Hurricanes and Tornadoes: how they form, when they are active, differences and similarities Flashcards
(9 cards)
How do hurricanes form?
Hurricanes only form over really warm ocean water of 80°F or warmer. The atmosphere (the air) must cool off very quickly the higher you go. Also, the wind must be blowing in the same direction and at the same speed to force air upward from the ocean surface. Winds flow outward above the storm allowing the air below to rise. Hurricanes typically form between 5 to 15 degrees latitude north and south of the equator. The Coriolis Force is needed to create the spin in the hurricane and it becomes too weak near the equator, so hurricanes can never form there.
How long do hurricanes last, and what speed do they travel at?
It can be up to 600 miles across and have strong winds spiraling inward and upward at speeds of 75 to 200 mph. Each hurricane usually lasts for over a week, moving 10-20 miles per hour over the open ocean. Hurricanes gather heat and energy through contact with warm ocean waters. Evaporation from the seawater increases their power.
Where and when do hurricanes occur?
Hurricanes (by whatever name) are by far most common in the Pacific Ocean, with the western Pacific being most active. In some years, the Philippines are struck by more than 20 tropical storms and typhoons. The term applied to various storms depends on their location. Only one hurricane force storm has ever occurred in the South Atlantic - Hurricane “Catarina” in 2004.
What is the hurricane rating scale?
It is called the Saffir-Simpson Hurricane Rating Scale, going from category 1 to 5, increasing with wind speed, air pressure, storm surge size, and degree of damage.
When is hurricane season?
The Atlantic hurricane season is from June 1 to November 30, but most hurricanes occur during the fall months.
The Eastern Pacific hurricane season is from May 15 to November 30.
How does a hurricane change from start to finish?
It begins with a “tropical wave”, or pressure system, and once it is a cyclone with wind speeds over 74 mph, it is considered a hurricane.
How do tornadoes form?
They start on a warm day, where moisture is condensed into clouds. The clouds form a thunder storm, which is the root cause of most tornadoes. There must be cool air up above, and two winds coming in from different directions and colliding, creating a rotating updraft (usually cool, fast moving winds up high, and slow, rainy warm winds on the ground).
In the US, warm moist air from the Gulf of Mexico and cool, dry air from Canada will meet, and create instability in the atmosphere. A change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the updraft tilts the rotating air from horizontal to vertical. An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.
How big are tornadoes, and how do they rank them?
They are ranked using a scale based upon level of damage and wind speed. They vary from F0 to F5. 69% of all tornadoes (most of them) are labeled “weak tornadoes” meaning they have a lifetime of 1-10+ minutes and winds less than 110 mph. 29% of all tornadoes are labeled “strong tornadoes” meaning they last 20 minutes or longer and winds reach 110-205 mph. 2% of all tornadoes are labeled “violent tornadoes” and can last over an hour.
Where and when do tornadoes occur?
Tornadoes can occur at any time of the year. Tornadoes can form anywhere in the world, but they form most often in regions with flat, dry terrain. Most devastating tornadoes form in Tornado Alley, a region of the Central United States that includes Northern Texas, Oklahoma, Kansas, and Nebraska.
