Tropical weather systems-1.pdf

Tropical weather systems Tropical Cyclone Structure Easterly wave Trough of low pressure Moves slowly on trade winds Over oceans 5-30°N of the equator Can grow into tropical cyclone  Most Powerful, Destructive Cyclonic Storms Its called a:...

Tropical weather systems Tropical Cyclone Structure Easterly wave Trough of low pressure Moves slowly on trade winds Over oceans 5-30°N of the equator Can grow into tropical cyclone  Most Powerful, Destructive Cyclonic Storms Its called a: Western Hemisphere → Hurricane Western Pacific → Typhoon Indian Ocean → Cyclone Tropical Develop from easterly waves 10-20°N & S Cyclone Grow from tropical depressions (a weak cyclone with a maximum wind speed of 38 MPH) Structure Once the cyclone speed passes 38MPH the storm is upgraded to a tropical storm (tropical storm is between 35- 74 mph winds) Once the winds are sustained past ≥ 74 mph → it’s a Tropical Cyclone  Tropical Cyclone Cross Section Extremely low pressure/Strong pressure gradient Intense convergence & uplift → Heavy rainfall Latent heat release provides energy aloft, temperature of the ocean provides convective energy transfer Why are cyclones consistently getting stronger? Because an increase in greenhouse gases in our atmosphere and ocean mean more trapped heat – so more convective energy Imagine turning the heat up on a stove and watching the increase in steam from the hot water  Eye of a Tropical Cyclone Eye Intense spiraling of storm keeps it clear Descending air warms → Water droplets evaporate Calm air prevails in the eye Positive Feedback in a Tropical Cyclone Easterly wave initiates convection Low pressure forms at surface Warm, moist air spirals inward from ocean Air rises, expands, cools, and condenses Condensation release latent heat into storm Warmer air rises faster Faster rising air drives inward spiral of air And so on… Tropical Cyclone Origins & Tracks Most tropical cyclones form at 10–20°N or S Follow cyclone tracks west turning to northeast Tropical cyclones fade in cool westerlies None in South Atlantic or SE Pacific Tropical Cyclone Needs To begin at least 5° from equator (No Coriolis there) Warm water (at least 26.5°C for a sustained period of time) for latent & sensible heat Unstable air (high env. lapse rate) Weak but uniform steering winds Very moist lower atmosphere Lacking any one factor → there is no tropical cyclone  Each region has its own list of names Alphabetical lists alternate male-female Naming Names are reused after some years Tropical Names of serious storms are retired Examples of retired Atlantic hurricane names: Cyclones Katrina (2005) Andrew (1992) Camille (1969) Hugo (1989) Measuring the Impact of Tropical Cyclones  Tropical Cyclone Hazards Wind Damage – some produce wind gusts >200 mph Fresh Water Flooding – can extend far inland Earthflows – due to heavy rainfall & saturated soil Storm Surge – this causes the most serious damage from a cyclone – can inundate coast - due to low pressure and high winds Height of storm surge Normal high tide  Impacts on Coastal Communities The Case of Katrina & New Orleans (2005) Eye hit Grand Isle, LA – 125 mph sustained wind New Orleans largely below sea level Levees protect north & east of New Orleans from Lake Pontchartrain/Mississippi Rainwater pumped from city through discharge canals Levees north & east of city overtopped or collapsed under the power of Katrina, and water just flowed into the city like a bowl being submerged in a tub of water Impacts on Coastal Communities The Case of Katrina & New Orleans (2005) At peak, over 80% of city under water Water 20 feet deep in places Over $100B in damage Over 1300 killed in New Orleans alone Two Weeks After Katrina Devastation caused by Katrina and broken levees Houses gone, and a barge washed ashore  Cyclical Patterns of Atlantic Hurricanes 1970-1994 was down time for Atlantic storms Since 1995: Warmer water off east coast of US On average, more hurricanes each year On average, more major hurricanes each year 2005 was record year with 28 storms Likely due to cycle in thermohaline circulation Next 20 years likely continued high hurricane activity