Picture: Image of Typhoon Nepartak taken using its Multi-angle Imaging SpectroRadiometer. The top left image depicts cloud heights; the middle image is a stereoscopic, natural-colour view; and the top right image reveals wind speeds and directions in the atmosphere. Credit: NASA JPL.

The most intense and destructive tropical cyclones generally go through a period of rapid intensification, where “rapid” means that the near-surface winds increase by more than 15 m/s (54km/hr) in 24 hrs. Because of the close connection between rapid intensification and the final intensity of the storm, accurately forecasting the timing and magnitude of such periods of intensification is important.

However, the physical processes by which storms rapidly intensify are not well understood and there has been little improvement in forecasting rapid intensification over the past three decades.

This study uses very high-resolution simulations with the UK Met Office Unified Model of the 2016 north-Pacific tropical cyclone, Nepartak, to explore the processes responsible for its rapid intensification. It found the inner core of Nepartak fluctuated between a structure that was ring-like and one that was monopolar. During the ringlike phase, the low-level wind intensified, whereas during the monopole phase the low-level wind remained mostly constant. The work explains the dynamics responsible for these fluctuations and their significance for rapid intensification.

  • Paper: Hardy, S., Schwendike, J., Smith, R. K., Short, C. J., Reeder, M. J., & Birch, C. E. (2021). Fluctuations in Inner-Core Structure during the Rapid Intensification of Super Typhoon Nepartak (2016), Monthly Weather Review, 149(1), 221-243.