210
FXHW60 PHFO 010613
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
813 PM HST Sat Oct 31 2026

.SYNOPSIS...
An approaching disturbance aloft combined with ample moisture and
a surface trough moving over the western end of the state have
triggered heavy showers and isolated thunderstorms over Kauai and
Niihau and may impact Oahu overnight. The tail end of a front
will move down the island chain late Sunday through Monday,
bringing breezy northeasterly trades and drier air in its wake.
Breezy easterly trades will bring periods of windward and mauka
showers through the rest of the week.


&&

.SHORT TERM UPDATE...Heavy rain continues over the Ko`olau range,
especially from around Punalu`u southeastward. Most of the heavy
rain has ended over Kauai, but flooding continues as runoff hasn`t
ended yet. A large area of showers, some quite strong, is moving
east through the Kauai Channel. This area should reach Oahu in the
next few hours, but at this time we don`t know if the heavier
showers will hit the island or stay south. Some high resolution
guidance shows it will, while some shows it remaining south. No
changes will be made to the forecast at this time.

&&

.PREV DISCUSSION...
Issued at 404 PM HST Sat Oct 31 2026
Trade wind showers anchored along the eastern slopes of Kauais
mountains have persistently produced heavy rain through the day in
a moist and unstable environment, as evidenced in this
afternoons upper air sounding at Lihue. Rainfall rates and gage
stream reports prompted the issuance of a Flash Flood Warning for
the entire island, with the main trouble spots including the
Hanalei Bridge along the Kuhio Highway and the South Fork of the
Wailua River. This warning remains in effect through 5:45 PM this
evening and will likely be extended. Heavy showers and isolated
thunderstorms firing along a surface trough edging over Niihau and
Kauai this afternoon will likely maintain the flood threat for
the next couple of hours. Showers have also been persistent across
Oahu through the day, but rainfall rates and stream gage
responses have been unimpressive so far. However, the heavy
showers and isolated thunderstorms currently over Kauai may
impact Oahu overnight into Sunday morning as an upper level trough
helps drive them eastward in advance of an approaching front,
depending on how well the surface trough and the various outflow
boundaries hold together.

The next pattern change arrives late Sunday into Sunday night as
the tail end of a shallow front pushes down the island chain
before dissipating. While this boundary will deliver an uptick in
showers to windward and north-facing slopes, its primary impact
will be the development of breezy and gusty northeast trade winds
spreading from west to east. Deep high pressure building behind
the front will usher in a drier, more stable air mass. This will
lead to a break from the muggy conditions weve been experiencing
this past week as dew points are expected to drop into the lower
60s on Monday and Tuesday.

Breezy and stable easterly trades will persist through much of
the workweek as the northern high becomes elongated in response to
broad low pressure system tracking across the North Pacific. Dew
points will gradually rebound closer to seasonal norms by midweek.
While rainfall will remain largely focused along windward slopes
with only brief leeward drift, a minor uptick in shower coverage
appears possible around midweek as trade moisture interacts with
added instability from a passing weak mid-level shortwave trough.

Heading into next weekend, forecast attention shifts back to the
tropics. While significant spread exists regarding timing and
track details, model guidance continues to hint at potential
tropical cyclone development far southeast of the state late in
the week, with the system potentially nearing or passing south of
the islands over the weekend. While background trades look to
hold, questions remain concerning their ultimate strength and how
much deep moisture is drawn into the region. The National
Hurricane Center continues to monitor this area, maintaining a
medium (40 percent) chance of tropical cyclone formation over the
next 7 days.

&&

.AVIATION...
Scattered showers currently between Kauai and Oahu will start to
push towards PHNL and PHJR (and the rest of Oahu) over the next
couple of hours. Persistent MVFR and some IFR ceilings and
visibilities are possible in the heavier showers. If these hold
together, they could affect Molokai, Lanai, and Maui by morning.

AIRMET Sierra remains in effect for IFR conditions on Kauai which
may need to be extended into Oahu. AIRMET Sierra is also in effect
for mountain obscuration on Oahu and windward areas of the Big
Island due to low ceilings and reduced visibility in showers.

&&

.MARINE...
Issued at 404 PM HST Sat Oct 31 2026
A High Surf Advisory has been posted for north and west facing
shores due to an incoming northwest swell. Additionally, a Small
Craft Advisory has been issued for all coastal waters due to
increasing winds and seas.

A trough to the northwest of Kauai will sink southward overnight,
allowing high pressure to the north to strengthen winds behind the
trough over the region. An incoming north-northwest (330 degrees)
swell will push seas in excess of 10 feet for exposed waters, and
the strengthening winds will bring SCA level winds to additional
areas. Moderate to fresh northeast trades are expected to continue
through much of the week.

The forerunners from the new moderate, long-period northwest swell
are expected to arrive in the next couple of hours, with the
swell building quickly overnight. By Sunday, advisory level surf
is expected for north and west facing shores, which is expected to
continue into Monday. The swell may shift to a slightly more
northerly direction on Monday before declining on Tuesday.
Depending on the exact direction, a Marine Weather Statement may
be issued for potential harbor surges at Kahului and Hilo during
that time. Another advisory level northwest swell is possible
Thursday into Friday.

The current moderate, medium period south swell will gradually
decline through the weekend. Surf above seasonal average returns
to seasonal average on Sunday as the south swell energy fades.
During the first half of next week, south shore surf will return
to below seasonal averages.

East-facing shores will see an increase in trade wind swell as
northeast winds return on Sunday. Surf along east-facing shores
will increase through Monday night and conditions will be choppy
as trades sustain through much of the week.

&&

.FIRE WEATHER...
Issued at 404 PM HST Sat Oct 31 2026
The anomalously wet conditions during the past few months and the
rainfall from the past few days has kept the Keetch-Byram Drought
Index (KBDI) below 500 across nearly all of the state. Fire
weather concerns will be low through early Sunday as trade winds
remain light and humidity elevated. Breezy and much drier trade
winds will develop by Monday, but since KBDI will remain
suppressed, fire weather conditions will be moderate.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory from 6 AM Sunday to 6 PM HST Monday for Kauai
East-Kauai North-Kauai Southwest-Koolau Windward-Maui Central
Valley North-Maui Windward West-Molokai North-Molokai Windward-
Niihau-Oahu North Shore-Waianae Coast-Windward Haleakala.

Small Craft Advisory from 6 AM Sunday to 6 PM HST Monday for
Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters-Big Island Windward Waters-Kaiwi Channel-Kauai
Channel-Kauai Leeward Waters-Kauai Northwest Waters-Kauai
Windward Waters-Maalaea Bay-Maui County Leeward Waters-Maui
County Windward Waters-Oahu Leeward Waters-Oahu Windward Waters-
Pailolo Channel.


&&

$$

DISCUSSION...Farris
AVIATION...PECHACEK
MARINE...M Ballard