Topic 13 - Hurricanes

Hurricanes are tropical cyclones with sustained winds of 74 mph (64 knots) or higher.
They rotate counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Hurricanes are part of a broader category called tropical cyclones, which also include tropical depressions and tropical storms.
The main parts of a hurricane:
- Eye: The calm, mostly cloud-free center where air sinks.
- Eyewall: Surrounds the eye with the strongest winds and intense thunderstorms.
- Rainbands: Spiral bands of clouds and rain extending outward from the eyewall.

Hurricanes form from thunderstorms near the Inter-Tropical Convergence Zone (ITCZ).
Sea surface temperatures must be at least 26.5°C (81°F) to provide enough heat and moisture.
Hurricanes rarely form within 5° latitude of the equator due to insufficient Coriolis force needed for rotation.
Warm ocean water causes water vapor to rise, cool, and condense, releasing heat that fuels the storm.
Air spirals inward near the surface and upward in the eyewall, creating strong winds.

Category	Wind Speed (mph)	Pressure (mb)	Storm Surge (feet)	Damage Level
1	74-95	> 980	4-5	Minimal
2	96-110	979-965	6-8	Moderate
3	111-130	964-945	9-12	Extensive
4	131-155	944-920	13-18	Extreme
5	> 155	< 919	> 18	Catastrophic

Rank	Hurricane	Year	Category	Minimum Pressure (mb)	Minimum Pressure (in)
1	Unnamed (FL Keys)	1935	5	892	26.35
2	Camille (MS, SE LA, VA)	1969	5	909	26.84
3	Andrew (SE FL, SE LA)	1992	5	922	27.23

These hurricanes had the lowest pressures recorded at landfall, indicating extreme intensity.

Year	Location	Category	Deaths
1900	Galveston, TX	4	8,000-12,000
1928	SE Florida	4	2,500-3,000
2005	Katrina	3	1,200
1893	Louisiana	4	1,100-1,400
1893	SC/GA Sea Islands	3	1,000-2,000
1881	GA/SC	2	700

These hurricanes caused massive loss of life, often due to storm surge and flooding.

Defined as a local rise in sea level caused by:
- Strong winds pushing water toward the shore.
- Low atmospheric pressure allowing sea level to rise.
- Waves generated by the storm.
Storm surge is not the same as storm tide, which includes the astronomical tide.
Example: A normal high tide of 2 feet plus a 15-foot storm surge results in a total water level of 17 feet.

Immediate impacts: Property damage, injuries, deaths.
Health issues: Infectious diseases, exposure to toxins from floodwaters contaminated with sewage, pesticides, agricultural waste, petroleum products, and dead animals.
Environmental impacts: Damage to maritime forests, wetlands, marshes, and wildlife disruptions.
Economic impacts: Losses from destroyed crops, infrastructure, and homes.

No major hurricane landfalls since 1900, but increased Atlantic storm activity raises the risk.
Potential for large storm surges due to shallow continental shelf.
Barrier islands are especially vulnerable, with sea level rise increasing risk.
Hurricanes can spawn tornadoes and cause heavy rainfall inland, leading to flooding.
Example: Hurricane Ivan (2004) caused $68.8 million in damage in Georgia, destroyed crops, and spawned tornadoes.

Use of satellites, aircraft, and GPS dropsondes to measure temperature, humidity, pressure, and wind.
Forecasts include:
- Track forecast cones (3-day and 5-day).
- Watches and warnings for affected areas.
- Wind speed and storm surge probabilities.
Dropsondes provide vertical profiles of the atmosphere as they fall through the storm.

Hurricanes weaken rapidly over land or cooler water.
The Coriolis force is essential for hurricane rotation; hence, hurricanes do not form near the equator.
Tropical cyclones have different names depending on the region: hurricanes (Atlantic, Eastern Pacific), typhoons (Western Pacific), cyclones (Indian Ocean, South Pacific).