Equatorial Waves: Precursors to Tropical Cyclone Occurrence and Intensification

Understanding and prediction of tropical cyclone (TC) occurrence and intensification on the medium range (3-15 days) remains challenging. Here, we find that the pre-existing dynamical westward-moving equatorial waves can inform the risk of TC occurrence and intensification, based on a new observational dataset synchronising TCs and dynamical equatorial waves. Globally, the westward-moving equatorial waves are responsible for 60–70% of TC genesis events and for >80% of genesis events with strong intensity, related to the favourable dynamical conditions provided by the equatorial waves. The waves have the strongest effect on TC genesis in the North Pacific and North Atlantic. We further find that the westward moving equatorial waves can enhance the intensification rate of TCs when storms locate in a certain phase of the waves, whilst the soon-to-follow phase causes TC intensity to grow slower, or even to decay. Coherent wave packets associated with TCs are identifiable up to two weeks ahead. Our findings show that dynamical westward-moving equatorial waves are reliable precursors to TC activity, indicating an unprecedented potential for improving medium-range prediction of TCs.