Why are the surface charts not updating?

The Surface Pressure Charts are jpeg images which are updated every 6 hours.

We instruct your browser to always load fresh images, however browsers are sometimes not good at taking instructions and frequently ignore this request and load the image from cache. To update with the latest images, click on the red REFRESH IMAGES button to the left of the maps, this will force the browser to upload the latest images,  or press the CTRL and the R keys at the same time or the CTRL and F5 key at the same time. This will clear the cache files and force the browser to fetch the latest images from the server.