The origins of Cyclone Leon–Eline were from a surge of energy within the monsoon trough that crossed the equator from the northwest, which spawned a low pressure area on February 1 in the eastern Indian Ocean, about 250 km (155 mi) south of the Indonesian island of Bali. Associated convection, or thunderstorms, was initially sparse due to wind shear in the region. Over the next few days, the low tracked west-southwestward without much development, moving around a large ridge over northwestern Australia. An anticyclone over the system provided outflow, allowing convection to increase despite the wind shear. At 22:00 UTC on February 3, Australia's Bureau of Meteorology (BoM) upgraded the tropical low to a Category 1 tropical cyclone on the Australian tropical cyclone scale, estimating 10‑minute sustained winds of 65 km/h (40 mph). At 04:00 UTC the next day, the BoM named the storm Tropical Cyclone Leon. On the same day at 03:00 UTC, the Joint Typhoon Warning Center (JTWC) began issuing advisories on the storm as Tropical Cyclone 11S. Around that time, Leon was located about 215 km (130 mi) south-southeast of Christmas Island, moving west-southwestward. With decreasing wind shear, the convection organized into rainbands, signaling that the storm was strengthening.