Meteorology

☁️Meteorology Unit 11 – Tropical Weather Systems and Hurricanes

Tropical weather systems and hurricanes are powerful atmospheric phenomena that form over warm ocean waters. These storms can bring devastating winds, heavy rainfall, and storm surges to coastal areas, posing significant threats to life and property. Understanding the formation, structure, and behavior of hurricanes is crucial for accurate forecasting and effective preparedness. From the eye and eyewall to rainbands and storm surge, each component plays a role in the storm's intensity and potential impact on communities in its path.

Key Concepts and Definitions

  • Tropical cyclone: a low-pressure system that forms over warm tropical oceans and has a closed low-level atmospheric circulation
  • Hurricane: a tropical cyclone with sustained winds of 74 mph (119 km/h) or higher in the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and eastern North Pacific Ocean
    • Known as typhoons in the western North Pacific and cyclones in the Indian Ocean and South Pacific
  • Eye: the calm, clear center of a hurricane characterized by low pressure, light winds, and descending air
  • Eyewall: the ring of thunderstorms surrounding the eye where the strongest winds and heaviest rainfall occur
  • Saffir-Simpson Hurricane Wind Scale: categorizes hurricanes based on their maximum sustained wind speeds from Category 1 (74-95 mph) to Category 5 (157 mph or higher)
  • Storm surge: an abnormal rise in sea level generated by a storm, potentially causing severe coastal flooding
  • Latent heat: the energy released or absorbed during a phase change (evaporation or condensation) without a change in temperature, crucial for hurricane development

Tropical Weather Patterns

  • Intertropical Convergence Zone (ITCZ): a low-pressure belt near the equator where the Northeast and Southeast Trade Winds converge, creating favorable conditions for thunderstorm development
  • Easterly waves: areas of low pressure that move westward across the tropics, often serving as seedlings for tropical cyclone formation
  • Monsoon troughs: elongated areas of low pressure associated with the seasonal shift of the ITCZ, contributing to enhanced rainfall and potential cyclone development in regions like the Indian Ocean and western Pacific
  • Sea surface temperatures (SSTs): warm ocean waters (typically above 26.5°C or 80°F) that provide the necessary energy for tropical cyclone formation and intensification
  • Wind shear: the change in wind speed or direction with height, with high wind shear disrupting tropical cyclone development and low wind shear favoring intensification
  • Saharan Air Layer (SAL): a dry, dusty air mass that originates over the Sahara Desert and can suppress Atlantic hurricane activity by introducing dry air and increasing wind shear

Hurricane Formation and Structure

  • Pre-existing disturbance: hurricanes typically develop from pre-existing areas of low pressure, such as easterly waves or monsoon troughs
  • Warm ocean waters: SSTs above 26.5°C (80°F) provide the necessary heat and moisture for hurricane development
  • Coriolis force: the apparent force caused by the Earth's rotation that helps to create the cyclonic (counterclockwise in the Northern Hemisphere) rotation of hurricanes
  • Convergence: the inflow of air towards the center of the storm, causing rising motion and thunderstorm development
  • Divergence: the outflow of air at the top of the storm, allowing for continued rising motion and intensification
  • Eyewall replacement cycle: a process in which a new outer eyewall forms and gradually replaces the original inner eyewall, often leading to temporary weakening followed by re-intensification
  • Rainbands: spiral-shaped bands of showers and thunderstorms that extend outward from the center of the hurricane

Hurricane Classification and Intensity

  • Saffir-Simpson Hurricane Wind Scale: categorizes hurricanes based on their maximum sustained wind speeds
    • Category 1: 74-95 mph
    • Category 2: 96-110 mph
    • Category 3: 111-129 mph (considered a major hurricane)
    • Category 4: 130-156 mph (considered a major hurricane)
    • Category 5: 157 mph or higher (considered a major hurricane)
  • Maximum sustained winds: the highest one-minute average wind speed measured at a height of 10 meters above the surface
  • Central pressure: the atmospheric pressure at the center of the hurricane, with lower pressures generally indicating a more intense storm
  • Rapid intensification: a significant increase in maximum sustained winds (typically 35 mph or more) within a 24-hour period, often associated with more dangerous and unpredictable hurricanes
  • Weakening factors: include increasing wind shear, dry air intrusion, movement over cooler waters, and interaction with land

