The highest of all spring tides occurs at the time of—

Spring tides occur twice a month during the full moon and new moon phases when the Sun, Moon, and Earth align in a straight line (syzygy), combining their gravitational forces [3]. While spring tides happen regularly, their magnitude varies based on astronomical cycles. The highest of all spring tides, often referred to as equinoctial spring tides, occur when these moon phases coincide with the equinoxes. During the equinoxes (March and September), the Sun is directly over the equator, maximizing the solar tide-generating force on the Earth's equatorial bulge. When this alignment coincides with the moon's perigee (closest approach to Earth), it results in the maximum possible tidal range. Although solstices also influence tides, the solar semi-diurnal tide specifically peaks near the time of the equinox, leading to the highest annual tidal ranges.

Sources

1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 13: Movements of Ocean Water > Tides based on the Sun, Moon and the Earth Positions > p. 110
2. [3] https://oceanservice.noaa.gov/facts/springtide.html