Lesson 21: Weather • AGENDA: • Causes of Weather • Weather Elements • Basic Weather Phenomena (Fronts, Systems) • Hurricanes/Typhoons • Marine Weather Prediction • Applicable reading: Hobbs WB, App A
Overview Weather: the state of the Earth’s atmosphere SPECIFICALLY: Air Flow: The circulation of air about the planet caused by temperature differentials. Pressure Areas: The relationship between temperature and pressure and wind. Fronts: The transition zone or interface between two air masses of different densities.
Weather Elements TEMPERATURE WINDS PRESSURE HUMIDITY CLOUDS PRECIPITATION
Temperature Temperature:the amount heat in the atmosphere. • Causes: • The Earth’s daily rotation about its axis • The Earth’s annual revolution about the sun • Effects: • The uneven heating and cooling of the Earth’s surface results in air flow about the planet.
Wind Wind: The horizontal movement of the atmosphere • Causes: • Temperature differentials • Coriolis Effect • Maritime significance: • Result in areas of High and Low pressure.
Air Flow Forces that define air flow: 1. Pressure 2. Earth’s Rotation 3. Friction from the surface of the earth
Pressure Atmospheric Pressure: The weight of the atmosphere. • Causes: • Divergence and convergence of air • Changes in Altitude/Depth • Maritime significance: • High/Low pressure systems • Low (L) - caused by converging winds; rotate counter-clockwise • High (H) - caused by diverging winds; rotate clockwise
Weather Fronts • High and Low pressure systems travel from the areas where they are created. • When air masses meet, they “compete” for dominance. • The boundary zone between these two masses is known as a front.
Weather Fronts Fronts: a zone of transition between air masses • Cold Front -when a cold air mass displaces a warm air mass by vigorously forcing it up. • move fast, 20-35+ kts • weather deteriorates rapidly • Warm Front - when a warm air mass displaces a cold air mass. • warm air slides over cold air • move slowly, 19-15 kts • weather deteriorates gradually
Basic Weather Phenomena • Clouds • Fog • Tropical storms/hurricanes/typhoons
Heavy Weather 1. Closed Cyclonic - Rotary circulation storms. 2. Noncyclonic - Storms produced by prevailing winds are identified by their accompanying winds - predictable.
Closed Cyclonic 1. Tornadoes - Violent, whirling storm of small diameter that travels across land. Appear as funnel shaped cloud, with a vortex that may or may not touch the earth. Winds blow spirally upwards from 150 - 300 mph. 2. Waterspouts - Similar to tornadoes, occurring over oceans or inland waters. Usually less destructive than tornadoes.
Closed Cyclonic 3. Squall - A wind of considerable intensity caused by atmospheric instability. Comes up & dies quickly, sometimes accompanied by thunder, lightning and precipitation. 4. Monsoons - Steady winds somewhat similar to trade winds. Can reach moderate gale proportions and are accompanied by heavy squalls and thunderstorms during the summer.
Closed Cyclonic 5. Hurricanes - Tropical storm with continuous winds greater than 75 mph (64 kts). 6. Tropical Storms - Categorized based on wind speed: - Tropical Depression: < 34 kts - Tropical Storm: 34 - 63 kts - Hurricane: > 63 kts
Noncyclonic ie: gale - with winds from 34 - 47 mph storm - with winds of 48 mph or greater.
Weather Elements(Review) TEMPERATURE WINDS PRESSURE HUMIDITY CLOUDS PRECIPITATION
Clouds Clouds: condensed water droplets or ice crystals suspended over the surface of the earth • Causes of clouds • Clouds are formed by the cooling of saturated air by the ocean of land surface beneath. • Basic Types of Clouds • Cirrus • Cumulus • Stratus
Coastal Fog Fog: a cloud that “touches” the surface of the earth. • Causes of clouds/fog • Clouds are formed by the cooling of saturated air by the ocean of land surface beneath. • Prediction of fog • If the difference between air temperature and dew point is less than 2°F, fog may result.
Hurricanes/Typhoons Hurricanes: violent storms with no associated weather front. • Causes: • Storms begin in a low-pressure area, lifting of the air, and a counter-clockwise inward wind flow. • Heat released by condensation of water vapor from the surface below aggravates the process and the storm builds in intensity.
Review/Summary • What 3 elements cause weather? • Name 4 of the 6 basic weather elements • What is a front? • Describe the following types of clouds • Cirrus • Stratus • Cumulus