Area Forecast Discussion for Hawaii

Area Forecast Discussion   Issued: 09/23/2026 04:43:00 PM UTC

                        
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FXHW60 PHFO 230643
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
843 PM HST Tue Sep 22 2026

.SYNOPSIS...
Moderate trades 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. A flood watch has been issued from noon
Wednesday to 6 PM Saturday for Maui County and the Big Island.

&&

.SHORT TERM UPDATE...
The forecast remains on track, and no updates expected overnight.
The main focus will remain on upcoming tropical cyclone
development and movement near the islands.

&&

.PREV DISCUSSION...
Issued at 330 PM HST Tue Sep 22 2026
Radar and satellite showed the usual for a trade wind regime...
with mostly cloudy skies and isolated to scattered showers
windward and mauka, and mostly sunny skies leeward. Winds were
averaging 10 to 20 mph in most areas, with the typical windiest
spots blowing 15 to 25 mph with gusts 25 to 40 mph.

The latest guidance has not changed the overall expectations for
TD 15E (future Nolo). Ensembles show a wide variety of solutions,
with some moving Nolo over part(s) of the state, but most missing
a direct landfall. Showers and/or isolated thunderstorms are
expected to begin to bring heavy rain, especially to the windward
and southeast sections of the Big Island and windward Maui
beginning Wednesday. We have issued a Flood Watch for flash
flooding, for the Big Island and Maui County from noon Wednesday
through 6 PM Saturday. Models continue to show Nolo forming
southeast of the Big Island, and then moving slowly northwest and
then north toward the Big Island. Therefore, we have increasing
confidence that heavy rain will be possible throughout the second
half of this week. In fact, it is conceivable that the watch may
even be extended into Sunday.

Of course, the exact track will determine how long heavy rain
will last and how much total rainfall occurs. At this time, there
is a large amount of uncertainty in the forecast track. Because
the storm is expected to begin to form tonight into Wednesday, we
could see some convergence in solutions during that time. But
with weak steering flow, we think there will continue to be a
large uncertainty in the track as we work through the next few
days. For now, our main concerns are heavy rain and increasing
winds.

Winds could become advisory or even warning level if Nolo
intensifies sufficiently, most likely Friday into the weekend. We
will hold off on issuing anything for the winds at this time, as
we may also be under tropical storm or hurricane watches or
warnings by then.

&&

.AVIATION...
Breezy trade winds will continue into Thursday. Moisture will
continue to increase tonight into Wednesday with shower activity
increasing across the Big Island Wednesday morning into the
afternoon. Shower coverage will spread northwestward through the
state late Wednesday into Thursday. Periods of MVFR ceilings and
visibility are likely in heavier showers.

AIRMET Sierra is in effect for mountain obscuration and may
continue into the morning.

AIRMET Tango is in effect for low level turbulence downwind of
island terrain.

&&

.MARINE...
Issued at 330 PM HST Tue Sep 22 2026
The gradient between the subtropical high to the northeast a low
pressure system (a developing tropical cyclone) to the southeast
will cause moderate to fresh trade winds across the Hawaiian
coastal waters through Wednesday. A Small Craft Advisory (SCA) is
in effect for the typical windy waters of Maui County and the Big
Island through Wednesday night. Depending on how the tropical
cyclone organizes and approaches the coastal waters from the
southeast, gales or tropical storm watches/warnings may also come
into play through the second half of the week. Rainfall and
thunderstorms will increase as the system nears, particularly
across the eastern waters.

Surf along south facing shores will decrease as the current
south-southwest swell fades. A moderate southwest swell will build
in around Friday into the weekend building surf back up across
south and west facing shores.

A small, short period, north northwest swell will fade through
Wednesday. Another small northwest swell will fill in this weekend
keeping surf slightly elevated along north and west facing shores.

East facing shores will maintain rough, short period wind waves
generated from the breezy trade winds. As trades strengthen on
Thursday through the weekend, surf will increase and become very
rough and choppy, possibly nearing advisory levels.

&&

.FIRE WEATHER...
Issued at 330 PM 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 has risen
rapidly to around 10000 feet today over the eastern end of the
state, and will be even higher there the remainder of the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Wednesday afternoon through Saturday afternoon
for Big Island East-Big Island Interior-Big Island North-Big
Island South-Big Island Southeast-Big Island Summits-Haleakala
Summit-Kahoolawe-Kipahulu-Kohala-Kona-Lanai Leeward-Lanai Mauka-
Lanai South-Lanai Windward-Maui Central Valley North-Maui
Central Valley South-Maui Leeward West-Maui Windward West-
Molokai Leeward South-Molokai North-Molokai Southeast-Molokai
West-Molokai Windward-South Haleakala-South Maui/Upcountry-
Windward Haleakala.

Small Craft Advisory until 6 AM HST Thursday for Alenuihaha
Channel-Big Island Leeward Waters-Big Island Southeast Waters-
Maalaea Bay-Pailolo Channel.

&&

$$

UPDATE...Wroe
PREV DISCUSSION...Parker
AVIATION...PECHACEK
MARINE...Foster
FIRE WEATHER...Parker