Chapter 12 Hurricanes ⢠Hurricanes = tropical cyclones = typhoons ...
Chapter 12 Hurricanes Hurricanes = tropical cyclones = typhoons. Convert heat energy of ocean into winds and waves Hurricanes push surges (large mass of sea water) onshore and raise sea level Long lasting: about an hour or two; bigger, slower, longer than tornadoes Hurricanes need: o Warm water – greater than 27 degrees C threshold. They are a heat engine extracting energy from warm (ocean) waters. Water must be greater than 60m thick o No or little wind shear (winds travelling different directions/velocities) o Air over the water must be warm, humid and unstable (usually around equator) Running off latent heat of condensation o Coriolis Effect must occur to spin the system - Air spirals upwind – cyclones, typhoons o Upper-level winds should be weak and preferably blowing in the same direction the storm is moving Hurricanes are unique: o Latent heat released by condensation inside a hurricane is its main energy source o Hurricanes weaken rapidly when they move onto land o Fronts are not associated with hurricanes o Weaker high-altitude winds = stronger hurricanes o Hurricane centers are warmer than their surroundings o Hurricane winds weaken with height o Air in the center of the eye sinks downward Hurricane development: o Tropical disturbance - low pressure zones that draw in a cluster of thunderstorms with weak winds o Tropical depression – surface winds strengthen and flow around a center. Converging surface winds send warm/moist air upwards to stratosphere where it condenses and releases latent heat. This warms surrounding air, and strengthens updrafts o Tropical storm – surface wind speed exceeds 63 km/hr o Hurricane – surface wind speed exceeds 119 km/hr Figure 12.12 – troposphere; northern hemisphere counterclockwise rotation by virtue of the Coriolis Effect. Air spirals upwards; convection is powered solely by the latent heat of condensation Hurricanes don’t form on the actual equator (because it’s Coriolis Effect is zero), and do not cross the equator. Form near the equator. Commonly off the Pacific Coast of Mexico, rarely off of Brazil Wind speeds: 320km/hr is fastest, tornadoes are faster. Diameter is approx 1000km, core where it’s fastest is >200km. Depending which side of the storm you’re on will determine how much damage occurs. On the side where wind speed goes in the same direction as the storm motion, damage will be greater than opposite side where wind speed goes in opposite direction from the storm motion o Damage is asymmetrical in storms o In the northern hemisphere, right side will experience speed of the storm body plus winds (wind comes from ocean), on the left you will feel the wind speed minus storm motion (wind comes from land)
Eye: calm area 30-60 km in the middle of the hurricane, no winds can reach this center when wind speeds exceed 119 km/hr. Cool air sinks, leaving eye clear/cloud free. Eye walls contain fastest winds Energy released by a hurricane by forming clouds and rain is 400x greater than the energy of its winds Saffir-simpson scale measure categories of hurricanes Post tropical transition: when some hurricanes unexpectedly gain strength by moving to higher latitudes and hit cooler/stronger air streams. Hurricane structure deforms and becomes less compact Surge: when the sea comes ashore. Drowning causes most hurricane fatalities. Sea level rises because water build-up beneath the eye because it’s a low pressure zone, and winds on the side of the storm where winds are additive push sea swells ashore. Fatalities caused by: o Majority is wind o Hydrostatic response to pressure Water coming ashore is more deadly than wind Figure 12.22/12.27 North Atlantic Ocean experiences 4-28 hurricanes a year. Late summer is greatest risk because the water retains the most energy from the whole summer (Aug-Oct) Hurricane seasons: early hurricanes stay in the Caribbean, or enter the Gulf of Mexico. Later in the season hurricanes are less likely in the gulf, more likely around the eastern coast of the US. Hurricane status usually revoked by the time storms hit Canada. Luis is a notable exception cat 3 1995 Newfound Land. No cat 4 or 5 in Canada since the confederation. Most common date for a hurricane to hit Canada is Sept 15 Hurricane paths hard to determine because they adjust to high/low pressure in the atmosphere. o At low latitudes, trade winds blow the storm west o Coriolis Effect adds a curve to the right that increases in strength with the distance of the equator o Bermuda High (high pressure zone above North Atlantic Ocean) push hurricanes north (away