A tornado forms within a thundercloud, where winds whirling in opposite directions cause a long funnel cloud to drop out of the main cloud. The violent updraft in the middle of the tornado can cause severe damage, since in the biggest tornadoes as much as feet across , it is strong enough to rip up houses. Hurricanes form near the equator, in the intertropical convergence zone ITCZ where contrasting winds meet. A combination of heat and moisture is necessary for the storm to get started: as the winds swirl around they cause moisture to condense in the air.
As this happens, heat increases and gradually a cyclone forms over the water. With hurricanes, there is an endless supply of water while they are over the ocean, so they can grow continuously. From the first stage, called a tropical depression, the storm can develop into a tropical storm, and then, when winds reach 74 mph or more, it becomes a hurricane.
Hurricanes, in spite of their devastating nature, are very orderly storms. They have a calm spot, the eye , in the center usually about 15 miles wide , surrounded by the strongest winds and dark nimbostratus storm clouds just outside it and then spiral rain bands of precipitation and clouds moving outward from that. In the Northern Hemisphere the top half of the world , hurricane winds move counter-clockwise, but in the Southern Hemisphere they move in the opposite direction.
As a hurricane approaches land, barometric pressure drops, causing the sea level to rise: in the vacuum brought about by the lowered pressure, seawater rushes up onto the land, causing flooding along with the destruction from the storm. Thursday, October 28, The Pacific Northwest experienced a memorable series of storms in late Oct.
At its minimum pressure highest strength , the system was reported by the National Weather Service to have had the lowest pressure of a system over the northeastern Pacific Ocean since reliable observations began in The system was notable Read More.
Comparing Typhoon Mindulle and Hurricane Sam. Friday, October 8, From late Sept. While neither storm posed a direct threat to land, Mindulle brushed by eastern Japan, leaving heavy rainfall accumulations in the area near Tokyo.
Tuesday, September 21, When wind near the earth's surface blows at one speed and wind above that blows at a much faster speed, the air between them whips around into a horizontal rotating column. If this column gets caught in the thunderstorm updraft, its winds tighten, speed up, and tilt vertically, creating a funnel cloud.
Tornadoes are dangerous—even deadly—because of their high winds and subsequent flying debris. A hurricane is a swirling, low-pressure system that develops over the tropics with sustained winds that have reached at least 74 miles per hour. Warm, moist air near the ocean's surface rises upward, cools, and condenses, forming clouds. With less air than before at the surface, the pressure drops there. Because air tends to move from high to low pressure, moist air from surrounding areas flows inward toward the low-pressure spot, creating winds.
This air is warmed by the ocean's heat and the heat released from condensation , so it rises. This starts a process of warm air rising and forming clouds and surrounding air swirling in to take its place. Before long, you have a system of clouds and winds that begins to rotate as a result of the Coriolis effect, a type of force that causes rotational or cyclonic weather systems. Hurricanes are the most dangerous when there is a big storm surge, which is a wave of seawater that floods communities.
Some surges can reach depths of 20 feet and sweep away homes, cars, and even people. Strong wind shear. The scale ranges from EF 0 to EF 5. The Saffir-Simpson Scale classifies cyclone strength based on the intensity of sustained wind speeds. Actively scan device characteristics for identification.
At home Go to your designated safe room, preferably in a basement or storm cellar on the lowest level of your home. If an underground shelter is not available, go to a small interior room, such as a closet, bathroom, or interior hallway, on the lowest level.
Avoid windows and doors. Put as many walls between you and the outside as possible. Get under something sturdy like a heavy table or work bench. Protect yourself from flying debris with pillows, heavy coats, blankets or quilts. Use bicycle or motorcycle helmets to protect your head. In a mobile home If you are in a mobile home, move to the closest substantial shelter well in advance of approaching severe weather.
If you live in a mobile home, even those with tie downs, seek more secure shelter. Have a prearranged location selected. Go to a friend's or a relative's house or a nearby building with a basement or tornado shelter. In your vehicle or outside Well in advance of approaching severe weather go inside a substantial structure. If you are under a tornado warning seek shelter immediately. Go to the best available, protective area if caught in your vehicle. It is unwise to try and outrun a tornado; however, you may be able to head at a right angle to the storm if you are sure of the direction in which the twister is heading.
Tornadoes can change directions suddenly. They can toss cars, and even large 18 wheelers, around like toys. The safest option is an underground shelter.
If there is no shelter nearby, get into the nearest ditch, depression or underground culvert and lie flat with your hands shielding your head. If you pull off the road, try to seek shelter in a safe structure first. If unavailable lie down in a low area with your hands covering the back of your head and neck to protect yourself from flying debris and shattering glass.
If you take shelter in a ditch make sure you are far enough away from your car, so it and other heavy debris do not wind up on top of you. Be alert to rising water in the ditch from the heavy rains. Taking shelter under an overpass is also not recommended, because most underpasses offer no place to hide. They can actually act like a wind tunnel and increase the storm's fury.
Away from home At work or school, know the emergency plans. If no specific plans exist, go to an interior hallway or small room on the building's lowest level.
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