Sicily

Sicily is the largest island in the Mediterranean — a triangle of terrain at the toe of Italy's boot, separated from Calabria by the Strait of Messina, fronting three different seas: the Tyrrhenian to the north, the Mediterranean proper to the south, and the Ionian to the east. The tidal regime across most of Sicily is Mediterranean microtidal: mean range at Palermo on the Tyrrhenian coast runs around 0.1 to 0.3 metres, with the signal so small that meteorological forcing routinely exceeds the astronomical tide. The exception is the Strait of Messina — a 3-kilometre-wide channel with a shallow sill where the Tyrrhenian and Ionian tidal systems, which are slightly out of phase, drive strong tidal currents on every cycle. Despite the negligible tidal range visible at any single point in the strait, the small phase difference between the two basins either side creates current velocities that can reach 3 to 4 knots on the spring ebb through the narrowest section, and the hydraulic roughness of the sill generates the upwelling eddies and whirlpools that were the original basis for the Charybdis mythology in Homer's Odyssey. The whirlpools are real; the 6-metre sea monster less so. The strait's ferry crossing (Villa San Giovanni on the Calabria side to Messina on the Sicily side) is one of the busiest short sea crossings in Europe, and the current through the strait is a real operational consideration for the ferries and for vessels transiting north-south along the Italian coast. North of Palermo, the Tyrrhenian Sea opens to Sardinia and the Ligurian Sea; to the south the African coast at Tunisia is just 145 kilometres away, and the Sicily Channel carries all east-west Mediterranean traffic between the two basins. Mondello, the city beach 11 kilometres northwest of Palermo in a sheltered bay between Monte Pellegrino and Capo Gallo, is the practical beach for Palermo residents — a wide sand beach inside a protected bay where the microtidal signal barely registers against the wind and sea-state variation. The ISPRA Italian national tide gauge network covers Sicily with gauges at Palermo and Catania; the Strait of Messina tidal current station is one of the few Mediterranean sites where current data, not just height, is operationally published.