Lantean storm

Every 20 to 30 years, Lantea's ocean experiences temperature fluctuations (similar to El Niño on Earth) which can cause large hurricanes, some of which can cover up to 20% the planet's surface. These storms, referred to as "Mega storms from hell", by Dr. Rodney Mckay, produce severe electrical activity as well as high winds and intense rain. If not for Atlantis' shield, the city would be incapable of tolerating the extreme conditions produced by the storm and would ultimately fail.