471
FXHW60 PHFO 241949
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
949 AM HST Sat Oct 24 2026

.SYNOPSIS...
Northeasterly trade winds should slightly strengthen to moderate
speeds today then gradually weaken Sunday into Monday. Brief
passing showers will drift into the islands on the trade winds,
favoring windward and mountain areas during the overnight to early
morning hours. A significant change to our weather pattern is
expected next week. Deep tropical moisture will bring the
potential for heavy rain and thunderstorms across the state
starting around Tuesday and persisting through at least Thursday.

&&

.SHORT TERM UPDATE...
Trade winds continue this morning, bringing showers to mainly
windward and mauka locations. Showers have been focused on
northwest Maui, from around Wailuku to Honokohau, so far this
morning, but have begun shifting slightly south towards Waikapu
since 9 AM HST.

The latest models continue to show the potential of heavy rain
from Tuesday through Thursday for at least a few of our islands,
but they have been slow to converge on the details. We will spend
the bulk of today attempting to coax a bit more information out of
the ensembles to better define risks/timing, but it may take one
more day to actually get a better feel for this unusual system.

No update is needed at this time.

&&

.PREV DISCUSSION...
Issued at 350 AM HST Sat Oct 24 2026
This morning`s satellite imagery shows an old frontal boundary
starting to move into Kauai. This should bring an uptick of
scattered showers over Kauai today especially windward and mauka
areas. No significant impacts are expected, but it will be showery
at times especially over north Kauai. Over on the eastern half of
the state, we do have some passing showers over windward and mauka
areas due to a weak surface trough located just east of the Big
Island. This trough is expected to gradually move east and away
from the state this weekend, but some enhanced moisture lingering
around east Maui and windward Big Island will produce scattered
showers.

For next week, while the forecast still remains complicated,
global models and its ensemble members have been slowly coming
into better agreement. A low pressure system embedded within a
monsoon trough is currently located just west of the Dateline near
14N. This low is expected to gradually move eastward along with
the monsoon trough that extends over 1000 miles east of the low
pressure system. An approaching upper level trough from the
northwest Monday into Tuesday will allow the monsoon trough to
lift northward and approach the Hawaiian Islands. Deep tropical
moisture with precipitable water values exceeding 2.5 inches is
expected to move over the state Tuesday into Wednesday. During
this time, an upper level short-wave trough will swing through the
state and will provide the support and lift (strong diffulence
aloft) for thunderstorms to develop. With the ample upper level
support, we could see organized thunderstorms such as squall lines
or an MCS (Mesoscale Convective System) develop and if they do,
they will be capable of producing damaging winds as well as
torrential rainfall.

While the threat of heavy rain and flash flooding will exist
across the state Tuesday into Wednesday and likely into Thursday
as well, the heaviest rainfall period based off of the 00Z Grand
Ensemble mean looks to be from Tuesday afternoon through
Wednesday. Latest model trends in the ensembles have been placing
the heaviest rainfall totals slightly further east with the
heaviest precipitation expected to be somewhere between Oahu and
the Big Island. The forecast has been trended this way, but
please keep in mind, there is still plenty of uncertainty and the
forecast will change in the coming days. Flood Watches will
eventually get issued for the entire state as we get closer to
next week.

In summary, next week looks to be a very unusual weather pattern
setting up for Hawaii. While we don`t know exactly where the
thunderstorms will set up, the greatest probability looks to be
somewhere between Oahu and the Big Island at this time. Due to the
very high precipitable water values (99th percentile) and ample
upper level support from the short-wave trough, extreme rainfall
rates will be possible especially around late Tuesday into
Wednesday.

&&

.AVIATION...

SIGMET Romeo remains in effect just north of the state for the
possibility of severe turbulence between 25,000 and 38,000 feet.

Otherwise, expect increasing showers today over Kauai and
windward and mountain areas of the rest of the islands where MVFR
ceilings and visibilities are possible in any shower that passes
through. A moderate to locally breezy trade wind pattern will
persist today before weakening slightly on Sunday.

No AIRMETs in effect.

&&

.MARINE...
Issued at 350 AM HST Sat Oct 24 2026
A surface low far north-northeast of the Hawaiian Islands will
dig southward through the weekend and will stall roughly 800 to
900 nm northeast of Oahu on Monday, keeping the subtropical ridge
just north of the area rather weak. Trade winds will be at gentle
to moderate strength during much of this time, though a brief
period of fresh northeast winds may accompany a shallow band of
showers moving over Kauai and Oahu this afternoon into tonight.
An area of low pressure is expected to move over the islands from
the southwest Tuesday and Wednesday, bringing variable winds and
the potential for heavy showers and thunderstorms.

Small surf along north-facing shores will begin to build rapidly
this afternoon and evening as a moderate, medium-period north-
northwest swell arrives. Surf will reach near seasonal average
during the peak of the swell tonight into Sunday. As this swell
declines on Monday, a long-period northwest swell will arrive.
This swell will generate moderate surf along north- and west-
facing shores through Wednesday. A small north-northeast swell
will be possible during the second half of next week.

A series of small overlapping south-southwest swells will push
surf back to around seasonal average today into early next week.
A larger south-southwest swell may push surf above seasonal
average late next week.

Surf along most east-facing shores will be small through early
next week, but areas exposed to wrapping northerly swells will
experience periods of moderate surf late Saturday through Monday.
East-facing shores should also see a bump in surf if the north-
northeast swell materialized during the latter half of next week.

&&

.FIRE WEATHER...
Issued at 350 AM HST Sat Oct 24 2026

Gentle to moderate trade winds with mostly dry conditions over
leeward areas will continue to produce low to moderate fire
weather conditions through the weekend. A drier airmass moving in
later tonight could produce lower humidities for Sunday with
minimum RH`s getting down to the low 40s for select leeward areas.
Ample tropical moisture will move in from the southwest sometime
beginning Monday night or Tuesday, bringing a threat for heavy
rain through at least Thursday. As a result, fire weather concerns
will be low through most of next week. Inversion heights will
range from 5,000 to 8,000 feet this weekend with the higher
inversion heights over the eastern end of the state due to a weak
trough just east of the Big Island.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Kino
AVIATION...PECHACEK
MARINE...Quesada