A three-dimensional hydrodynamic model is applied to explore the development of phytoplankton blooms in the Arafura Sea during the southeast monsoon (June-November). Before this season, blooms are restricted to nearshore waters covering a total area of ˜25,000 km2. Satellite data indicate that the bloom area grows substantially to >90,000 km2 during the southeast monsoon covering most of the northwestern Arafura Sea. Findings confirm that the southeast monsoon creates undercurrents via the classical lee effect driving nutrient-rich Banda Sea slope water into this region. This nutrient-rich slope water is driven over vast distances (˜300 km) into the northwestern Arafura Sea where it upwells and/or is entrained into the surface mixed layer. The associated overturning circulation is slow but continuous and it takes 1-2 months before nutrient-rich water appears in surface waters of the region. The predicted pathways of nutrient-rich inflows across the shelf break both north and south of the Ara Islands agree with observational evidence.