Read the excerpt from How Hurricanes Form. The wind and the clouds that form create a system. A system is a pattern of weather. The system of clouds and winds continues to spin and grow. The water evaporating from the ocean's warm surface acts as the fuel, which is what helps this spinning and growing. The system rotates faster and faster until the eye of the storm forms in the center area. Ironically, the eye of the storm is the calmest part, and it has very low air pressure. The higher pressure above the hurricane continually flows down into the eye.

a view of a hurricane from space with the eye of the hurricane visible in the center of the hurricane
© iStock 2015

Outside of the eye of the hurricane, is the eye wall. This is where the most dangerous winds are found. Further outside that are the rain bands. The rain bands are a group of thick clouds. These clouds create the unique look of the hurricane. Hurricanes start out as tropical storms. They are known as hurricanes once their winds reach 74 miles per hour. The speed of the wind determines the category. Category 1 hurricanes have wind speeds of 74-96 miles per hour. Category 5 hurricanes move at 157 miles per hour or higher.

How do hurricanes escalate from tropical storms to hurricanes? (2 points)

a
If cool, dry air from the land continues to fuel the storm, it can continue to grow in speed, and once it reaches 157 miles per hour, it becomes a hurricane.

b
If warm, moist air from the ocean continues to fuel the storm, it can grow in speed, and once it reaches 74 miles per hour, it becomes a hurricane.

c
If the warm, moist air from the ocean keeps giving the storm energy, it continues to escalate, and once it reaches 96 miles per hour, it becomes a hurricane.

d
The more powerful the precipitation from the tropical storm, the moister the air becomes, and once 50 inches of rain has fallen, it becomes a hurricane.