25th Conference on Hurricanes and Tropical Meteorology

Monday, 29 April 2002
A climatology of intense tropical cyclones in the south-west Indian Ocean
Karl Hoarau, Cergy-Pontoise University, Cergy-Pontoise, France; and R. Robert and J. P. Hoarau
ABSTRACT

The variations in the number of intense tropical cyclones with maximum sustained (1 min) surface winds of 100 knots and more is investigated over the last thirty years (1969-1970/ 1998-1999) in the south-west Indian Ocean east of 90°E. The intensity of cyclones has been estimated through the interpretation of satellite pictures. A comparison is made with the data given by the Joint Typhoon Warning Center and those reported by Meteo-France Reunion for the 1984-1985/1998-1999 period. This study shows that an annual average of three intense cyclones formed in the south-west Indian Ocean. The analysis over the three past decades indicates that the number of intense cyclones has a tendency to increase ; this is especially the case of the extreme cyclones (120 knots and more) for which a stronger increase in frequency occurred in the 1990s. This increase is not steady : a light decrease in the number of intense cyclones took place over the 1980-1989 decade. It is however remarkable that the ENSO which occurred in the 1980s were accompagnied by no intense cyclones. And only one intense cyclone formed during the 1997-1998 El Nino. The 1990-1999 decade constitutes the one for which the greatest number of intense cyclones has been observed since the data exists. The monthly distribution of intense cyclones shows that 16% occurred at the beginning of the season (November and December), 51% during the full season (January and February), and 33% at the end of the season (March and April). Considering the extreme cyclones, the figures are 24%, 35%, and 41%, respectively. Physical mechanisms are exposed to attempt to explain these variations.

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