2013 Swim Season: Great Lakes Current Incident Summary
Totals through 9/25/2013
An archive of incidents caused by rip currents, structural currents, outlet currents, and channel currents on the Great Lakes
The number of current related rescues and drowning fatalities for summer 2013 fell below the Great Lakes average of 12 fatalities and 26 rescues per year (2002-2012), with 7 fatalities and 14 rescues at least partially attributed to dangerous currents. Cool summer air temperatures and below average water temperatures likely kept most swimmers from venturing too far into the water, especially on high-swim risk days with northerly winds (waves are bigger and currents are stronger, yet temperatures are often cooler).
Figure 1. Number of current related incidents 2002-2013. The years highlighted in red boxes each had 1 day where over 20 people were rescued. This skews the data, making it seem like the number of incidents is increasing with each year. General reporting of the incidents increased after 2005, when the NWS launched the rip current outreach campaign. Data also varies widely from year to year because the number of current related incidents depends on tourism, air and water temperatures, the number of moderate-high risk days, and even the number of cloudy vs sunny days. (GLCID, 2013).
Figure 2. A majority of current related incidents occured on Lake Michigan in 2013 (GLCID, 2013)
Current related incidents on the Great Lakes most often occur from late July into early August, as water temperatures, air temperatures, and tourism are at their peak. On Lake Michigan, where most current related incidents on the Great Lakes occur (Figure 2), water temperatures were several degrees below normal for this time frame (Figure 3).
Figure 3. 2013 Lake Michigan Water Temperatures vs. 1992-2012 normal (GLERL, 2013).
Additionally, air temperatures for July-August were below normal for the Great Lakes. In southwestern Lower Michigan, where a majority of the current related incidents occur, 2013 was the coldest summer since 2009 (See the NWS Grand Rapids Summer Climate Summary). This can be seen in the data as well (Figure 1), with drowning fatalities and rescues at lows during those two years (with the exception of one high-rescue day in August 2009, which increases the number of rescues by 23).
Type of Current
As is typical, a majority of the 2013 incidents on the Great Lakes were related to structural currents. These dangerous currents form near shoreline structures like piers, breakwalls, and peninsulas. For more information on the different types of currents on the Great Lakes, visit the main menu.
Figure 4. All incidents in the GLCID were classified as either structural, classic rip , outlet, or channel currents. Incidents where it was not known where the victim was swimming at the time of the incident were classified as a combination (e.g. structural/classic would be a beach with a shoreline structure and properties of an intermediate beach type/sandbars). (GLCID, 2013)
Weather and Wave Conditions Observed During Current Related Incidents
Dangerous currents typically develop once waves reach 3-5 feet, except near shoreline structures or river mouths, where currents can be present at any time. In 2013, all but one incident occurred during wave heights of 3 feet or greater. The one incident where wave heights were less than 2 feet occurred near a shoreline structure. The National Weather Service had a high swim risk in effect with a Beach Hazards Statement during all of the 2013 incidents where applicable (some Great Lakes office's do not issue these products).
Figure 5. Wave heights observed during current related incidents in 2013 (GLCID, 2013)
Generally, classic rip currents are most likely when moderate to large waves approach the shoreline at a near-normal angle (near perpendicular). Structural currents, however, are more likely when waves approach the shoreline at more oblique angles to shore (45 degree angle is best).This trend was supported by the 2002-2013 GLCID data, seen in Figure 6. A majority of the incidents on the Great Lakes are due to shoreline structures, so one would expect a majority of the incidents to occur as waves approach the shoreline at an oblique angle.
Figure 6: A majority of the incidents in 2013 occurred when the wave direction was at a near normal angle to shore (represented by 60-90 degreess). The remainder of the incidents in 2013 occurred under more oblique wave incidence angles (0 to 59 degrees relative to shore). Data from the GLCID, 2013.
Wave periods (the time between each passing wave) during current related incidents on the Great Lakes typically fall between 4 and 5 seconds, which is classified as a "short period." Current-related incidents on the ocean are most often observed with longer wave periods, generally greater than 9 seconds. Short period waves add an additional hazard to swimmers, especially those caught in currents. Moderate to large waves crashing into the swimmer every 4 to 5 seconds can prevent them from completing the typical rip current-escape methods, like "flip, float, and follow" or "Swim parallel to shore." The shorter wave periods also create a more disorganized wave field, making rip currents tougher to spot on the Great Lakes (versus the ocean). In 2013, a majority of the current related incidents occurred with wave periods of 6 to 7 seconds.
