AUSTIN, Texas — No matter where you are this summer, it is likely you will feel the nasty brunt of the summer heat. 

A mean heatwave is gripping two-thirds of the country this weekend, bringing heat advisories and heat emergencies to nearly two million Americans. 

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KVUE

Some of America's most populated cities like Chicago, St. Louis, Columbus, Washington, D.C., Philadelphia, New York City and Boston will be bracing for what could be the hottest temperatures this year. Heat index values are expected to top the century mark and emergency officials are urging everyone to stay hydrated and to stay indoors during peak heat hours. 

One of the most ironic things that people are being alerted to right now is the possibility that while staying hydrated from the heat, our water bottles left behind in our vehicles could focus light to form a beam of heat, and ignite a spark to cause an interior car fire.

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Your car's outdoor temperature reading is usually wrong

So how does this happen? 

When light shines through our car windows, it hits the plastic bottle. The bottle acts like a magnifying glass and the water inside the bottle focuses the light and heat to one spot. If left lying on the seat for an extended period of time, that focused light gets hotter and can start a burn.

So make sure you either try to park in the shade or take those water bottles out of the car before heading inside.

Please also keep in mind that heat-related illness are a major killer with over 100 lives lost in 2018 alone. 

Here are the signs to look for: 

heatillness
KVUE

We already know the dangers of leaving children and pets behind in vehicles, but to leave our water bottles, something you would least expect right? 

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KVUE

Bear in mind how interior temperatures can spike inside your vehicle with a surface temperature of 95 degrees. For example, in 30 minutes it feels like 129 degrees. 

Our temperatures in the forecast ahead are expected to stay in the 90s with the best chance of rain early next week. 

7dayforecast
KVUE

WATCH: 'Look before you lock' Reminder to never leave kids alone in a hot car

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