Impacts of Climate Variability and Change on Eastern North Pacific Tropical Cyclones

Book excerpt: Damages inflicted by tropical cyclones (TCs) worldwide have increased in recent decades with climate change and variability playing key roles in altering TC characteristics. In this thesis, the impact of natural variability is explored, using ENSO conditions, and climate change on the nature of eastern North Pacific (ENP) TCs. The first research objective of the thesis focused on a spatial-temporal separation of ENP storms based on El Niño-Southern Oscillation (ENSO) phase (temporal variability, El Niño, La Niña, neutral) and regional storm stratification (spatial variability, east and west). The western development region (WDR) storms were found to be more sensitive to influences of ENSO. In particular, during El Niño years, there were more WDR storms. The second research objective explored the ENSO impact on the trajectory of ENP storm tracks by examining the locations for genesis and downgradation points and storm track movements. The storm tracks were strongly influenced by ENSO phases, with significant differences detected for many ENSO pairings. However, when storm data are regionally separated the latitudinal movement of WDR storms tend to be more extensive during El Niño conditions and as a result there are more landfalling TCs. The third research objective of the dissertation explored the importance of near-time sea surface temperatures (SSTs) on storm intensities. SST thresholds were found that were critical for the sustenance of stronger ENP storms that achieve hurricane and major hurricane status. Significantly, the minimum SST threshold varied between the MDR subdivisions. For major hurricanes, the SST requirements for EDR and WDR are substantially lower than that found in the North Atlantic basin at 28.25°C. Although SSTs appear to contribute little in determining the ultimate maximum storm intensity for ENP storms in general, when ENP storms are regionally divided, SSTs are found to be highly associated with the WDR major hurricanes. Evidently the recent warming shown in the distribution of storm-bounded SSTs has led to the rise of maximum potential intensity for ENP storms. Overall, the common theme that emerged from these three studies is that ENP storm characteristics associated with WDR are inherently more sensitive to climate variability and change.