The Kelvin Wave Reaching California: What the Tide Gauges Show

Updated October 28, 2026. This update adds two more weeks of tide gauge data, the October 24 to 27 spring tides at Port San Luis and the next big tides. The October 13 update and the original analysis from September 29 follow it.

If you've seen a headline this week about a "Kelvin wave" heading for California, you may have pictured a wall of water. It isn't one. A Kelvin wave is a bulge in sea level a few inches high and hundreds of miles long. It moves up the coast at about the speed of a bike ride, and it can keep the ocean higher than normal for weeks or months. You won't see it arrive. You'll see it in the tide tables when the high tides come in higher than predicted, and later in the winter when a storm lands on a king tide.

We pulled the NOAA tide-gauge data from La Jolla to San Francisco ourselves. Below is what it shows so far, and what the wave could mean for the Central Coast between now and January.

The short version

• The water went higher again. After Tropical Storm Rachel passed, the gauges dropped back to 9 to 12 inches above prediction on October 15. They climbed again to 14.5 to 18 inches on October 21 and held at 12 to 16.5 inches through October 27, about where they stood just before Rachel.
• Record-level mornings on ordinary spring tides. Port San Luis reached 7.66 ft at 10:48 am on October 27 and 7.68 ft at 11:36 am on October 28, more than a foot above the predicted highs. Both top the gauge's highest monthly reading since 1980, 7.64 ft in January 2005, by a fraction of an inch (NOAA preliminary data).
• The El Niño keeps strengthening. In its October 8 update, NOAA's Climate Prediction Center (CPC) raised the chance of a "historic event that would exceed the strength of previous El Niño events dating back to 1950" to 83% for October through December, up from 75% in September. Niño-3.4 reached +2.1 °C in September.
• The wave arrived. The tide gauges show Southern California rising from about September 26 and the Central Coast from September 29 to 30, a few days later. NC State's Dillon Amaya told Patch on October 9 he thinks the wave "has made it to San Diego/LA," and the San Luis Obispo Tribune reported it reached San Luis Obispo County by October 7.
• The size is inches, not feet. NOAA Fisheries describes each coastal-trapped wave as "relatively small changes in sea level (approximately 15 cm or 6 inches)." Amaya estimates the wave makes up "something like 6 inches" of the high water at San Diego. Readings of a foot or more come from the wave plus warm-water expansion, the seasonal high and weather.
• The gauges agree. From September 30 to October 8, before Tropical Storm Rachel, water levels ran 10 to 12 inches above the same days of 2025 in Southern California, 9 inches above at Port San Luis and 6 to 7 inches above at Monterey and San Francisco. That is roughly double the gap of the week before.
• Rachel showed the risk. On top of that higher baseline, Rachel's surge and swell pushed Port San Luis to 7.14 ft on the morning of October 10, 1.36 ft above the predicted high.
• More are coming. Amaya told NPR on October 19 that a strong El Niño year usually brings five to six Kelvin waves, and that he expects the next one to reach San Diego in late October or early November. The next big tides are November 7 to 10, and the king tides are November 24 to 26, December 23 to 25 and January 21 to 22.

Update, October 28: higher water and a record-level tide

What the gauges show now

We pulled NOAA's preliminary water levels and predictions for the same six gauges through October 28. The table continues the daily average residual (observed minus predicted, in inches) from the October 13 update below. These days are averaged from the 24 hourly readings, so they can differ by a fraction of an inch from an average of every 6-minute reading.

Daily average residual, 2026 (inches)

Day	La Jolla	Los Angeles	Santa Barbara	Port San Luis	Monterey	San Francisco
Oct 15	+12.2	+11.8	+11.0	+9.2	+9.7	+9.4
Oct 18	+14.6	+13.2	+12.8	+11.1	+13.1	+12.6
Oct 21	+18.0	+16.9	+17.8	+15.5	+15.2	+14.5
Oct 24	+16.5	+16.1	+16.2	+13.1	+13.1	+12.6
Oct 27	+15.4	+15.9	+15.3	+13.0	+12.7	+12.2
24 hours to 8 am Oct 28	+15.4	+15.7	+15.4	+13.0	+12.4	+11.8

The last row is the past-day average residual our Conditions Console showed for each gauge on the morning of October 28.

