HF RADAR observations of coastal currents induced by the 29-30 September 2009 tsunami South of O’ahu

A High-Frequency RADAR collected radial current observations at 1.5 km resolution every 15 minutes along O’ahu’s South Shore. Following the arrival of the tsunami generated by the September 29 Samoan earthquake, radial currents fluctuations of up to 4 cm/s were recorded 25-35 km off shore. The bursts of shoreward surface current associated with the tsunami are located at the transition between deep and shallower water on Penguin Bank, a submerged bank extending westward from the Lanai-Molokai group. The RADAR currents and supporting sea level data from other sensors in the area, showed oscillations at a dominant period of 500 sec. excited by the tsunami, which persisted for more than 8 hours after the tsunami’s initial arrival.