WEATHER

Several factors have combined to make the storm wetter than most, with potentially deadly consequences for the Texas coast. (Nat Geo News)

Use MapMaker Interactive’s precipitation layer to put Harvey’s rainfall in perspective.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• The Nat Geo News article reports that up to 50 inches of rain will fall in the Houston area through Thursday. Now take a look at the precipitation layer on MapMaker Interactive, which maps a region’s yearly rainfall patterns. How does Tropical Storm Harvey’s rainfall compare to Houston’s average annual rainfall?
  • The amount of rainfall Houston is predicted to get over the next five days is about its average for the entire year.
    • We figured this out by converting millimeters to inches. MapMaker Interactive uses millimeters, and reports Houston gets about 1000-15000 millimeters of rain every year. (Check out the “Legend” tab to get the numbers.) To convert millimeters to inches, you need the conversion factor. The conversion factor is 25.4, meaning there are 25.4 millimeters per inch.
      • 1000/25.4=39
      • 1500/25.4=59
      • Houston usually gets between 39 and 59 inches of rain every year.
    • Yes, Google will also do the conversion for you.

• The Nat Geo News article says “It’s unusual for a hurricane as intense as Harvey—which had peak winds of 130 miles an hour at landfall—to be such a rainmaker.” Why?
  • “Powerful hurricanes are less prone to stalling out, since their structure extends high into the atmosphere, and over a large area of the atmosphere, and are thus more likely to ‘feel’ the steering influence of the larger scale planetary winds,” says one meteorologist.
  • In other words, unlike most hurricanes, Harvey is going to stay parked above the Houston urban area and “‘basically train a fire hose’ on a stretch of the Texas coast.”

• Why is Harvey staying put? Read the section on starting “A front is a narrow zone …” in our encyclopedic entry for some help.
  • Harvey is stalled along a “stationary front.” A stationary front is a weather pattern that develops when a warm air mass and a cold air mass meet, but neither is strong enough to displace the other and the boundary between the two does not move.
  • “Basically there are almost no winds to push it one way or the other,” says one hurricane expert.

• Where is Harvey picking up all that moisture it’s dumping in Houston?
  • The warm Gulf of Mexico, of course. “Obviously, Harvey is currently virtually stationary and, unfortunately, close enough to the Gulf of Mexico that it’s able to tap all of that Gulf moisture.”

TEACHERS TOOLKIT

Nat Geo: Harvey May Become the Rainiest Storm in U.S. History—Here’s Why

USA Today: Why Harvey’s future is so uncertain, hard to predict

Nat Geo: MapMaker Interactive—Precipitation and Rainfall

Nat Geo: What is weather?