Flood in Alaska, September 15, 2025

Name: Flood in Alaska, September 15, 2025
Start: 2025-09-15T11:06
End: 2025-09-15T22:55
Location: Alaska

September 15, 2025 · NWS AJK · 1 event in 1 county or zone

A strong low pressure system moved out of the North Pacific Ocean on September 14th and into the Gulf of Alaska through September 15th. The weather front associated with this strong low tapped into sub-tropical moisture as it lifted out of the North Pacific and transported this moisture in a very narrow but long plume which is described as an atmospheric river.

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.

What happened

The episode as NWS AJK wrote it up.

This atmospheric river moved over the Ketchikan area of Southeast Alaska through Monday and produced very heavy, localized, rain for approximately 12 hours. Area precipitation stations reported a range of rainfall amounts of 2 to 8 inches throughout the duration of the event (36hrs), including a new daily rainfall record for the airport and the 4th wettest day on record ever. When looking at rainfall intensity return periods, this 24 hour amount was a 5 year return period, but most of that fell in a 12 hour period with 6.60 inches from 0700AKST to 1900AKST (a 25 year return period). Looking at a finer scale, the 6 hour amount at the Ketchikan airport of 3.94 inches was a 10 year return period.

This very heavy and record breaking rainfall produced significant runoff across the Ketchikan area. This significant runoff produced mainly urban flooding of roads causing road closures and did raise area hydroelectric dams significantly.

What forecasters said that day

The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Juneau, AK wrote its last area forecast discussion before the first event at Sep 15, 5:53 AM AKST, 5 hours 13 minutes earlier.

Area forecast discussion, Sep 15, 5:53 AM AKST, 5 hours 13 minutes before

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
653 AM AKDT Mon Sep 15 2025

.SHORT TERM...The strong system in the gulf has reached the outer
coast of the panhandle overnight, with major impacts peaking in
the next few hours. Only minor changes were made to the forecast
overnight, with the main focus remaining the high end gale to low
storm force eastern gulf winds early Monday morning. Speeds were
brought down from the initial forecast as the front pushes into
the panhandle this morning and buoy obs start to come in. Still
thinking majority high end gales around 40 to 45 knots along the
outer coast, with isolated pockets of storm force winds offshore
out of Cross Sound. Gusts are expected to reach 50kts at their
peak. Gulf winds will begin to decrease through the early
afternoon, though still remaining near gales in the central gulf,
offshore of Cape Suckling, and from Dixon Entrance into Southern
Clarence Strait until the next system enters the gulf Tuesday.
South to southeasterly winds over the panhandle are peaking at
around 20 to 30 knots Monday morning and decreasing through the
day until the next southerly push tomorrow. Winds with the next
system following close after are looking to be as strong if not
stronger as the current system.

Mariners will have a difficult time navigating the channels
through this period, as high winds will be persistent through the
next few hours. Unsheltered areas in the southern and central
panhandle will feel the greatest impacts. High significant wave
height in the gulf will increase channel entrance wave heights to
upwards of 15 feet through the morning.

Accompanying this strong system will be widespread moderate to
heavy rainfall through Monday morning, decreasing as the day goes
on everywhere except Yakutat and areas of the southern panhandle.
The greatest total accumulations with this first system will be
in the southern panhandle, with up to 2 inches of rain
anticipated. The rest of the panhandle will see around half an
inch in 24 hours. The next system will bring more evenly
distributed precip between a half an inch to an inch on Tuesday,
with accumulations continuing into the long term. Highest
accumulations will be for higher elevated areas. Cloudy
conditions will persist through the period, keeping high
temperatures in the upper 50s to low 60s.

.LONG TERM...
Key messages: Tuesday through the weekend: Very active pattern
continues with multiple systems anticipated.

-A band of moderate to heavy rain moves through the panhandle
 on Tuesday, with a brief period of drier weather behind it.

-A storm force low spins up and moves across the outer Gulf
 Coast Tuesday night into Wednesday, bringing another round of
 stronger winds and rain, especially for coastal communities.

