Tropical cyclone Dera, the unusual 2000/01 tropical cyclone season in the southwest Indian Ocean and associated rainfall anomalies over Southern Africa

摘要

Austral summer 2000/01 in the southern African regionwas unusual in several respects. Tropical cyclone activityin the southwest Indian Ocean was substantially less thanaverage despite large areas of this region showing anomalously warm sea surface temperatures (SST) for much ofthe season. Many areas of southern Africa experienced aboveaverage rainfall with local flooding in parts of Mozambique.In the tropical southeast Atlantic, a large warm SST anomaly evolved off the coast of Angola and northern Namibiain late summer suggesting a Benguela Nino event. Duringthe late summer (February-April 2001), three particularlywidespread and intense wet spells occurred over tropicalsouthern Africa, one of which coincided with tropicalcyclone Dera. This study considers the generation and evolution ofthe middle wet spell of late summer 2001 and its relationship with tropical cyclone Dera. This storm wasgenerated in the northwestern part of the MozambiqueChannel and then tracked more or less due south throughthe Channel and into the subtropical southwest IndianOcean. Rainfall associated with Dera contributed to theongoing floods over central Mozambique that arose fromrains earlier in the season. Dera occurred in early Marchfollowing a relatively long period of no tropical cycloneactivity in the southwest Indian Ocean. A build up offavorable conditions during the preceding weeks contributed towards the storm whereas an anticyclonic anomalyeast of Madagascar led to the northerly steering current andthe southward track of tropical cyclone Dera out of theMozambique Channel.