Olwyn, Nathan, Pam and 03W March 11 2015 0330Z

A westerly wind burst is a phenomenon commonly associated with El Niño events, whereby the typical east-to-west

trade winds The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisp ...

across the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can also ...

ial Pacific shift to west-to-east. A westerly wind burst is defined by Harrison and Vecchi (1997) as sustained winds of over a period of 5–20 days. However, no concrete definition has been determined, with Tziperman and Yu (2007) defining them as having winds of and lasting "at least a few days". On average, three of these events take place each year, but are significantly more common during El Niño years. They have been linked to various mesoscale phenomena, including tropical cyclones, mid-latitude cold surges, and the Madden–Julian oscillation. Their connection with Kelvin waves also indicate a connection with the onset of El Niño events, with every major occurrence since the 1950s featuring a westerly wind burst upon their onset. Recent studies, including Yu et al. (2003), have indicated some correlation between westerly wind bursts and the El Niño–Southern Oscillation (ENSO). These events occur more frequently when the equatorial Pacific warm pool is extended by ENSO events. A significant relationship exists between the frequency of westerly wind bursts and the central equatorial Pacific

sea surface temperature Sea surface temperature (SST), or ocean surface temperature, is the ocean temperature close to the surface. The exact meaning of ''surface'' varies according to the measurement method used, but it is between and below the sea surface. Air mas ...

s, with events commonly taking place when temperatures were present. The wind bursts also traveled along with the warm pool, propagating west to east. A westerly wind burst event can often result in the formation of twin tropical cyclones in the Pacific, with events occurring annually on average. These events spur counter-clockwise rotation in the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

and clockwise rotation in the Southern Hemisphere—a key component of low pressure systems. For example, during July 2015 Typhoon Chan-hom and

Cyclone Raquel Tropical Cyclone Raquel was the first tropical cyclone to exist within the South Pacific Ocean during the month of July on record. The system was first noted during June 28, 2015, while it was located to the northeast of Honiara in the Solomon Is ...

developed simultaneously over the Northwestern and Southwestern Pacific, respectively, in conjunction with a westerly wind burst. This was also the only known instance of twin cyclones during July and attributed to the record strength of the 2014–16 El Niño event. Another unusually strong wind burst led to the atypical formations of Tropical Depression Nine-C and

Hurricane Pali Hurricane Pali was the earliest-forming Pacific hurricane on record, and the first Pacific hurricane to occur in January since Hurricane Ekeka in 1992. The first tropical cyclone of the 2016 Pacific hurricane season, Pali originated as an are ...

in late December 2015 and early January 2016, respectively along with the formation of

Cyclone Ula Severe Tropical Cyclone Ula was a powerful and long-lived tropical cyclone during late December 2015 and mid-January 2016. It originated from a tropical disturbance on December 26, 2015, east of the Solomon Islands. Moving generally east, dev ...

in the Central and Southwestern Pacific. Similarly, the formation of twin cyclones along the equatorial Pacific can spur the formation of a westerly wind burst and enhance El Niño events. In May 2002, a strong westerly wind burst moved from west to east across the Indian Ocean, producing two separate sets of twin cyclones. It first led to the development of

Cyclone Kesiny Tropical Cyclone Kesiny was the first recorded tropical cyclone – the equivalent of a minimal hurricane – to make landfall in the month of May in the south-west Indian Ocean. The final named storm of the busy 2001–02 South-West Indian Ocea ...

in the south-west Indian Ocean and a storm that struck Oman, and later spawned a deep depression that struck Myanmar and Tropical Storm Errol to the southwest of

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...

References

{{reflist, 30em Tropical meteorology Tropical cyclone meteorology Weather hazards

See also

References