-Another front arrives from the West Wednesday night and
 moves through on Thursday.

-A gale force system with an associated plume of moisture,
 enters the panhandle Friday into Saturday.

-More systems arrive over the weekend.

Details: A much more active weather pattern continues to show no
sign of abating anytime soon, as a broad area of longwave
troughing across the Gulf (Rossby Wave) sees continued systems
sweeping into the panhandle. A band of rain meandering across the
panhandle on Tuesday will bring with it a brief period of drier
weather in its wake for the southern panhandle alongside more
inland areas further north. This break may be the only
'substantial' break in the active weather for the upcoming week.

Forecaster confidence has increased in the positioning of a
follow up low which will up and moving near the Gulf Coast Tuesday
night into Wednesday will reach storm force, and so strengthened
winds to storm force in some of the outer coastal waters during
that time frame. Alongside another round of rain, this system will
bring a period of strong winds to the outer coast and potentially
to some more pressure-gradient impacted locations along the inner
channels.

In the wake of this low, onshore flow will ensure that chances of
rain remain across the panhandle through Wednesday. A weaker
front arriving Wednesday night into Thursday will bring with it
another period of more organized precipitation, and another round
of breezy conditions across the area.

Past this point, a stronger system is in store moving in through
the latter half of Thursday and then lasting through Friday.
Pinning down the exact details of this system remains a challenge,
given multiple embedded shortwaves and a potential plume of
moisture. Do have growing confidence however in a plume of
moisture associated with the system. QPF totals between Thursday
and Friday will be anywhere from 2-4 inches, though precise
amounts are difficult to pin down given the array of smaller
details that still need to be worked out.

Ensembles continue to show enhanced rainfall rates and winds
through the weekend, indicative of high confidence in more systems
ahead, although actual timing and strength of these systems
remains murky at this stage as overall run to run consistency
falls apart.

&&

.AVIATION.../through 12z Tuesday/
Predominate VFR flight conditions across the panhandle this early
morning as a strong front pushes across the eastern Gulf and into
the SEAK coastline. Flight conditions will quickly deteriorate
through 18z Monday down to MVFR ceilings AoB 2500ft with
intermittent IFR to LIFR visibilities likely as front pushes
inland with heavier precip, LLWS, and elevated winds. Brief
periods of low- end VFR conditions possible this afternoon post-
front with CIGS AoB 4000ft, quickly deteriorating again as
another system approaches the S Panhandle through 06z Tuesday.

Winds will remain elevated through the TAF period, strongest
sustained winds up to 20kts with isolated gusts up to 40kts
expected along the coastal TAF sites through Monday morning at
Sitka. Winds will gradually slacken slightly through the
afternoon, with sustained winds around 10 to 15kts or less with
gusts up to 25kts.

Main aviation concern for Monday continues to be stout
southeasterly LLWS for the majority of the panhandle TAF sites
through the afternoon. Anticipate widespread LLWS up to 30kts
across the panhandle between 1000 to 2000ft, with strongest LLWS
around 40kts near Ketchikan and Klawock. Brief break in LLWS for a
couple hours this afternoon before a reinforcing shortwave moves
northward from the southern panhandle by 03z to 06z Tuesday,
sending another wave of LLWS over the central and southern TAF
sites.

&&

.MARINE...
Outside Waters: Dangerous and impactful weather is impacting the
gulf for the next few days. A high end gale force front with
isolated areas of storm force winds has reached the outer coast of
the panhandle overnight. Strongest winds have begun to decrease
through Monday morning, but will stay elevated in the outer gulf
waters, off the coast of Cape Suckling, coming out of Cross Sound,
and in Dixon Entrance going into Clarence Strait through the day
as another strong low jumps into the gulf. Storm force gusts up to
52 kts are expected to funnel out of Cross Sound through the
morning. Significant wave heights of 30 ft are possible in the
outer coastal waters early this morning, but will decrease to
around 20 to 25 ft this afternoon. Waves will continue to decrease
as the front diminishes, but will be reinforced back up to 20 to
28 ft from the south as the next low enters the gulf. Strong
southeasterly swell will turn southwesterly through the afternoon
before turning back to southerly and strengthening again Tuesday
afternoon. Gale warnings and small craft advisories persist
through the period.

