Barometric pressure, or air pressure, is lowest at high altitudes. However, barometric pressure also varies according to the weather. The lowest barometric pressures have been recorded during strong tropical cyclones.
The lowest barometric pressure ever observed on earth occurred during Super Typhoon Tip in October 1979. This measurement was taken in open water near the Pacific island of Guam. A similarly low pressure occurred during Cyclone Monica in April 2006, in the Gulf of Carpentaria near Australia.
Sometimes very low barometric pressure occurs outside the tropics. In January 1993, scientists measured very low barometric pressure in the middle of a storm in the northern Atlantic ocean between Iceland and Scotland.