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Hurricane Basics

Published by Annmarie Mudge Buckley in Weather Emergencies · 25/5/2015 12:57:00
Tags: Hurricane
Don’t wait until a storm threatens! Now is the time to review or develop a hurricane plan.

Day 1 Topic: Hurricane Basics

Hurricanes are swirling tropical storms that begin in the warm waters off the coast of Africa near the equator. The winds of a hurricane swirls around a calm center called the eye that is defined by dark clouds called the eyewall. The eye has no rain, is calm and has large puffy clouds. The Eyewall typically has some of the strongest winds due to the drastic and rapid changes in pressure. Hurricanes gather heat and energy through contact with warm ocean waters. While the Atlantic hurricane season runs June 1 through November 30, August and September are peak hurricane months.

Hurricanes form under a specific set of conditions. There must be a warm layer of water with surface termperaturs better than 80 degrees Fahrenheit, causing the warm seawater to evaporate and be absorbed in the air. As the warm moist air rises, it lowers the pressure of the air beneath it. The column of air that extends from the surface of the water to the top of the atmosphere is less dense and weighs less. The nature of air is that it tends to move from high pressure areas to low pressure areas causing wind. Hurricanes cannot form in strong wind shear. Wind shear is the difference in speed and direction between the winds at the upper and lower elevations. If the winds are distinctly different, the storm breaks up because the wind knocks it over or takes the top off.

The Life Cycle of a Hurricane

Hurricanes develop in 4 stages: Tropical disturbance, tropical depression, tropical storm and hurricane. A tropical disturbance is when rain clouds are building, when the warm moist air rises and cools down. As the air cools down, it cannot hold as much water and forms clouds out of the water droplets. These clouds are exactly like the thunderstorm clouds you see all the time. They are tall, gradually darken and typically produce heavy short bursts of rain. Under the right conditions (enough heat and moisture), more cumulonimbus clouds form as others are breaking up. If the storm begins to blow in a circular pattern around a center, it is called a tropical depression. Normally, meteorologists won't call it a tropical depression unless it is big enough to see on a map. The winds swirl around the low pressure area feeding the thunderstorms. As the pressure becomes lower it draws in more warm, moist air causing the wind to blow faster. This storm reaches tropical storm stage when the winds around the center reach 38 miles per hour. When the wind speed reaches 74 miles per hour the storm reaches hurricane status. Once it has reached hurricane status it is then separated into categories.

Hurricane Categories

Category 1: Winds at 74-95 MPH. The damage is typically minimal and resembles a strong thunderstorm. This type of storm could cause power outages, large branches falling and some roof damage.

Category 2: Winds at 96-110 MPH. The damage is considerable. Winds at these speeds can knock down trees, cause major roof damage and extensive power outages.

Category 3: Winds at 111-129 MPH. The damage is extensive. Strong winds could lift entire roofs off of houses, even well rooted trees are toppled and electricity and water will be out for large areas over several weeks.

Category 4: Winds at 130-156 MPH. The damage is extreme. Strong winds will lift roofs, damage exterior walls and snap most trees and power poles. Category 4 storms will keep people from their homes for weeks/months.

Category 5: Winds at greater than 157 MPH. The damage here is catastrophic. Category 5 storms and winds at this speed will destroy building and houses. Roads will not be passable and the destruction is significant.

Check back tomorrow for an explanation of Storm Surge.

Get a head start on your evacuation plan check .

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