If your hosting package includes an SQL database (most include at least one), use WeatherCat's SQLDriver (Tools menu->SQLDriver) to upload and keep up to date the data to a database on your website. Then you can use one of the many graphing packages available to generate your graphs (or access the data from your own code).
For more information, see the WeatherCat manual (page 86 in the current manual); searching the forum for 'SQL' will also throw up some useful info.