A short-duration low-level westerly wind event along and near the equator in the western Pacific Ocean (and sometimes in the Indian Ocean). This surge may last from one day to several days and is closely linked to deep equatorial convection to its east. The westerly wind burst is most common during El Niño years from September to January and in normal years from October to December. It is absent in the Pacific in La Niña years. It is also thought to be associated with the Madden–Julian oscillation. The westerly winds are usually greater than 5 m s⁻¹(10 knots), and reach 15 m s⁻¹(30 knots) in well- developed systems. These intense westerly wind bursts are associated with a large cluster of deep convective clouds along the equator and are necessary precursors to the formation of tropical cyclone twins symmetric about the equator.