Weekly Tropical Climate Note

Issued on Tuesday 29 July 2014

Tropical activity picks up over the Pacific Ocean

The Madden-Julian Oscillation (MJO) has gained some strength over the Pacific Ocean during the past week. Active tropical weather has increased along South East Asian monsoon and extends across the western and central Pacific Ocean just north of the equator. It is likely that the MJO has contributed to this increase in activity. In contrast, the tropical Indian Ocean has continued to experience a lull in tropical activity, as is often observed when a MJO is active in the Pacific Ocean. While the MJO remains active over the Pacific Ocean, the risk of tropical cyclone formation across the tropical Pacific Ocean remains elevated.

The outlook for the MJO for the coming two weeks indicates it is likely to continue to move east across the western hemisphere, reappearing in the Indian Ocean region by late next week. However, the models do not completely agree on the strength of the MJO signal over the coming weeks. Some models maintain a weak wave as it moves east while others predict it will weaken, having little influence on tropical weather for the next two weeks.

See the Bureau's MJO Monitoring for more information on location and tracking of the MJO.

ENSO state: neutral

Early this year a warming trend across the tropical Pacific Ocean primed the climate system for El Niño in 2014. However a general lack of atmospheric response to the warm ocean has caused El Niño development to stall. The El Niño-Southern Oscillation (ENSO) is a coupled ocean and atmosphere system with feedback required from both the atmosphere and ocean for an El Niño to develop fully. This lack of atmospheric response over the last two months has resulted in some cooling of the central tropical Pacific Ocean, with the latest NINO3.4 sea surface temperature (SST) anomaly now near the long-term average. The latest 30-day Southern Oscillation Index value to 27 July is −5.2—weakly negative, but not low enough to indicate an El Niño pattern is present.

When the MJO is in the Pacific Ocean, it often weakens trade wind flow over the western Pacific Ocean. This change in trade wind strength could act to re–invigorate and reinforce the El Niño pattern of ocean warming currently observed in the tropical Pacific Ocean.

See the Bureau's ENSO Wrap-Up for official information about the current state of the El Niño-Southern Oscillation.

Indian Ocean Dipole update

The Indian Ocean is currently showing a negative Indian Ocean Dipole (IOD) pattern, with warmer than normal SSTs in the east near the equator and cooler than normal SSTs in the tropical west. This pattern has been in place since mid-June. The Bureau's IOD index reflects this observed SST pattern and is currently below −0.6 °C. Most climate models indicate the IOD index will return to neutral levels by October.

Next update expected by 5 August 2014| Product Code IDCKGEW000

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