Answer
In summer, daytime temperatures in many areas of Uruguay are often around 25–30 °C, but this is not a hard-and-fast rule. Heat waves with higher temperatures, cool, windy days on the coast, and sharp changes in the weather after a thunderstorm front are possible.
In Montevideo and resort towns, humidity and sunshine affect how the temperature feels at least as much as the temperature shown on the thermometer. The ocean-facing side of Punta del Este is usually windier, and inland departments can become hotter during the day. Temperatures drop at night, so a light outer layer remains useful.
When planning a trip, check the forecast for a specific city and the UV index. For walks, choose the morning or evening, drink water, and use sun protection. Hot weather does not guarantee a calm sea: swimming conditions are determined by the waves and lifeguard flags.