According to the Portuguese Institute of Sea and Atmosphere (IPMA), most mainland districts will be under yellow warning today as well as on Tuesday, with the exception of Viseu, Bragança, Porto, Viana do Castelo, Aveiro, Coimbra and Braga, where they will be under yellow warning until Wednesday.
Additionally, the Western (Flores and Corvo) and Central (São Jorge, Terceira, Faial, Pico and Graciosa) groups of the Azores are under yellow warning until 9pm today.
The yellow warning is issued by IPMA whenever there is a risk situation for certain activities depending on the weather situation.
According to IPMA, at the origin of these warnings are the "lines of instability" associated with the extratropical cyclone Danielle, which will lead to heavy precipitation accompanied by thunderstorms and strong gusts of wind on the west coast, gradually evolving to the East.
This precipitation scenario is expected to continue throughout the week, although with lower amounts of accumulated precipitation from Wednesday.
The IPMA expects "precipitation and sometimes heavy rain, accompanied by thunderstorms" and the possibility of significant water accumulation "in short periods and strong winds, especially in the regions of the North, Centre and between the districts of Lisbon and Setúbal."
In coastal areas, is expected a "west/northwest swell, during the day today with a significant height up to 3.5 meters, especially on the West Coast of the Southern region during the night of the 12th and 13th of September.
Civil Protection warns that "special attention should be paid to areas identified as vulnerable to flooding and in particular in unregulated and fast-flowing watersheds".
To prevent accidents, the population is asked to pay special attention to structures that may come loose in the wind, to the possibility of falling trees, and to be careful if staying near the coastline and riverside areas.
Civil Protection also asks to ensure the unblocking of rainwater drainage systems and the adoption of cautious driving on the roads due to the formation of sheets of water and the "possible accumulation of snow" in some areas.