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Hurricanes Reading

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McGill University
Earth & Planetary Sciences
EPSC 185
John Stix

EPSC 185 – Natural Disasters Fall 2013 Hurricanes  Introduction  tropical cyclone: warm-core, low pressure system without any “front” attached  develops over tropical/subtropical water  has an organized circulation  have different names depending on location  Atlantic/Eastern Pacific Oceans  hurricanes  Western Pacific  typhoons  Indian Ocean  cyclones  favourable environmental conditions  warm ocean water (at least 80 F/27 C) throughout depth (150 ft/46 m)  atmosphere that cools fast enough with height, for potentially unstable moist convection  relatively moist air near mid-level of troposphere (16 000 ft/4 900 m)  minimum distance of 300 miles/480 km from equator  pre-existing near-surface disturbance  low values (<23 mph/37 km/h) of vertical wind shear between surface & upper troposphere  vertical wind shear: change in wind speed with height  rare that they don’t form within 5 degrees latitude of the equator  due to lack of sufficient Coriolis Force (what causes cyclone to spin)  tropical cyclone observations started 1886 in North Atlantic; 1945 in western North Pacific  form in 7 regions around the world  Typhoon Vamei (formed near Singapore, not near equator) formed December 27, 2011  maximum sustained surface wind reported = 87 mph; gust wind, 120 mph  previous recorded lowest latitude for tropical cyclone = 3.3 degrees N (Typhoon Sara, 1956)  Typhoon Vamei’s circulation on both sides of equator  disturbances: seedlings of tropical cyclones  once formed & substance convection develops, can become more organized under certain conditions  if moves/stays over warm water & upper level winds remain weak, disturbance can become more organized, forming a depression  easterly waves/tropical waves  inverted trough of low pressure moving generally westward in tropical easterlies o trough: region of relative low pressure o majority of tropical cyclones form from this  West African Disturbance Line (WADL)  line of convection which forms over West Africa & moves in Atlantic Ocean  usually move faster than tropical waves  Tropical Upper Tropospheric Trough (TUTT)  trough, cold core low in upper atmosphere, which produce convection  Old Frontal Boundary  remnants of polar front can become lines of convection & occasionally generate a tropical cyclone o occurs early or late in hurricane season in Gulf of Mexico or Caribbean Sea  warm water = important key to cyclone since it powers it  as water vapour rises it cools  causes vapour to condense into liquid (clouds)  during condensation, heat is released  heat warms atmosphere making air lighter so it continues to rise  more air then moves in near surface to replace it  strong wind felt from storms  once eye of storm moves over land, weakens rapidly due to lack of moisture & heat sources of ocean  weakens ability to produce thunderstorms  purpose of tropical cyclones: to take heat stored in the ocean & transfer it to the upper atmosphere where upper level winds carry that heat to the poles  keeps polar regions front being as cold as they could be & keeps tropics from overheating  suggestions for mitigation  “seeding” storms to soak-up some of the moisture  use nuclear weapons to disrupt circulation & decrease their intensity  decrease in intensity = oceans retain more heat which could enhance subsequent storms & lead to more numerous and/or stronger events  Classification  tropical depression: tropical cyclone with an organized systems of clouds and thunderstorms with a defined circulation, maximum sustained winds of 38 mph/ 61 km/h or less o once the winds reach 39 mph/63 km/h they are a tropical storm  if winds 74 mph/119 km/h it is called a:  hurricane in North Atlantic Ocean, Northeast Pacific Ocean east of dateline & South Pacific Ocean east of 160°E  typhoon in Northwest Pacific Ocean west of the dateline  severe tropical cyclone in Southwest Pacific Ocean west of 160°E or Southeast Indian Ocean east of 90°E  severe tropical storm in North Indian Ocean  tropical cyclone in Southwest Indian Ocean  further classified by Saffir-Simpson Hurricane Wind Scale  1-5 rating based on present intensity  only addresses wind speed, not potential for other hurricane-related impacts (storm surge, rainfall-induced floods, tornadoes)  earlier versions incorporated central pressure & storm surge BUT hurricane size, local bathymetry (depth of near-shore waters), topography, speed & angle to coast also affect surge  category 5  157 mph; 252 km/h  very high risk of injury/death from flying/falling debris, even indoors  almost complete destruction of all mobile homes; high percentage of framed homes destroyed  total roof failures, collapsed walls  complete collapse of older metal buildings  nearly all windows blown out  nearly all trees snapped/uprooted  fallen trees/power poles isolate residential areas  power outages last for weeks-months  ie/ Hurricane Mitch (1998) over Western Caribbean; Hurricane Gilbert (1988) in Atlantic  category 4  130-156 mph; 209-251 km/h  very high risk of injury/death from flying/falling debris  nearly all older mobile homes destroyed  poorly constructed frames homes  complete collapse of all walls + loss of roof structure; well built homes  severe damage + loss of roof structure & some exterior walls  high percentage of structural damage to top floors of apartment buildings  most windows blown out of high-rise buildings  most trees snapped/uprooted; power poles down  residential areas isolated  power outages last for weeks-months  ie/ Hurricane Luis (1995) over Leeward Islands; Hurricanes Felix & Opal (1995)  category 3  111-129 mph; 178-208 km/h  high risk of injury/death  nearly all older mobile homes destroyed; most newer will sustain severe damage  poorly constructed frame homes can be destroyed; well-built ones can experience major damage  high percentage of roof covering & siding damage to apartment/industrial buildings  numerous windows blown out  many trees snapped/uprooted, blocking roads  electricity/water unavailable for several days-few weeks after storm  ie/ Hurricane Roxanne (1995) at Yucatan Peninsula & Fran (1996) at North Carolina  category 2  96-110 mph; 154-177 km/h  substantial risk of injury/death  older mobile homes = very high chance of destroyed  poorly constructed frame homes have high chance of having roof removed; well constructed frame homes could sustain major roof & siding damage  failure of swimming pool enclosures common  substantial percentage of roof & siding damage to apartment/industrial buildings  windows in high rises broken by falling debris  shallowly rooted trees will be snapped/uprooted  near-total power loss expected; outages last days-weeks  potable water scarce  ie/ Hurricane Bonnie (1998) at North Carolina; Hurricane George (1998) of Florida Keys/Mississippi Gulf Coast  category 1  74-95 mph; 119-153 km/h  people/animals struck by falling/flying debris could be injured/killed  older mobile homes could be destroyed; newer mobile homes can sustain damage  poorly constructed frame homes can experience major damage; well constructed homes could have some damage  some apartment building & shopping center roof coverings partially removed  large branches of trees will snap; shallow rooted trees can be toppled  extensive damage to power lines & poles likely result in power outages lasting few-several days  ie/ Hurricane Allison (1995); Hurricane Danny (1997)  Structure  air spirals toward centre in counter-clockwise pattern in northern hemisphere (clockwise in southern hemisphere) & out top in opposite direction  the eye  the very centre  relatively calm, generally clear area of sinking air & light wind  typically 32-64 km wide  usually develops when maximum sustained wind speeds go about 119 km/h  cause of formation not fully understood  most likely has to do with
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