1. Hurricanes Earth’s Largest Storms

2. Hurricanes Hurricanes are the largest storms that occur on Earth. Hurricanes are very large, swirling, low pressure systems that form over tropical waters (water temp. must be at least 80 0 F). Hurricanes can last for days due to the constant supply of energy from the warm waters.

4. When Does A Storm Become A Hurricane? To be classified as a hurricane there must be sustained winds of greater than 74mph. –G–Greatest winds recorded are 236mph; Category 5 “Mitch” in Nov 1998= most deadly hurricane ever.

6. What is a Pressure System? Pressure = as particles move and collide they exert pressure.Pressure = as particles move and collide they exert pressure. Differences in air pressure have a great affect on the weather.Differences in air pressure have a great affect on the weather.

7. Pressure Systems When particles are more densely packed together they exert high pressure.When particles are more densely packed together they exert high pressure. –High air pressure usually means clear, fair weather. When they are less densely packed they exert less (low) pressure.When they are less densely packed they exert less (low) pressure. –Low air pressure usually means clouds and rainy weather.

9. High Pressure System Cold air is dense and it sinks. As the air sinks it warms up. Warm air holds more water vapor. –The total amount of water vapor remains the same. As the air warms the relative humidity decreases as droplets in the clouds evaporate. A high pressure system usually means fair weather as the moisture in the air is evaporated so few clouds form.

10. Low Pressure System Warm air has low density and it rises (forced upwards by surrounding denser air).Warm air has low density and it rises (forced upwards by surrounding denser air). As the air rises it cools.As the air rises it cools. As the air cools the relative humidity increases – eventually reaching the dew point.As the air cools the relative humidity increases – eventually reaching the dew point. –At the dew point condensation takes place and clouds form. Low pressure systems usually form along fronts where warm air and cold air meet.Low pressure systems usually form along fronts where warm air and cold air meet. A low pressure system leads to precipitation in the form of rain, snow, hail, sleet.A low pressure system leads to precipitation in the form of rain, snow, hail, sleet. Low pressure systems cause most of the severe weather in the US.Low pressure systems cause most of the severe weather in the US.

14. Where Hurricanes Form Hurricanes form in the “Tropics”. The “Tropics” are centered around the equator (00 latitude) extending north to the Tropic of Cancer (23.50 N latitude) and south to the Tropic of Capricorn (23.50 S latitude).

16. Hurricane Origins

17. Pinpointing Locations On Earth In order to find exact locations on Earth a system of grid lines is used. (Similar to graph paper). latitude run east/westLines of latitude run east/west around the earth, parallel to the equator. longitude run north/southLines of longitude run north/south through the poles of the earth.

19. Latitude latitudeThe latitude lines are east/west lines based on the geometry of the earth using the axis of the earth and the equator. –Latitude range is 0 0 to 90 0 –Latitude range is 0 0 to 90 0. equator is 0 0 latitudeThe equator is 0 0 latitude, (this is the longest distance around the earth traveling on the same latitude line). North Pole is 90 0 North latitudeThe North Pole is 90 0 North latitude. South Pole is 90 0 South latitudeThe South Pole is 90 0 South latitude. Your latitude is the angle created using the axis (center of the earth), the equator and your location.

20. Latitude Lines

21. Longitude longitude Longitude range is 0 0 to 180 0The longitude lines are north/south lines, based on time (the rotation of the earth), using the Prime Meridian and the North and South Poles. Longitude range is 0 0 to 180 0. LongitudeLongitude lines are all the same length as each one connects the North and South Poles and splits the earth into equal halves – this is why they are often referred to as meridians. Prime Meridian is 0 0 longitude.The Prime Meridian is 0 0 longitude. Prime MeridianThe Prime Meridian passes through Greenwich, England which is the time keeping capital of the world. Your longitude is your time (of the Earth’s rotation) away from the Prime Meridian.

22. Earth’s Lines of Longitude

23. How Hurricanes Form Hurricanes form over warm tropical oceans where two opposing winds meet and begin to swirl. A low pressure forms in the middle of the swirling winds and begins rotating. Warm moist air is forced upwards in the center. The dropping pressure in the center pulls more air toward the center creating increasing winds and lower pressure. This cycle of increasing strength continues as long as the storm remains over warm water. Hurricanes weaken as they hit land because there is no longer a supply of energy (from the warm water) available.

25. Life Cycle of a Hurricane 1.Form first as a low pressure system, 2.Grow into a tropical depression (<31mph winds), 3.Grow into a tropical storm (32-74mph winds), 4.Grow into a hurricane (>74mph winds). Out of the 10 tropical storms per year average, 6 will develop into hurricanes and 2 will strike the US.

26. Measuring Strength of Hurricanes Saffir-Simpson ScaleThe strength of hurricanes is measured using the Saffir-Simpson Scale. This scale takes into account several variables of hurricanes including atmospheric pressure, wind speed and storm surge. Category 1 (weakest) Category 5 (strongest).Once a storm becomes a hurricane they can range from Category 1 (weakest) to Category 5 (strongest).

27. Hurricane Strength The Saffir – Simpson Scale CategoryAtm. Pressure (mb.) Wind Speed (mph) Storm Surge (feet) 1>98074 – 954 – 5 2965 -97996 – 1106 – 8 3945 -964111 – 1309 – 12 4920 -944131 – 15513 – 18 5<920>155>18