Singapore is commonly assigned the Köppen climate code Af, meaning tropical rainforest climate.
The first letter, A, identifies a tropical climate in which every month has an average temperature of at least 18°C. The second letter, f, means there is no true dry season: rainfall remains sufficiently high throughout the year. Singapore's equatorial location, maritime surroundings, high humidity, and abundant precipitation fit these criteria.
Singapore lies about one degree north of the Equator, so seasonal temperature changes are small. Monsoon patterns still influence rainfall, especially from November to February, but they do not create a dry season strong enough to change the classification to Aw or Am under the usual Köppen thresholds.
The main mix-up is with Am, tropical monsoon climate, which has a distinct short dry period, or Aw, tropical savanna climate, which has a more pronounced dry winter season. Singapore can experience relatively drier months, but its year-round rainfall keeps Af as the standard classification.