This is very easy. Only change a parameter. It will change the weather
storm to meteor storm.
First, search "WeatherConBolts=" and then change "WCCLOUD1,WCCLOUD2,WCCLOUD3" to "METLARGE,METSMALL".
Then correct the error pallette and extract the sounds in Tibsun.mix. Or you can get these animations and sounds in Psycho's Fake Meteor Storm Tutorials.
Last, remove the weather storm's clouds (change "WeatherConClouds=").