I don't understand
Why is "Tima vetero" different/incorrect here?
I have read the Tips and Notes...
"tima" would be something like "fearful" or "... of fear" - related to "timi" (to fear, be afraid). PIV gives the examples "tima krio, gesto" (a fearful cry or gesture; a cry or gesture of fear).
But the weather is not afraid or fearful, it is scary or intimidating, making other people fear.
La vetero timigas homojn, do ĝi estas timiga.
It's the Plena Ilustrita Vortaro de Esperanto ("Complete Illustrated Dictionary of Esperanto"), one of the biggest monolingual Esperanto dictionaries. A few years ago, it was made available online for free after registration at vortaro.net (if you have a Lernu account, that also works for the online PIV).
It's not official, but because of its size and comprehensiveness, it has become somewhat of a quasi-standard dictionary.
It may have a bit of a French bias due to the nationality of its authors, e.g. recommending gazono over razeno for "lawn".
What's the point of Esperanto having so many words for the same thing? I've seen this a lot. In English usually there is a slight difference even if it's minor but this doesn't seem to be the case in EEperanto.
Dunno about 'so many words', but if you don't have subtlety, you can't DO subtle. Besides, some nations NEED subtlety to differentiate e.g. biero, elo, and cxevalurino.
Someone might describe the weather as frightful without suggesting the weather is full of fear.