2023 hurricane forecast: Get ready for a busy Pacific storm season, quieter Atlantic than recent years thanks to El Niño
Published in Science & Technology News
That seesaw pattern is largely driven by the El Niño-Southern Oscillation, or ENSO, which includes varying strengths of El Niño and its opposite, La Niña.
During El Niño, the trade winds that blow from east to west weaken, allowing warm ocean water to build up at the equator, west of South America. This causes a shift in the jet streams – strong upper-level winds – which affects rainfall and temperature patterns.
In the Atlantic Ocean, El Niño causes an area of low pressure in the upper atmosphere known as a trough and stronger upper-level winds, resulting in increased vertical wind shear – a change in wind speed or direction with height in the atmosphere. Wind shear can tilt and stabilize storms, allowing fewer hurricanes to form.
Conversely, El Niño typically causes an upper-level ridge, or area of high pressure, and decreased vertical wind shear in the eastern North Pacific basin, and often results in an active hurricane season.
La Niña – El Niño’s opposite, with cooler water in the tropical Pacific – reverses this pattern. The record 2020 and destructive 2021 Atlantic hurricane seasons were both during strong La Niña years.
On longer time scales, the Atlantic Multidecadal Oscillation, a fluctuation of North Atlantic sea surface temperatures, affects hurricane activity in cycles that span several decades. The AMO’s current warm phase, which began in 1995, has hosted seven of the 10 busiest Atlantic hurricane seasons. Hurricane activity often lessens in a cool phase of the AMO, during which the Atlantic is on average about 1 degree Fahrenheit (0.6 Celsius) cooler.
El Niño also changes who is at risk in the Pacific.
During El Niño events, storms in the eastern North Pacific tend to form farther to the west. With these events, the environmental conditions in the western portion of the basin tend to become more conducive than normal to tropical cyclones, such as having reduced environmental vertical wind shear and warmer ocean temperatures. That places Hawaii and the central Pacific at greater risk from damaging storms than normal.
The highly destructive Hurricanes Manuel in 2013 and Willa in 2018 show the immense impact Pacific storms can have in the region. Both triggered widespread flooding and mudslides in Mexico, and together led to over 125 deaths. In Hawaii, Hurricane Iniki’s storm surge and winds in 1992 destroyed over 1,400 homes on Kauai and damaged thousands more.
El Niño years also increase the viability of storms affecting the southwestern U.S. In 1997, multiple storms affected California and Arizona, including some that moved into the region after landfall in Mexico. Famously, in 2014, rough surf and swells associated with Hurricane Marie caused over US$16 million in damage at the Port of Long Beach.
...continued
Comments