Tempest League Guide

Tempests were introduced as a hardcore challenge league alongside Warbands in softcore with the patch 2.0.0 on July 10^th, 2015. They affect the whole map they're active in and can cause a variety of effects that influence both monsters and players. These include changing their sizes, causing damage, altering drop rates or even automatically animating weapons that drop.

Tempests randomly spawn swirling ground effects, detonating after 4 seconds and applying buffs or damage to both players and monsters within their area. The Tempest buffs for a short duration while damaging effects apply immediatly. Most of the Tempests that actively harm players also grant additional Increased Item Quantity (IIQ) and Rarity (IIR).

During the actual league, Tempests used to have a Prefix, which define the effect of the Tempest itself, and a Suffix that added side effects such as more Experience or adding 10 Invasion Bosses to the Map. Tempests currently accessible in Path of Exile do not have any Suffix. For a complete list of Tempest Prefixes and Suffixes, check out this PoEDB link.

Tempest is not an easily accessible mechanic in the core game of Path of Exile, since it was mostly accessed through Prophecies which has been retired. Yet, there are still some sources allowing players to deterministically access it:

Atlas Passive Tree
Shaping the Skies is a notable related to Kirac on the Atlas Passive Tree, which has a chance on completing maps to grant you special Map Device modifiers for later use. One of these mods is the Corrupting Tempest (Area contains a Corrupting Tempest). This Tempest was originally accessible through the Vaal Winds Prophecy and corrupts all items dropped by the monsters affected. This is a nice way to farm 6-Links, mainly to vendor them into Divine Orbs and potentially to get some interesting Corruption Implicit Modifiers. Some sought-after outcomes are Curse on Hit on Gloves or Corrupted Blood Immunity on Jewels.

Incursion Room
There is an Incursion Room themed around Tempests:

Tempest brought some exclusive unique items which are now part of the core drop pool, meaning they can drop anywhere in the game.

Tempests are a long-forgotten Path of Exile mechanic which are nearly inaccessible in the core game besides the actual Tempest League and the Legacy League. Using the Shaping the Skies notable from the Atlas Passive Tree for Corrupting Tempests is the only way to interact with the mechanic.