For a tiny creature, the few-millimeter-wide Irukandji jellyfish (Carukia barnesi, pictured) has an outsized sting. A brush with the transparent marine animal causes severe muscle pain, vomiting, and a spike in blood pressure and heart rate that can kill. Lifeguards in areas of Australia that are prone to Irukandji blooms close beaches when a single sting is reported. Now, scientists have developed an early warning system for the deadly jellies that could prevent stings, unnecessary beach closures, and the resulting blow to the tourist industry. When the researchers analyzed all documented Irukandji attacks at the Great Barrier Reef from 1985 through 2012, as well as local weather patterns, they found that stings most often occurred after a calming of nearby southeasterly trade winds. The change in winds, they think, alters currents, pulling offshore, deep-water critters to shallower waters. Closing beaches where winds have relaxed, they calculated, could decrease the number of days with jellyfish stings by 61%. The new observation, reported online today in the Journal of the Royal Society Interface, could not only help focus beach closures, but could also lead to new, earlier ways to inform beachgoers about such events—smart phone alerts rather than last-minute signs, for example.