What we read in this:

1. Rachel's extra water drained, then the level came back. By October 15 the gauges were 9 to 12 inches above prediction, a little below the October 12 readings. Every gauge was higher on October 18 and higher again on October 21.
2. October 21 nearly matched the Rachel day. Daily averages reached 14.5 to 18 inches, within about 1.5 inches of October 10 at most gauges and above it at Port San Luis (15.5 against 15.0).
3. It held. From October 24 to 28 the gauges stayed 12 to 16.5 inches above prediction, about where they stood on October 8, before Rachel. Southern California stayed about 2 to 4 inches higher than the Central Coast and the Bay Area, as it has since late September.

We can't yet say how much of the October 18 to 21 rise was weather and how much was more Kelvin wave water. A rise this even from La Jolla to San Francisco looks more like a change in sea level than a local storm, but a year-over-year comparison would be needed to separate them, and October data is still preliminary.

Port San Luis on the October spring tides

High tide (PDT)	Predicted	Observed	Above prediction
Oct 24, 9:04 am	5.68 ft	6.80 ft	+1.12 ft
Oct 25, 9:30 am	6.06 ft	7.33 ft	+1.27 ft
Oct 26, 10:01 am	6.36 ft	7.61 ft	+1.25 ft
Oct 27, 10:36 am	6.52 ft	7.66 ft	+1.14 ft
Oct 28, 11:16 am	6.52 ft	7.68 ft	+1.16 ft

Observed is the highest 6-minute reading within an hour of the predicted high (NOAA preliminary data).

On October 13 we estimated the October 27 high would reach about 7.3 ft if the gauge kept running 9 to 10 inches above prediction. It ran about 13 inches above, and the gauge read 7.66 ft at 10:48 am. NOAA's monthly records for the gauge since 1980 top out at 7.64 ft in January 2005, followed by 7.58 ft in January 1983 and 7.51 ft in January 2026. The next morning went higher still: 7.68 ft at 11:36 am on October 28. So October 28 and 27 now sit just above the 2005 record, by 0.04 and 0.01 ft, and October 26 (7.61 ft) comes next, above the El Niño storm of 1983. These are preliminary readings that haven't finished NOAA's quality control, and the margins are under half an inch, so we'd call it a tie with the record until the data is verified. The predicted highs themselves were ordinary for an October spring tide. The extra foot came from water the gauge had been carrying for days.

The next big tides at Port San Luis

The October 29 high (6.33 ft at 12:03 pm PDT) is the last of this series. The next are below. Daylight time ends November 1, so these times are PST. The last column adds the 13 inches the gauge has been running above prediction. The residual changes from day to day, so treat it as arithmetic, not a forecast.

Date	Predicted high	Time (PST)	With 13 in on top
Nov 8	6.07 ft	8:28 am	about 7.2 ft
Nov 9	6.05 ft	8:55 am	about 7.1 ft
Nov 23	6.59 ft	7:53 am	about 7.7 ft
Nov 24	6.85 ft	8:31 am	about 7.9 ft
Nov 25	6.93 ft	9:14 am	about 8.0 ft
Nov 26	6.81 ft	10:00 am	about 7.9 ft
Nov 27	6.48 ft	10:53 am	about 7.6 ft

November 24 to 26 are the Coastal Commission's king tide dates. Our king tides guide has every high and low for all three king tide windows.

What the reporting says

• More waves. NC State's Dillon Amaya told NPR on October 19 that the Kelvin wave had already raised sea levels about six to eight inches. He said a strong El Niño year usually brings five to six Kelvin waves, and he expects the next one to reach San Diego in late October or early November. "It makes the background conditions more favorable towards coastal flooding, but what you need are triggering factors," he said.

Update, October 13: the wave has arrived

What the gauges show now

We extended our analysis of NOAA's 6-minute water levels through October 13. The table shows the daily average residual (observed minus predicted, in inches) at six gauges. NOAA's predictions are based on the 1983 to 2001 epoch, so in a normal year these numbers run about 1 to 4 inches positive. For the same dates in 2025 they averaged +1 to +4 inches.

