Rip Currents and Rip Current Forecasting in New Jersey Tom Herrington Stevens-NJ Sea Grant Cooperative Extension in Coastal Processes LONG BRANCH, NEW JERSEY Lifeguard Symposium Friday July 15, 2006
Outline Rip Current Basics Rip Currents along Stabilized Coasts Outreach and Education Efforts Local Rip Current Prediction Efforts Local Resources
What is a Rip Current? Narrow seaward moving current of up to 3 knots Related to mass transfer of water trough the breaker zone
Fixed Four Types of Rips
Four Types of Rips Fixed Flash
Four Types of Rips Fixed Flash Traveling
Four Types of Rips Fixed Flash Traveling Permanent
Rip Current Generation Rip currents are fed by both variations in the alongshore and crossshore current inside the surf zone Currents in the surf zone are generated by variation in Wave Height across surf zone.
Flow in the Surf Zone is Very Complex! From Svendsen and Lorenz (1989)
Wave Setup in the Surf Zone is Key Parameter Svendsen, et al. (1987)
Cross-shore Current Forcing
Undertow If return flow at bottom ( undertow ) is always present then how come rip currents are not everywhere along the beach? Water seeks the path of least resistance to return offshore.
Flow through gaps in the sandbar system Hass, et al. (2000)
Water Depth over the Bar is also a key Parameter Constricts the volume of water that can flow over the bar. More flow forced into Rip Channel Intensifies the rip current/. Antidotal evidence points to more rescues during mid to low tide
Seasonal Variation of Dc
What about Stabilized Coasts?
Rip Current Formation between Groins Dean (1978)
Other Rip Current Headaches along Stabilized Coasts Notched or Porous Structures Beach Fill Impacts
Notched Groins
Current and Sediment Measurements Near Notched Groin
Measured Alongshore Current through Notched Groin Rankin, et al. (2003)
Beach Nourishment
Increases Beach Height as Well..
Transformation takes time How Long?
it depends
Developing Public Awareness Rip Currents are an unperceived threat: Appear relatively randomly Are typically around for only a short duration Appear to jump for location to location Hard to see from beach
National Outreach Initiative Spearheaded by NOAA (National Weather Service & Sea Grant) and the USLA. Recognition that rip currents generate the second highest weather related fatalities nationwide. Most fatalities occur when the beaches are not guarded Need for public education and improved forecasting!
Education & Outreach Works Steady decline in rip current related deaths in SE Florida since issuance of daily advisories in 1991by NWS. Awareness of rip current threat by public
What about After Hour Swimmers?
Passive Message How to identify rip currents What to do if caught in a rip current WHEN IN DOUBT, DON T GO OUT Message designed to be informative, not prohibitive Easy to understand graphics to reach young children and non-english speakers.
Marine Forecasts and Tidal Information from NWS
Surf Zone Forecast Issued Daily SURF ZONE FORECAST FOR NEW JERSEY AND DELAWARE NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 456 PM EDT THU JUL 14 2011.FOR THE BEACHES OF NEW JERSEY AND DELAWARE... DEZ004-NJZ014-024>026-152015- DELAWARE BEACHES-EASTERN MONMOUTH-ATLANTIC COASTAL CAPE MAY- COASTAL ATLANTIC-COASTAL OCEAN- 456 PM EDT THU JUL 14 2011 THE RIP CURRENT RISK FOR TOMORROW IS...LOW. WAVES IN THE SURF ZONE TODAY/TOMORROW WILL BE 2 TO 4 FEET. SURF TEMPERATURES ARE IN THE LOW TO MID 70S. A LOW RISK OF RIP CURRENTS IMPLIES THAT WIND AND WAVE CONDITIONS ARE NOT EXPECTED TO SUPPORT THE DEVELOPMENT OF ENHANCED RIP CURRENTS. HOWEVER, RIP CURRENTS ARE ALWAYS POSSIBLE, ESPECIALLY NEAR JETTIES AND OTHER STRUCTURES. http://www.erh.noaa.gov/er/phi/ripcurrent/getsrf.php#help_moderate
Rip Current Forecast Definitions Low Risk: Weather conditions are not likely to create strong rip currents. However, rip currents can occur at any time, especially near jetties, and piers. Always pay attention to lifeguards. Moderate Risk: There is a better chance of seeing strong rip currents given the expected weather. High Risk: Strong rip currents are likely given the expected weather. Rip currents are dangerous to anyone going swimming in the ocean. Photo courtesy of NWS Wilmington
Low/Moderate/High Risk Determination Sum of the elements: Wind Factor (onshore wind not associated with the seabreeze) Wave Factor (> 3 ft at buoy 44009) Period Factor ( 5 to 7 Sec) Tidal Factor (greater than normal variation between high and low tide levels, I.e. new moon or full moon) Collaboration (with adjoining NWS offices, local lifeguards) Day After Factor (rips often persist after swell subsides or wind changes)
Feedback Very Important Daily visual observations of surf zone conditions are need to improve forecasts Daily contact with the Mount Holly NWS forecast office allows for improved public rip current advisories Tabulation of rip current rescues allows for improvement in forecasting methods.
