Heatwaves usually come with dry conditions because the regions under the so-called heat dome, which is typically responsible for severe heatwave events, are deprived of moisture and rainfall. However, in the southern US states under semi-tropical environments, “moist” heatwave events may occur, causing both the temperature and humidity stresses on human physiology. But, you may wonder what a “moist” heatwave event may feel like. As a person who has lived in Miami for more than 20 years, I can tell you exactly what it feels like. If you travel to a northern state or other subtropical climate regions and then back to the Miami International Airport, you will not feel anything different initially. But, once you open a glass door to the parking lot, you will immediately feel like you are in a steam sauna. That’s right. “Moist” heatwave feels exactly like you are in a steam sauna, but with no exit door. A new paper published in Nature Geoscience (Duan et al., 2024) suggests that the likelihood of “moist” heatwave will increase in the future climate. More specifically, as the climate warms, lower atmospheric air becomes less saturated because the saturation vapor pressure increases with warming temperature. Entrainment of undersaturated air in turn limits deep convection. Without deep convection, the heat and moisture trapped in the atmosphere cannot be released to cool down the atmosphere or produce rainfall (i.e., latent cooling of the atmosphere) increasing the production of “moist” heat wave events. The study warns that regions with large-scale subsidence and a dry lower atmosphere, such as coastal areas adjacent to hot and arid land, are particularly susceptible to the increasing “moist” heatwaves.
Image Credit: https://www.goodhousekeeping.com/health/fitness/a31196789/steam-room-vs-sauna/
Duan, S.Q., Ahmed, F. & Neelin, J.D. Moist heatwaves intensified by entrainment of dry air that limits deep convection. Nat. Geosci. (2024). https://doi.org/10.1038/s41561-024-01498-y
Ocean to Climate 