In game weather is one of the two uncontrollable aspects of fishing. The second being time. Changing every 4 hours in game, the weather seems to have no pattern.
There are sites like Cat Became Hungry and Garland Bell that help track the weather, but apart from those you are S.O.L.
This is a list of all the “normal” weather conditions pulled from the FFXIV wiki.
There are other weather conditions that happen in game, but those are restricted to raid bosses or rare monster spawns.
Not all weather happens on all the maps. This example is from a map in La Noscea. Most of La Noscea is coastal, or has weather you would see in coastal cities during the summer in real life.
Thanalan, a deep south desert map, will have parts that don’t get rain and will get heat waves.
Coerthas, located far North and mostly snow covered, won’t get rain, but will get snowfall and blizzards.
You can see in all three examples there are at least “Clear Skies” and “Fair Skies.” You will find those on most (if not all) maps.
FFXIV does not have seasons. Even though The Black Shroud is located relative to The upper part of North America or England, it will not get snow.
How does this relate to fishing? Just as in real life, there are fish in game that will only appear during certain weather conditions. Olgoi-Khorkhoi is a Big Fish that is hard to catch. He will only appear during “Heat Waves.” The Fullmoon Sardine, on the other hand, is relatively common in most weather conditions on the sample shown.
That’s pretty much it as far as weather is concerned. It’s 50% of where fishing frustration comes from. There is no skill involved and is 100% luck based. Just use the resources available to you and hope for the best! Join me next time for The Trials and Tribulations of Time!