onda de calor
Published 6 November 2026, 09:07
onda de calor — a heatwave as defined by IPMA
Six days in a row when the daytime maximum temperature is at least 5 degrees above the long-term average for that place and time of year. It is measured against the local norm, not a round number: 35 degrees in Lisbon in September fits the rule, but the same 35 in July does not.
Where you come across it. IPMA reports and weather news, notices from schools and about outdoor work, health service warnings.
A heatwave and a yellow warning are different things: warnings are issued by district and by the hour, while a heatwave is declared under the six-day rule, often after the fact. Neither tells you about fire risk — that has its own scale, perigo de incêndio rural.
Official website: ipma.pt/pt/oclima/ondas.calor