Pandemic science in the time of COVID-19 has done a remarkable job of understanding the virus, its spread, and the mechanics of prevention. What we missed – as we did in the 1918 flu pandemic – was an understanding of how to anticipate community behavioral responses to the disease. Our health behaviors were strongly driven by the ways we understood the disease, who we trusted as reliable sources of information, and our capacity to take protective measures such as working from home. HPC in the City: Pandemics focuses on discovering how novel digital signals can explain community behaviors and anticipate epidemiological trends, with a focus on using anonymized mobility data to anticipate and understand mass gathering events and health equity and using community conversations on the Reddit platform to understand protective behaviors like mask wearing and opinions related to local pandemic policy changes. The hackathon is hosted by the Texas Advanced Computing Center as part of SC23 in Denver, CO.