A destructive tropical cyclone season in the Sw Indian Ocean: January-February 1984

The characteristics of a destructive tropical cyclone season in the SW Indian Ocean are analysed. Circulation anomalies contributing to active cyclone seasons in the SW Indian Ocean include enhanced upper easterlies north of 20° S, upper cyclonic and anticyclonic rotors to the west and south of Madagascar, respectively, and a low level cyclonic circulation anomaly centered over Madagascar involving increased NW monsoon flow to the north and increased easterly trade winds to the south. In the first two months of 1984, eight tropical disturbances tracked westward across the SW Indian Ocean. SSTs were 2–3°C above normal and exceeded 28°C around Madagascar. OLR anomalies were 15–20 W m 2 below normal in the ITCZ cyclogenesis region and a convective axis extended NW–SE across Madagascar. Low level wind anomalies were cyclonic and NW monsoon outflow was at a historical peak, penetrating toward northern Madagascar. Trade wind flow to the south of Madagascar was enhanced by a midlatitude ridge and a strengthened SW Indian Ocean anticyclone. Upper easterly flow was above normal over the 0–20° tropical belt across much of the Indian Ocean. Climatic conditions were thus set for a destructive tropical cyclone season. The case of cyclone Domoina, which served as a conduit for the NW monsoon, is analysed using satellite imagery and OLR data, ECMWF winds and radiosonde sections. Following dissipation of the cyclone, a convective spell brought relief to the drought stricken plateau of SE Africa. The mechanisms sustaining this event are studied.