The heavy rain and cooler temperatures are caused by the ongoing La Nina phase, the Madden-Julian Oscillation and the Northeast Monsoon. SINGAPORE: Heavy rain this past week saw cooler temperatures across Singapore, with flash flood warnings issued in several areas, including Jurong East and Dunearn Road. On Thursday (Feb 19), the mercury dipped below 21°C at three stations, with the lowest temperature of 20.3°C recorded at Newton at 9.12pm, the Meteorological Service Singapore said on Friday.