927
FXHW60 PHFO 161352
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
352 AM HST Thu Oct 16 2025

.SYNOPSIS...
An unstable moderate to locally breezy trade wind weather pattern
will continue into Saturday as an upper low near Kauai and Oahu
and low level convergent cloud bands riding in on the easterly
trade winds bring periods of showers to all islands. Some of these
showers will be locally heavy at times with thunderstorms possible over
the western half of the state through Saturday morning, and
portions of the Big Island later today. Enhanced showers will
linger into early next week as another upper low moves in from the
north and settles in over the western half of the state.

&&

.DISCUSSION...
The satellite imagery this evening shows the upper level low
center settling in over Kauai and Oahu. Deeper convection and
showers are developing under this upper level disturbance. The
heaviest showers last night appeared to pass just north of the
smaller islands likely due to east-southeasterly steering winds at
around 5,000 feet, causing the stronger showers to move parallel
to the smaller islands. The north shore and east Maui observed up
to a quarter inch of rainfall last night, and the north and
eastern slopes of Kauai also received up to a half inch of
rainfall in the stronger shower bands. Temperature inversion
heights as measured by upper air balloon soundings from Lihue and
Hilo at 2 AM HST (12Z) this morning were observed around the 7,000
to 8,000 foot range. Overall these higher inversion heights
continue to support periods of wet weather for all islands.

These periods of enhanced showers are forecast continue into
Saturday, with slightly decreasing trends into Sunday as the
upper low drifts westward away from the islands. The forecast
challenge today will be in forecasting the low level cloud
steering wind directions. A more easterly direction will push
these clouds directly into island mountains, producing higher
rainfall totals. The steering winds last night from the east-
southeast direction likely limited rainfall totals for the smaller
islands as compared to our forecast. The latest short range model
solutions show a more easterly direction on these low level
steering winds later today into Friday as the upper low beings to
drift westward, allowing higher pressure to build back into the
region.

Another upper level low descends over the western islands on
Monday, producing a very similar wet weather pattern over the
islands through the first half of next week. Rainfall amounts for
each island will heavily depend on smaller (mesoscale) convergent
bands. Trade winds will lift unstable clouds over windward island
mountain areas where the highest rainfall totals are favored.
Western islands may see locally heavy rainfall and possible
thunderstorms during this time period. Stay tuned for more weather
details for early next week as this next system approaches the
islands from the north.

&&

.AVIATION...
An upper level low centered near Kauai will drift slowly west
southwest today and bring unsettled weather to all islands.
Trade wind flow will bring bands of scattered to numerous showers
over windward areas with slightly less coverage over leeward
sides. Instability aloft should allow for isolated thunderstorm
development over areas north and west of Oahu today with isolated
thunderstorms possible over all of the smaller islands tonight.
Isolated thunderstorms may also develop over leeward portions of
the Big Island this afternoon due to diurnal heating. Heavier
shower and storm activity will be capable of producing MVFR and
isolated IFR ceilings and visibility.

AIRMET SIERRA for tempo mountain obscuration remains in effect
for north thru east sections of Kauai, Maui, and the Big Island
above 2000 feet due to low clouds and showers. SIERRA will likely
continue through the remainder of today as the clouds continue to
bank up along the windward sides of the island.

AIRMET TANGO remains in effect for Oahu, Molokai, Maui, and the
Big Island for tempo moderate turbulence between FL220 and FL350.
This is expected to continue through the day.

&&

.MARINE...
Moderate to locally strong trades winds have filled in across the
Hawaiian coastal waters as a surface high strengthens far
northeast of the state. A Small Craft Advisory (SCA) remains in
effect for typical windy waters around Maui County and the Big
Island through 6 PM HST Friday. The SCA will likely be extended
into the weekend as another high quickly builds north of the state
and tracks east. An upper low will drift from east to west across
the state today into the weekend, keeping isolated thunderstorms
over the forecast waters into the weekend.

A reinforcing moderate, long period northwest swell energy will
fill in early this morning, maintaining near to above average surf
along north and west facing shores through Friday. A brief
moderate, long period NNW swell will move through Friday, but
should taper off Saturday keeping surf elevated. Surf along north
and west facing shores will trend down through the weekend. A
hurricane force low is expected to develop east of Japan later
today and could bring another round of moderate, long period
northwest swell early next week, elevating surf along north and
west facing.

A series of small, medium to long period south to southwest
swells will continue to filter into the area through the rest of
the week and into the weekend, keeping south-facing shores from
going flat. East-facing shores surf will gradually pick up today
into the weekend as trades strengthen and persist.

&&

.FIRE WEATHER...
Wind speeds and afternoon minimum humidity levels will likely
remain below critical fire weather thresholds this week. Unstable
conditions will produce increasing wet weather trends across the
state into Saturday. Locally heavy rain and thunderstorms are
possible during this time period. Temperature inversion heights
near Maui and the Big Island will range from the 7,500 to 8,500
feet elevation range today.

&&

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

&&

$$

DISCUSSION...Bohlin
AVIATION...JT
MARINE...Almanza
FIRE WEATHER...Bohlin