910
FXHW60 PHFO 090721
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
921 PM HST Sun Mar 8 2026

.SYNOPSIS...
A powerful Kona storm is expected to impact the state this week
into next weekend, bringing numerous hazards across the islands.
A combination of flash flooding, damaging winds, and strong
thunderstorms, some potentially severe, will threaten Hawaii from
Tuesday through at least Saturday. The risk for flash flooding
could begin as early as Tuesday over Kauai and Oahu as deep
tropical moisture spreads into the western end of the state. This
threat will expand eastward across the state by the latter half of
the week, with the likelihood for severe thunderstorms increasing
late this week and into the weekend.

&&

.DISCUSSION...
A significant transition in the large-scale weather pattern is
expected to unfold across the Hawaiian Islands over next couple
of days and continuing through the upcoming weekend. The current
dry and relatively stable regime, characterized by moderate east-
southeast flow, will persist through Monday. Conditions will
begin to deteriorate Monday night into Tuesday as a deep upper-
level trough amplifies northwest of the islands.

Deterministic models and their respective ensembles remain in
strong agreement regarding the evolution of this system. A
powerful jet streak with core winds of 100 to 140 kt at 250 mb is
forecast to dig southward along the western flank of the trough.
As this occurs, the trough will gradually acquire a negative tilt
while expanding toward the island chain through the week. The
islands will increasingly fall beneath the jet streaks left-exit
region, supporting enhanced divergence aloft and large-scale
ascent across the region.

At the surface, model guidance depicts a broad area of low
pressure consolidating northwest of the islands in response to
strong upper-level height falls. Central pressures could fall
to near 990 mb while remaining well northwest of the state. The
resulting pressure pattern will shift winds across the islands
out of a southerly direction, drawing a plume of deep tropical
moisture northward across the region.

Precipitable water values are expected to increase into the
1.5 to 2.0 inch range beginning Tuesday across the western
islands, then spread eastward across the remainder of the state
through midweek. This pattern will then persist through next
weekend, with PWAT values potentially rising into the 2.0 to 2.3
inch range statewide later this week.

The combination of strong upper-level forcing for ascent, deep
tropical moisture, and persistent southerly flow will create a
favorable environment for periods of heavy rainfall with embedded
thunderstorms. Repeated rounds of convection may occur as smaller
disturbances rotate through the broader upper trough, increasing
the potential for training rainfall bands along terrain-favored
areas.

Flooding concerns are expected to increase statewide as the week
progresses, particularly where the heavier rainfall persists over
the same areas for multiple days. By late week and next weekend,
soils will already be saturated, increasing the likelihood that
additional rainfall will produce rapid runoff and dangerous
flooding conditions.

In addition to the rainfall threat, strengthening south to
southwest winds may develop during the latter portion of the week
and upcoming weekend as the pressure gradient tightens between
the developing low to the northwest and high pressure to the east.
If this materializes, strong kona winds and localized downslope
wind events will be likely.

While thunderstorms are certainly possible earlier in the event,
the environment will become increasingly favorable for severe
storms later in the week and into the weekend as as the
thermodynamics and kinematics (MU CAPE of 1500 to 2500 J/kg, 50
kt 850 winds with up to 40 kt or more of 0-6 km bulk shear)
become more supportive.

While uncertainty remains regarding the exact timing and location
of the heaviest rainfall, confidence continues to increase that
the islands will experience a prolonged period of unsettled and
potentially impactful weather this week. Residents and interests
across the state should continue to monitor forecasts as details
regarding the timing and location of impacts become clearer.

&&

.AVIATION...
Mostly VFR with areas of MVFR in showers and low clouds tonight
and tomorrow. Areas of MVFR will be mainly on eastern and
southern sections of each island. ESE surface winds will weaken
slightly Monday.

AIRMET Sierra for mtn obsc is in effect above 020 for windward
locations of Kauai, Oahu, and Maui.

&&

.MARINE...
Strong high pressure far northeast of the state will maintain
fresh to locally strong trade winds tonight, mainly over the
eastern half of the state. The Small Craft Advisory (SCA) has
been scaled back to include just the central and eastern waters
through tonight. As winds slowly decrease, the SCA will likely be
trimmed back to just the windier waters and channels around Maui
County and the Big Island through Monday afternoon.

A front approaching from the west will begin to ease the trades
further and shift them southeasterly on Monday, with the winds
becoming southerly and increasing to fresh to locally strong speeds
Tuesday through late this week. Heavy rain, thunderstorms, and
rough seas are expected to accompany this storm system for the
rest of this week and into the weekend.

Surf along east facing shores will gradually trend downward on
Monday, then fall below normal levels Tuesday through late this
week. A series of small long period west-northwest swells will
keep some small surf in place along north and west facing shores
during the forecast period. A small medium period north swell is
possible late this week.

Surf along south-facing shores will remain small, with the
exception of areas exposed to trade wind swell wrap. Rough and
choppy conditions will develop Tuesday and continue through late
week as southerly winds increase in advance of a front. A series
of small long-period south swells will also move through Monday
through late this week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Monday for Kaiwi Channel-
Maui County Windward Waters-Maui County Leeward Waters-Pailolo
Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island
Leeward Waters-Big Island Southeast Waters.

&&

$$

DISCUSSION...Gibbs
AVIATION...Walsh
MARINE...Shigesato