Dangerous Currents on the Great LakesJuly 14th, 2014 at 9:20 pm by Bill Steffen under Bill's Blog, News, Weather
The National Weather Service has issued a Beach Hazards Statement for Tuesday. The Statement warns of high waves, dangerous swimming conditions and strong currents. There is a danger of longshore currents, rip currents and especially structural currents. Click on the graphic to enlarge. This is an overhead view of Grand Haven State Park. Structural currents occur along the breakwaters of the Great Lakes. What we often call piers are actually breakwaters. Technically, piers allow water to flow underneath them. Breakwaters stop the water and are often along river outlets to prevent sand from filling in the channels. Structural currents are not a factor on calm days, but can be deadly on windy days. When the wind pushes the water into a breakwater, the water has no place to go. It can’t go up on the beach, or up or down. So a current is created that moves along the breakwater out toward open water. With a brisk south or southwest wind the dangerous structural current is on the south side of the breakwater (Grand Haven St. Park). With a northwest wind (which will be the case on Tuesday), the dangerous current is on the north side of the breakwater ( North Beach in S. Haven, Holland St. Park, Muskegon St. Park, Mears St. Park, Stearns Park in Ludington). The most dangerous place in the entire Great Lakes is the south side of the breakwater at Grand Haven. It’s more of an issue when a strong south to southwest wind because the air tends to be warmer and more people are in the water. On days with a strong north wind like Tuesday, the air is usually colder and fewer people are in the water. Look at the picture here – it’s best to swim well off to the right (south) away from the breakwater, especially on windy days or days with significant waves. Most of the fatalities in the Great Lakes due to currents are on days when waves are 2-5 feet. Waves on Tuesday are expected to be 2-5 feet.
There is always a chance of a waterspout when you have cold air coming over warm water. This is most common from September into early November. This year, the Great Lakes are colder than average due to both the cool spring and the cool temperatures this July (for the first two weeks of July, Muskegon is 3.7° colder than average and Manistee is a whopping 6.6° colder than average). Waterspouts are weaker than most tornadoes and tend to dissipate as they come into shore.