Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 04/09/2026 11:46:00 PM UTC

                        
726
FXHW60 PHFO 091346
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
346 AM HST Thu Apr 9 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 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...
Forecast confidence continues to increase in a high-impact
weather event evolving across the state today through Friday, with
the primary concerns being heavy rainfall capable of producing
flash flooding, 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 quickly tighten through the day, resulting in increasingly
strong south to southeast winds across the island chain.

This flow will transport a deep tropical moisture plume northward
over the state, with PWs hovering around or above 2 inches.
Combined with increasing large-scale ascent and strengthening low-
level convergence, conditions 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 will most likely begin over Kauai
and Oahu today before spreading eastward across the remainder of
the state tonight 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
today through tonight, which has led to an upgrade from the
High Wind Watch to a High Wind Warning for north and east facing
slopes.

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 near Wind Advisory thresholds by
later today or Friday, particularly across wind-prone and
terrain-enhanced areas.

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 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...
Shower activity continues this morning across the islands. Latest
radar imagery shows another broad expanse of showers approaching
from the southwest, expected to arrive around sunrise. This will
be followed by what is expected to be a more potent band arriving
at Kauai around the early afternoon hours, spreading eastward
across the islands through the overnight hours heading into
Friday. With this band, gusty winds from the south will follow,
making for periods of IFR or worse conditions under heavy showers
and even isolated thunderstorms. Until this band moves through,
however expect borderline MVFR conditions as light rain and low
ceilings prevail across the islands.

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

AIRMET Tango also remains 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.

AIRMET Zulu is also in effect for moderate icing as this ongoing
weather pattern envelops the islands with extensive cloud cover.
Expect this to remain in effect through the period as well.

&&

.MARINE...
South to southeast winds are expected to steadily increase
to strong to gale force speeds later this morning through
tonight, as a low pressure system develops just west of the state
and lifts northward. A Gale Warning has been issued for the
western half of the coastal waters and the offshore waters due to
the strengthening winds today. Small Craft Advisory (SCA) is in
effect for most of the remaining waters for today.

For tonight, Gales are expected to continue over the western half
of the coastal waters through the first half of the night then
gradually shift eastward throughout the night. A Gale Watch
remains in effect for the eastern half of the coastal waters. 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.

The current south swell that peaked during the day yesterday has
dropped below advisory thresholds this morning. But due to the
strong to gale force southerly winds that are expected to quickly
develop today over the western half of the state, a High Surf
Advisory remains in effect for Kauai County and Oahu through
tonight. Large disorganized surf is expected along south facing
shores of Kauai and Oahu through at least tonight. Depending on
how the low pressure system evolves today, the High Surf Advisory
may need to be expanded towards Maui County tonight.

Along north facing shores, a moderate long-period northwest
(310-320 degree) swell peaked during the day yesterday and will
steadily lower today and dissipate to background levels on Friday.
However a smaller short-period northwest swell generated by the
low developing just west of us 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 Friday for Niihau-Kauai
Leeward-Waianae Coast-Kauai South-East Honolulu-Honolulu Metro-
Ewa Plain.

High Wind Warning until 6 AM HST Friday 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 noon today to 6 PM HST Friday for Big Island
Summits.

Small Craft Advisory until 6 AM HST early this morning for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-
Kauai Channel-Oahu Leeward Waters.

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

Small Craft Advisory until 6 PM HST this evening for Kaiwi
Channel-Maui County Windward Waters-Maui County Leeward Waters-
Alenuihaha Channel.

Gale Watch from this evening through Friday afternoon for Kaiwi
Channel-Maui County Windward Waters-Maui County Leeward Waters-
Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.

Small Craft Advisory until 6 PM HST this evening for Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.

&&
$$

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