Daily average residual, 2026 (inches)

Day	La Jolla	Los Angeles	Santa Barbara	Port San Luis	Monterey	San Francisco
Sep 25	+7.7	+8.1	+7.7	+6.3	+6.7	+6.6
Sep 28	+10.3	+10.4	+10.2	+6.2	+6.3	+6.2
Sep 30	+12.6	+13.0	+12.5	+9.3	+9.1	+9.1
Oct 3	+13.1	+13.5	+12.5	+10.1	+11.1	+10.9
Oct 8	+16.8	+15.5	+14.2	+12.5	+13.7	+12.7
Oct 10 (Rachel)	+18.3	+18.4	+18.5	+15.0	+15.9	+16.1
Oct 12	+13.6	+12.9	+13.3	+11.0	+11.9	+11.6

Average residual, September 30 to October 8 (before Rachel), inches

Gauge	2026	Same days 2025	Difference
La Jolla	+13.9	+1.6	+12.3
Los Angeles	+13.3	+1.9	+11.4
Santa Barbara	+12.7	+2.3	+10.4
Port San Luis	+10.5	+1.3	+9.2
Monterey	+11.1	+4.0	+7.1
San Francisco	+10.6	+4.1	+6.5

What we read in this:

1. The rise started in the south. Southern California's three gauges climbed from about +8 to +12 inches between September 26 and 29. Port San Luis, Monterey and San Francisco held near +6 inches until September 28, then rose together to +9 to +11 inches between September 29 and October 3. A lag of about three days between the two regions is roughly what the AP's figure for the pulse, about 6 mph or 150 miles a day, would predict, though weather could produce some of it.
2. It kept building before Rachel. Every gauge rose another 1.5 to 4 inches from October 3 to 8, before Rachel's swell and surge arrived. Some of that is weather. Some may be what UCLA climate scientist Daniel Swain describes: "thermal expansion of sea water from the extreme marine heatwave" adding 6 to 10 inches under the Kelvin wave. Swain puts the Kelvin wave's own share at another 9 to 12 inches, more than Amaya's estimate of about 6.
3. Rachel rode on top of it. Rachel's surge and swell, on top of whatever was already building, added another 1.5 to 4.5 inches to the daily averages from October 8 to 10. Individual high tides came in more than a foot over the tables. By October 12 and 13 the storm's extra water was mostly gone, but the gauges were still about 9 to 13 inches above prediction. That remaining height is the baseline the next storm will start from.

The same caveats apply as before. October data is preliminary and has not finished NOAA's quality control, and a year-over-year comparison doesn't remove weather. The pattern of the rise, south first and then north, holding through every tide, is what a Kelvin wave looks like on a gauge.

Port San Luis during Rachel

High tide (PDT)	Predicted	Observed	Above prediction
Oct 9, 9:42 am	5.62 ft	6.67 ft	+1.05 ft
Oct 10, 10:08 am	5.78 ft	7.14 ft	+1.36 ft
Oct 11, 10:35 am	5.85 ft	7.05 ft	+1.21 ft
Oct 12, 11:02 am	5.80 ft	6.74 ft	+0.95 ft
Oct 13, 11:29 am	5.65 ft	6.39 ft	+0.74 ft

Observed is the highest 6-minute reading within an hour of the predicted high (NOAA preliminary data).

The National Weather Service had forecast highs near 7.5 ft on Sunday, October 11. The gauge peaked at 7.05 ft that morning, after 7.14 ft on Saturday. For comparison, the highest reading at the gauge since 1980 is 7.64 ft (January 2005), and the El Niño storm of January 27, 1983 reached 7.58 ft. A Saturday in October, before the High Surf Advisory began and with no king tide, came within half a foot of those. Our Tropical Storm Rachel post covers the storm itself.