Figure 7. Wave periods observed during current related incidents in 2013 (GLCID, 2013)
Wind speed is an indirect factor in current development. Depending on the direction, strength, and longevity of the winds over the Great Lakes, moderate to high waves can be generated. When the waves approach the shoreline, they can lead to dangerous currents. Wind speeds during current related incidents in 2013 were primarily in the 10-20 mph range or greater. Only one incident in 2013 occurred with winds in the 0-10 mph category-and it was near a shoreline structure. Again, even when conditions appear benign, swimming near shoreline structures or river mouths is hazardous as currents exist with these features all the time.
Figure 8. Wind speeds observed during current related incidents in 2013 (GLCID, 2013)
2013 Victim Demographics:
As is typical of beach fatalities on the ocean and the Great Lakes, 52% of the victims were male and 33% were female. For 14% of the incidents, the gender of the victims was not known. The average age of the victims was 22 years old (only 11/21 cases had age information), and they lived an average of 35 miles from the location of the incident (only 12/21 of the cases had hometown information).
Case Study, 2013: Factors Come Together for a High Swim Risk Day
Late July into early August is when current related incidents on the Great Lakes peak, mainly due to the combination of warm water temperatures, warm air temperatures, and the high number of vacationers. July 19th was the perfect set up for high swim risk conditions, with water temperatures on Lake Michigan in the 70s and air temperatures along the western Michigan coastline in the 80s. By mid afternoon, a cold front was situated just west of Lake Michigan, so winds over the lake were out of the south-southwest. Waves that day were 3 to 6 feet, also out of the south-southwest, with a wave period of 6 seconds. South-southwest wind/wave directions typically lead to the development of a strong longshore current on the eastern shores of Lake Michigan, which can intersect a breakwall and move lakeward as a structural current. Though structural currents are the most likely of the beach hazards on the eastern Lake Michigan shoreline during south-southwesterly winds, classic rip currents are also possible. Typically, classic rip currents form under shore-normal wave incidence (at a 60-90 degree angle from shore) but they can also form under more oblique incidence (0-59 degrees), which makes the rip current circulations more diagonal (versus moving directly outward from shore). As a result, the National Weather Service in Grand Rapids, Michigan issued a Beach Hazards Statement (around 4 am the 19th), citing that waves would be high, structural currents would form on the south sides of breakwalls, and classic rip currents were possible. Overall, the swim risk was high, and people were encouraged to steer clear from the lake.
Figure 9. Surface map from the Weather Prediction Center at 2:00 PM EDT on July 19, 2013, just prior to the first set of incidents. The times surrounding the passage of a cold front are responsible for a majority of current related incidents on the Great Lakes (GLCID, 2013).
Around 3 pm EDT, six people had to be rescued from classic rip currents off Stearns State Park, near Ludington, Michigan (Figure 9). Surfers at the beach made several observations of rip currents that afternoon. They reported that the rip currents were developing after larger sets of waves, moving offshore at an angle, primarily towards the northwest. They also reported a strong longshore current. After two hours of prime surf time, they heard the cry of struggling swimmers within the swimming area at Stearns Park. Luckily, despite the strong currents and waves, they were able to rescue them.
Figure 10. Stearns State Park, Mason County, MI. Images from Google, 2013. Note the complex sandbars, the darker areas representing old rip current channels. The swimmers were rescued at the northern end of the designated swim area (away from the breakwall to the south).
Later that evening, around 7:30 PM EDT two additional incidents occurred. Two sisters were swimming near the south side of the breakwall at Pere Marquette Park in Muskegon, Michigan when they were caught in a structural current. The younger sister recounted, "we weren't too far from shore when the current began to pull us out further into the lake. We both began to struggle and began grabbing onto each other before being separated." The young girl then told authorities that she lost sight of her sister as she struggled in the waves. Luckily, the younger sister was rescued by a 20 year old woman. Unfortunately, her sister wasn't recovered until the 21st of July.
Figure 11. Pere Marquette Park, Muskegon Michigan. Images from Google, 2013. The victims in this case were swimming on the south side of the breakwall when they were caught in a structural current.
This data was collected by the National Weather Service in Marquette, Michigan. All incidents in the database were at least partially due to a dangerous current. Many of the incidents are likely a combination of currents and high, short period waves. All readers are encouraged to read about how the data is collected here. These numbers must be viewed relative to the number of people that visit these beaches each year, which is on the order of millions.
Rip current development references: HERE