Armed with an array of active and passive sensors, TRMM's primary mission is to measure rainfall from space; however, it also serves as a valuable platform for observing tropical cyclones. This image from TRMM shows Helen just after the cyclone made landfall along the west coast of Australia's Northern Territory. The image was taken at 13:46 UTC (11:16 pm Australian CST) on 4 January 2008 and shows the horizontal distribution of rain intensity within the system. Rain rates in the center swath are from the TRMM Precipitation Radar (PR), and rain rates in the outer swath are from the TRMM Microwave Imager (TMI). The rain rates are overlaid on infrared (IR) data from the TRMM Visible Infrared Scanner (VIRS). At this stage, the storm still has a pronounced circulation as evidenced by the banding (curvature) in the rain field; however, in the center, the storm is already showing signs of weakening with the northern half of the eyewall missing (white area within the blue area). Despite downing trees and powerlines in Darwin, Helen's main impact was heavy rain. After making landfall, Helen quickly weakened as it moved east. It re-emerged over open water in the Gulf of Carpentaria but did not re-intensify. Instead the remnants of Helen moved ashore over the York Peninsula in Queensland and stalled out, bringing heavy rain to the area.

In addition to the rains from Helen, the northern coastline of Australia was already experiencing wet weather due to the interaction of a monsoon trough, a trough of low pressure associated with the inter-tropical convergence zone that is a focus for shower and rain activity, with 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 is in the process of moving from the Maritime Continent into the western Pacific Ocean. 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 7-day period 1 to 8 January 2008 for northern Australia and the surrounding area. The highest rainfall totals for the period (shown in dark red) are over 500 mm (~20 inches) in the eastern Gulf of Carpentaria. Over land, a broad area of 100 mm (~4 inches) extends from the northern coastline of Western Australia across the Northern Territory and into the York Peninsula in the east (green areas). Within this band, there are areas of much higher amounts--namely the northern part of the York Peninsula where amounts range upwards of 300 mm (~12 inches, shown in orange) and in the far northwest.

In addition to the activity in the north, the east coast of Australia saw record rainfall, which left many residents stranded. This final image shows MPA rainfall totals for the same period along the eastern coastline where up to 6 inches of rain (orange area) are shown just south of Brisbane. A good bit of southeastern Australia has been experiencing a long-term drought. However, La Niña, the counterpart to El Niño, has been providing some relief. Instead of above normal ocean temperatures in the central Pacific and below normal values in the western Pacific, La Niña brings the opposite. This results in enhanced rainfall over the western Pacific, Maritime Continent, and northern and eastern Australia as enhanced trade winds pile up even warmer waters in the region. These above-normal water temperatures are expected to enhance this season's tropical cyclone activity around Australia.

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