In the context of predicting rainfall based on past data, an outlier refers to a data point that significantly deviates from the other observations in the dataset.
Among the choices given, the most fitting example of an outlier is:
a higher-than-average rainfall due to an unseasonable hurricane that month.
This is because such an occurrence would be unusual and could significantly impact the rainfall data for that month, making it an outlier compared to typical seasonal rainfall patterns.