Weather & Hurricanes State Objectives 4.c, 4.d, 4.h.

What are some ways in which weather affects your everyday life? Discussion What are some ways in which weather affects your everyday life?

Discussion What facts do weather forecasters seem to tell us most about when they are predicting the weather ?

What is Weather? Most Weather occurs in the troposphere Weather is the conditions of the atmosphere. Temperature Air Pressure Wind Humidity Clouds Precipitation Most Weather occurs in the troposphere Main cause for changes in weather is energy from the sun.

How does the Earth stay warm? Discussion How does the Earth stay warm? Earth absorbs energy from the sun & release it back to the atmosphere

Temperature Indicates the amount of heat (kinetic energy) in the atmosphere. Represents the speed of the molecules. The higher the temperature, the faster the air molecules are moving. Measured with a thermometer. Standard unit is Fahrenheit (°F) SI Unit is Celsius (°C)

Air Pressure/Barometric Pressure Air pressure is a measure of the force of air being exerted on a given area of Earth’s surface. Air has weight because it has mass. Different regions of Earth absorb, reflect and re-emit radiation in different ways causing pressure to vary As air warms it becomes less dense, rises, & pressure decreases As air cools it becomes more dense, sink, & pressure increases

Convection in the Atmosphere The rising & sinking of air causes convection currents in the atmosphere.

Altitude affects Air Pressure As altitude increases, air pressure decreases due to the gravitational force.

Weather and Air Pressure Changes in pressure indicated a change in weather is approaching. Low pressure systems are associated with clouds & precipitation. High pressure systems are associated with clear skies. Steady pressure indicates current conditions will continue. Measured with a barometer in inches of mercury or in millibars.

Wind Caused by differences in air pressure Air moves from areas of high pressure to areas of low pressure Wind Speed Measure of how fast the air is moving. Measured with an anemometer.

Wind Wind Direction: observed from where the wind is coming, NOT the direction it is blowing Ex. North winds blow from N to S Measured with a wind vane.

Global Winds Large convection currents cause winds to blow steadily across Earth in paths that are thousands of kilometers long Help move weather around the world

Coriolis Effect https://www.youtube.com/watch?v=zNlV_Trkrs4 Earth’s rotation causes winds to curve to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Global Wind Patterns Surface winds at lower altitudes: Westerlies: blow from west to east in the mid-latitudes. (United States) Trade winds: blow from east to west near the equator.

Global Wind Patterns Higher Altitude Global Winds Jet streams: high altitude bands of strong winds (up to 350 km/h) near the top of the troposphere Race from west to east

Humidity Amount of water vapor in the air. Relative humidity is a percentage of the amount of water vapor in the air compared to the maximum amount of water vapor it can hold at that temperature. The warmer the temperature the more water vapor it can hold. Saturated means the air is holding 100% of the water vapor it can hold at that temperature. Measured with a hygrometer or a psychrometer.

Relative Humidity

Dew point Causes clouds to form high in the atmosphere Dew point is the temperature at which water vapor condenses into a liquid and becomes saturated. Depends on two factors: Amount of water vapor in the air (humidity) Temperature near the surface Causes clouds to form high in the atmosphere

Clouds Clouds form when air rises, cools to the dew point, and condenses.

Clouds Clouds are classified by height and shape

The Water Cycle Changes in weather depend on the water cycle. Constant movement of water on Earth. Energy is provided by the Sun.

Parts of the Water Cycle 1. Evaporation: water changes from a liquid into a gas after gaining heat energy from the Sun. Transpiration: evaporation of water from the leaves of plants.

Parts of the Water Cycle 3. Condensation: water vapor changes into a liquid to form clouds or fog. water vapors reaches dew point 4. Precipitation: drops of water or crystals of ice become too large to be suspended in a cloud and fall back to Earth rain, freezing rain, sleet, snow, or hail

What is an Air Mass? An air mass is a large body of air that develops over a particular region. It has characteristics of the area over which it develops.

Types of Air Masses Cold, dry air masses develop over land in the North Warm, dry air masses develop over land in the South Cold, moist air masses develop over the oceans in the North Warm, moist air masses develop over the oceans in the South

Air Mass Locations

Fronts A front is a boundary between two air masses in an area of low pressure.

