Tab linking directly to htm doc.

Good morning all, forgive me, I have searched but can’t really find an answer. I am a relative noob at this.

I run a weather station that uplaods an htm document/page to my web host. I need to creat a tab that links to it so people can see my weather page.
The tab is called Weather and I have input the following on the tab
Weather

When you use the tab, it just says page not found, have I done something wrong? or do I need a plugin.

Please be kind enough to keep it simple !,LOL.

Website is http://www.woodyspembs.org.uk
Many many thanks
kind regards woody