An unusually powerful El Niño is expected to keep strengthening through the fall, with federal forecasters estimating more than an 80% chance it will surpass every event recorded since 1950. The Pacific warming is already pronounced. In September, parts of the equatorial Pacific were more than 4 degrees Celsius above normal. In the Niño 3.4 region, a key area used to monitor the climate pattern, the average daily sea-surface temperature reached 86 degrees Fahrenheit this week, a record. Parts of the eastern Pacific below the surface are more than 10 degrees Celsius warmer than average, a deep reserve of heat that can help sustain the event. For California, the developing pattern raises the prospect of a wet winter. A recent European seasonal-model forecast places El Niño’s peak in December, and that model has increased its precipitation outlook for the state, favoring above-average rainfall in many locations. The pattern can favor wetter California winters, particularly when unusually warm water is concentrated in the eastern Pacific. Seasonal projections, however, do not determine how much rain any specific city or watershed will receive. The effects are already showing up around the world. Indonesia experienced extended dry conditions and fires that had burned roughly 500,000 acres through July. Eastern and northeastern India had their driest monsoon season since records began in 1901, with rainfall 26% below average. Tokyo recorded 35 consecutive rainy days, its longest streak since records began there in 1886. The Pacific and Atlantic storm seasons have also diverged. Twenty named storms have formed in the eastern and central Pacific, including three that reached Category 5 strength, tying a record while the season was still underway. Four named storms passed close to Hawaii. The Atlantic, by contrast, has been unusually quiet; a tropical storm that formed in the Gulf of Mexico on Wednesday was poised to become the basin’s first hurricane of the season. That split is common during strong El Niño events. Warmer Pacific waters and weaker wind shear can help storms develop there, while stronger, persistent wind shear over the Atlantic can disrupt storm formation. Forecasters expect the strong El Niño to last into spring, meaning its influence could continue through the coming months as California communities watch for winter rain.