South African Geophys. J., 75(2), 53-59

A Destructive Tropical Cyclone Season in the SW Indian Ocean: January-February 1984

Mark R. JURY and Beenay PATHACK
Oceanography Department, University of Cape Town, South Africa

Meteorology Department, University of Hawaii at Manoa, Honolulu, Hawaii

AOML, Hurricane Research Division, Miami, Florida

Nirivololona TAHOLIJAO
Weather Forecasting Division, Antananarivo, Madagascar

(Manuscript received 20 May 1991, in revised form 19 November 1991) ABSTRACT

The characteristics of a destructive tropical cyclone seasons in the SW Indian Ocean are analyzed. Circulation anomalies contributing to active cyclone seasons in the SW Indian Ocean include enhanced upper easterlies north of 20S, 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. SST's were 2-3C above normal and exceeded 28C 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 mid-latitude 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 monsoons, is analyzed 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.

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