There have been 15 heatstroke deaths of children left in hot cars in 2019. And it's not even July.

There have been 15 heatstroke deaths of children left in hot cars in 2019. And it's not even July.

Fifteen children have died from heatstroke in the USA this year as a result of being left in hot cars – and it's not even July.

Three of the deaths occurred since last Saturday, and extreme heat is likely in the South and parts of the Midwest on Sunday heading into the Fourth of July.

The latest hot car death came Thursday evening in Morristown, Tennessee, when a 3-year-old boy was found in a minivan after he had been reported missing since 4 p.m. The temperature had reached 90 degrees.

"Officers found the child deceased on the floorboard of a minivan that was parked on the property," the city of Morristown wrote in a statement on Facebook. "Investigators believe, at this time, the child entered the vehicle without anyone knowing and became trapped."

Morristown police spokeswoman Michelle Jones said authorities "do not have any evidence of foul play at this time. It appears to be a tragic accident."

More: 3-year-old boy found dead in minivan in Morristown

On average, 38 children under the age of 15 die each year after being left in cars during hot weather, which turns the vehicle into a virtual oven.

Temperatures can soar to 120 or 130 degrees even when the outdoor temperature is only in the 80s. The body's natural cooling methods, such as sweating, begin to shut down once the core body temperature reaches 104 degrees. Death can occur at 107 degrees.

More than 800 children have died in hot cars since 1998.

The requirement for children to sit in back seats after juvenile deaths from air bags peaked contributed to the climb since children are more easily forgotten in the back seat than the front.

The annual number has increased each year since 2016, when 39 children died from heatstroke in hot cars. In 2017, there were 43 deaths, and in 2018, there were 52, the highest recorded.

Figures, cited by the National Safety Council, are compiled by Jan Null, a meteorologist with the Department of Meteorology and Climate Science at San Jose State University who has tracked U.S. child vehicular heatstroke deaths since 1998.

Safety experts recommend parents always lock car doors and consider putting something in the back seat, such as a purse, near a child's car seat. There are also car seat monitors and various apps such as Kars 4 Kids Safety that can be programmed for reminders.

On June 22, a 1-year-old boy died after being left inside a hot car in Galveston, Texas, for about five hours in a parking lot of a restaurant where his father was working.

Tot dies: 1-year-old boy dies in Texas after being left in hot car, police say; 13th death nationally in 2019

A parent left the child in the family's Chevrolet Tahoe before work at 11 a.m., the Galveston Police Department told the Houston Chronicle. When the parent returned around 4 p.m., the boy was unresponsive.

The temperature reached a high of 92 in Galveston that day. Experts said the air temperature in the truck probably exceeded 135 degrees.

No one has been charged in either the Texas or Tennessee deaths.

The Galveston death was the third hot car death in three consecutive days in Texas after a 4-year-old boy and an 11-month-old girl in other parts of the state died after being left in sweltering vehicles. Texas records more heatstroke car deaths than any other state.

800 deaths: In the past 20 years, 800 children died while trapped inside oven-like cars

Contributing: Doyle Rice

This article originally appeared on USA TODAY: Hot car deaths: 15 children have died of heatstroke in 2019