Tropical night  A tropical night is a term used in United Kingdom and some other European countries to describe days when the temperature does not fall under 20 °C during the night time. This definition is in use in many European countries, such as United Kingdom, Spain, Sweden, Norway, the Netherlands, Germany, Finland and Latvia. The Met Office began tracking 'tropical nights' in 2018. This criterion is infrequently met at the moment, with the 30 years between 1961 and 1990 seeing just eight tropical nights. In the 10 years between 2008 and 2017, there were four such nights, and in 2018 there were two warm nights that stayed above 20 °C.