NASA combined data from multiple satellites to estimate the rainfall from Tropical Cyclone Ana in the Southwest Pacific Ocean amid an ongoing Madden-Julian Oscillation (MJO) event. The Madden-Julian Oscillation is a 20 to 90 day pattern of alternating wet and dry conditions that often begins in the tropical Indian Ocean and moves eastward into the Pacific. This animation shows rainfall rates (blue/yellow shading) and rainfall accumulations (green shading) at half-hourly intervals from January 26 - February 2, 2021, using NASA's IMERG algorithm, overlaid on shades of white/gray from NOAA infrared satellite data which shows cloudiness.

 
The potential for heavy rainfall and tropical cyclone development was particularly high in late January 2021, when the Australian Bureau of Meteorology reported a strong, stalled MJO event over the Southwest Pacific Ocean. When the MJO is active over this region, it is typical to see large-scale, persistent patches of heavy precipitation arcing to the southeast, as seen throughout the animation. The MJO has also been linked to increased tropical cyclone formation in the region. On January 26, 2021, The Fiji Meteorological Service began tracking a tropical disturbance near the island nation of Vanuatu. This disturbance, which later developed into Tropical Cyclone Ana, reached the equivalent strength of a Category-1 hurricane on the Saffir-Simpson Scale on January 30 as it passed over Fiji (seen in the center of the animation), just as Tropical Cyclone Lucas began to form to the west of Vanuatu. During the 8-day period of this animation, IMERG estimated that areas near the Solomon Islands, Vanuatu, and Fiji saw over 300 millimeters (12 inches) of rainfall. NOAA’s Climate Prediction Center and the Australian Bureau of Meteorology reported that the MJO event and its heavy rainfall were likely to persist through mid-February