US federal forecasts put the chance of a very strong El Niño above 90% this autumn and winter, with a 75% probability that the event could reach historic strength. California has declared a state of emergency ahead of the winter weather threat, while Hurricane Polo remains a Category 5 storm off Mexico.
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California Gov Gavin Newsom declared the emergency on Monday to mobilize resources before the El Niño peaks this winter. The order allows the state to position resources in advance and coordinate preparations for severe weather.
California is likely to be among the US areas most exposed to the unusually strong climate cycle. Previous strong El Niño events have frequently brought damaging conditions to the state, while studies have associated them with above-normal precipitation, Cable News Network (CNN) reported.
The effects are already being seen along the California coast, where El Niño has pushed sea levels higher. As the event reaches its expected winter peak, the state could face coastal flooding, heavy rainfall at lower elevations and mountain snow.
Scientists regard widespread flooding along the coast as close to certain. El Niño can also add energy to waves generated by Pacific storms, increasing the risk of coastal erosion and closures on key transport links.
Those coastal risks do not depend entirely on the path taken by major Pacific storms. El Niño itself raises coastal water levels, adding to sea-level rise already linked to climate change.
The El Niño also coincides with the peak of an 18-year astronomical high-tide cycle. Patrick Barnard, research director at the Center for Coastal Climate Resilience at the University of California, Santa Cruz, said the cycle will push King Tides above their usual levels.
Barnard said studies have found wave energy from Pacific storms to be about 30% higher during El Niño years. The increase reached as much as 50% during the 2015-16 event.
He said a projected rise of about 15cm to 30cm in coastal water levels during the current El Niño could put another 170,000 people and $60 billion in property at risk compared with a non-super El Niño year.
Polo remains Category 5 after winds peak at 285kmph
Off Mexico, Hurricane Polo remained at Category 5 strength on Tuesday after rapidly intensifying amid favourable atmospheric conditions and warmer water associated with the super El Niño.
Polo's sustained winds peaked at about 285kmph at 3pm CST, when its minimum central pressure fell to 892mb, according to the National Hurricane Center. By 9pm, sustained winds had eased to about 270kmph and the hurricane was drifting northeast at about 2kmph. Its minimum central pressure had risen to 905mb, but it remained an “extremely dangerous” Category 5 storm.
Between Monday and Tuesday morning, Polo's winds increased by about 175kmph, rising from around 80kmph as a tropical storm to about 260kmph at Category 5 strength.
A storm meets the threshold for extreme rapid intensification when its wind speed rises by at least about 95kmph within 24 hours. The centre called Polo's rate of strengthening “truly remarkable” and said it was among the fastest recorded in the eastern Pacific.
For comparison, Hurricane Patricia set the eastern Pacific 24-hour intensification record in 2015 with an increase of about 195kmph. In 2023, Hurricane Otis gained about 170kmph in 21 hours before hitting and devastating Acapulco.
California, southwest Mexico face flood threat
California could see flooding, mudslides and landslides as heavier precipitation combines with stronger storm waves.
Newsom's emergency order directs agencies to prepare roads and other infrastructure, coordinate public-safety measures with local and tribal governments and pre-position equipment for flood response and snow removal. The California National Guard is also being readied for flood-response, search-and-rescue, engineering and logistics operations.
A Tropical Storm Warning was in effect along Mexico's southwest coast from Tecpan de Galeana to Punta San Telmo. Polo's core was expected to remain offshore, but heavy rain posed a risk of life-threatening flooding and mudslides in Guerrero and Michoacán.
Mexican authorities suspended classes in affected areas along the Pacific coast, the Associated Press reported.
Reuters reported that authorities were monitoring the risk of rivers overflowing and had urged residents to stay away from flooded areas, secure loose outdoor items and plan routes to higher ground.
Guerrero and Michoacán were forecast to receive about 8cm to 15cm of rain through Thursday, with isolated totals of up to 20cm. Coastal parts of Oaxaca, Colima and Jalisco could receive about 5cm to 10cm.
