How to read the table
Each card is one calendar day in Irish local time. High water is marked with a triangle pointing up, low water with a triangle pointing down. The height beside each time is the predicted level in metres above Ordnance Datum Malin, the same datum used on Irish Ordnance Survey maps. A bigger number means more water over the sand, the slip or the rocks.
Most days have two highs and two lows. Every so often a day has only three events. That is normal: the tidal cycle is about 12 hours 25 minutes long, so one high or low slips over midnight into the next day.
The clock runs on Europe/Dublin time, so the tables already account for the change to and from summer time. You never need to add or subtract an hour.
Spring tides and neap tides
Around full moon and new moon the sun and moon pull together and the tide swings furthest: very high highs and very low lows. These are spring tides, and they arrive roughly every two weeks all year round, nothing to do with the season. At the quarter moons the range shrinks and you get neap tides, when the water barely moves off the beach.
You can spot springs in the tables without a calendar. Look for the days where the gap between high and low is largest. Those are the mornings when the widest strand appears at low water, and the evenings when the sea comes right up to the wall.
The largest springs of the year, around the March and September equinoxes, are the ones that flood car parks and coastal roads if they coincide with an onshore gale.
Why weather changes the real level
These predictions only account for the moon and the sun. Air pressure and wind are ignored, because nobody can forecast them weeks ahead. A deep Atlantic low can lift the sea by 30 to 50 cm (a positive surge) and a strong onshore wind piles water against the coast on top of that. High pressure and offshore winds do the opposite.
In practice the times are very reliable and the heights are reliable in settled weather. In a storm, treat the predicted high water as a floor rather than a ceiling, and add the surge that Met Éireann mentions in the sea area forecast.
Best times for swimming, walking and fishing
Swimmers on a shelving beach usually want the hour either side of high water, when the water is deep close in and you are not wading out over 100 m of sand. At steep-to spots such as harbour steps or the Forty Foot, mid tide to high tide is safest because the ladder still reaches the water.
Walkers, rock poolers and dog owners want low water. Aim to arrive an hour before the predicted low, which gives you two hours of falling and slack water before the flood starts to come back in. On sand flats and around tidal islands the flood can return faster than walking pace, so know your low water time before you set off.
Shore anglers generally fish the last two hours of the flood and the first hour of the ebb. Boat owners need the height as much as the time: a slip that dries at 1.0 m is unusable at a 0.6 m low.