Recorded presentation2.1
Rip Currents: An Underrated Hazard
Steven R. Pfaff, NOAA/NWS, Wilmington, NC
Rip currents are a global hazard that can occur anywhere breaking waves exist along a coastline. In the United States, rip currents rank in the top three of all weather related fatalities, and are the leading hazard in the Carolinas. In fact, between 2000 and 2007, rip currents were responsible for 40% of all weather related deaths in the Carolinas.
Rip currents are generated by pressure gradient variations in the surf zone that are a result of persistent onshore synoptic-scale flow and/or long period swell conditions from large offshore cyclones. Their intensity can be modulated by tides, especially within two to three days of a full or new moon. The primary danger of these currents is their flow away from the beach at speeds that can exceed 2.5 m s-1, or faster than the pace of an Olympic swimmer.
These currents pose a challenge to public safety and awareness because they are difficult to identify, and often encountered by people with very little knowledge of rip current. Typically, the most significant rip current events (those events with multiple fatalities) occur during benign weather conditions along the shore., adding to the challenge of heightening public awareness.
In order to reduce rip current-related fatalities, National Weather Service Forecast Offices (WFOs) have developed forecasting techniques to identify those days when rip currents are expected to become strong. These empirical schemes must be adapted locally, due to differences in local conditions that have bearing on rip current development and intensity, including beach slope, bathymetry, sediment type, and orientation of the coastline. Also, local and national educational outreach programs have been developed to promote rip current awareness.
Although the National Weather Service faces challenges with the refinement of rip current forecast techniques and increasing public awareness, significant strides have been made in recent years.. Rip current schemes continue to be enhanced through feedback and verification from coastal engineers and lifeguards, the deployment of additional real-time wave gauges and development of operational near-shore wave models.
Session 2, High Impact Marine Events
Tuesday, 13 January 2009, 11:00 AM-12:00 PM, Room 230
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