Bulgaria's weather institute NIMH has warned on its website of heavy rain and issued a yellow code for 18 provinces in western and central Bulgaria.
The code covers all of Haskovo, Kardzhali, Vidin, Montana, Vratsa, Pleven, Lovech, Gabrovo, Sofia city, Sofia province, Pernik, Kyustendil, Blagoevgrad, Pazardzhik, Plovdiv and Smolyan provinces.
In Veliko Tarnovo and Stara Zagora, it covers only some municipalities.
The institute forecasts that in places in western and central Bulgaria the rain will be heavy, with thunder. Winds from the east will be moderate to strong.
Lows will be between 6C and 11C, and highs mostly between 10C and 15C. Temperatures will change little during the day. In Sofia, the low will be about 7C and the high about 9C.