Friday for East Honolulu-Ewa
Plain-Honolulu Metro-Kauai South-Kauai Southwest-Niihau-Waianae
Coast.

High Wind Warning until 6 AM HST Friday for Central Oahu-Kauai
Mountains-Kauai North-Koolau Leeward-Koolau Windward-Oahu North
Shore-Olomana-Waianae Mountains.

Ashfall Warning until midnight HST tonight for Big Island East-
Big Island Interior-Big Island Southeast.

Wind Advisory until 6 PM HST Friday for Big Island Summits.

Winter Weather Advisory until 6 PM HST Friday for Big Island
Summits.

Gale Warning until 6 AM HST Friday for Kauai Channel-Kauai
Leeward Waters-Kauai Northwest Waters-Kauai Windward Waters-Oahu
Leeward Waters-Oahu Windward Waters.

Small Craft Advisory until 6 PM HST Friday for Alenuihaha
Channel-Big Island Leeward Waters-Big Island Southeast Waters-
Big Island Windward Waters-Kaiwi Channel-Maui County Leeward
Waters-Maui County Windward Waters.

&&

$$

DISCUSSION...Vaughan
AVIATION...DT
MARINE...Quesada