Rossby waves originating in the Pacific often extend across North America, influencing weather and climate events. Such was the case for the June 2023 Texas heatwave (THW) – the deadliest heatwave in the region in the past 45 years. The focus of this study is on identifying the remote forcings of that wave, using the NASA’s Goddard Earth Observing System (GEOS) model and Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data.
The results reveal a strong heat-induced circulation response to the northwest of a tropical Pacific heat source, along with significant vorticity transients over the extra-tropical Pacific. The Rossby wave generated by these sources propagated across the North Pacific and western North America, leading to above-average geopotential height and temperatures that persisted over Texas. GEOS model experiments in which the model is constrained to reproduce MERRA-2 over the tropics, and stationary wave model simulations, confirm that the tropical Pacific heat source is crucial, while transient vorticity sources in the extra-tropical Pacific also contribute to the development of the large-scale wave that impacted Texas.
The ability to predict the THW is assessed using NASA’s subseasonal to seasonal forecast model. The model does predict the observed maximum temperatures for the heatwave period in Texas up to three weeks ahead, and seasonal warmth in Summer 2023 up to three month ahead.
Additional analysis for July and August also shows an important role of Rossby waves in driving THWs and the model’s ability to predict them up to three weeks ahead.