Raven has printed a table from the National Hurricane Center. "Average dates," she says. "When the first storm, the second storm, and so on usually form."
Rocket reads down the list. "First named storm around June 20. Seventh one around September 3. They pile up in late summer."
"What do you notice about the hurricane column?" Raven asks.
"It starts later," Rocket says. "The first hurricane is usually in August."
Nova adds a second sheet beside it: the wind speeds for each hurricane category.
"Weather science is partly history," she says. "Where and when storms happened before helps forecasters say where they are likely again."
Rocket picks up a pencil. "So a calendar is a forecasting tool. I did not expect that."
The Atlantic hurricane season runs from June 1 to November 30. The peak is September 10, with most activity between mid-August and mid-October.
Based on the years 1991 to 2020, an average season has 14 named storms, 7 hurricanes and 3 major hurricanes.
The National Hurricane Center table below shows the date by which a given number of storms has usually formed.
| Number | Named storms by | Hurricanes by | Major hurricanes by |
|---|---|---|---|
| 1 | June 20 | August 11 | September 1 |
| 2 | July 17 | August 26 | September 19 |
| 3 | August 3 | September 7 | October 28 |
| 4 | August 15 | September 16 | |
| 5 | August 22 | September 28 | |
| 6 | August 29 | October 15 | |
| 7 | September 3 | November 15 |
The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based only on a hurricane's maximum sustained wind speed.
Categories 3, 4 and 5 are called major hurricanes.
| Category | Sustained winds (miles per hour) |
|---|---|
| 1 | 74 to 95 |
| 2 | 96 to 110 |
| 3 | 111 to 129 |
| 4 | 130 to 156 |
| 5 | 157 or higher |
Tornado history has patterns too. Around 1,200 tornadoes form in the United States in a typical year.
The peak of the season is April through June. More tornadoes strike the central United States than any other place in the world.
Tornadoes are most common in the Central Plains and the southeastern United States, yet every state has reported one.
Forecasters rate a tornado after it passes, using the Enhanced Fujita scale, which has been in use since 2007.
| Rating | Estimated winds (miles per hour) |
|---|---|
| EF0 | 65 to 85 |
| EF1 | 86 to 110 |
| EF2 | 111 to 135 |
| EF3 | 136 to 165 |
| EF4 | 166 to 200 |
| EF5 | Over 200 |
| Statement | True or false? |
|---|---|
| The peak of tornado season is April through June. | ? |
| An average Atlantic season has 3 major hurricanes. | ? |
| The EF scale rates a tornado before it forms. | ? |
| Tornadoes happen only in one part of the country. | ? |
Every area has its own mix. A coastal area watches the hurricane calendar. An inland area may watch the spring tornado season.
Nearly every area gets thunderstorms, and flooding can happen almost anywhere there is heavy rain.
With a grown-up, list the storm hazards that matter most for your area and the months when each is most likely.
Excellent reading. Tomorrow you put all the safety rules together and start the family plan.