Croatia, Slovenia: Adverse weather forecast across much of both countries through at least Sept. 13

Severe weather is forecast across much of Croatia and Slovenia through at least Sept. 13. Thunderstorms are forecast to break out across northwestern Slovenia late Sept. 11 before spreading across the region over the coming days; heavy rainfall, strong wind gusts, lightning, and possible hail may accompany the storms. Heavy downpours may cause flooding in low-lying areas, and strong winds could cause property damage and power outages.

As of Sept. 11, Croatia's Meteorological and Hydrological Service has issued orange thunderstorm warnings (the middle level on a three-tier scale) across Rijeka Region and yellow thunderstorm warnings across the rest of the country Sept. 12. Yellow heavy rainfall warnings are in place for Gospic, Knin, Rijeka, and Split regions and yellow strong wind warnings for Dubrovnik, Rijeka, and Split regions.

The Slovenia Environment Agency has issued yellow thunderstorm warnings across northwestern regions Sept. 11 and orange rainfall, yellow thunderstorm, and yellow strong wind warnings across the country Sept. 12. Orange rainfall warnings remain in place for central, northeastern, and southeastern regions Sept. 13, as well as yellow strong wind warnings for northeastern, northwestern, and southwestern regions.

Officials could update and extend the coverage of the weather alerts over the coming hours and days.

The storms could produce rounds of heavy rainfall, strong winds, and isolated thunderstorm activity across the affected areas. Sustained heavy rainfall could trigger flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed stormwater drainage systems. Sites located downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Landslides are possible in hilly or mountainous areas, especially where heavy rain has saturated the soil.

Authorities could issue mandatory evacuation orders for flood-prone communities over the coming days. Where significant flooding, landslides, or strong winds impact utility networks, disruptions to electricity and telecommunications services are possible.

Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters. Strong winds might also pose a hazard to high-profile vehicles.

Severe weather could also trigger flight delays and cancellations at airports across the affected areas. Authorities may temporarily suspend port operations or close beach fronts along the Adriatic coast if strong winds trigger hazardous sea conditions. Flooding could block regional rail lines; freight and passenger train delays and cancellations are possible in areas with heavy rainfall and potential track inundation.

Localized business disruptions may occur in low-lying areas; some businesses might not operate at full capacity because of flood damage to facilities, possible evacuations, and some employees' inability to reach work sites.