Shonan seasonal overview
Best Surf Season (October - March)
The core of the surf year at Shonan comes when the Pacific storm track and the Siberian High start flexing their muscles. From October through March, strong offshore N-NNE winds blow down the coast, grooming the south-facing beaches while low pressure systems spinning up in the East China Sea and western Pacific send S, SSE and SSW swell into Sagami Bay. Average wave heights sit around 2.3-2.6ft (0.7-0.8m) with periods in the 7.8-8.7s range, and the ideal-wind count peaks near 20% in October. It is not Hawaii-sized, but the combination of clean texture, punchy period and south-quadrant swell makes this the most consistent window for quality surf. Water temperatures drop from the low 20s to the mid-teens Celsius, so a full wetsuit is in order.
Fair Surf Season (April and September)
April and September are the bridge months. In April, the south swell train is already firing -- SSE, S and SSW make up the bulk of the energy -- but the offshore winter wind is fading, and onshore SSW/SW flow starts to dominate. September is the mirror image: the ocean is still warm from summer and typhoon season injects longer-period southern energy, while the first autumn N-NNE offshore winds restore clean surfaces. Both months can deliver excellent days, but they require more patience and a close eye on the weather maps.
Low Surf Season (May - August)
May through August is Shonan's low season. The swell direction is actually excellent -- S, SSE and SSW dominate -- but the summer monsoon and daily sea breeze blow directly onshore from the same south/southwest quadrant, turning the waves into soft, lumpy, choppy lines. Average heights remain around 2.3ft (0.7m), periods hover in the 7.8-9.3s range, and ideal offshore wind drops to 13-16%. Water temperatures warm from 19C to 27C, but the surf quality is largely limited to groveling conditions on a log or funboard.