Fire is actually quite common when it is in season. Start watching for it late this week, as it is currently May on the game calendar.

Those charts and the reporting at that ffx11info site are not using a complete data set...this has been brought up before in previous threads. You can spot some of the discrepencies yourself if you compare the data in the charts at that site--one shows weather when the other does not, and vice verce. It has also been forecast by NPC/Moogle's Almanac and found in game in time slots not represented at that site (it periodically drops complete zones from it's reporting, and goes through phases of no reporting at all).