Hurricanes

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Swordfishing (Because) §

• Swordfishing was originally done by harpooning
  • This is very rarely done now, because the Swordfish are being fished out by other methods, to the point of overfishing
  • Longline fishing has replaced harpooning
• Longline fishing is commercial fishing at its worst, where boats drag up to 40 miles of line with over 1,000 hooks
  • Leads to overfishing of swordfish (including juveniles) and the killing of seabirds, sea turtles, sharks, and anything else unlucky enough go get caught
  • Since the advent of longline fishing, stocks of swordfish have dropped by more than 90%
• The best fishing grounds off the northeast coast are now the shallows of the Grand Banks and the Flemish Cap (the rest of the continental shelf has been fished out)
• 5,400 Gloucester fishermen have died at sea since 1623
• Fishing remains one of the most dangerous occupations with a very high fatal injury rate

Hurricane Formation and Paths §

• A hurricane is a tropical cyclone, an organization of many thunderstorms originating in the tropics into a single, massive, rotating storm system
• They are low pressure systems
• Hurricanes, cyclones, and typhoons only differ in their location. They are all types of cyclones technically, but called different things depending on location.
• Everything here referring to hurricanes also applies to typhoons and cyclones (because they’re really the same)
• Hurricane development in the Atlantic
  • Tropical Disturbance (weak and unorganized)
    • Just a group of storms, not much interaction yet
  • Tropical Depression (< 39 miles per hour)
    • Wind speeds start causing the clouds to interact from here down
  • Tropical Storm (39-74 miles per hour)
  • Hurricane (> 74 miles per hour)
• The presence of thunderstorms and hurricanes means that warm, moist air is rising, offsetting the pressure of the Atmosphere. Thus stormy regions are always low pressure
• In contrast, regions where cool, dry air is descending regions of high pressure - thunderstorms will not form
• A barometer is an instrument that measures atmospheric pressure. If it shows the atmospheric pressure is dropping, then a storm may be approaching
• Global trade winds are caused by how convection in the atmosphere is influenced by the spinning of the Earth. Trade winds push North Atlantic storms to the west in the tropics and East in the northern Atlantic
• The warm water is what fuels the hurricanes, so if a hurricane is pushed North by trade winds or over land, it quickly (relatively) dissipates
• When hurricanes venture over land they lose their energy source, causing winds to diminish rapidly
• All hurricanes start out as tropical storms, build to hurricane force winds, then lose that energy and drop back to tropical storms when they venture over land or cooler waters to the North
• North Atlantic hurricane season is August - October, when tropical waters are the warmest
• Cyclones rotate in opposite directions in the northern and southern hemispheres
  • ALWAYS the case.
  • Clockwise in the Southern hemisphere
  • Counter-clockwise in the Northern hemisphere
  • This is due to the Coriolis effect
    • The Earth’s rotation causes thunderstorm systems to rotate and become cyclones, with the direction of rotation depending on the hemisphere
    • The high pressure air constantly rushes to the low pressure area in the middle, but due to the Coriolis effect the air is consistently pushed off course
  • Without rotation induced by the Coriolis effect, thunderstorms cannot organize themselves into cyclones
    • Thus, cyclones cannot form near nor cross the equator because the Coriolis effect disappears there

The Calm and Power §

• One of the most distinct characteristics of a cyclone is its calm eye
• Warm air rising causes pressure to drop, reaching a minimum at the center of the eye. This low pressure draws in air from the surrounding regions, causing high winds
  • The highest winds occur within the eyewall, as winds cannot penetrate into the eye
  • The transition from the eye of the hurricane to the eyewall can be pretty dramatic
  • The eye of a hurricane has the lowest pressures and lowest winds, while the eyewall has the highest winds
• With warm rising air unable to reach the eye of the hurricane because of the Coriolis force, cool air from above descends into the eye
• Descending air will always warm due to increasing pressure (same energy contained in a smaller volume of air) no matter the speed of descent
• Strong cyclone winds can blow a lot of debris
• The Saffir-Simpson Intensity Scale classifies hurricanes based on wind speed
  • The stronger the storm (high at category), the higher the windspeed and lower the atmospheric pressure
  • Categories 1 through 5
• A higher category rating does not mean a larger storm, it simply means higher winds