What the reporting says

• San Diego and Los Angeles. Amaya told Patch on October 9 that "sea levels around San Diego are about 1.2 ft higher than normal," and that the Kelvin wave "makes up something like 6 inches of that." Swain wrote on October 12 that California's coastal water levels "are already running 1-2 feet above astronomical tidal predictions." He added that "nearly the entire Balboa Peninsula was inundated at a depth of up to 2-3 feet locally" over the past week.
• The Bay Area. San Francisco Mayor Daniel Lurie said in early October that tides were "already running about six inches higher than normal," SFist reported. KQED quoted UC Santa Cruz's Mike Beck before the Rachel weekend: "By the end of the weekend we should probably see water levels a foot and a half above normal."
• San Luis Obispo County. The Tribune quoted meteorologist John Lindsey that Kelvin waves "can add another 6 to 12 inches of sea level," on top of king tides near 7 feet. "All those things together could really produce some coastal flooding this year," Lindsey said. "El Niño is a promise. It's not a guarantee." KSBY reports the county has formed a multi-department El Niño task force, and the City of San Luis Obispo is receiving more than $1.3 million in state funding for storm drain upgrades.
• The state. The Governor's office said on October 9 that Kelvin waves have raised sea levels this year and that hurricane swells have caused coastal flooding scientists attribute to El Niño. It directed the Coastal Commission to fast-track protective projects and said the Commission can act on qualifying emergency permit requests within 24 hours. The release also says the Department of Water Resources has stockpiled 4.4 million sandbags at 68 sites.
• Not on its own. "It's not that this Kelvin wave is going to come and flood anything on its own," NOAA's Mike Jacox told the AP. "The effects can be amplified." USGS's Sean Vitousek added that "the loss of protective beaches also increases wave impacts and coastal flooding on property and infrastructure."

Warm-water visitors

• National Geographic reported a whale shark off Catalina Island and spinetail rays near San Diego.
• The Log reported olive ridley sea turtle nests at Seal Beach and Huntington Beach in September, "the first known natural sea turtle nesting events documented on the U.S. West Coast." It also reported a yellow-bellied sea snake at Crystal Cove and "dorado and yellowfin tuna arrived unusually early this year."
• SFGATE reported that California White Shark Project researchers saw a white shark off Point Reyes with an escort of pilotfish, something they had "never seen before in over 20 years of research" there.
• NOAA's marine heatwave tracker said on September 30 that late-September warming off Southern California "may finally be the result of more direct warming due to El Niño drivers, such as oceanic Kelvin waves."

What a Kelvin wave actually is

In a normal year the trade winds blow east to west along the equator and pile warm water up in the western Pacific. Sea level near Indonesia sits higher than near Ecuador, and the thermocline (the boundary between warm surface water and cold deep water) tilts: deep in the west, shallow in the east. That shallow eastern thermocline is why cold, nutrient-rich water wells up off South America.

When the trade winds weaken or reverse, which is how an El Niño starts, that pile of water sloshes back east. NOAA's Nate Mantua (Southwest Fisheries Science Center) describes it this way: "When the wind stops blowing or weakens, the force that's holding that pile of water in place goes away, so that water surges or sloshes back towards California." The slosh travels as an equatorial Kelvin wave: a pulse that pushes the thermocline down (a downwelling wave) and raises sea level as it goes. It crosses the Pacific in about two to three months. This year CPC's September discussion describes subsurface temperature anomalies "in excess of +10.0°C at depth" and "a deeper-than-average thermocline" across the eastern Pacific.

When the wave hits the Americas it can't keep going east. JPL oceanographer Severine Fournier describes what happens next: "when the wave reaches the coast of South America, it cannot continue to go eastward. So it goes north and south." Part of its energy turns into a coastal-trapped Kelvin wave. In the Northern Hemisphere, Earth's rotation holds that wave against the coast on its right, so it runs north along Central America, Mexico and California with the shoreline on its right. It is strongest at the coast and fades within about 12 to 20 miles offshore.

