Rip Current Observation and Prediction - MDL
Introduction
Rip Currents are powerful, channeled currents of water flowing away from shore. They typically extend from the shoreline, through the surf zone, and past the line of breaking waves. Rip currents can be generated by various mechanisms on any beaches with breaking waves, including beaches on open oceans, the Great Lakes, and bays.
As waves travel from deep to shallow water, they eventually break near the shoreline. As waves break, they generate currents that flow in both the offshore (away from the coast) and alongshore directions. This offshore or seaward flow of water can be as fast as 2 meters per second.
Rip Current Observations
The MDL Decision Support Division (DSD) works with National Weather Service offices and local lifeguard agencies to observe and report rip current conditions. This information allows for validation of existing rip current models -- in particular, the operational model running in the Nearshore Wave Prediction System (NWPS) -- and development of new ones, specifically MDL's Rip Current Model Output Statistics (RCMOS) model. The form below is typical of those provided by MDL DSD to local lifeguards.
Rip Current Prediction.
MDL DSD developed the Rip Current Model Output Statistics (RCMOS) model using NWPS forecast data (predictors) and lifeguard observation data (predictand) to provide locally and seasonally developed RC forecasts. Using real-time input data from the NWPS, the RCMOS model issues real-time probabilistic and deterministic hourly rip current forecasts, out to 144 hours. RCMOS currently provides experimental guidance for eight NWS Weather Forecast Offices (WFOs).
Below is a sample time series display of RCMOS hourly and daily mean & maximum forecast guidance. The guidance provides threshold probability values for moderate and high risk (indicated in the display by solid horizontal lines). Colors indicate low, moderate, and high risk.
MDL has computed verification scores for each RCMOS location. Adjacent is an example of a verification result for RCMOS probability forecast guidance. The Reliability Diagrams (both in warm and cools seasons) show that RCMOS verification values are close to the Perfect Score line. The Brier Skill Scores indicate that RCMOS made an improvement over the sample climate, also in both warm and cool seasons.
RCMOS Guidance Availability
The text-formatted "experimental" real-time RCMOS forecast guidance is available to anyone in NOAA (link here) and the graphical products are available to participating WFOs who have signed MOUs with MDL to join a demonstration to evaluate MDL's prototype RCMOS guidance (please contact Michael Churma at Michael.Churma@noaa.gov for information about how to join the demonstration).
RCMOS Feedback
The MDL RCMOS demonstration performed during July 1 - September 30, 2022 received very positive feedback from the 5 participating WFOs (i.e., overall, very satisfied (71%) and somewhat satisfied (29%)) in the surveys on the MDL real-time RCMOS forecast guidance. In 2024, the NWS Office of Science, Technology, and Integration (OSTI)'s Social, Behavioral, and Economic Sciences (SBES) team conducted focus group interviews for the RCMOS demonstrations performed since 2022. This also resulted in very positive feedback and comments from the 7 participating WFOs (the 8th WFO was added subsequently):
- RCMOS increased confidence
- Added confidence to forecasts of rip currents
- RCMOS has reduced workload for them
- Used RCMOS to fine-tune surf zone forecasts
- Increased speed of forecasts
- Greatly improved situational awareness
- RCMOS is more accurate
- Text in AWIPS really helps
- Graphical outputs are very helpful for a quick look
- RCMOS very helpful in long-term forecasts
- RCMOS has proved to be invaluable
- Absolutely wonderful tool
- Great for outreach efforts – if they can use outputs
Additional NOAA Rip Current Resources
For more information on NOAA rip current resources, please see the NOAA Rip Current Page
MDL Rip Current Resources
For further information about MDL's Rip Current Observation and Prediction activities, please contact Michael.Churma@noaa.gov and Jung-Sun.Im@noaa.gov.