Tropical wet climate (Af)


Tropical climates are characterized by constant high temperatures (at sea level and low elevations); all 12 months of the year have average temperatures of 18 °C (64.4 °F) or higher; and generally high annual precipitation. There is no winter, per se. Frost does not occur, allowing tropical vegetation to flourish.

All 12 months have an average precipitation of at least 60 mm (2.4 in) in a tropical wet climate. These climates usually occur within 10° latitude of the equator. This climate has no natural seasons in terms of thermal and moisture changes. When it is dominated most of the year by the doldrums low-pressure system due to the presence of the Intertropical Convergence Zone  (ITCZ) and when there are no cyclones then the climate is qualified as equatorial. When the trade winds are dominant most of the year, the climate is a tropical trade-wind wet climate. Typically 1800 – 2500 mm (70 – 100+ inches) of rain falls a year. There is enough moisture in the soil all year to support tropical rain forests.


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

Some of the places with this climate are indeed uniformly and monotonously wet throughout the year (e.g., the northwest Pacific coast of South and Central America, from Ecuador to Costa Rica; see, for instance, José María Córdova International Airport, Columbia, but in many cases, the period of higher sun and longer days is distinctly wettest (as at Palembang International, Indonesia) or the time of lower sun and shorter days may have more rain (as at Penang International Airport, Malaysia). Among these places some have a pure equatorial climate (Singapore Changi Airport) with the dominant ITCZ aerological mechanism and no cyclones or a subequatorial climate with occasional cyclones.

Flight safety and planning considerations

Thunderstorm activity is often greatest in the late afternoon/evening when downdrafts can be severe with risk of flooding and aquaplaning on runways. Although total overcast conditions are rare, cumulus clouds are typically present with maximum coverage over land in the late afternoon/evening. Fog frequently occurs with the high humidities.

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