A few properties matter for anyone who reads tide tables:

• It's a rise in the mean water level, not a wave you surf. "It's a wave unlike the ones you're used to at the beach," NOAA oceanographer Mike Jacox said. "They don't crash, you can't really [see] them come by."
• It lasts. The wave is hundreds of miles long, so its crest takes weeks to pass a given pier. A series of waves can hold sea level up for most of a winter.
• It brings warm water. A downwelling wave pushes the cold layer deeper, so the upwelling winds that usually cool the coast lift warm water instead. NOAA Fisheries notes that this, with weaker upwelling winds, produces "unusually high temperatures that are prominent in a nearshore band extending from Baja California to Alaska."
• It moves fast along the coast. Coastal-trapped waves travel roughly 100 to 160 miles a day. The Weather Channel put this one at about 6 mph. At that speed a crest takes only a few days to get from San Diego to San Francisco, which is why the whole California coast rises at nearly the same time.

Where the 2026 El Niño stands

The numbers from the official forecasters (October updates in bold):

Source	Date	What it says
NOAA CPC ENSO discussion	Sep 10, 2026	El Niño Advisory; >90% chance of a very strong event this fall and winter; 75% chance (Oct to Dec) of exceeding every El Niño since 1950
CPC August Niño indices	Sep 10, 2026	Niño-3.4 +1.8 °C, Niño-3 +2.5 °C, Niño-1+2 +3.4 °C (the region nearest South America is warmest)
NOAA GFDL SPEAR (30 members)	Sep 2026	All 30 members "compete with, if not surpass, the strongest events in the historical record"; peak slightly weaker than August's forecast
California Governor	Sep 21, 2026	State of emergency for the 2026 to 2027 El Niño: sandbags and pumps staged, Guard on standby, permits fast-tracked
NOAA CPC ENSO discussion	Oct 8, 2026	Strong-to-very strong El Niño likely through Jan to Mar 2027 (more than 83%); historic-event odds 83% for Oct to Dec, up from 75%
CPC September Niño indices	Oct 8, 2026	Niño-3.4 +2.1 °C, Niño-3 +3.0 °C, Niño-1+2 +3.9 °C
NOAA GFDL SPEAR	Oct 2026	"This historic El Niño is nearing its peak, with weakening expected by early winter," but its impacts "may continue to intensify"
World Meteorological Organization	Oct 8, 2026	Niño-3.4 forecast near +3.7 °C for Oct to Dec, peaking around December; the record is +2.6 °C (Nov 2015 to Jan 2016)

One headline needs a correction. Several outlets called this "the most powerful El Niño in 1,000 years." The research behind that line is a Science study led by Julia Cole (University of Michigan) using Galápagos corals. It found that El Niño events of the last four decades were stronger than any in the 1,000 years before about 1850, and nearly 40% stronger than preindustrial events. It is a statement about recent El Niños in general, not a measurement of this one, which hasn't peaked yet. If this event does beat 1982-83, 1997-98 and 2015-16, it will top a record that already stands out against a millennium.

What the tide gauges already show

We didn't want to rely on headlines, so we pulled NOAA's hourly water levels and tide predictions for six California gauges. Every tide prediction is astronomy only: the Moon, the Sun and the local seasonal cycle. The difference between observed and predicted water level is the residual. It captures everything the astronomy leaves out, including wind setup, air pressure, and slow sea-level changes like a Kelvin wave.

NOAA's predictions use the 1983 to 2001 tidal epoch, and the sea has risen since then. So even in a quiet year the residual runs 1 to 4 inches positive. To take that out, we compared 2026 with the same days of 2025, a year with no El Niño.

Average residual, September 22 to 29 (inches)

Gauge	2026	Same week 2025	Difference
La Jolla (9410230)	+8.4	+2.1	+6.3
Los Angeles (9410660)	+8.9	+2.3	+6.6
Santa Barbara (9411340)	+8.9	+2.8	+6.1
Port San Luis (9412110)	+6.6	+2.2	+4.4
Monterey (9413450)	+7.1	+4.2	+2.9
San Francisco (9414290)	+7.2	+4.3	+2.9

Half-month average, 2026 minus 2025, Port San Luis (inches)

Period	2026 minus 2025
Jul 1 to 15	+2.5
Jul 16 to 31	+3.1
Aug 1 to 15	+4.9
Aug 16 to 31	+3.6
Sep 1 to 15	+5.4
Sep 16 to 29	+4.7

Three things stand out:

