Subseasonal forecasts can be affected by trends, like those related to climate change, which can make forecast skill appear better than it actually is. This study found that the skill of forecasts can be inflated when trends are present, especially for categorical forecasts in the tropics. This means that when evaluating forecasts over longer periods, we need to be cautious about the impact of trends on the accuracy of predictions. This is important not only for subseasonal forecasts but also for seasonal and decadal predictions.