An area of low pressure that formed over the western part of Europe over the weekend has shifted southeastward and has now settled over the Adriatic Sea.
The circulation is expected to linger at least through Thursday which will mean the Balkan countries, as well as Italy, will see days of rain and likely flooding.
The storm has already brought significant amounts of rain to the region. In Croatia, the city of Ogulin picked up 93.7 millimetres in just 24 hours, almost its monthly May average.
Bihac, in Bosnia, registered 84.2mm of rain.
Along with the rain, there have been damaging winds that have brought down trees and power lines in the Croatian capital of Zagreb. Overnight Sunday and into early Monday, winds gusted to over 80 kilometres per hour. Further south in the city of Split, winds reached just over 86 km/h.
The heavy rain in Croatia has also caused the Puhar River to flood into the neighbouring communities of Prijedor, damaging homes and business.
More heavy rain is likely in coming days and that means flooding and flash flooding likely along the eastern coast of Italy and the higher elevations of Croatia, Serbia and Bosnia. Another 150mm of rain is expected in the next three days.
Severe thunderstorms will also bring another threat to the region. On Monday, more storms will move through and bring strong damaging winds, but the countries along the eastern Adriatic could see the risk of tornadoes.
The unsettled weather is expected to continue through Thursday before the storm weakens and finally begins to move to the east.