The highest daily mean sea levels recorded at the Honolulu Harbor tide gauge occurred during September 2003. Examination of tide gauge, satellite altimeter, and hydrographic measurements in the region indicate that the extreme event was largely due to an anticyclonic eddy with offshore amplitude of about 15 cm and a diameter of 300 km. The eddy propagated from approximately 3,000 km to the east over a one- to two-year period. Although eddies of this size are not uncommon at Hawaii, the September 2003 sea level was extreme because the eddy coincided with high periods in both the seasonal and decadal cycles, and because sea level at Honolulu has been rising at ~1.5 cm/decade for the past century. This long-term trend has increased the impact of short-term events on coastal sea level. Prediction of such events requires real-time altimeter data and improved modeling near Hawaii.