how hurricanes form
- surface water >27 deg C provide hurricanes with energy and increased intensity
- Warm moist air and weak upper-level winds in low pressures systems cause quick updrafts and CCW movement of air into LPC (tropical depression) to form a tropical storm, winds reach 119 km/h forms eye (high pressure zone) around centre forms hurricane
- 500 km from equator, Coriolis effect happens, causing rotation (atlantic hurricane, pacific typhoon, indian cyclone)
positive feedback mechanisms of storms
storms create conditions providing them with more energy
1. high winds chop waves, causing water molecules to be suspended in air as seaspray, increases evaporation 100-1000 times, creating more rising vapour
2. updrafts carry vapour into dry upper troposphere, condenses into liquid and releases latent heat E in upper troposphere causes new moist air rising, keeps adding E to sys
saffir-simpson scale
hurricane intensity based on wind speed, category 1 (119 km min, some dmg) to 5 (>252 km/h, catastrophic total dmg), recent work argues to extend the scale to 6 and 7 because wind speeds reach much higher than 252 km/h, causing inadequate preparation of communities
what to do during hurricane
- stay away from glass areas
- listen to emergency information on a battery-powered radio
- do not shelter in mobile homes, vehicles, or under bridges/overpasses, find other cover
- if req, evacuate to designated shelter following evacuation routes
- if power lost, unplug major appliances to prevent power surges and fire hazard risks
North Atlantic hurricanes
1. frequency
2. path
3. probabilty
4. return frequency in US
- every hurricane season, start naming with a through z for every storm, latin then greek alphabet, some years may go through entire alphabet (>26)
- low pressure hurricanes originating near SE Africa flow around seasonal Bermuda high pressure zone to right along the east coast of North America
- atlantic multidecadal variability (natural cycles through high and low temp in Atlantic) influence frequency of hurricanes
- return frequency of hurricane highest in the SE coast
building homes near coastline
pilling (foundation beams) driven deep into bedrock and cross bracing to limit shear, when water washes away some of the unconsolidated ground below house, house can still stay in place without being washed away
hurricanes: people factor
survey from Hurricane Sandy warnings which provided long list without priorities, 90% made some preparations, 50% storm shutter (protect windows from debris and prevent wind from entering house) owners put them up, 20% under evacuation orders planned to go, most thought winds would cause most dmg not flooding, therefore people need education on the dangers and what to do, organizations need to prioritize top items for survivability
differing wind speed around hurricane eye
- greater wind speed + storm surges on side of storm where rotation is same direction as motion of storm, lesser wind speed on opp side, thus location of community relative to side of eye impacts survival
- in northern hemisphere, highest wind speeds and largest storm surges in N when storm moves W or NE when moving N
driving through floodwaters
is extremely dangerous if water is more than 2 feet deep since vehicle will float and lose traction, muddy water hides washed out road thus can unexpectedly drop into deep water
Hurricane Katrina: results
- many people stranded without immediate aid, water heavily contaiminated, many people hospitalized for GI problems from water and dehydration, mold grew rapidly in submerged buildings
- many deaths and >1 mil displacment, most fatalities were older adults, considerable financial loss and less than 1/2 of residents had flood insurance
Hurricane Katrina: overview
New Orleans over inactive delta 7m below sea level, levee and flood control sys pumps block and remove water designed for cat 3, Katrina cat 5 caused failure of levees/pumps and strong storm surges, poorest neighbourhoods in lowest parts of cities completely submerged in 4m water
Hurricane Katrina: evacuations
majority complied, but many residents in poor neighbourhoods could not since they did not have adequate transportation or necessary finances, main evacuation centres did not have adequate resources
Hurricane Maria, 2017
1. Dominica
2. Puerto Rico
- cat 5 hurricane, small island complication with evacuations, no electricity, clean water, communications, tourism based economy in ruins, widespread poverty and inaccessibility
- cat 4 hurricane, same as Dominica, fatalities from heat and lack of medical access from complications due to dmg, power not fully restored causing schools to close and families to emigrate to US
Indian ocean and southern hemisphere cyclones
Ganges Rives delta and Bay of Bengal are high vulnerability to cyclones and slow onset flooding due to densely populated islands with high poverty, low-elevation farmlands, narrow bays concentrating cyclone E, and v. high storm surges, cyclones have large death tolls despite relatively small areas and millions at risk due to few resource and poor logistics and high secondary disaster risk
