This is a map with a function attached called "Natural Disasters". This function adds tornados, hurricanes, and hailstorms to vanilla Minecraft. Although they don't spawn naturally and can only be summoned by spawn eggs, they're still fun to mess around with, especially in the example world. :P
TO GET THE SPAWN EGGS:
For a Tornado, run the command /give @p spawn_egg 1 0 {display:{Name:"Tornado"},EntityTag:{id:zombie,Tags:["Tornado"]}}.
For a Hurricane, run the command /give @p spawn_egg 1 0 {display:{Name:"Hurricane"},EntityTag:{id:zombie,Tags:["Hurricane"]}}.
For a Hailstorm, run the command /give @p spawn_egg 1 0 {display:{Name:"Hailstorm"},EntityTag:{id:zombie,Tags:["Hailstorm"]}}.
Wanna use this function in another world aside from this one?
HOW TO INSTALL
1. Click the button to download the map.
2. On Windows press the Windows key + R, then type in "%appdata%", then go to .minecraft and then to saves. Copy the folder you just downloaded into the "saves" folder.
On mac I have absolutely no idea unfortunately, but here's a tutorial I *think* works.
3. Open the folder you just moved, then open "data" and "functions".
4. Copy the "Yeshuabro's Natural Disasters Function" folder.
5. Go back to "saves", then to whatever world you want the function to be able to run in, then go to "data" and "functions".
6. Paste it.
7. Join the world.
8. Do /give @p command_block.
9. Enter in the command /function, then press space and tab. The rest of the command should automatically come up.
10. Click "Always Active"
That's it 
If you get stuck at any point or get confused feel free to leave a comment either here or on the YouTube video.