IDD20730 Australian Government Bureau of Meteorology Northern Territory Darwin RSMC - Australia

El Nino-Southern Oscillation Update
The 30-day Southern Oscillation Index [SOI] to 28 June was +3. Contributing pressure anomalies were +0.7 hPa at Darwin and +1.1 at Tahiti. The official monthly SOI for May was -4, and its 5-month running mean [centred on March] was +10.

El Nino - Southern Oscillation [ENSO] indicators show that the climate system has essentially returned to an ENSO-neutral state, after the La Nina event of 2007/08. Over the last month or so the cool SST anomalies have weakened over the central equatorial Pacific, while warm anomalies have emerged both in the surface and sub-surface ocean in the far eastern Pacific, near South America. During this time the SOI has fallen from previously large positive values to now being small in amplitude, and cloudiness has increased to near-normal values about the near-equatorial date-line.

See the Bureau's "ENSO Wrap-Up" at www.bom.gov.au/climate/enso/ which includes a compilation of ENSO dynamic model predictions. Most model guidance shows a continuation of the warming trend in near-equatorial Pacific SST, though not reaching thresholds typically associated with El Nino events and so suggesting a persistence of neutral-ENSO conditions through the southern hemisphere spring.

Intra-Seasonal Patterns
Following the last southern hemisphere summer, the central tropical Indian Ocean has seen the development of three active phases of the Madden-Julian Oscillation [MJO], evidenced by tropical convection increasing in vigour and extent over that region. These events occurred around mid March, mid April and late May. The March event had a weak signal as it progressed across the longitudes of the Maritime Continent, with little apparent impact over much of northern Australia. Active convection associated with the April event lingered about the western Pacific until the middle of May. See: http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR_modes/h.6.MJO.EQ.html and http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/phase.Last90days.html.

The MJO associated pulse of active convection that progressed into the equatorial Indian Ocean around late May to early June displayed slow eastward progression over the northern tropical latitudes and contributed to the onset and progress of the Indian Monsoon. Unlike other recent events, this active phase of the MJO appeared to weaken as it approached the western Pacific, and now seems to have little structure. The northern hemisphere monsoon remained active over northeastern India and China during the past week or so. Some model guidance is suggestive of a renewed active MJO developing west of the Indian Ocean in about one to two weeks time. In the interim, it appears as though the MJO could have little if any influence on the climate system.

* Darwin RSMC chart area extends from 40S to 40N, 70E to 180
The Weekly Tropical Climate Note is updated each Tuesday by about 0330 UTC.
http://www.bom.gov.au/climate/tropnote/tropnote.shtml
For more information please contact climate.tropical@bom.gov.au