August 21
- 1521 – The earliest documented tornado in the Americas struck Tlatelolco near Tenochtitlan, now Mexico City, during the final days of the Fall of Tenochtitlan.
- 1883 – A devastating F5 tornado hit Rochester, Minnesota, killing at least 37. Many others were seriously injured and may have died later. More than 135 homes in Rochester were destroyed and at least 10 farms outside of town were leveled.
- 1918 – An F4 tornado destroyed much of Tyler, Minnesota, killing 36 people, and damaging or destroying about 600 homes and businesses.