<P> Tropical cyclones generally need to form more than 555 km (345 mi) or poleward of the 5th parallel north and 5th parallel south, allowing the Coriolis effect to deflect winds blowing towards the low - pressure center and creating a circulation . Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest . However, each particular basin has its own seasonal patterns . On a worldwide scale, May is the least active month while September is the most active month . November is the only month that activity in all the tropical cyclone basins is possible . Nearly one - third of the world's tropical cyclones form within the western Pacific Ocean, making it the most active tropical cyclone basin on Earth . </P> <P> Wind is initially accelerated from areas of high pressure to areas of low pressure . This is due to density (or temperature and moisture) differences between two air masses . Since stronger high - pressure systems contain cooler or drier air, the air mass is denser and flows towards areas that are warm or moist, which are in the vicinity of low - pressure areas in advance of their associated cold fronts . The stronger the pressure difference, or pressure gradient, between a high - pressure system and a low - pressure system, the stronger the wind . Thus, stronger areas of low pressure are associated with stronger winds . </P> <P> The Coriolis force caused by the Earth's rotation is what gives winds around low - pressure areas (such as in hurricanes, cyclones, and typhoons) their counter-clockwise (anticlockwise) circulation in the northern hemisphere (as the wind moves inward and is deflected right from the center of high pressure) and clockwise circulation in the southern hemisphere (as the wind moves inward and is deflected left from the center of high pressure). A cyclone differs from a hurricane or typhoon only on the basis of location . A hurricane is a storm that occurs in the Atlantic Ocean and northeastern Pacific Ocean, a typhoon occurs in the northwestern Pacific Ocean, and a cyclone occurs in the south Pacific or Indian Ocean . Friction with land slows down the wind flowing into low - pressure systems and causes wind to flow more inward, or flowing more ageostrophically, toward their centers . A low - pressure area is commonly associated with inclement weather, while a high - pressure area is associated with light winds and fair skies . Tornados are often too small, and of too short duration, to be influenced by the Coriolis force, but may be so - influenced when arising from a low - pressure system . </P>

Which way do winds blow around a low pressure system in the northern hemisphere