Tropical Cyclones TROPICAL CYCLONES HURRICANES TYPHOONS Katrina aiming for New Orleans 27 August 2005 Tropical Cyclones

Tropical Cyclones A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms Tropical Cyclones: Grounds of rotating, low-pressure storms. cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure

Cyclones, Hurricanes, Typhoons Named according to region where they develops Cyclones – Develop over the Indian Ocean on warm waters Hurricanes - Develop over Atlantic and eastern Pacific Oceans Typhoons – Develop over western Pacific Oceans All produce similar effects Eye Typhoon Odessa, Philippines

Developmental Stages Progression: depression storm cyclone Classified according to wind speeds Tropical Depression - sustained winds less than 39 m/h Tropical Storm - between 39 m/h and 73 m/h Tropical Cyclone - at least 74 m/h

Tropical Cyclones Introduction Tropical cyclones are intense, rotating, low- pressure storms Develop over warm, tropical oceans Produce strong winds and heavy rainfall Can lead to immense flooding Destructive Winds

Formation of tropical cyclones Tropical Cyclones require to basic conditions to form: an abundant supply of very warm ocean water and some sort of disturbance to lift warm air and keep it rising.

Formation of Tropical Cyclones Warm water generates formation of tropical cyclones Ocean temperatures must be at least 26.5°C which is warm Over warm oceans moist, humid air (water vapour) Warm air moves along the surface This air converges and rises rapidly Intense rising of air forms low pressure systems

Formation of Tropical Cyclones As air rises, it cools, becomes saturated and condenses Water vapour condenses into liquid droplets Formation of thunderclouds Condensation releases heat stored in water vapour This latent heat warms the atmosphere Air becomes lighter causing strong updrafts

Formation of Tropical Cyclones Air expands and diverges at higher levels Occurs only where wind speed/direction remain constant (no wind shear) Air moves in at surface taking the place of rising air This intensifies convergence Creates wind and increases rising movement Builds and progresses into a mature cyclone

Coriolis Effect Spinning of earth on its axis produces wind deflections (Coriolis Effect) Causes rising air to spiral around center (core) Spirals with great force Winds are now rotating, rising and moving in to fill spaces Wind speeds increase and cyclone grows

Coriolis Effect Northern hemisphere winds are blowing counter- clockwise around center core Southern hemisphere winds are blowing clockwise around center core

The Eye, Eyewall, Rainbands The Eye - the clear, calm center of storm Cool air descends into this center (downdrafts) Eyewall – ring of thunderstorms close to eye Eyewall produces the most devastating winds Rainbands – curved groups of clouds and thunderstorms Rainbands travel away from eye in a spiral motion

Storm Surges Occur when tropical cyclones reach land Storm surge – raised swell of water 60 to 80 km across Around 2 to 5 meters higher than normal tides Created by heavy winds and cause flooding

WIND PENETRATING BUILDING ENVELOPE CAUSES OF DAMAGE WIND PENETRATING BUILDING ENVELOPE UPLIFT OF ROOF SYSTEM FLYING DEBRIS SEVERE WINDSTORMS STORM SURGE IRREGULARITIES IN ELEVATION AND PLAN DESIGN PROBLEMS FLOODING AND LANDSLIDES

AUSTRALIA’S COMMUNITIES HAZARDS INVENTORY AT RISK VULNERABILITY LOCATION CYCLONE RISK ACCEPTABLE RISK UNACCEPTABLE RISK RISK CYCLONE DISASTER RESILIENCE DATA BASES AND INFORMATION AUSTRALIA’S COMMUNITIES PREPAREDNESS PROTECTION EARLY WARNING EMERGENCY RESPONSE RECOVERY and RECONSTRUCTION POLICY OPTIONS HAZARDS: GROUND SHAKING GROUND FAILURE SURFACE FAULTING TECTONIC DEFORMATION TSUNAMI RUN UP AFTERSHOCKS