Types of Fronts 1. A cold front forms when a cold air mass pushes under a warm air mass. Often associated with thunderstorms

Types of Fronts 2. A warm front forms when a warm air mass moves up and over a cold air mass. Cirrus and stratus clouds form and light, steady precipitation occurs.

Types of Fronts 3. A stationary front forms when a warm air mass meets a cold air mass but neither advances.

Types of Fronts 4. An occluded front forms when a fast-moving cold air mass overtakes a slower warm air mass. Weather is similar to, but less severe than, the weather along a cold front.

Meteorologists A scientist that studies the weather & uses the data to make predictions about weather. Observe patterns & create weather maps A weather forecast is a prediction of present conditions based on observations and data.

Weather Map Symbols

Weather Map Symbols HIGH PRESSURE SYMBOL LOW PRESSURE SYSTEM

Severe Weather Thunderstorms: brief, intense storms produced by rapidly rising clouds. Cumulonimbus (thunderheads) - vertical clouds that may be over four miles tall. They form where cold air forces warm air to rise quickly. May produce hail Lightning is huge electrical discharges. A tornado is a violent, whirling wind that moves in a narrow path over land.

TORNADOES!!!!!!

What is a Hurricane? A hurricane is a low-pressure system that forms over tropical oceans. Also called typhoons or tropical cyclones.

Disturbances, Depressions, and Storms A tropical disturbance is an area of organized convection that originates in the tropics. It has no eye or rotation. A tropical depression is a cyclone that has a maximum wind speed of 38 mph. A tropical storm has a wind speed between 39 mph and 73 mph.

Conditions Required for Hurricane Formation Warm ocean waters of at least 80° F. High humidity in the troposphere. An atmosphere that quickly cools with altitude. A distance of at least 300 miles from the equator. A surface system with convergent winds. Low wind shear. Wind shear is the rate of wind speed or direction change with altitude.

Parts of a Hurricane The eye is the circular area of calm, relatively light winds at the center of a hurricane. It is the area of lowest pressure. The eyewall is the ring surrounding the eye that contains the highest wind speeds. Rainbands are bands of heavy rain that spiral outward from the storm’s center.

Parts of a Hurricane

Where Hurricanes Form

When Hurricanes Occur The Atlantic hurricane season lasts from June 1- November 30. These dates include about 97% of hurricanes. Most occur from August to October.

When Hurricanes Occur

Paths of Hurricanes Hurricanes can be tracked using satellites, radar (near land), and hurricane hunters. Gathers data including wind direction and speed, pressure, temperature, and humidity from the planes altitude to the water’s surface. Path depends on where the hurricane forms. Trade winds cause hurricanes to move west near the equator. As hurricanes move north, they begin to turn back to the east after the 30N latitude line.

Hurricane Paths

Hurricane Ike

Effects of Hurricanes High winds Heavy rain and flooding Tornadoes after landfall Storm surge is the rising wall of water that comes ashore with a hurricane. It causes the most damage and is responsible for 90% of deaths.

Storm Surge Storm Surge Animation

Rating Hurricanes The Saffir-Simpson scale is uses wind speed to rate the strength of hurricanes. Category 1- 74-95 mph Minimal Category 2- 96-110 mph Moderate Category 3- 111-130 mph Extensive Category 4- 131-155 mph Extreme Category 5- 156+ mph Catastrophic

Strongest Hurricanes in History Typhoon Tip (1979) was the most intense (lowest pressure- 870 mb) hurricane in history. Hurricane Wilma (2005) was the strongest Atlantic hurricane. Typhoon Nancy (1961) had maximum sustained winds (two minute average) of 213 mph.

Size of Typhoon Tip Had a diameter of almost 1,400 miles.

Path of Typhoon Tip

Hurricane Katrina (2005) Costliest hurricane in U.S. history ($81 billion in damage). Fifth deadliest hurricane (1,836 deaths) Crossed Florida as a Category 1 but gained strength in the Gulf of Mexico. Made landfall in Louisiana and Mississippi on August 29 as a Category 3.

Path of Katrina

Katrina from Satellite

Katrina Damage

Katrina Damage

Waveland, Mississippi

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