Besides record rainfall and devastation, Harvey also has the distinction of being one of the biggest natural disasters in the U.S where social media has played a key role.
As emergency lines and first responders are being inundated with more calls than they can handle, Houston residents have taken to social media to organize volunteers, share the latest storm updates, and even call for rescues.
In addition to platforms like Reddit and Twitter, a handful of other apps are emerging as essential tools for people in Houston as they look to connect with rescuers and get the most up-to-date information.
Here's how apps are helping.
Rescuers and people in need of help are turning to Zello, a walkie talkie-like app, to get in touch with first responders who are on the ground.
The app has a simple push-to-talk interface that allows people to record voice messages to dedicated rescue channels being used by the Cajun Navy and other first responders. People can also send text and photo messages that can be viewed by anyone on the channel as well.
Image: zello app/screenshot
It's also becoming a key resource for people who need real-time updates on road closures, shelter locations, and where volunteers are most needed.
Zello has more information about the channels being used by rescue groups in Houston on its blog.
Also being used by the Cajun Navy and other rescue groups, Glympse's real-time location sharing app is helping people keep track of the location of rescue boats. By using the app with Zello's messaging, people in need of help are better able to coordinate with rescuers who are nearby.
This video has detailed instructions on how to use Zello and Glympse to get help.
Snapchat's becoming an unlikely source of information for people trying to get up-to-date information on the effects of Harvey. The app's Snap Maps feature is helping people keep track of the storm's effects in different Houston neighborhoods.
And with hundreds of thousands of publicly viewable Harvey-related Snaps submitted over the last few days, Snapchat is also providing those farther away with an unfiltered look at how people are dealing with Harvey.
The Cajun Navy is also using this Google Map to keep track of locations where people are in need of rescue. Anyone who needs help can fill out the accompanying Google Form to get their address added to the map.
The floods have also taken a toll on Houston's four-legged residents. Pawboost, an app that crowdsources help for lost pets, is working with weather.com to help reunite animals with their owners in the wake of Harvey.