 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.
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.
The Coriolis force caused by the Earth's rotation is what gives winds within low-pressure systems 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). 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.
- Trough (meteorology)
- East Asian monsoon
- Intertropical convergence zone
- North American Monsoon
- Surface weather analysis
- Tropical wave
- Weather map
- High-pressure area
- Arctic Climatology and Meteorology (2009). Cyclogenesis. National Snow and Ice Data Center. Retrieved on 2009-02-21.
- Glossary of Meteorology (2009). "Cyclogenesis". American Meteorological Society. Retrieved 2009-02-21.
- Glossary of Meteorology (June 2000). "Cyclonic circulation". American Meteorological Society. Retrieved 2008-09-17.
- Glossary of Meteorology (June 2000). "Cyclone". American Meteorological Society. Retrieved 2008-09-17.
- BBC Weather Glossary (July 2006). "Cyclone". British Broadcasting Corporation. Archived from the original on 2006-08-29. Retrieved 2006-10-24.
- "UCAR Glossary — Cyclone". University Corporation for Atmospheric Research. Retrieved 2006-10-24. External link in
- Robert Hart (2003-02-18). "Cyclone Phase Analysis and Forecast: Help Page". Florida State University. Retrieved 2006-10-03.
- I. Orlanski (1975). "A rational subdivision of scales for atmospheric processes". Bulletin of the American Meteorological Society. 56 (5): 527–530.
- Glossary of Meteorology (June 2000). "Rossby wave". American Meteorological Society. Retrieved 2009-11-06.
- Glossary of Meteorology (June 2000). "Short wave". American Meteorological Society. Retrieved 2009-11-06.
- Glossary of Meteorology (June 2000). "Polar vortex". American Meteorological Society. Retrieved 2009-12-24.
- Joel Norris (2005-03-19). "QG Notes" (PDF). University of California, San Diego. Retrieved 2009-10-26.
- Glossary of Meteorology (2009). Short Wave. American Meteorological Society. Retrieved on 2009-03-02.
- Glossary of Meteorology (2009). Upper-Level Trough. American Meteorological Society. Retrieved on 2009-03-02.
- Carlyle H. Wash, Stacey H. Heikkinen, Chi-Sann Liou, and Wendell A. Nuss (1989). A Rapid Cyclogenesis Event during GALE IOP 9. Monthly Weather Review pp. 234–257. Retrieved on 2008-06-28.
- Shay Johnson (2001-09-25). "The Norwegian Cyclone Model" (PDF). University of Oklahoma, School of Meteorology. Archived from the original (PDF) on 2006-09-01. Retrieved 2006-10-11. External link in
- E. A. Rasmussen and J. Turner (2003). Polar Lows: Mesoscale Weather Systems in the Polar Regions. Cambridge University Press. p. 612. ISBN 978-0-521-62430-5.
- Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division (2004). "Frequently Asked Questions: What is an extra-tr