Skyhook took a look at how the island fared during the critical 4-day period that accounted for most of the damage by examining Wi-Fi signals. The overall usage patterns show a collapse in activity within an hour of Maria making landfall near Yabucoa, PR on the morning of September 20, 2017.
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<a href="//commons.wikimedia.org/wiki/Category:Vimeo" title="Category:Vimeo">Vimeo</a>: <a rel="nofollow" class="external text" href="https://vimeo.com/236745013">Puerto Rico Hurricane Maria Wi-Fi Signal Analysis</a> (<a rel="nofollow" class="external text" href="//web.archive.org/web/*/https://vimeo.com/236745013"><span style="color:#9602fc">view archived source</span></a>)