Prevailing currents are mostly tidal in the Port and surrounding water areas, and rarely exceed four knots. Coastal and offshore conditions are influenced by prevailing seasonal winds.

A group of tide gauges, operated by different authorities, is located on Fort Hill Wharf, adjacent to the Darwin Port Office. Another gauge will be installed at the East Arm Port in due course. The highest astronomical tide is 25.9 ft (7.9 m) and local authorities state that these large tides enable deep drafts to be accommodated.

The strength of the tidal currents diminishes considerably near the entrance to the harbor, and the direction within the harbor usually corresponds with the direction of the channel. However, care must be taken to guard against the fact that the currents do not always run directly along the jetties, but may set towards or away from them. The currents in this area are considerably affected by heavy rains and by strong northwest or southeast winds.

Source: http://www.nrlmry.navy.mil/port_studies/thh-nc/australi/darwin/text/sect6.htm