Tracking and Forecasting Methods

  • Satellite imagery: provides a visual representation of the storm's structure, intensity, and movement
    • Visible satellite imagery shows the storm's cloud patterns during daylight hours
    • Infrared satellite imagery detects the temperature of cloud tops, with colder temperatures indicating higher, more developed clouds
  • Weather radar: detects precipitation and wind speeds within the storm, helping to identify the eye, eyewall, and rainbands
  • Reconnaissance aircraft: specially equipped planes that fly into hurricanes to directly measure wind speeds, pressure, and other variables
  • Computer models: numerical weather prediction models that simulate the atmosphere and ocean to forecast hurricane track and intensity
    • Dynamical models: solve physical equations to predict storm behavior (e.g., GFS, ECMWF, HWRF)
    • Statistical models: use historical relationships between storm characteristics and environmental factors to forecast intensity (e.g., SHIPS, LGEM)
  • Ensemble forecasting: running multiple forecasts with slightly different initial conditions or model configurations to assess uncertainty and improve overall forecast accuracy
  • National Hurricane Center (NHC): the U.S. government agency responsible for issuing official hurricane forecasts, watches, and warnings for the Atlantic and eastern Pacific basins

Impacts and Hazards

  • Storm surge: the abnormal rise in sea level generated by a hurricane, often the deadliest and most destructive hazard
    • Factors influencing storm surge include storm intensity, size, forward speed, and coastal bathymetry
  • Heavy rainfall: can cause inland flooding, particularly when a storm moves slowly or stalls over an area
  • Strong winds: can cause structural damage, power outages, and tree damage
  • Tornadoes: can form in the outer rainbands of hurricanes, adding to the storm's destructive potential
  • Rip currents: strong, narrow channels of fast-moving water that can pose a drowning risk to swimmers along the coast
  • Economic losses: hurricanes can disrupt businesses, agriculture, and infrastructure, leading to significant economic impacts
  • Environmental impacts: storms can cause erosion, saltwater intrusion, and damage to coastal ecosystems such as coral reefs and mangroves

Preparedness and Response Strategies

  • Emergency planning: developing and practicing hurricane response plans at the individual, community, and government levels
  • Evacuation: moving people away from areas threatened by storm surge, flooding, or other hazards
    • Evacuation orders: issued by local officials based on the storm's projected impact and the vulnerability of the area
    • Evacuation routes: designated roads and highways that facilitate the safe and efficient movement of people away from danger
  • Sheltering: providing safe locations for people to stay during the storm, such as schools, community centers, or hotels
  • Communication: disseminating timely and accurate information to the public through various channels (e.g., news media, social media, emergency alerts)
  • Supplies and provisions: ensuring adequate food, water, medicine, and other essentials are available for the duration of the storm and its aftermath
  • Post-storm assessment: evaluating the storm's impact, identifying areas of need, and coordinating relief efforts
  • Resilience and mitigation: implementing strategies to reduce the long-term risk and vulnerability to hurricanes, such as building codes, infrastructure improvements, and coastal restoration projects

Case Studies and Notable Hurricanes

  • Hurricane Katrina (2005): one of the deadliest and costliest hurricanes in U.S. history, causing widespread damage and over 1,800 deaths along the Gulf Coast, particularly in New Orleans
  • Hurricane Harvey (2017): a slow-moving storm that brought record-breaking rainfall and catastrophic flooding to the Houston metropolitan area
  • Hurricane Maria (2017): a Category 5 hurricane that devastated Puerto Rico, causing widespread damage to infrastructure and thousands of deaths
  • Hurricane Dorian (2019): a powerful Category 5 storm that stalled over the Bahamas, causing unprecedented damage and loss of life
  • Hurricane Ida (2021): a Category 4 hurricane that made landfall in Louisiana on the 16th anniversary of Hurricane Katrina, causing significant wind damage and storm surge flooding
  • Hurricane Ian (2022): a Category 4 storm that caused severe damage and numerous deaths in southwestern Florida, particularly in the Fort Myers area
  • Hurricane Camille (1969): a compact but powerful Category 5 hurricane that caused catastrophic damage along the Mississippi coast
  • Hurricane Andrew (1992): a Category 5 storm that caused extensive damage in South Florida and prompted significant changes to building codes and hurricane preparedness strategies


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© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.