Unexpected rip currents induced by a meteotsunami in Lake Michigan

Session: Physical Processes in Lakes (1)

Alvaro Linares, UW Madison, [email protected]
Chin Wu, University of Wisconsin-Madison, [email protected]
Adam Bechle, Wisconsin Sea Grant, [email protected]
Eric Anderson, NOAA/GLERL, [email protected]
David Kristovich, Illinois State Water Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, [email protected]

Abstract

Rip currents are narrow, rapid seaward flows that can sweep swimmers to open water. In the Great Lakes, meteotsunamis (meteorological tsunamis), caused by moving atmospheric disturbances, or seiches, caused by transient wind forcings, can create conditions favorable to rip currents. In this talk, we will report a tragic drowning event occurred along southeastern beaches of Lake Michigan on a sunny and calm July 4, 2003, hours after a fast-moving convective storm had crossed the lake. Data forensics indicates that a moderate-height (~ 0.3 m) meteotsunami was generated by the fast-moving storm impacting the eastern coast of the lake. Detailed Nearshore Area (DNA) modeling forensics on a high-resolution spatial O(1m) grid reveals that the meteotsunami wave generated unexpected rip currents, changing the nearshore condition from calm to hazardous in just a few minutes and lasting for several hours after the storm. Cross-comparison of rip current incidents and meteotsunami occurrence databases suggests that meteotsunamis present severe water safety hazards and high risks, more frequently than previously recognized. Overall, meteorological tsunamis are revealed as a new generation mechanism of rip currents, thus posing an unexpected beach hazard that, to date,has been ignored.