Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 09/23/2026 12:14:00 AM UTC

                        
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FXHW60 PHFO 221414
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
414 AM HST Tue Sep 22 2026

.SYNOPSIS...
Moderate trades this morning will gradually strengthen each day
over the next several days with widespread strong trades expected
by Thursday and very windy conditions possible on Friday. The
main focus for the weather this week will be the tropical cyclone
development southeast or south of the Big Island over the next
few days. While the potential wind impacts remain uncertain, the
threat for flash flooding will increase over the Big Island during
the second half of the week.


&&

.DISCUSSION...
This morning`s satellite and radar imagery shows some scattered
showers riding in with the moderate trades over windward and mauka
areas. For today, while conditions are stable, we are seeing
higher than normal moisture levels as seen in the 12Z soundings
from Lihue and Hilo. This will allow for some brief downpours at a
few windward and mountain areas. Otherwise, we should see a fairly
typical trade wind day with breezy trades returning by later this
afternoon.

This week`s forecast remains very challenging and will be highly
dependent on the formation of a tropical cyclone near the Big
Island over the next several days. Latest Tropical Weather Outlook
from the National Hurricane Center has a high chance of formation
over the next 48 hours. While strong shear has been keeping the
system from getting organized, the models do show a decrease of
windshear over the next 24 to 36 hours. So the expectation is for
the thunderstorms southeast of the Big Island to become better
organized with a tropical depression likely to form over the next
day or two.

Around Thursday, global models and the latest ensembles are
showing the potential tropical cyclone drifting northward towards
the Big Island as it reaches the western periphery of a
subtropical ridge of high pressure. At this time, there is still
high uncertainty on the strength and position of this potential
tropical cyclone as it slowly drifts northward. While there is a
great deal of uncertainty, there is a significant potential for a
prolonged heavy rain event over windward and southeast Big Island
due to the deep tropical moisture and weak steering flow. While
there is a lot of moisture available, due to the high uncertainty
on the intensity of the potential tropical cyclone, rainfall rates
remain very uncertain. While tropical moisture could begin
impacting windward and southeast Big Island as early as Wednesday,
the heavier rain rates looks to be more Thursday into Friday, thus
we held off on a Flood Watch for the Big Island for now. A Flood
Watch will be issued for the Big Island eventually, as we get a
better handle on the potential tropical cyclone development.

As for the potential wind impacts, while there is high
uncertainty, there is a high likelihood of at least windy trades
by Friday of this week with gusts of 50 mph to even 60 mph
possible over the typical windy areas around the eastern half of
the state. The potential for stronger wind gusts will be highly
dependent on the tropical cyclone development.


&&

.AVIATION...

Breezy trade wind will persist today. Starting tonight, attention
will turn to a disturbance southeast of Hawaii as associated
moisture gradually increases, especially across eastern and
windward areas with periods of MVFR ceilings and visibility
possible in heavier showers.

AIRMET Sierra is in effect for mountain obscuration and will
likely be extended.

AIRMET Tango is in effect for low level turbulence downwind of
island terrain and will likely be needed through the day.


&&

.MARINE...

The gradient between high pressure to the northeast and an
approaching trough that may develop into a tropical cyclone to
the southeast will maintain moderate to locally strong trade
winds through Wednesday. A Small Craft Advisory is in effect for
the typical windy waters of Maui County and the Big Island through
early Wednesday evening with the possibility of it being extended
as well as expanded. Wind speeds will strengthen during the
latter half of the week as the trough or potential tropical
disturbance moves near the islands. Shower coverage will also
increase, along with the potential for isolated thunderstorms,
particularly across the eastern waters.

Surf along south facing shores will gradually drop heading into
midweek as the current south-southwest swell fades. A slightly
smaller, long-period south-southwest swell will fill in late this
week into next weekend generated by a series of lows near New
Zealand. West facing shores will experience a bit of the southerly
wrap through most of the week.

Breezy trade winds will maintain moderate surf along east facing
shores for the next several days. Surf along north facing shores
will see a bump today into Wednesday as a small, medium- period
north-northwest swell fills in from an Aleutian low. Then a small,
long- period west-northwest swell generated by Typhoon Dujuan as
it curves northeast near Japan, will build locally Friday into
next weekend, increasing surf along north and west facing shores.


&&

.FIRE WEATHER...
Issued at 333 AM HST Tue Sep 22 2026

Breezy trades will return by this afternoon and steadily
strengthen each day over the next several days. With winds
strengthening, moderate fire weather conditions will be possible
this week mainly over drier leeward areas. The inversion is
around 5000 feet this morning, but will rise over the eastern end
of the state Wednesday as deeper moisture moves in.


&&

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


&&

$$

DISCUSSION...Kino
AVIATION...PECHACEK
MARINE...Walsh