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Tropical waves, also known as easterly waves, are elongated areas of relatively low air pressure, oriented north to south, causing areas of cloudiness and thunderstorms. They form in the easterly flow along the southern side of the subtropical ridge or belt of high pressure which lies north and south of the Intertropical Convergence Zone (ITCZ). Tropical waves are generally carried westward by the prevailing easterly winds along the tropics and subtropics near the equator. They can lead to the formation of tropical cyclones.
Characteristics
A tropical wave is preceded by an area of sinking, intensely dry air, oriented as a northeast wind. With the passage of the trough line, the wind veers to the southeast, the humidity abruptly rises, and the atmosphere destabilizes, producing widespread showers and thunderstorms, occasionally severe. As the wave moves off westward, the showers gradually diminish.
Atlantic
Atlantic tropical waves develop from disturbances which drift off the continent of Africa onto the Atlantic ocean. These are generated or enhanced by the African Easterly Jet. The clockwise circulation of the large transoceanic high-pressure cell or anticyclone centered near the Azores islands impels easterly waves away from the coastal areas of Africa towards North America.
Approximately 60% of Atlantic tropical cyclones originate from tropical waves, while approximately 85% of intense Atlantic hurricanes (Category 3 and greater) develop from tropical waves.
Tropical cyclones can sometimes degenerate back into a tropical wave. This normally occurs if upper-level wind shear is too strong, and the storm would be able to redevelop if the upper level shear abates.
If a tropical wave is moving quickly, it can have strong winds of over tropical storm force, but would not be considered a tropical storm unless it had a closed circulation. An example of this is Hurricane Claudette in 2003, where the wave had winds of 45 mph before developing a circulation.
East Pacific
Most eastern Pacific Ocean tropical cyclones are formed out of tropical waves that originate in North Africa and move across the Atlantic. During the summer months, tropical waves can extend northward as far as the desert southwest of the United States, producing spells of intensified shower activity embedded within the prevailing monsoon regime.
See also
References
External Links
- Tropical Waves Presentation
- African Easterly Wave Variability and Its Relationship to Atlantic Tropical Cyclone Activity
Tropical cyclone meteorology | Onde tropicale | Tropische Welle | Tropische golf
"Tropical wave"