Tropical Cyclone Impacts in the Western United States with a Changing Climate

In August of 2023, Hurricane Hilary impacted the California coast as a post-tropical storm, bringing catastrophic rainfall to the region. Trees were uprooted, roads were damaged, and an economic loss of $900 million occurred in the Southwestern United States. Although many individuals were aware of the incoming storm, there was a general unpreparedness due to the lack of experience with these systems. Tropical cyclones (TCs) in the Southwestern United States are considered rare — the Eastern North Pacific basin becomes highly unfavorable for TCs north of 25°N, and the majority dissipate south of this latitude. TCs that survive north of this latitude occasionally reach the SW U.S. as disorganized remnants, but receive limited attention, as they do not bring impacts associated with major tropical systems such as extreme winds. However, nearly every year, flooding and dangerous lightning occur as a direct result of the systems. With a changing climate, these impacts currently going under the radar may be amplified significantly. Climate change has already started altering the tendency and intensity of hurricanes worldwide, so it is important to assess the potential change in activity in the Eastern North Pacific basin, as it may affect the Southwest United States later in the 21st century. This study will examine the ingredients necessary for tropical cyclone development and maintenance (e.g., sea surface temperature, wind shear) along the historical northern periphery of Eastern North Pacific TC activity. In particular, we will study recent changes in the spatial distribution of these ingredients (through reanalysis data) and projected changes in the future (using global climate model output).