The tropical circulation in the Australian and Asian region - November 2008 to April 2009

Abstract

A summary of the broadscale tropical circulation from 70°E to 180° for the six months November 2008 to April 2009 is presented. A weak La Niña state of the El Niño Southern Oscillation (ENSO) developed early in the season, weakening towards the end of the season to neutral conditions. The sea-surface temperature (SST) cool tongue pattern in the near-equatorial far eastern Pacific near the South American coast extended west, close to the date-line. The warmest waters in the equatorial Pacific remained close to their climatological location in the northwestern Pacific. The Southern Oscillation Index (SOI) remained mostly positive throughout the season. Onset of the Australian monsoon over northern Australia occurred around 18 December 2008, earlier than the climatological onset date, but it retreated north of the Australian continent in mid-February. The signal of the Madden-Julian Oscillation (MJO) showed a regular periodicity of around 30 to 35 days during most of the season. A total of 22 tropical cyclones, close to the long-term average, developed in the Darwin Regional Specialised Meteorological Centre (RSMC) area during the period