Here's how to use Zello, the walkie-talkie app people are downloading ahead of Hurricane Florence

Hurricane Florence

Hurricane Florence is expected to make landfall later this week, and a free smartphone app is rising through the App Store charts as people prepare for the worst.

Called Zello, the app lets you use your phone as a walkie-talkie or two-way radio as long as you have a network or WiFi connection. Users can join channels and instantly send messages or photos, and the app even works over older 2G networks.

Zello is currently ranked No. 4 among social networking apps in the US, as well as No. 38 among all iPhone apps overall. According to app analytics firm Sensor Tower, that's a major jump from just one day ago — on Monday, Zello was ranked No. 25 among social networking apps and No. 389 overall.

This isn't the first time Zello has come in handy. Back in August, Zello saw a significant jump in new installs as Tropical Storm Lane approached Hawaii. And last year, Zello reached No. 1 on the App Store as Hurricane Irma ripped through the Caribbean.

If predictions hold, Hurricane Florence may be the strongest storm ever to make landfall north of Florida. It's important to note that if cell towers are wiped out in the storm and WiFi goes down, Zello will not work. But if you have cell service — even a 2G or 3G connection — the app could help in the event of an emergency.

Here's how it works.