1. The whole coast is running high, and has been since early summer. That fits NOAA Fisheries' note that the first Kelvin waves reached California in May and June. Port San Luis has run 2.5 to 5 inches above 2025 for three months.
2. Southern California jumped in September. La Jolla, Los Angeles and Santa Barbara went from about +4 inches in August to +6 to +7 inches in September. Monterey and San Francisco went up less. That pattern fits a pulse arriving from the south, though weather can produce it too.
3. It's already the size the scientists described. Six inches above normal in Southern California is about what NOAA Fisheries predicts for one coastal-trapped wave. Headlines of "a foot" would take more waves on top of this one, and that is what scientists warn about for the months ahead.

These are our numbers, not NOAA's, and they come with caveats. September data is preliminary: NOAA hasn't finished quality control yet. A week of residuals also includes weather: a run of south winds or low pressure can add a few inches for a few days. Comparing year over year removes the tidal-epoch offset but not any weather that differed between the two years. Treat the table as a strong signal, not a precise measurement of the wave.

How it compares with past super El Niños

Monthly averages smooth the weather out. We took NOAA's monthly mean sea level since 1980, removed the long-term rise (about 0.4 inch per decade at Port San Luis and 0.6 at Los Angeles and San Francisco), and compared each month with its 1980 to 2025 average:

Gauge	1982-83 peak	1997-98 peak	2015-16 peak	August 2026
Port San Luis	+6.6 in (Nov 1982)	+7.6 in (Nov 1997)	+5.7 in (Oct 2015)	+3.4 in
Los Angeles	+6.3 in (Jan 1983)	+7.2 in (Nov 1997)	+6.6 in (Oct 2015)	+3.9 in
San Francisco	+10.7 in (Mar 1983)	+11.2 in (Feb 1998)	+5.2 in (Oct 2015)	+3.4 in

At the end of August Port San Luis stood about halfway to the past super El Niño peaks. September's residuals suggest another inch or two since then. In all three past events the peak came in October through March, so if this El Niño follows the pattern, the highest water is still ahead. The San Francisco column shows another pattern: in 1983 and 1998 the northern coast peaked late, in the heart of the storm season, when the wave's rise combined with storm-driven water piling against the coast.

What it means on the Central Coast

King tides with extra water

The California Coastal Commission's king tide dates this season are November 24 to 26, December 23 to 25 and January 21 to 22. Our king tides guide has every day's highs and lows for all three windows. At Port San Luis, NOAA predicts:

Date	Predicted high	Time (PST)	Predicted low that afternoon
Nov 25	6.93 ft	9:14 am	−1.46 ft (4:52 pm)
Dec 23	6.99 ft	8:16 am	−1.76 ft (3:54 pm)
Dec 24	7.02 ft	9:04 am	−1.85 ft (4:41 pm)
Dec 25	6.83 ft	9:54 am	−1.72 ft (5:28 pm)
Jan 21	6.78 ft	8:10 am	−1.84 ft (3:37 pm)

For scale: mean higher high water at Port San Luis is 5.33 ft above MLLW, so a 7-foot king tide is already about 1.7 feet above an ordinary high tide. The highest monthly water levels at the gauge since 1980 are 7.64 ft (January 2005), 7.58 ft (January 1983) and 7.51 ft (January 2026). If the Kelvin wave keeps 5 to 6 inches on top of the December 24 prediction, the still-water high would reach about 7.5 ft. If the gauge is still running 9 to 10 inches above prediction, as it did in early October, it would be about 7.8 to 7.9 ft. At the 13 inches it ran in late October, it would be about 8.1 ft. Any of these is record territory before any storm adds surge or big surf adds wave setup. Kelvin waves come and go, so the extra water on December 24 could be more or less than today's.

October's spring tides already showed it. On October 13 we wrote that if the gauge kept running 9 to 10 inches above prediction, the 6.52 ft spring tide predicted for 10:36 am on October 27 would reach about 7.3 ft. It reached 7.66 ft at 10:48 am, with the gauge running 13 inches above prediction that day, and 7.68 ft the next morning. That is higher than the Rachel weekend's 7.14 ft peak and level with the gauge's highest reading since 1980, on ordinary October spring tides. The October 28 update above has the readings. California Coastal Commission executive director Kate Huckelbridge put it plainly: "the most damaging storms are often those that coincide with the highest tides."

