Lesson 15 A Weather Lesson 21 Weather AGENDA

Lesson 15 A: Weather

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 HUMIDITY PRESSURE CLOUDS PRECIPITATION

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: 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 counterclockwise High (H) - caused by diverging winds; rotate clockwise

Low Pressure System Air Flow

High Pressure System Air Flow

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: 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

Frontal Passage

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 HUMIDITY PRESSURE CLOUDS PRECIPITATION

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: 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

Questions?