Persistent heavy rains have lead to flooding and landslides over parts of Indonesia, resulting in numerous fatalities and crop losses. Hardest hit was the island of Java where at least 112 have died. In addition to the regular rainy season, which lasts from December through February as a result of the ITCZ or Inter-tropical Convergence Zone migrating southward during the southern hemisphere winter, there are two additional climatological factors that are contributing to the rainfall. The first is La Nina, the counterpart to El Nino. Instead of above normal ocean temperatures in the central Pacific and below normal values in the western Pacific, La Nina brings the opposite. This results in enhanced rainfall over the western Pacific and Maritime Continent as enhanced trade winds pile up even warmer waters there. The other factor is a 30 to 60 day oscillation known as the 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 moved from the Indian Ocean to the Maritime Continent during the latter half of December.

The primary mission of the Tropical Rainfall Measuring Mission or TRMM satellite is to measure rainfall over the global Tropics. It was placed into service in November of 1997. From its low-earth orbit, TRMM has been measuring rainfall over the global Tropics using a combination of passive microwave and active radar sensors. It can 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. MPA rainfall totals are shown here for the 9-day period 24 December 2007 to 2 January 2008 for central Indonesia and the surrounding area. The highest rainfall totals for the period (shown in dark red) are over 250 mm (~10 inches). Although the highest amounts are over water, parts of Java are shown to have received in excess of 6 to 8 inches (orange and red areas). Deforestation in the region is believed to be a contributing factor in the devastating mudslides.

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