You are the most important link!
But which wave events are of most interest Extremely Large Wave Events April 18, 2003 Ocean City, NJ 44009: Hm0=4m, Tp =10 sec Surfer/Lifeguard drowned at this beach
Low energy Wave Events July 5, 2003 44009: Hm0=1m, Tp=6 sec Over 100 rescues along NJ coast
Tropical Cyclone Swells Hurricane Fabian Sept. 4, 2003 Surf City, LBI 44009: Hm0=1.75m, Tp=14 sec
Any wave event? June 5, 2005 Harvey Cedars, LBI LBI CMN: Hm0=0.6m, Tp=11 sec Man drowned after being pulled out next to groin
Contributing factors to rip currents: Swell Tides Onshore Wind
Analysis of Observed Rip Current Events In New Jersey Revealed 2 conditions: 1. Extreme waves (> 8 ft) with periods > 8 sec 2. Long-period swell of any height Rate of wave energy propagation to coast appears to be important P = nec
Rip Current Index In order to weight large swell higher than wind waves and smaller swell a Rip Current Index (RI) that is the ratio of swell energy flux to wind wave energy flux multiplied by the ratio of the wave height to water depth appears reasonable. H RI = 0.1* * h P P swell windwave
Evaluation of Rip Current Index Against known Events in 2003 July 4th Fabian Isabel Juan
U.S. Integrated Ocean Observing System (IOOS) Observing, Data Management, Modeling Regional Components NOAA-Led IOOS Components 1) International Component 2) National Component a) 17 Federal Agencies b) 11 Regional Associations
Regional Associations (RAs) Building IOOS Partnerships - 480 and Growing. National Federation of Regional Associations 11 IOOS Regional Associations Business and Industry (66) Shipping (18) Researchers and Universities (149) State agencies (59) NGOs (58) International Organizations (11) Local and Tribal Governments (8) Federal Agencies (106)
Phased Deployment and Operation of the Mid-Atlantic Regional Coastal Ocean Observing System (MARCOOS) 30 Co-PIs, 20 Institutions Investigator Affiliation Investigator Affiliation A. Allen U.S. Coast Guard L. Atkinson Old Dominion University A. F. Blumberg Stevens Institute of Technology W. Brown University of Massachusetts W. Boicourt University of Maryland M. Bruno Stevens Institute of Technology D. Chapman University of Delaware A. Cope NOAA Mount Holly WFO A.Gangopadhyay University of Massachusetts T. Herrington Stevens Institute of Technology D. Holloway OPeNDAP E. Howlett Applied Science Associates D. King University of Maryland J. Kohut Rutgers University B. Lipphardt University of Delaware A.MacDonald Monmouth University NWS WFOs Std Radar Sites Mesonet Stations LR HF Radar Sites Glider AUV Tracks USCG SLDMB Tracks NDBC Offshore Platforms CODAR Daily Average Currents J. McDonnell Rutgers University J. Moisan NASA Wallops J. O Donnell University of Connecticut M. Oliver Rutgers University O. Schofield Rutgers University H. Seim University of North Carolina J. Titlow WeatherFlow Inc. D. Ullman University of Rhode Island J. Wilkin Rutgers University R. Wilson SUNY, Stony Brook W. Wittman Public Service Electric & Gas M. Yarosh CIT A. Voros NY/NJ COAST S. Glenn Rutgers University
DATA and MODELING ASSETS
Compact CODAR HF Radars 5 MHz Receive Antenna Transmit Antenna 25 MHz and 13 MHz
MARCOOS
Sandy Hook testbed Algorithm Development - Wave Refraction - Shallow Water Dispersion Wave Validation - CODAR (All Freq. vs In Situ) -In Situ vs In Situ Nearshore Current Validation - CODAR (All Freq. vs In Situ) -In Situ vs In Situ
Wave Height Wave Period Wave Direction Breezy Point Average Standard Deviation 1.4 m 0.8 m 9.4 s 1.2 s 135 degrees 27 degrees Buoy 44025 Average Standard Deviation 1.5 m 0.7 m 8.1 s 2.2 s 138 degrees 39 degrees Far Field Wave Comparison (2006)
Advanced warning (24 hours) so lifeguards can prepare Real-time update to alert lifeguards of changing conditions and threat level User Needs NYHOPS Coastal Wave Model
Composite Data & Forecast Product + + Remote Sensing Model Forecast With Data Assimilation Data/model processing = High resolution hourly blended advisory product
What do you need? Photo courtesy of Dave Baker, Wrightsville Beach Ocean Rescue