Abstract

Perhaps the most dramatic effect that El Niño has upon the climate system is in changing tropical cyclone characteristics around the world. This chapter reviews how tropical cyclone frequency, intensity, and areas of occurrence are altered in all of the cyclone basins by the phases of El Niño/Southern Oscillation (ENSO). In addition to ENSO, other global factors (such as the stratospheric Quasi-Biennial Oscillation) and local factors (such as sea surface temperature, monsoon intensity and rainfall, sea level pressures, and tropospheric vertical shear) can also help modulate tropical cyclone variability. Understanding how these various factors relate to tropical cyclone activity can be challenging owing to the fairly short record (on the scale of only tens of years) of reliable data. Despite this limitation, many of the variables that have been linked to tropical cyclones can be utilized to provide seasonal forecasts of tropical cyclones. Details of prediction methodologies that have been developed for the North Atlantic, Northwest Pacific, South Pacific, and Australian basin tropical cyclones are presented as well as the realtime forecasting performance for Atlantic hurricanes as issued by Prof. William Gray.

Introduction

Tropical cyclones are the costliest and deadliest natural disasters around the world, as the approximate 300,000 death toll in the infamous Bangladesh Cyclone of 1970 and the $26.5 billion (U.S.) in damages due to Hurricane Andrew in the southeast United States can attest (Holland 1993; Hebert et al. 1996).