As Harvey continues to wreak havoc on southern Texas, and specifically Houston -- the fourth-largest city in America -- the worst may be yet to come.

The average annual rainfall in Houston is 50 inches, but the city has already seen half that much in the last two days, and another 25 inches could fall by Saturday.

FEMA says Hurricane and Tropical Storm Harvey, based on current estimates, will send some 30,000 people into shelters and at least 450,000 people will be seeking some disaster assistance.

The Houston Independent School District has canceled school for the week, affecting 215,000 students.

One thing people who are watching this from afar want to do is help, or stay up to date with information.

Here are some helpful links:

Donate to Northwest Response: Hurricane Harvey

City of Houston – Emergency Information

On Twitter: Emergency Information from the City of Houston

Power Outage Tracker

Harris County Flood Control District rainfall totals

Rice University & Texas Medical Center flood alert system (rainfall totals and radar images)

Facebook Safety Check

KHOU (KING 5's sister station)