Central America: Annual rainy season underway in Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama through Dec. 31 /update 1

The annual rainy season is underway across Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama through at least Dec. 31, bringing an elevated potential for flooding and landslides/mudslides across the region.

The onset of an El Nino phase of the El Nino Southern Oscillation (ENSO) is likely to have an impact on the 2023 rainy season. Typically, El Nino suppresses the rainy season to a certain extent, with drier-than-average spells likely across much of the region, especially along the Pacific coast. However, excessive rainfall is possible in areas on the Caribbean Sea coast, and periods of heavy rainfall are still possible at times throughout the region.

The risk of flooding is highest in low-lying communities near watercourses in recognized floodplains. Central America has several major rivers and lakes, including the Aguan, Cahabon, Choluteca, Chucunaque, Coco, Dulce, Lempa, Los Esclavos, Motagua, New, Patuca, Reventazon, San Juan, Tempisque, and Ulua rivers that could flood during periods of intense rainfall. Flash floods, which can occur with little to no warning, often threaten communities downstream of major rivers or dams in the event of structural failure. Urban flooding is possible in areas with poorly maintained or inadequate drainage systems, while storm surges may trigger flooding in coastal areas. Landslides and mudslides are possible in hilly and mountainous areas.

Heavy downpours, flooding, and landslides could affect business, transport, and utility services in many areas. Localized disruptions could persist well after hazardous events have concluded; floodwaters may take days to subside, and crews may take weeks to clear debris from mudslides. Rural communities and informal settlements often sustain the greatest damage and casualties during such events due to poor infrastructure.

Transport
Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas, especially in rural areas, where infrastructure is already of a poor standard. 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.

Severe weather could trigger flight delays and cancellations at domestic and international airports. Officials may temporarily suspend port operations along the Caribbean Sea and the Pacific Ocean if strong winds trigger hazardous sea conditions. Flooding could block regional rail lines; freight and passenger train delays and cancellations are likely in areas that see heavy rainfall and potential track inundation. Localized business disruptions may occur; some businesses might not operate at full capacity because of flood damage to facilities, possible evacuations, and some employees' inability to reach work sites.

Health
The threat of disease outbreaks is elevated during the rainy season. Backflow from drains that have mixed with floodwaters can become trapped in open areas when inundations recede. These stagnant pools often become a breeding ground for mosquitoes and bacteria, increasing insect- and waterborne diseases. Exposure to contaminated water from inundated industrial sites, sewer systems, and septic tanks also poses a significant health threat.