Weekly Tropical Climate Note

Widespread rainfall continues across Indian subcontinent

Heavy rainfall due to the active Indian Southwest Monsoon continued across much of the northern Indian subcontinent. Locations affected spanned the breadth of the subcontinent, from Pakistan in the west to Bangladesh in the east.  Widespread flooding, landslides and multiple fatalities in several regions were reported. The northern part of the Indian subcontinent has experienced the heaviest rainfall in the past week as an active monsoon trough remained near-stationary over the region. Multiple tropical lows developed within the trough in recent weeks providing further focus for the rainfall. The northern limit of the monsoon is over northern India, slightly further south than its average position for this time of year. To follow the progress of the Southwest Monsoon, see the India Meteorological Department's monsoon page.

Parts of South East Asia, particularly Vietnam, also experienced flooding rainfall in the last week due to tropical storm Talas which made landfall over Vietnam’s central provinces during Monday. Loss of life along with property and crop damage was reported.

Madden–Julian Oscillation reappears over Indian Ocean

The flooding and tropical storm development over India and South East Asia coincided with a strengthening Madden–Julian Oscillation (MJO) signal over the region. The MJO signal is currently over the central Indian Ocean where it typically enhances rainfall over India and, to a lesser extent, South East Asia and the western Maritime Continent.

In Australia, when the MJO is over the Indian Ocean at this time of year, it usually strengthens the easterly winds over the Coral Sea and northeast Australia. As a result, parts of Queensland, particularly northern coastal regions, typically see above-average rainfall. The MJO can also contribute to warmer minimum temperatures over the Top End and most of northern Queensland at this time of year. These effects across northern Australia typically diminish as the MJO moves further east into Maritime Continent longitudes.

Most climate models suggest the MJO signal will persist over the Indian Ocean at relatively weak amplitude, while some indicate it may marginally strengthen and move into the eastern Indian Ocean or western Maritime Continent in the coming week. In either scenario, the Indian monsoon would be expected to remain active, whereas the latter scenario would typically result in above-average rainfall over South East Asia and much of the Maritime Continent in the coming week.

ENSO-neutral climate state continues

Atmospheric and oceanic indicators used to measure the El Niño–Southern Oscillation (ENSO) are currently within neutral bounds. All international climate models surveyed by the Bureau indicate the tropical Pacific Ocean is likely to remain ENSO neutral for the remainder of 2017.

The Indian Ocean Dipole (IOD) remains neutral. Two out of six climate models suggest positive IOD thresholds will be reached during winter-spring, with only one model suggesting these levels will last long enough to be considered a positive IOD event. A positive IOD is typically associated with drier than average conditions over much of central Australia and parts of northern Australia during the build-up months of September to November.

See the Bureau’s ENSO Wrap-Up for official El Niño, La Niña and Indian Ocean Dipole information.