La Niña, the counterpart to El Niño, brings below normal ocean temperatures to the central Pacific and above normal values in the western Pacific. These anomalies in sea surface temperature (SST) are mirrored in the rainfall pattern with warmer-than- normal SSTs resulting in enhanced rainfall. As enhanced trade winds pile up even warmer-than-normal waters in the western Pacific, a classic pattern of enhanced rainfall emerges over the West Pacific, Maritime Continent, and northern Australia.

The Tropical Rainfall Measuring Mission (TRMM) was launched into service with the primary mission of measuring rainfall from space. It can also be used to calibrate rainfall estimates from other satellites. The TRMM-based, near-real time Multi- satellite Precipitation Analysis (MPA) at the NASA Goddard Space Flight Center monitors rainfall over the global Tropics. The image here shows rainfall anomalies (or deviations from long-term average rainfall amounts, which are based here on a 9-yearclimatology) for the previous 30-day period (19 December 2007 to 18 January 2008). A classic horseshoe pattern of above average rainfall (blue areas) covers parts of the West Pacific, Maritime Continent, and northern Australia with below normal rainfall (brown area) near the dateline. Superimposed on this pattern is the most recent Madden-Julian Oscillation (MJO). The MJO is a large, slow-moving area of enhanced tropical convective (i.e., thunderstorm) activity that propagates eastward from the Indian Ocean into the Pacific. The most recent MJO event, which is in the process of moving from the Maritime Continent into the western Pacific, can be seen as the dry anomalies centered over Malaysia. In an average La Niña, this region would also be wetter then normal. The current MJO is also contributing to the enhanced rainfall north and northeast of Australia for the period.

TRMM is a joint mission between NASA and the Japanese space agency JAXA