The Kelvin Wave Reaching California: What the Tide Gauges Show

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.

This post covers what the wave is, where it came from, what NOAA's tide gauges from La Jolla to San Francisco already show (we pulled the data ourselves), and what it means for the Central Coast between now and January.

The short version

• The El Niño is very strong. NOAA's Climate Prediction Center (CPC) puts the odds of a very strong event this fall and winter above 90%. It gives a 75% chance, for October through December, of a "historic event that would exceed the strength of previous El Niño events dating back to 1950."
• The wave is real and already here in part. NOAA Fisheries says this year's Kelvin waves "first reached California in May/June" and expects the fall and winter ones to hit harder. Recent coverage put the next pulse's arrival around October 1.
• 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)." Headlines of "up to a foot" describe several waves stacking up, together with the seasonal high and warm-water expansion.
• The gauges agree. For September 22 to 29, observed water levels ran 6 to 7 inches above the same week of 2025 in Southern California and about 3 to 5 inches above it on the Central Coast and at San Francisco.
• The risk is in the timing. A few inches matter when they land on the year's highest tides and a winter storm. The king tides are November 24 to 26, December 23 to 25 and January 21 to 22.

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 a few tens of 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 200 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, as of their latest updates:

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

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 roughly a third 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

What we read in this:

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. 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. That's record territory before any storm adds surge or big surf adds wave setup. 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." The state's emergency declaration uses a similar estimate: 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… now they're on your front porch."

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 dorado, striped marlin and yellowfin tuna as species that typically increase during El Niño, along with market squid moving north. 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 seabirds on the Farallones and Oregon coast failed to breed during 2015 to 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, so expect a −1.8 ft prediction to come in closer to −1.4 ft. That's still an excellent 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 (+0.3 to +0.6 ft), rather than jumping around with the weather, is the Kelvin wave signal.
• 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.
• 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, 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
• 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. 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.