King tides

A popular name for an astronomical peak

Nobody at NOAA forecasts a "king tide"; the National Ocean Service uses the phrase in public outreach and explains it as a non-scientific term for an especially high tide. The physics behind it is ordinary tide physics turned up to the maximum. Every two weeks, the sun and moon line up at new and full moon and produce spring tides, with higher highs and lower lows than average. Once a month, the moon passes perigee, its closest approach, and its pull on the oceans grows. When a spring tide falls within a day or so of perigee, the two effects stack, and the result is a perigean spring tide. Those are the days that make the local news when water creeps over a seawall on a sunny afternoon.

A third boost comes from the sun. The Earth reaches perihelion, its nearest point to the sun, in early January, which slightly strengthens the solar tide in midwinter. A fourth is seasonal: along much of the Atlantic and Gulf coasts, mean sea level itself runs a few inches higher in late summer and fall, partly from warm water expanding and from shifts in winds and currents. NOAA's predictions include that seasonal cycle, which is why fall dominates the eastern list.

When the highest tides arrive at US stations

The table lists, for ten contrasting gauges, the average higher high (NOAA's MHHW datum), the highest high tide predicted between October 1, 2026 and December 31, 2027, how far that peak rises above an ordinary higher high, and its date. The mini tool above shows the top five for any station.

Two patterns stand out. On the Pacific, Seattle peaks at 13.1 ft on January 25, 2027 and San Diego at 7.6 ft on December 24, 2026: winter, when perigee, a full or new moon and a sun far south of the equator combine on a mixed tide. On the southern Atlantic, Miami tops out on September 30, 2027 and Norfolk on October 1, 2027, in the fall season that South Florida residents know well. The Gulf of Maine follows its own calendar: Bar Harbor reaches 13.2 ft on August 4, 2027.

The "above average" column matters more than the raw height. A king tide that exceeds the ordinary higher high by a foot is a big event on a coast where a foot is a large share of the range, and a modest one in a harbor that moves ten feet a day.

From king tide to high tide flooding

High tide flooding, sometimes called nuisance or sunny-day flooding, happens when the water reaches levels at which local streets, storm drains and low yards start to take on water, without any storm offshore. NOAA's high tide flooding page explains that it now happens much more often than a few decades ago in many US coastal communities, because relative sea level has risen and in places the land is sinking. The astronomical peak alone may be harmless; add a foot from a stalled northeaster or an onshore breeze and storm drains begin to run backward.

Three facts follow for anyone living near the water:

• The calendar of risk is known years ahead. The dates in the table and on every station page are the days to watch.
• Weather decides the outcome. On the predicted peak, check the marine forecast; strong onshore wind or a nearby low-pressure system can add more than the tide itself.
• Saltwater flooding is corrosive and often hides depth. Driving through it damages vehicles and can be dangerous where the road edge is invisible.

Getting ready for a peak week

For people who keep a boat, a car or a house near the water, a king tide week is a short checklist rather than a crisis. Floating docks ride up on their pilings, so check that the pile caps still stand well above the predicted peak plus a margin for wind; fixed docks and launch ramps can go awash, and parking lots at ramps are often the first pavement to take water. Dock lines tied at an ordinary high may come up tight. Cars parked on low streets near tidal creeks are worth moving the night before the highest tide of the cluster, because the water can arrive through storm drains well before it tops a seawall.

Homeowners on low lots can look at the predicted peak on the station page, then watch where the water actually reaches on a calm day. That observation, repeated over a few king tides, tells you more about your own street than any map, and it gives you a baseline for the stormy day when the wind adds its share. Many coastal towns also post their own flood alerts for those dates.

Why the extreme low tides come with them

The same alignments that lift the highs also pull the lows down, so king tide days are often the best minus tide days of the season. On the Pacific, which of the two lows of the day gets the extreme depends on time of day and season, a pattern the negative low tides guide lays out. Photographers and beach walkers sometimes visit the same shoreline at the morning low and the afternoon high of a king tide day to see the full spread.

How sure are the dates?

Very sure for the astronomy. The predicted heights come from harmonic analysis of long tide records and are published by NOAA well in advance; the gap between prediction and observation on a calm day is usually a matter of inches. The uncertainty lies in the atmosphere and the rivers. A dry offshore wind can keep the water below a predicted record, while a storm on an ordinary spring tide can do far worse than any king tide. Treat the predicted peaks as a calendar of when the sea is primed, not as a flood forecast. The NOAA king tide explainer has more on the naming and the causes, and the spring and neap tides guide covers the two-week rhythm underneath.