Area Forecast Discussion
Issued by NWS Honolulu, HI

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407
FXHW60 PHFO 181339
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
339 AM HST Sat Oct 18 2025

.SYNOPSIS...
A upper-level low currently northeast of the Hawaiian Islands
will move south over the next several days, aiding in maintaining
relatively unstable conditions. Moderate to locally breezy trades
will also continue through today into tonight. This combination
will continue to bring enhanced showers and a slight chance of
thunderstorms to the region throughout the next couple days.


&&

.DISCUSSION...
Latest satellite imagery continues to illustrate thunderstorm
activity north and west of Kauai and Niihau this morning progged
to move further westward away, while extensive cloud cover
blankets Maui and the Big Island. Observations over the past few
hours have indicated that light precipitation has fallen over the
Hawaiian Islands, with the heaviest fallen over much of Maui and
western portions of Molokai. Trends suggest that additional
precipitation is expected, primarily across windward and mauka
areas for all islands through early tomorrow morning before
clearing Sunday.

Moderate to locally breezy trades continue today into tonight,
maintaining enhanced shower activity across windward and mauka
areas. Winds thereafter begin to ease to a light to locally
moderate pattern persisting through midweek. Trades strengthen
toward the latter end of the week and prevailing through the
weekend.

Model guidance of the GFS and ECMWF also continues to depict an
upper-level trough will remain over the vicinity of the Hawaiian
Islands, sustaining unstable conditions. Within said trough
remains two individual closed low circulations that have been
steering the state`s weather these last couple days. One is
situated to the west of the island chain and is propagating
westward away, while the second is positioned northeast of the
islands. The previous discussion mentioned that the second closed
low will end up centered very close to the islands by Wednesday,
however, latest guidance has depicted the circulation to stay east
of the islands at this time while propagating southward through
the remainder of the outlook period. Much of the coldest air aloft
has been progged to remain north of the island chain, limiting
any thunderstorm potential, however, model guidance does hint at
periods of enhanced shower activity throughout the week in
conjunction with the wet trades regime.


&&

.AVIATION...
An upper level low pressure system west of the state continues to
create an unstable atmosphere allowing enhanced showers to be
embedded within easterly trade winds. These showers are mostly
focused over windward and mountain areas, but they can spread into
leeward areas as well. MVFR conditions are expected within
passing showers, otherwise VFR conditions prevail.

AIRMET SIERRA is not in effect, but could be issued tonight due
to potential low clouds and showers causing mountain obscurations.

AIRMET Tango is in effect across the island chain for tempo
moderate turbulence between FL300 and FL350. Conditions will
continue through the evening but will likely weaken later
tonight.

High clouds streaming over Maui and the Big Island are causing
light icing conditions in LYR 155-FL210. These conditions are
expected to continue through the evening, but chances of light
icing should decrease late tonight.


&&

.MARINE...
Moderate to locally strong trades will remain in place over the
Hawaiian coastal waters through today. Trades then weaken into the
moderate to locally fresh range through early next week. A Small
Craft Advisory (SCA) remains in effect over the windier waters and
channels surrounding Maui County and the Big Island through
Saturday afternoon. An upper low north of Kauai will continue to
drift over the northern waters through the weekend keeping a
slight chance of thunderstorms in the forecast.

Two moderate, long-period NW and NNW swells moving through the
waters will maintain elevated surf along N and W facing shores
through Saturday and then trend down on Sunday. A hurricane force
low E of Japan will bring another round of moderate, long- period
NW (330 deg) swell into the islands towards the middle of next
week leading to building surf along N and W facing shores. This
next long-period swell may reach low-end High Surf Advisory
thresholds Wednesday into Thursday.

A series of small, medium-to long-period S to SW swells will
filter into the area through the weekend keeping surf along S
facing shores from going flat. Short-period surf along E facing
shores increases slightly on Saturday due to the stronger trades,
then trends down slightly Sunday through early next week.


&&

.FIRE WEATHER...
Wind speeds and afternoon minimum humidity levels will remain
below critical fire weather thresholds through the forecast
period. Locally heavy rain and thunderstorms are possible through
this morning. Unstable conditions will continue to produce wet
weather across the state through early next week. Temperature
inversion heights near Maui and the Big Island will range from the
8,500 to 9,500 feet today.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.


&&

$$


DISCUSSION...Pierce
AVIATION...Bohlin
MARINE...JVC
FIRE WEATHER...Pierce