A Storm Chest is an objective in Fortnite: Save the World. It's appearance is that of a purple-tinted Tier 6 Chest surrounded by a purple smoke. It can be found mostly on the outskirts of maps, similar to Anomalies, but can sometimes appear in the central area of a map, even near buildings.
Upon activating the Storm Chest, an atonal sound effect can be heard, and Husks will begin to spawn in the vicinity of the chest. The amount of rewards granted by the Storm Chest depend on the completion of three phases: the first phase requires killing 25 of the spawning husks in 1 minute. If 25 husks have been killed before the timer is up, the second phase begins, requiring the players to kill 50 husks. If all 50 husks have been slain, the third phase begins. Two Mist Husks will spawn, either Blasters or Takers. You must kill both Mist Monsters to fully complete the Storm Chest.
Storm Chests grant valuable rewards due to the amount of effort required to complete them. Rewards generally include a good quantity of crafting materials and ammunition, and one to two weapons. The tier of the crafting material and weapon rewards scales with the power level and zone of the mission— Silver Ore and Malachite-tier weapons are likely in mid-Plankerton, for example.