The IPMA had previously placed the districts of Évora, Setúbal, Lisbon, Beja, Santarém, Faro and Portalegre under a yellow warning.
In a new statement, the institute extended the yellow warning to the districts of Viseu, Guarda, Leiria, Castelo Branco, Aveiro and Coimbra also due to the rain.
The districts of Évora, Setúbal, Lisbon and Beja will be under warning between 03:00 and 15:00 on Thursday, Santarém, Leiria and Portalegre between 06:00 and 15:00 and Faro between 12:00 and 6pm.
Viseu and Aveiro will be under a yellow warning between 03:00 and 12:00 and Guarda, Leiria and Coimbra between 06:00 and 12:00.
The IPMA also issued a yellow warning for the districts of Setúbal, Santarém, Lisbon and Leiria due to the forecast of strong winds from the southwest, with gusts of up to 70 kilometres per hour between 09:00 and 12:00 on Thursday.