from land) if it’s small and north. Push hurricanes along east coast of the States if it’s strong and extensive North Atlantic Oscillation (NAO) describes shifting atmospheric pressures, include Bermuda High Figure 12.6 1954 hurricane hazel, Caribbean storm that tracked across eastern US and ended up by Toronto. Caused flooding in T.O that killed thousands Figure 12.5 Saxby-Gale navy astronomer who predicted high tides Texas 1990 deadliest natural disaster in the States. Cat 4 hurricane + high tide. 9m waves, 210 km/hr winds - 6000 died. Went through post-tropical transition and hit Ontario and the Maritimes, disappeared in the North Atlantic Juan 2003 formed off of Africa and travelled across Atlantic. Cat 2 hurricane+ high tides hit Halifax, Dartmouth, Nova Scotia, Prince Edward Island Hurricanes can form where the trade winds meet the equator (Intertropical convergence zone) where a low pressure area creates thunderstorms. Mitch 1998 formed at the ITCZ over the Caribbean Sea. Cat 5 hurricane 290 km/hr winds, gusts greater than 320 km/hr for 33 consecutive hours. Hurricane never hit land but acted like a vacuum that sucked up all the sea water and then dumped it as rainfall over Honduras and Nicaragua. Water filled a volcano and initiated a lahar. Lasted 15 days, and killed 11000
Cape-Verde and Caribbean/Gulf of Mexico type hurricanes Forecasting: more thunderstorms when o Western Africa is wet o Sea-surface temperatures are warmer o Low atmospheric temperatures in the Caribbean o La Nina conditions exist in the Pacific Ocean (west blowing winds encourage hurricanes), If El Nino exists, east blowing winds break up hurricanes Bangladesh – unfavorable shoreline, sits on sediments, 7 recent cases of hurricanes. The shoreline is less than a meter above sea level – densely populated in a small area. o Floods are common o Cyclone killed almost 400 000 people 1970, 7m waves, 255km/hr winds o Another cyclone killed 140 000 in 1991 235km/hr winds, 6m waves There are more hurricanes in the Pacific Ocean, but they don’t hit land as often as Atlantic Ocean hurricanes because trade winds blow them out into the Pacific Ocean, and the difference in water temperature. Freda 1962 worst hurricane to hit Canada’s west coast. California and BC hit Reducing Hurricane damage: o Build houses on higher ground, parks/golf courses etc on lower grounds o Design buildings that pass wind energy from the roof through the walls so roof doesn’t lift off. Strap roofs to walls o Ban the common practice of using rapid-fire staples to secure thin asphalt roofing sheets onto plywood Fabian, Bermuda 2003 cat 3 hurricane caused little damage because Bermuda government enforces strict building policies
Movie: Hurricane Katrina August 23-31, 2005 – tropical storm. 25th it becomes a hurricane. 26th it becomes a level 2 hurricane, people are preparing for hit. 28th it becomes category 4. 29th is it hit New Orleans, it became category 5 (rare-highest ranking) and mandatory evacuation is implemented 61 thousand died; 1 million people evacuated; 500, 000 homeless Only moves at 8 miles/hour, usually reaches 15 m/hour Hurricane died a bit after hitting FL, when it went over Gulf of Mexico warm water strengthened it again New Orleans is 6m below sea level, due to subsidence ground is still sinking and levees are built higher. Levees keep out water, but also new sand/mud to strengthen new land Not a surprise, major hurricane was predicted for years to hit New Orleans FEMA is the organization that handles national natural disasters Hurricane Hazel October 1954, 1000 fatalities in Haiti. Less in North Carolina Original storm combined with another tropical storm and headed towards Toronto
Eye: calm area 30-60 km in the middle of the hurricane, no winds can reach this center when wind speeds exceed 119 km/hr. Cool air sinks, leaving eye clear/cloud free. Eye walls contain fastest winds Energy released by a hurricane by forming clouds and rain is 400x greater than the energy of its winds Saffir-simpson scale measure categories of hurricanes Post tropical transition: when some hurricanes unexpectedly gain strength by moving to higher latitudes and hit cooler/stronger air streams. Hurricane structure deforms and becomes less compact Surge: when the sea comes ashore. Drowning causes most hurricane fatalities. Sea level rises because water build-up beneath the eye because it’s a low pressure zone, and winds on the side of the storm where winds are additive push sea swells ashore. Fatalities caused by: o Majority is wind o Hydrostatic response to pressure Water coming ashore is more deadly than wind Figure 