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Pg. 47 Hurricanes are a type of cyclone that form in subtropics – use heat energy from ocean evap. at low latitudes= storm (called typhoon in western Pacific) Low pressure system NEED 1) WATER 80o in upper 200’-surface 2) Warm and humid air-unstable 3) upper level weak winds-same direction system is already moving 4) wind at ground > 74 mph=hurricane REMEMBER Coriolis Effect-Winds in N. Hemisphere move counterclockwise Add pg. 47 STAGES OF DEVELOPMENT GENERAL FORMATION-ND pg. 338 fig. 12.3 STEPS 1.) Tropical disturbance -low pressure zone that draws in a poorly organized cluster of thunderstorms w/ weak surface winds 2.) Tropical depression – surface winds intensify, receives identifying number, storm begins to rotate counter clockwise a.) center air rises b.) water vapor (lots of energy remember specific heat) releases heat as condenses c.) this heat is released and contributes to further updrafts Add pg. 47 STAGES OF DEVELOPMENT (continued) 3.) Tropical storm- when surface wind speeds reach 39mph 4.) Hurricane - when surface wind speeds reach 74 mph Form at low latitudes, but not TOO low. About 5o or closer to equator the Coriolis Effect is not large enough to produce adequate rotation ADD pg. 47 SO HOW MUCH HEAT WE TALKIN’? The average hurricane generates energy at a rate 200 times greater than out worldwide capacity to generate electricity ADD pg. 47 ND pg. 338 fig. 12.3 again THE EYE 1.) As more and more wind converges (now this is at the surface) /comes rushing in at the center it becomes difficult for all wind to reach the very center 2.) at 74 mph the eye forms hence hurricane status. 3.) Air in the center cools at altitude and sinks, but warms as it descends-backwards/opposite-clear skies 4.) THE EYE WALL has the highest speed winds. Pg. 47 Produce winds up to 150 mph and create storm surge (raising sea level up to 20 feet) DEMO Courtesy of NOAA Magazine ADD Pg. 47 SO…. There are two components or ways to create storm surges 1.) low pressure (rising air) sucking up the ocean surface 2.) the storm system (cyclone) “bulldozing” the ocean surface in front of the cyclone system Here is a new site and animation describing storm surge- Thanks Elizabeth ADD pg 47 Different wind speeds at different points DEMO Storm motion 20 mph Wind speed 120 mph Right hand side Storm Surge? Bulge at center Low pressure Wind speed 80 mph Left-hand side Storm Surge? Wind speed 100 mph ADD pg. 47 Saffir-Simpson Hurricane Damage Potential Scale LINK 1.) barometric pressure-why is this so important? 2.) wind speed 3.) storm surge 4.) damage HOW are each of these things related? THESEWILL BE ON THE TEST STRONG AND WEAK HIGHES AND LOWSND pg. 340/ Table 12.1 DEMO ADD pg. 47 HURRICANE ASPECTS 1.) Latent heat release from condensation of water vapor inside a hurricane system is its main source of energy 2.) Hurricane weaken rapidly over land. WHY? 3.) Fronts are NOT associated with hurricanes. WHY? 4.) The weaker high altitude winds the stronger the hurricane becomes. WHY? 5.) Hurricane centers are warmer than their surroundings. WHY? 6.) Air in the very center sinks downward. Air rises up eye wall. WHY? Pg. 47 CASE HISTORY ANDREW August 1992 Initially formed in Africa - moved over Atlantic and came aground in Florida Tornado-like vortices Storm surge 17’-why so high? Predictable? 33 dead, 80,000 buildings destroyed moved over Gulf of Mexico and hit Louisiana killed 15 more building codes had been in force. Pg. 47 Continued CASE HISTORY ANDREW August 1992 Most destructive in US history until??? 30 billion dollars damage Much of the loss could have been prevented if higher standard Pg. 48 CASE HISTORY KATRINA Evacuation dilemmas? Population relationship? NS pg. 351-knew of the problem. Sept. 2004 Hurricane Ivan Cat. 4 caused evacuation 1 million people fled 72,000 in Superdome But Ivan just missed we are safe now, whew!!! SOCIAL-POLITICAL TIMELINE- I know, politics. Liberal Conservative Another interesting take Pg. 48 We knew the levees wouldn’t hold a Cat.4+to 5 We knew Cat. 5 are possible AND how hurricanes destroy-storm surge New Orleans below sea level. We knew Katrina was coming days in advance (Governor, President, Mayor, Citizens) We are the richest nation in the world. WHAT IS/WAS THE PROBLEM?? CONSIDER AN EQ IN LOGAN HOW WOULD YOU FEEL IF…. Pg. 48 HUGO - ATLANTIC COASTLINE 1989 Charleston, South Carolina Hit land and moved north as tropical-storm intensity 11 people died $7 billion in damage ADDITIONAL CASE HISTORIES IN BOOK? DON’T WORRY ABOUT IT JUST FOCUS ON THESE (IN NOTES AND SLIDES) CROSS OUT IN NOTES Pg. 48 BANGLADESH 1.) Densely populated-big numbers little area 2.) Country is low elevation delta 3.) nation of water 35% of nation is lower than 6m elevation 20% of land floods annually-rivers during wet season 1988-67% of nation was covered by river floods THEN can cyclones and the 6m storm surges. Bad set-up Pg. 48 BANGLADESH continued 4.) Coastline is a funnel that catches and directs cyclones up the Bay of Bengal ND pg. 356 fig. 12.24 5.) Up to 400,000 people have died in cyclone weather (single event) VIDEO THEN A COUPLE MORE EXAMPLES/PUZZLES IF YOU UNDERSTAND THESE YOU WILL DEFINITELY BE ON THE RIGHT TRACK