I'll try to show all steps with comments and visual examples. Also am using Final Sun Standalone editor but just classic Final Sun will works for everyone. Step 0 (not sure you need this step if you already have new Ion Storm trigger - how to create one shown below Step 1)
Step 1 - Ion Storm Starts (Create Trigger - Trigger Options)
Step 2 - Ion Storm Starts (Events)
Step 3 - Ion Storm Starts (Actions)
Step 1 - Ion Storm Ends (Create Trigger - Trigger Options)
Step 2 - Ion Storm Ends (Events)
Step 3 - Ion Storm Ends (Actions)
This Trigger will work only once. If you want to make trigger repeat I'll have to make another tutorial for that. Thats all for this one.
All known Ion Storm maps on cncnet: http://mapdb.cncnet.org/search.php?game=ts&age=0&search=ion storm
Need more details sure just ask... have a grate day Sir!