Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 04/09/2026 04:44:00 PM UTC

                        
438
FXHW60 PHFO 090644
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
844 PM HST Wed Apr 8 2026

.SYNOPSIS...
An increasingly active weather pattern unfolding across the
Hawaiian Islands 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, isolated strong to severe
thunderstorms, particularly from Thursday through Friday. Although
some brief improvement for portions of the state is possible by
Saturday, another active period appears likely from Sunday
through early next week.

&&

.DISCUSSION...
Forecast confidence continues to increase in a high-impact
weather event evolving across the state from late tonight through
Friday, with the primary concerns being heavy rainfall, strong
southerly winds, and strong to severe thunderstorms.

Model guidance remains in good agreement depicting a deep upper
trough and embedded shortwave energy digging southeastward toward
the islands while surface low pressure deepens northwest of the
state. As this system strengthens, the local pressure gradient
will continue to tighten through Thursday, resulting in
increasingly strong south to southeast winds across the island
chain.

This flow will continue to transport a deep tropical moisture
plume northward over the state, with PWs expected to hover around
or above 2 inches. Combined with increasing large-scale ascent
and strengthening low-level convergence, conditions continue to
favor widespread and organized heavy rainfall and isolated strong
to severe thunderstorms (despite the best instability remaining
off to the northwest).

The greatest rainfall impacts still appear most likely to begin
over Kauai and Oahu late tonight and into Thursday before
spreading eastward across the remainder of the state Thursday
night through Friday. Confidence remains highest across the
western end of the island chain for the most significant rainfall
totals and flash flooding concerns during the initial phase of the
event.

Wind impacts are also becoming increasingly concerning. Guidance
supports strong and gusty southerly winds across Kauai and Oahu
Thursday through Thursday night, and an upgrade from the current
High Wind Watch to a High Wind Warning appears likely with the
overnight forecast cycle.

Farther east, guidance also indicates gusty southerly winds
across exposed portions of the Big Island during the same time
period. While winds there are not currently expected to reach
warning criteria, speeds may become strong enough to warrant a
Wind Advisory, particularly across wind-prone and terrain-enhanced
areas by late Thursday or Friday.

Although forecast confidence decreases somewhat beyond Friday,
some gradual or temporary improvement is anticipated Friday night
into Saturday 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...
Showers are expected to envelop the islands for most of the night.
Conditions will vary depending on shower intensity as a result,
but expect at least borderline MVFR conditions for most sites
through at least early morning Thursday. Weather models suggest a
brief break in the rain for at least the eastern half of the
state around daybreak Thursday, before rain recommences by
Thursday afternoon and evening. Winds will ramp up across most
sites by Thursday afternoon as well, mainly out of the south.

AIRMET Sierra is in effect for mountain obscuration above 020 ft
across all islands. Some relief is possible as showers decrease in
coverage, but confidence in exact timing is low, so expect Sierra
to persist through the TAF period.

AIRMET Tango is also in effect for moderate turbulence between
FL200 and FL350 across the entire islands. This is also expected
to remain in effect through the TAF period.

&&

.MARINE...
South to southeast winds are expected to steadily increase through
Thursday night, as a low pressure system develops just west of
the state. A Small Craft Advisory (SCA) remains in effect for
portions of the coastal waters tonight and will expand in coverage
on Thursday. A Gale Watch remains in effect for Thursday into
Thursday night across the Hawaiian Waters. At this time, it is
looking like the strongest winds will start off over the western
half of the state Thursday into Thursday night and expand towards
the eastern half of the state Thursday night into Friday.

As the low pressure system further deepens Thursday into Friday,
we will likely see a greater coverage of thunderstorms and gusty
winds. Very rough boating conditions are expected late Thursday
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.

The current south swell that peaked during the day today will
slowly drop tonight through the rest of the week. A High Surf
Advisory is in effect for all south facing shores of the Hawaiian
Islands through 6 AM.

As the long-period south swell declines on Thursday, strong to
gale force southerly winds are expected to develop and strengthen
even further Thursday night into Friday. This increase of
southerly winds will bring a rapid increase of short-period
energy Thursday into Friday and will once again bring surf heights
above the advisory thresholds for south facing shores. Large
disorganized surf is expected along many south facing shores
Thursday into Friday.

Along north facing shores, a moderate long-period northwest
(310-320 degree) swell peaked during the day today and will
steadily lower Thursday into Friday. However a smaller short-
period northwest swell generated by the low developing just west
of us at the moment will fill in over the weekend into 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 Hawaii islands-

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

High Wind Watch from 6 AM HST Thursday through late Thursday
night for Kauai Mountains-Oahu North Shore-Olomana-Central Oahu-
Waianae Mountains-Kauai North-Koolau Windward-Koolau Leeward.

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

Wind Advisory from 2 PM Thursday to 6 PM HST Friday for Big
Island Summits.

Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Leeward Waters-Big Island Windward Waters-Big Island
Leeward Waters-Big Island Southeast Waters.

Gale Watch from 6 AM HST Thursday through late Thursday night
for all Hawaiian waters-


&&
$$

DISCUSSION...Gibbs
AVIATION...Evans
MARINE...Kino