UC Santa Cruz's Patrick Barnard gives a rule of thumb for why a few inches matter: because West Coast extreme water levels don't vary much, "every 2 to 4 inches of sea level doubles our flood risk." He also told CNN that six inches to a foot of extra water would put about 170,000 more Californians and $60 billion more in property at risk than in a year without a super El Niño.

Where it shows up locally

• Harford Pier, Port San Luis and Avila Beach: watch the promenade seawall along Front Street and the beach parking lots on the morning king tides.
• Pismo Beach and Oceano the dunes and the Pier Avenue ramp at Oceano are exposed to wave runup on a high tide. Driving on the beach at the Oceano Dunes SVRA gets tight when the high-tide line moves up.
• Morro Bay and Cayucos watch the low sections of the Embarcadero and the marsh edges at the back of the bay. In Cayucos, the beachfront and the pier approach take a west swell on a high tide head-on.
• Cliffs and bluffs from Shell Beach to Cambria: higher water lets surf reach the base of bluffs more often. That speeds up erosion even without a big storm. UCLA coastal engineer Timu Gallien's warning is about exactly this: "if you have enough water level to support those waves so they dump right on your coast, they're right there."

Surf

A higher mean sea level acts like a permanently higher tide. Breaks that work best at low tide get fewer good hours, and reefs and points that need lower water may barely break at a normal high. Beach breaks can close out on the upper tide. When the winter storms arrive, the extra water lets surf reach farther up the beach. That pulls sand offshore faster and can leave rocky, cobbled beaches by spring, as happened across California in the 2016 El Niño winter.

Fishing and tidepooling

• Warm water and visitors from the south. NOAA Fisheries lists market squid moving north as an El Niño sign. Dorado, striped marlin and yellowfin tuna have already moved north in recent marine heatwaves without an El Niño, so it no longer counts them as reliable signs. In the 2014 to 2018 warm period, scientists logged 36 unusual species off California, 14 of them recorded in the California Current for the first time. Also watch for pelagic red crabs washing up on beaches.
• The cost. Warm, stratified water is poor food for the cold-water food web. NOAA Fisheries notes that warm-water copepods carry less fat, "usually unfavorable for salmon," and common murres on the Oregon coast failed to breed in 2015 and 2016.
• The good news for tidepoolers. The king tide series also brings the winter's lowest afternoon tides, down to −1.85 ft on December 24 at Port San Luis. A Kelvin wave raises the lows too. With September's extra water (about 5 inches above last year) a −1.8 ft prediction would have come in near −1.4 ft. With early October's (about 9 inches), it would be closer to −1.0 ft. With late October's 13 inches above prediction, about −0.8 ft. That's still a good tidepool tide. Check the residual before you go and adjust your timing.

How to watch the Kelvin wave yourself

You don't need a research vessel. Every NOAA tide gauge measures it. On this site:

• Conditions Console (Port San Luis): the Now panel shows the current water level in feet vs predicted. A reading that stays positive for days, rather than jumping around with the weather, is the Kelvin wave signal. It ran +0.3 to +0.6 ft in September, +0.8 to +1.0 ft in early October and about +1.1 ft at Port San Luis in late October.
• Tide Intelligence (Port San Luis): the observed vs predicted chart has a residual lane under it, over 24 or 72 hours. A residual bar that stays above zero through every tide is what a sea-level bulge looks like.
• Coast Map (/map): compare stations from Crescent City to San Diego. A wave from the south should show up in Southern California a few days before it reaches the north.
• Ocean Signals (/ocean-signals): every California tide gauge on one page, north to south, with its residual for each of the last seven days. Bars that stay above zero day after day, at gauge after gauge, are the same signal.
• Plan around the predictions, then add the residual. If the residual has held at +0.4 ft all week, add about 5 inches to every high tide in the table (and every low) for the next several days.