Nor’easters §

• Nor’easters are extratropical cyclones
  • They are in the Winter time, and in the Northeast part of the U.S.
  • They get their name from the way the wind blows
• Nor’easters form when cold arctic air collides with and lifts warm, moist air above the Gulf Stream
  • Nor’easters are referred to as cold core storms since cold air underlies them, as opposed to Hurricanes which are warm core storms since they are underlain by the warm air of the tropics
• Nor’easters can be just as destructive as hurricanes, plus they can bring heavy snow
• They differ from hurricanes in several ways
  • Source of energy: Both rely on warm waters, but nor’easters require a cold front that lifts the warm moist air
  • Locations: Nor’easters form in north Atlantic, hurricanes in the tropics
  • Snow: Only nor’easters have snow
  • Season: Nor’easters are most common in winter; hurricanes occur in late summer
  • A distinct eye: Though they rotate, nor’easters rarely form a distinct eye
• The Perfect Storm in 1991 was a combination of a cold front from Canada, Hurricane Grace from the south, and a low pressure (Nor’easter) from the Northeast

Storm Surges and Big Seas §

• Cyclone winds can push water onshore, causing sever coastal flooding. This is called a storm surge
  • Like super-high tides with a lot of wind
  • Storm surges occur only on the side of the cyclone where the winds are blowing onshore
• Most deaths due to cyclones are caused by the storm surge (49%)
• Big storms produce big seas
• Rogue Waves
  • Rogue waves are ocean waves whose height is more than twice the height of other waves in the area
  • It is now believed that at any given moment 10 giant rogue waves are churning through the worlds oceans
  • The Draupner wave measured at an oil platform in the North Sea in 1995 confirmed the existence of rogue waves, which had previously been considered mythical
  • In the past two decades, rogue waves are suspected of sinking dozens of big ships and taking hundreds of lives
  • Rogue waves are thought to be caused by one of two phenomena or a combination
    • Merging waves: Waves traveling in the same direction but at different speeds and wavelengths may combine
    • Ocean currents: Waves and winds heading into powerful ocean currents may cause a surge of water to rise
  • They don’t occur in calm seas

Hurricane Mitigation and Record Storms §

• Rescue Swimmers
  • Coast Guard Aviation Survival Technician/Rescue Swimmer School (A-School)
    • Prospective rescue swimmers take a 6-month build-up training course for physical conditioning
    • Only 75 of these are invited each year to attend A-School and less than 50% graduate
  • The coast guards elite
  • The most difficult thing for rescue swimmers to deal with is non-compliant people needing rescue
• Hurricanes are slow movers, once you hear bout it you usually have several days to finalize plans, but don’t wait til the last minute
  • Evacuate if mandatory or you live in a mobile home, high rise, or area prone to a storm surge
  • If evacuating, go early to avoid traffic, find a place to stay, and have time to change plans
  • If staying gather food, water, emergency supplies to last for a week. If your house uses an electrical pump fill a bathtub with water (good for drinking and flushing)
    • Bring in all outside furniture and consider taping up windows to prevent shattering
    • Shelter in place as with a tornado
• Deadliest: Bhola Cyclone, Bangladesh ,1970
  • With 500,000 fatalities, the Bhola Cyclone was the deadliest cyclone of all time
• Fed by hot El Nino waters, Hurricane Patricia (2015) had the strongest sustained winds (215 mph) ever recorded
• With sustained winds of 196 mph (gusts up to 235 mph), Typhoon Haiyan (2013) was the strongest cyclone ever over land
  • Because the Philippines are surrounded by warm waters, Typhoon Haiyan hit it at full strength
• Largest Hurricane: Hurricane Sandy, 2012; 1,150 miles
• Record for most expensive is Hurricane Katrina at $108 billion dollars
  • Katrina’s storm surge caused over 50 levees (floodwalls designed to keep back the sea) to fail, leaving New Orleans under more than 10 feet of water
• Longest sustained winds: Typhoon Nancy, 1961. 155 mph winds lasting for 5 and half days
• Longest lasting and furthest traveling Hurricane AND Typhoon John, 1994. Lasted 31 days and covered 8,000 miles, moving from a hurricane region to a typhoon region and back
  • When a typhoon crosses the international date line it gets renamed, and then renamed if it crosses back etc.
• The biggest recorded waves: The Perfect Storm, 1991
  • A buoy off the coast of Nova Scotia reported several waves over 100 feet during the Perfect Storm. Not rouge waves, those would have been even bigger.