  We clarify the distinction between direct and indirect effects of disasters
such as Hurricane Mar\'ia and use data from the Puerto Rico Vital Statistics
System to estimate monthly excess deaths in the immediate aftermath of the
hurricane which struck the island in September of 2017. We use a Bayesian
linear regression model fitted to monthly data for 2010--16 to predict monthly
death tallies for all months in 2017, finding large deviations of actual
numbers above predicted ones in September and October of 2017 but much weaker
evidence of excess mortality in November and December of 2017. These deviations
translate into 910 excess deaths with a 95 percent uncertainty interval of 440
to 1,390. We also find little evidence of big pre-hurricane mortality spikes in
2017, suggesting that such large spikes do not just happen randomly and,
therefore, the post-hurricane mortality spike can reasonably be attributed to
the hurricane.
