SINGAPORE – Two different rain-bearing climate phenomena are expected to be felt in Singapore by December, when the country usually experiences its wettest weather. <\/p>\n
But their arrival may not increase total rainfall over Singapore during the year-end holidays, experts told The Straits Times, as these events tend to influence rainfall during other parts of the year instead. <\/p>\n
The Republic\u2019s usual rainy season in December and January is caused by the<\/p>\n wet phase of the north-east monsoon<\/p>\n <\/a>, when winds blow from the cool Northern Hemisphere towards the equator. <\/p>\n This period will also usually see one to three episodes of monsoon surges, which results in higher rainfall over Singapore, <\/p>\n as was the case in January<\/p>\n <\/a>. <\/p>\n These surges refer to bursts of cold air from the north-east, such as Central Asia. As the cool air flows over the warm waters of the South China Sea, it picks up moisture, bringing widespread rainfall, strong winds and cooler weather to Singapore.<\/p>\n But ST checks show that in 2025, the rainy season will coincide with the <\/p>\n return of La Nina<\/p>\n <\/a> and the negative phase of the Indian Ocean Dipole (IOD). <\/p>\n Both climate phenomena tend to result in higher rainfall over Singapore, owing to changes in atmospheric pressure and sea surface temperatures across the Pacific and Indian oceans. The Republic sits between both ocean basins, and can be influenced by weather patterns there. <\/p>\n The Meteorological Service Singapore under the National Environment Agency noted on its website that Singapore is on \u201cLa Nina watch\u201d, which it says is expected to persist until at least the end of 2025. <\/p>\n In response to ST\u2019s queries, a spokesperson for the Met Service said it is likely that La Nina conditions have already been established, based on preliminary assessments of sea surface temperatures in October.<\/p>\n Separately, the Met Service also noted on its website that a negative IOD is present, and that it is expected to persist until December. <\/p>\n Professor Matthias Roth from NUS\u2019 department of geography said: \u201cA developing La Nina paired with a negative IOD typically enhances rainfall, making the November to December period, and the early north-east monsoon season, wetter.\u201d <\/p>\n These climate phenomena have a wide footprint, and can influence rainfall patterns differently across the entire ocean basin. <\/p>\n In Singapore, the Met Service told The Straits Times that La Nina events usually have no noticeable effects on Singapore\u2019s total rainfall during the December to January period. <\/p>\n Instead, they increase the likelihood of wetter conditions during the dry phase of the north-east monsoon season, <\/p>\n between February and March<\/p>\n <\/a>. During this phase, the monsoon rainband moves farther south towards northern Australia, causing Singapore to experience slightly drier conditions. <\/p>\n Similarly, negative IOD events \u201ctend to have little effect on Singapore\u2019s rainfall during the north-east monsoon season\u201d, the Met Service spokesperson added. <\/p>\n<\/picture><\/div>\n<\/figure>\n