In appearance, a tropical cyclone is like a huge whirlpool - a gigantic mass of revolving moist air. Tropical cyclones or storms are between kilometres wide and km high. The Coriolis force caused by the rotation of the Earth causes the tropical cyclone to spin.
The central part of the tropical cyclone is known as the eye. The eye is usually km across. If a hurricane's winds reach speeds of miles per hour kilometers per hour , it is upgraded to an "intense hurricane.
While the Atlantic hurricane season runs from June 1 through November 30, the typhoon and cyclone seasons follow slightly different patterns. In the northeastern Pacific, the official season runs from May 15 to November In the northwestern Pacific, typhoons are most common from late June through December. And the northern Indian Ocean sees cyclones from April to December.
Whatever you choose call them, these monster storms are powerful natural events with the capacity to wreak some serious havoc. According to NOAA's National Hurricane Center , the average hurricane eye—the still center where pressure is lowest and air temperature is highest—stretches 30 miles 48 kilometers across, with some growing as large as miles kilometers wide.
The strongest storms, equivalent to Category 5 on the Saffir-Simpson scale , have sustained winds that exceed miles per hour kilometers per hour. A supercell thunderstorm strikes in South Dakota. Among the most severe storms, supercells can bring strong winds, hail, and even tornadoes. See more extreme weather pictures.
With the aid of satellites and computer models, such storms can be predicted several days in advance and are relatively easy to track. But as Hurricane Sandy showed recently, predicting the path that a hurricane or typhoon or cyclone will take after it's formed is still tricky.
In recent years, scientists have debated whether human-caused global warming is affecting hurricanes by making them stronger or causing them to occur more frequently. In theory, warmer atmospheric temperatures should lead to warmer sea surface temperatures, which should in turn support stronger hurricanes. Relatively high levels of activity in the eastern Pacific tend to be spread out over a longer portion of the season than in the Atlantic, with most tropical cyclones occurring between late June and early October.
The figures below show the points of tropical cyclone genesis by day periods during the hurricane season. These figures depict named storms only. These maps show where tropical cyclones named storms and hurricanes tend to occur during each month of the hurricane season.
The data are shown as the number of named storms or hurricanes whose centers pass within nautical miles of a point on the map during a year period. For the Atlantic basin, the analyses are based on data from the year period from to starting at the beginning of the aircraft reconnaissance era but normalized to years.
For the eastern and central Pacific basins, the analyses are based on data from the year period from to starting when there was reliable satellite imagery but also normalized to years. Please note that the map legends vary from basin to basin and between named storms and hurricanes but not between months in order to make climatological patterns more apparent. Bars depict number of named systems yellow , hurricanes red , and category 3 or greater purple , Download hires image Download table of data PDF.
Hurricane return periods are the frequency at which a certain intensity of hurricane can be expected within a given distance of a given location for the below images 50 nm or 58 statute miles.
In simpler terms, a return period of 20 years for a major hurricane means that on average during the previous years, a Category 3 or greater hurricane passed within 50 nm 58 miles of that location about five times. We would then expect, on average , an additional five Category 3 or greater hurricanes within that radius over the next years. Estimated return period in years for hurricanes passing within 50 nautical miles of various locations on the U.
Estimated return period in years for major hurricanes passing within 50 nautical miles of various locations on the U. Hurricane Strikes. Hurricane Strikes - West Gulf. Weaker tornadoes may spawn from either multi-cell or single-cell thunderstorms.
Tornadoes come in many sizes but are typically in the form of a visible funnel with the narrow end touching the ground. A cloud of debris commonly encircles the lower portion of the funnel. They usually average 75 metres or less in diameter and travel several kilometres before dissipating, although some are in excess of a kilometre across and can stay on the ground for more than kilometres.
Tornadoes typically have a short life span of only a few minutes, but are powerful events which can cause extensive damage. The six-point enhanced Fujita scale EF0 to EF5 was established to quantify the intensity of a tornado and its danger. Severe storms can occur anywhere in Australia and do so more frequently than any other major natural hazard. Insurance statistics reveal that severe thunderstorms account for the majority of damaging events. The most common areas for severe thunderstorms are along the east coast from central Queensland to central NSW.
The main source of energy for tropical cyclones is the warm oceans in the tropical regions. To initiate a tropical cyclone the sea-surface temperature generally needs to be above However, existing cyclones often persist as they move over cooler waters. The development of a tropical cyclone also relies on favourable broad-scale wind regimes and can persist for several days with many following quite erratic paths.
They lose their source of energy when they move over land or colder oceans causing them to dissipate. Weakening may also occur if the cyclone moves into an unfavourable wind regime which disrupts the structure of the system. Sometimes a decaying tropical cyclone may interact with a weather system in higher latitudes to cause impacts far from the tropics. In an average season, tropical cyclones are mostly experienced in northwest Australia between Exmouth and Broome in Western Australia and in northeast Queensland between Port Douglas and Maryborough.
In the Australian region, the official tropical cyclone season runs from 1 November to 30 April, with most occurring between December and April.
On average, about 10 cyclones develop over Australian waters each year and around six of these cross the coast.
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