What to do before winter

1. Know your elevation. If you live or park near the water, find out whether your site floods at 7 ft MLLW. The Coastal Commission's King Tides Project photos from past years show where the water reaches.
2. Photograph the king tides. The California King Tides Project asks for photos on the November, December and January dates. This year's photos will show a king tide on top of an El Niño, which is a preview of the sea level the coast is expected to see as a normal high tide in coming decades.
3. Sign up for alerts. The governor's office points residents to Listos California for county emergency alerts.
4. Watch the calendar, not just the forecast. The worst-case day is a storm on a king tide. When a winter storm lines up with the dates above, stay off low seawalls, jetties and bluff edges, and keep cars out of low beach lots overnight.

Sources

• NOAA Climate Prediction Center, ENSO Diagnostic Discussion, October 8, 2026
• NOAA GFDL, October 2026 El Niño Predictions (SPEAR)
• World Meteorological Organization, Sea-surface temperatures reflect strengthening El Niño, October 8, 2026
• Office of the Governor, Ahead of El Niño this winter, Governor Newsom prepares California for winter storms and flooding impacts, October 9, 2026
• Patch, Kelvin Wave Raises SoCal Sea Levels As Tropical Storm Rachel Threatens Coast, October 9, 2026 (Amaya quotes)
• Daniel Swain, Weather West, October 12, 2026 post
• AP via PBS NewsHour, What to know about the Kelvin wave raising the sea level along the West Coast, October 3, 2026 (Jacox and Vitousek quotes)
• San Luis Obispo Tribune, A record-breaking El Niño could strike SLO County this winter. Here's how to prepare, October 10, 2026 (Lindsey quotes)
• KQED, This Weekend, an El Niño-Driven 'Kelvin Wave' Will Raise Bay Area Sea Levels and Flooding Risk, October 9, 2026 (Beck quote)
• SFist, SF braces for unusually high tides as El Niño sends Kelvin waves toward the coast, October 5, 2026
• KSBY, SLO County launches task force as residents prepare for potential El Niño flooding and San Luis Obispo receives $1.3 million in state funding to prepare for potential El Niño storms
• National Geographic, Kelvin wave reporting, October 6, 2026 (whale shark, spinetail rays)
• The Log, Warm Water, Wild Visitors: El Niño Is Reshaping Southern California's Marine Neighborhood, October 8, 2026
• SFGATE via Yahoo, Bay Area scientists see rare shark entourage as El Niño looms, October 13, 2026
• NOAA California Current IEA, Marine Heatwave Tracker (Blobtracker), update of September 30, 2026
• NOAA Climate Prediction Center, ENSO Diagnostic Discussion, September 10, 2026
• NOAA GFDL, September 2026 El Niño Predictions (SPEAR)
• NOAA Fisheries, Ocean Indicators We're Tracking for El Niño's Arrival on the West Coast
• Office of the Governor, Governor Newsom proclaims state of emergency to bolster statewide El Niño preparedness, September 21, 2026
• UC Santa Barbara, El Niño has become more intense over last 40 years than the previous 1,000 years (Cole et al., Science)
• The Weather Channel, El Niño drives Kelvin wave closer to California, September 12, 2026
• The Guardian, reporting on the Kelvin wave, September 28, 2026 (quotes from Fournier, Mantua, Jacox and Huckelbridge)
• CNN, Sudden sea level rise tied to El Niño is about to hit the California coast (Barnard quote)
• iHeart, Kelvin Wave Could Lift California Sea Levels By a Foot, September 28, 2026 (Gallien quote)
• California Coastal Commission, California King Tides Project
• NPR via OPB, A Kelvin wave raised sea levels on the West Coast. More are coming, October 19, 2026 (Amaya quotes)
• Tide gauge data: NOAA CO-OPS Tides & Currents hourly heights, 6-minute preliminary water levels, predictions, monthly means and datums for stations 9410230, 9410660, 9411340, 9412110, 9413450 and 9414290, through October 28, 2026, and the Port San Luis high/low record for January 1983. The analysis is ours: residual is observed minus predicted, comparisons are 2026 against the same dates in 2025, and monthly anomalies are detrended against a 1980 to 2025 monthly climatology.