12.22/12.27 North Atlantic Ocean experiences 4-28 hurricanes a year. Late summer is greatest risk because the water retains the most energy from the whole summer (Aug-Oct) Hurricane seasons: early hurricanes stay in the Caribbean, or enter the Gulf of Mexico. Later in the season hurricanes are less likely in the gulf, more likely around the eastern coast of the US. Hurricane status usually revoked by the time storms hit Canada. Luis is a notable exception cat 3 1995 Newfound Land. No cat 4 or 5 in Canada since the confederation. Most common date for a hurricane to hit Canada is Sept 15 Hurricane paths hard to determine because they adjust to high/low pressure in the atmosphere. o At low latitudes, trade winds blow the storm west o Coriolis Effect adds a curve to the right that increases in strength with the distance of the equator o Bermuda High (high pressure zone above North Atlantic Ocean) push hurricanes north (away from land) if it’s small and north. Push hurricanes along east coast of the States if it’s strong and extensive North Atlantic Oscillation (NAO) describes shifting atmospheric pressures, include Bermuda High Figure 12.6 1954 hurricane hazel, Caribbean storm that tracked across eastern US and ended up by Toronto. Caused flooding in T.O that killed thousands Figure 12.5 Saxby-Gale navy astronomer who predicted high tides Texas 1990 deadliest natural disaster in the States. Cat 4 hurricane + high tide. 9m waves, 210 km/hr winds - 6000 died. Went through post-tropical transition and hit Ontario and the Maritimes, disappeared in the North Atlantic Juan 2003 formed off of Africa and travelled across Atlantic. Cat 2 hurricane+ high tides hit Halifax, Dartmouth, Nova Scotia, Prince Edward Island Hurricanes can form where the trade winds meet the equator (Intertropical convergence zone) where a low pressure area creates thunderstorms. Mitch 1998 formed at the ITCZ over the Caribbean Sea. Cat 5 hurricane 290 km/hr winds, gusts greater than 320 km/hr for 33 consecutive hours. Hurricane never hit land but acted like a vacuum that sucked up all the sea water and then dumped it as rainfall over Honduras and Nicaragua. Water filled a volcano and initiated a lahar. Lasted 15 days, and killed 11000
Cape-Verde and Caribbean/Gulf of Mexico type hurricanes Forecasting: more thunderstorms when o Western Africa is wet o Sea-surface temperatures are warmer o Low atmospheric temperatures in the Caribbean o La Nina conditions exist in the Pacific Ocean (west blowing winds encourage hurricanes), If El Nino exists, east blowing winds break up hurricanes Bangladesh – unfavorable shoreline, sits on sediments, 7 recent cases of hurricanes. The shoreline is less than a meter above sea level – densely populated in a small area. o Floods are common o Cyclone killed almost 400 000 people 1970, 7m waves, 255km/hr winds o Another cyclone killed 140 000 in 1991 235km/hr winds, 6m waves There are more hurricanes in the Pacific Ocean, but they don’t hit land as often as Atlantic Ocean hurricanes because trade winds blow them out into the Pacific Ocean, and the difference in water temperature. Freda 1962 worst hurricane to hit Canada’s west coast. California and BC hit Reducing Hurricane damage: o Build houses on higher ground, parks/golf courses etc on lower grounds o Design buildings that pass wind energy from the roof through the walls so roof doesn’t lift off. Strap roofs to walls o Ban the common practice of using rapid-fire staples to secure thin asphalt roofing sheets onto plywood Fabian, Bermuda 2003 cat 3 hurricane caused little damage because Bermuda government enforces strict building policies
Movie: Hurricane Katrina August 23-31, 2005 – tropical storm. 25th it becomes a hurricane. 26th it becomes a level 2 hurricane, people are preparing for hit. 28th it becomes category 4. 29th is it hit New Orleans, it became category 5 (rare-highest ranking) and mandatory evacuation is implemented 61 thousand died; 1 million people evacuated; 500, 000 homeless Only moves at 8 miles/hour, usually reaches 15 m/hour Hurricane died a bit after hitting FL, when it went over Gulf of Mexico warm water strengthened it again New Orleans is 6m below sea level, due to subsidence ground is still sinking and levees are built higher. Levees keep out water, but also new sand/mud to strengthen new land Not a surprise, major hurricane was predicted for years to hit New Orleans FEMA is the organization that handles national natural disasters Hurricane Hazel October 1954, 1000 fatalities in Haiti. Less in North Carolina Original storm combined with another tropical storm and headed towards Toronto
