Tropical monsoon climate (Am)


An area of tropical monsoon climate (occasionally known as a tropical monsoon and trade-wind littoral climate) is a type of climate that corresponds to the Köppen climate classification category "Am". Tropical monsoon climates have monthly mean temperatures above 18 °C (64 °F) in every month of the year and a dry season. Tropical monsoon climates is the intermediate climate between the wet Af (or tropical wet climate) and the drier Aw (or tropical savanna climate).

A tropical monsoon climate, however, has its driest month seeing on average less than 60 mm, but more than . This latter fact is in direct contrast to a tropical savanna climate, where the driest month sees less than 60 mm of precipitation and also less than  of average monthly precipitation. In essence, a tropical monsoon climate tends to either see more rainfall than a tropical savanna climate or have less pronounced dry seasons. Soil moisture is adequate to support a rain forest. Additionally, a tropical monsoon climate tends to see less variance in temperatures during the course of the year than a tropical savanna climate. This climate has a driest month which nearly always occurs at or soon after the winter solstice for that side of the equator. The term monsoon refers to a seasonal shift in wind direction which corresponds to changes in rainfall occurrence.


Köppen–Geiger climate classification map for Tropical - source: wikicommons, authors: Beck, H.E., Zimmermann, N. E., McVicar, T. R., Vergopolan, N., Berg, A., & Wood, E. F. Köppen–Geiger climate classification map for Tropical - source: wikicommons, authors:  Beck, H.E., Zimmermann, N. E., McVicar, T. R., Vergopolan, N., Berg, A., & Wood, E. F., 2018

There are generally two versions of a tropical monsoon climate:

  • Less pronounced dry seasons. Regions with this variation of the tropical monsoon climate typically see copious amounts of rain during the wet season(s), usually in the form of frequent thunderstorms. However, unlike most tropical savanna climates, a sizeable amount of precipitation also falls during the dry season(s). In essence, this version of the tropical monsoon climate generally has less pronounced dry seasons than tropical savanna climates.
  • Extraordinarily rainy wet seasons and pronounced dry seasons. This variation features pronounced dry seasons similar in length and character to dry seasons observed in tropical savanna climates. However, this is followed by a sustained period (or sustained periods) of extraordinary rainfall. In some instances, up to (and sometimes in excess of) 1,000 mm of precipitation is observed per month for two or more consecutive months. Tropical savanna climates generally do not see this level of sustained rainfall.

Tropical monsoon climates are most commonly found in West and Central Africa (e.g. Monrovia/Roberts International, Liberia), South and South East Asia (e.g. Manila/Ninoy Aquino International Airport, Philippines), South and Central America (e.g. Philip S W Goldson International Airport, Belize). This climate also occurs in sections of the Caribbean, North America, and northern Australia (e.g. Miami International Airport, Florida, USA).

Flight safety and planning considerations

During the rainy season, heavy rains can cause disruption to infrastructure and airport emergency services. Thunderstorms can be accompanied by severe downdrafts and heavy rain causing flooding on airport surfaces and the risk of aquaplaning on runways. Strong thunderstorms and high winds are more common with the onset of the monsoon rains. Cumulus clouds are common in the rainy season.  Much less cloud cover occurs in the drier months.

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