Weekly Tropical Climate Note
Madden–Julian Oscillation boosts Indian monsoon
The Bay of Bengal was a focus for tropical convection during this past week, as the Indian monsoon continued to migrate north while the Madden–Julian Oscillation (MJO) moved eastward over the region. This contrasted with supressed convection over the Arabian Sea and much of the western tropical Pacific Ocean. There is general agreement between international models that the MJO will move over the Maritime Continent and then rapidly weaken later in the week as it interacts with other tropical waves. Typically, an MJO over the Maritime Continent at this time of year would see increased convection over the eastern Indian Ocean, parts of Indonesia and to a lesser extent the western tropical Pacific Ocean. Should the MJO weaken later in the week it is unlikely to influence tropical weather until it restrengthens.
See the Bureau's MJO Monitoring for current MJO information.
Negative Indian Ocean Dipole likely for winter–spring
Indian Ocean sea surface temperatures (SSTs) off the African coast began returning to near average levels during May. Waters off Indonesia remain warmer than average and so a negative Indian Ocean Dipole (IOD) pattern has formed in the ocean. The latest weekly Dipole Mode Index (DMI) to 19 June is -0.6 °C and the DMI has remained below the negative IOD threshold of -0.4 °C for four consecutive weeks. In the atmosphere, broad-scale cloudiness patterns during the last month over the tropical Indian Ocean are consistent with a negative IOD pattern—above-average convection in the east and below average in the west. This means there are likely ocean-atmosphere feedbacks occurring, which would help establish a negative IOD event.
Negative IOD events typically bring warmer than average temperatures to Australia's tropics.
Warm start to northern Australian dry season
Temperatures over northwest Australia have been unseasonably warm. Darwin recorded its first daily minimum temperature below 20 °C this dry season on 21 June. The previous latest date in the season to record a sub-20 °C temperature at Darwin Airport was 20 June 1980, making this a new record in 75 years of temperature observations. Darwin has recorded four nights this June when the temperature didn't fall below 25 °C; previously there have only been single instances of this occurring in June. The lack of cool, dry, southerly winds combined with near-record warm SSTs off the coast, is influencing the unusual weather.
Potential La Niña weaker than 2010-12
The tropical Pacific Ocean remains in a neutral El Niño–Southern Oscillation (ENSO) state—neither El Niño nor La Niña – with all ocean and atmospheric indicators now near normal.
Recent observations and climate model forecasts suggest that La Niña will develop in the coming months, though some models have recently eased slightly in the cooling of the central Pacific Ocean. Hence the Bureau’s ENSO Outlook remains at La Niña WATCH level. A La Niña WATCH means there is a 50% likelihood of La Niña developing during the second half of 2016.
See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.
Product code: IDCKGEW000