Inside Waters: Inner channels will be experiencing impactful
weather through the period. The gale to storm force front pushing
over the panhandle early Monday morning is bringing strong
breezes to near gales (22 to 33 kts) to most of the inside waters.
Southern Clarence Strait will see gales (34 to 40 kts) coming
from Dixon Entrance this morning. Winds will begin to decrease and
turn more easterly through the day as the front begins to
diminish, but southerly winds will increase again overnight into
Tuesday with the next southerly push from the next low jumping
into the southern gulf. Channel entrances will have the highest
wind speeds as well as significant wave heights up to 16 ft going
into Southern Chatham Strait and 12 ft going into Clarence and
Sitka Sound and coming out of Cross Sound. The rest of the
channels will see around 5 to 6 ft of significant wave heights at
the peak of the system, may be higher when combined with strongest
winds. Lynn Canal is the one exception to all of this, staying
around moderate to fresh southerly breezes (11 to 21 kts) until
turning northerly Tuesday morning in the more calm period before
the next front. Once that front reaches the panhandle Tuesday
evening, a tightening pressure gradient turning N/S will increase
channel winds to strong breezes with potential for near gale to
gale force gusts.

&&

.HYDROLOGY...
Active pattern kicks off as moderate to heavy rainfall is
expected through early week as a strong front pushes
northeastward through the Panhandle on Monday, before eventually
being pulled back westward across the panhandle through Tuesday
afternoon. Widespread forecast rainfall totals from Monday morning
through Wednesday afternoon are around 2 to 4 inches, with
isolated higher amounts at higher elevations. Freezing levels will
remain around 6,000 ft, allowing for some additional melt around
glacial systems. Due to the heavy rainfall and potential melting,
in combination with already saturated soils from recent rainfall,
rises in area rivers and streams are expected.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind until 7 AM AKDT this morning for AKZ322.
Strong Wind until 10 AM AKDT this morning for AKZ324.
MARINE...Storm Warning for PKZ662>664-671-672. Gale Warning for
PKZ036-641>644-651-652-661. Small Craft Advisory for
PKZ021-022-031>035-053.

&&

SHORT TERM...ZTK
LONG TERM...GFS
AVIATION...NM
MARINE...ZTK
HYDROLOGY...NM

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The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

1 flood. Local standard time, as filed.

Flood, Ketchikan Gateway Borough

When: September 15, 11:06 AM AKST to 10:55 PM AKST
Where: Ketchikan Gateway Borough County, 2.79 mi WNW of Ketchikan to 1.15 mi N of Ketchikan
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 55.376, -131.755

Through the late morning hours of September 15th reports from the local emergency manager reported significant runoff from the steep hillside that surrounds the Ketchikan area from the very heavy rain. This overland flow continued and increased into the afternoon, which flooded numerous roads that had to be closed due to the depth of water and the risk to life and property to the drivers. Some of this urban flooding did occur in poor drainage areas, during the tourist season, and affected traffic and the safety of the visitors. In the afternoon, the emergency manager reported brown water in the runoff, causing elevated concern for landslides, although no landslides were recorded from this event. The peak wind measured at the airport during this event was 44 mph at noon AKDT.

The Ketchikan airport recorded a new daily rainfall record for September 15th of 7.66 inches. This broke the previous daily record of 2.65 inches set in 1981.

From the record rainfall, local hydro-electric dams rose significantly, ranging from 3 to 4 feet. Along Ketchikan Creek, which is fed from overflow of Ketchikan Lakes Dam, the water level rose almost 3 feet in 6 hours, cresting just below 62 feet. Even though it remained below minor flood stage of 63.5 feet, there was a lot of water moving down the creek and right through downtown Ketchikan which caused some concerns.

What these are

Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Alaska in 2025 Every state in 2025 This day in weather history Warnings in Alaska, September 2025

Sources

NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1293441.