On the morning of 14 March 2026, the tide at Dingle Harbour came up two centimetres higher than the published prediction. The harbourmaster, Padraig Fitzgerald, noted it in pencil at the bottom of the daily sheet and went on with his work.
Two centimetres is not much. It is, however, exactly the sort of small over-prediction one would expect in 2026, near the end of a slow lunar phase that has been running, unnoticed by almost everyone, since 2015.
The cycle is called the lunar nodal cycle. It runs for 18.61 years. Across that span the angle of the moon's orbit relative to the Earth's equator drifts from a minimum of about 18.3 degrees to a maximum of about 28.6 degrees, then back again.
The drift is gentle. It is also, for tides, consequential.
When the lunar orbit is at its highest inclination, the moon's monthly path takes it far north and far south of the equator. Its gravitational pull is more often off-axis from any given coastline, and the diurnal component of the tide grows slightly stronger. Semi-diurnal tides, the kind found on most Atlantic coasts, become slightly less extreme. The neap tides are a fraction higher and the spring tides a fraction lower.
When the lunar orbit is at its lowest inclination, the opposite happens. Spring tides reach a touch farther up the harbour wall. Neap tides recede a touch farther into the channel. The amplitudes are larger.
The amplitude swing between those two phases is small. Three to four percent of the tidal range, at most. On a coast like Dingle, with a mean spring range of about 3.4 metres, that works out to around eleven centimetres over the full cycle.
Eleven centimetres is not much either. The trouble is that it stacks on top of everything else.
Sea level rise at the Dingle tide gauge, measured by the Marine Institute station at Castletownbere and corrected to local datum, has been running at about 3.6 millimetres per year. Storm surge from a strong southwesterly can lift the water another 60 to 90 centimetres at the harbour mouth.
The nodal cycle is a slow whisper underneath all of that. But in the years near maximum amplitude, called the major lunar standstill in older literature, it pushes the highest astronomical tides up by that small extra fraction. The next standstill arrives in 2025 and 2026. Coastal engineers have been planning for it for a decade.
Reidar Vik, who served on Norwegian coastal ferries before he started writing about them, points out that the cycle is well-known to harbour pilots in places where the tide does real work. In Bergen, the predicted tide tables are routinely cross-checked against the nodal phase before any deep-draft vessel attempts the inner channels at low water.
In Newfoundland, the tide-table books printed by the Canadian Hydrographic Service carry a small note in the front matter about the nodal correction. Most recreational mariners have never read it.
The cycle was first quantified by James Bradley, the British Astronomer Royal, in 1748. He was looking for the parallax of stars and found, instead, the slow wobble of the lunar orbit. The same nodal cycle that smudges his star positions also nudges every coastline on Earth.
At the harbour wall in Dingle, Padraig Fitzgerald keeps a small spiral notebook with the over-and-under predictions for each spring tide of the year. He has been keeping it since 2011.
In 2015, near the previous nodal minimum, his entries trended negative. The water came in lower than the book said it would, by one or two centimetres, week after week. In 2020 the entries crossed back through zero. By 2024 they were running positive.
"It's a thing you only see if you write it down," he said in February. "Anyone who watches a single tide thinks the book is exact. Anyone who watches a thousand of them knows it isn't."
The next maximum amplitude phase peaks in mid-2026. By 2030 the entries in Fitzgerald's book should begin to flatten and reverse. By 2035 they should be solidly negative again.
It is the slowest signal a small-harbour man is likely to track. It does not, in any given year, mean a flood that wouldn't otherwise have come. It means, instead, that on the worst weeks of every year, the water sits a finger's width higher than it once did.
That finger's width is the difference, sometimes, between a wet quay and a dry one. Between a flooded cellar and an inconvenient puddle. Between needing the bilge pump and not.
Padraig Fitzgerald does not own a bilge pump. He owns a harbour wall and a notebook, and he expects the notebook will outlast him.
