Portugal’s weather service, IPMA (the Portuguese Institute for Sea and Atmosphere), published its seasonal forecast for November, December and January on October 20. All regions of the country are expected to experience above-average temperatures, with higher-than-usual rainfall in most areas.
On mainland Portugal, temperatures are expected to be 1–1.5°C above average in all three months. In November, rainfall is forecast to increase by 5–20 mm north of the Montejunto–Estrela mountain range, covering the north and central parts of the country. In December and January, precipitation is expected to be 5–15 mm above average per month across the entire mainland.
On Madeira, temperatures are forecast to be 0.5–1°C above average. Rainfall is expected to be close to normal in November and December, with an additional 5–10 mm in January.
In the Azores, temperatures are expected to be 0.5–1°C above average, except in December, when the difference is forecast to be 0.25–0.5°C. In November, rainfall is expected to increase by 5–10 mm on the western islands of Flores and Corvo. In December and January, precipitation is forecast to be 5–15 mm above average per month across the entire archipelago.
As Executive Digest points out, a seasonal forecast indicates probabilities and total monthly rainfall, not how precipitation will be distributed from day to day. The extra rainfall could come from frequent light showers or a few heavy downpours. Frost and snow are also possible, while these models cannot predict how many storms there will be or how severe they will be.
For day-to-day weather, it is best to check the short-range forecast on the IPMA website.
