Forecasting Tropical Annual Maximum Wet-Bulb Temperatures Months in
Advance from the Current State of El Niño
Abstract
Humid heatwaves, characterized by high temperature and humidity
combinations, challenge tropical societies. Extreme wet-bulb
temperatures (TW) over tropical land are coupled to the warmest sea
surface temperatures (SST) by atmospheric convection and wave dynamics.
Here, we harness this coupling for seasonal forecasts of the annual
maximum of daily maximum TW (TWmax). We develop a multiple linear
regression model that explains 80% of variance in tropical mean TWmax
and significant regional TWmax variances. The model considers warming
trends and El Niño and Southern Oscillation (ENSO) indices. Looking
ahead, a moderate-to-strong El Niño with an Oceanic Niño Index (ONI) of
1.5 by the end of 2023 suggests a 42% (11%, 78%) probability of
breaking the tropical mean TWmax record in 2024. For an El Niño similar
to 2015/2016 (ONI of 2.64), the probability escalates to 90% (50%,
99.5%). This approach also holds promise for regional TWmax
predictions.