Hurricane Irma

Hurricane Irma — page 7 — CHAPTER TWO A HURRICANE IS BORN On August 27 2017 a weak wave of low pressure in the atmosphere left the western African coast accompanied by showers and thunderstorms as it moved into the Atlantic Ocean Just nine days later it would slam into Barbuda as a devastating hurricane While the strength of Hurricane Irma was unusual the way it formed was not Weather disturbances like the one that became Hurricane Irma move off the African coast every few days during hurricane season Most of them fail to develop any further They may be disrupted by arid winds coming from the Sahara Desert or they may be torn apart by strong high altitude air currents blowing from west to east Stormy weather in the ocean off the coast of Africa eventually morphed into a deadly hurricane thousands of miles to the west

Hurricane Irma — page 8

Hurricane Irma — page 9 — For a hurricane to develop from one of these low pressure waves it needs several things One of the most important is warm ocean water at least 80 degrees Fahrenheit 27°C That's because above all else a hurricane needs energy and warmer water provides more of it than colder water The first step in a hurricane's formation is the familiar water cycle Water at the surface of the ocean evaporates rises forms clouds condenses and falls as rain creating thunderstorms Some areas have conditions that lead them to develop more thunderstorms than others As a Hurricanes result from and are sustained by the complex interaction of warm and cool air in the atmosphere

Hurricane Irma — page 10 — result the air in those areas contains more water vapor That water vapor traps the heat from the warm ocean water causing even more evaporation and a general upsurge of warm air As that air rises other air rushes in to take its place The newly arriving air becomes warm and humid rises to form more clouds and generates more rain This creates a self reinforcing cycle As thunderstorm activity continues to grow a disturbance forms If this disturbance begins to spin around a closed center it becomes a tropical depression This spin happens because as the Earth rotates it drags the atmosphere along with it However this rotation is fastest at the equator so the air closer to the equator moves faster than the air farther from the equator This phenomenon is called the Coriolis effect Storms north of the equator spin counterclockwise while storms south of the equator spin clockwise When the winds in the system reach or exceed 39 miles per hour 63 kmh it is called a tropical storm and is given a name When the storm intensifies further reaching 74 miles per hour 119 kmh it becomes a hurricane An area known as the eye forms in the center This is where

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