The tropical circulation in the Australian/Asian region - November 1996 to April 1997

A summary of the broadscale tropical circulation from 70°E to 180°, for the six months November 1996 to April 1997, is presented. The weak La Niña phase, which characterised 1996, declined and some early El Niño indicators emerged by the end of the season. These included the appearance of strong westerly equatorial wind anomalies near the date-line, increasing sea-surface temperature in the tropical Pacific and a fall of the Southern Oscillation Index to negative values. The monsoon in the summer hemisphere was of average development or better, with strongest anomalies in the southwest Pacific. The near-equatorial trough was active in the northwest Pacific near the date-line. Twenty-nine tropical cyclones were analysed, twenty in the southern hemisphere and nine in the north. Overall, tropical cyclone occurrences were slightly above long-term averages. Three full cycles of the 30 to 60-day intraseasonal oscillation were diagnosed.