One of the features of Mac OS 10.9 is AppNap. This reduces the priority of applications running in the background so they use less processor time.
In WeatherCat, AppNap can slow down custom web generation - this slows down updates to your web-site and causes any additional file processing to wait, which can lead to warnings being logged by WeatherCat about the additional web files queue being full.
If you are seeing slow custom web updates on 10.9, AppNap can be switched off by getting info. on WeatherCat in the Finder and ticking the 'Disable AppNap' checkbox.