Weather — Noozify Original — October 21, 2026

Rapid Intensification: Why Pacific Hurricanes Explode Overnight

By Adam Cannizzaro

Watch the story in half a minute

On Wednesday, September 30th, Hurricane Rachel was on the edge of something the eastern Pacific has been doing a great deal lately. The National Hurricane Center's afternoon advisory had Rachel as an 85-mph Category 1 hurricane moving northwest off southwestern Mexico, and the forecast called for it to reach major-hurricane strength, about 115 mph, within a day. The forecasters were candid about what could get in the way. Winds higher in the atmosphere were still pushing against the top of the storm, enough to tilt it and slow its growth, and its path crossed a stretch of ocean that Hurricane Polo had already churned up and cooled. Rachel strengthened anyway. By the next afternoon its winds had reached about 120 mph, a gain of about 35 mph in 24 hours, exactly the line that defines rapid intensification, and it stayed well offshore, south of the Baja California Peninsula.

Polo is the reason nobody is treating the word "rapid" as boilerplate. It was a tropical depression on September 20th, and by September 22nd its maximum sustained winds had risen by 90 knots, about 104 mph, in 24 hours, taking it to Category 5. A NOAA Hurricane Hunter crew estimated winds near 180 mph that day. NASA's Earth Observatory titled its account "Explosive Intensification for Hurricane Polo" and noted that the National Hurricane Center, in forecast discussions not known for raising their voice, had called the rate "truly remarkable." A week later, Rachel followed on a smaller scale. The phenomenon is the more durable story, because it decides how much warning the people in a hurricane's path actually get.

The term has a precise meaning, and it is less exotic than the adjectives around it. The Hurricane Center defines rapid intensification as an increase in maximum sustained winds of at least 30 knots in 24 hours, about 35 mph, typically enough to lift a storm a category or two in a day. The threshold traces to a 2003 study by the NOAA researchers John Kaplan and Mark DeMaria, who looked at the 24-hour intensity changes of Atlantic storms from 1989 to 2000 and drew the line at roughly the 95th percentile. Their other finding is the one worth keeping. Eighty-three percent of major hurricanes, and every Category 4 and 5 in the sample, had rapidly intensified at least once. Rapid intensification is not a rare malfunction. Most of the time, it is how a storm becomes a major hurricane in the first place. What sets the eastern Pacific's recent storms apart is how far past the threshold they go, clearing it three times over in a single day.

The ingredients are well understood. NASA lists the key ones as warm surface water, a deep layer of warm water beneath it, and low wind shear, meaning little change in wind speed and direction from the surface to the upper atmosphere. Warm water and the humid air above it supply the energy. The depth of that warm layer decides whether the fuel lasts, because a hurricane's winds stir up cooler water from below. Shear is the spoiler, and in NASA's phrase it "rips the tops off" developing hurricanes. Even with everything in place, many storms never take off, because the final trigger is inside the storm, in tall, rotating thunderstorms near the center that are usually no wider than 6 miles and last an hour or less. That is why forecasters have become much better at predicting where a hurricane will go, which large-scale winds mostly decide, than how strong it will get. Rachel's forecasters said as much, writing that rapid strengthening was possible "if the tighter inner core that Rachel is trying to develop maintains itself."

I have lived through two serious hurricanes, Bertha in the Carolinas in 1996 and Sandy in New York in 2012. Both were on forecast maps for about a week before they came ashore. That kind of notice is what better track forecasts buy, and it is exactly what rapid intensification takes away.

The waters off southern Mexico often have all of these ingredients. A 2024 Congressional Research Service review cites research that counted more rapidly intensifying storms in the eastern Pacific than in the Atlantic between 1986 and 2020. This year the water has been warmer still. Polo crossed water as warm as 90°F, roughly 4 to 5 degrees above normal for the date, when about 82°F is generally the minimum a hurricane needs to keep strengthening. With El Niño warming the eastern Pacific, NASA reported that the season's storm activity, a measure that combines how strong storms are and how long they last, was nearly twice normal by September 24th. The scientists NASA consulted cautioned that El Niño makes the season busier but does not explain any one storm.

The eastern Pacific's recent history shows what that can look like. In October 2015, Hurricane Patricia's winds rose from about 85 mph to 205 mph in 24 hours on the way to a peak of about 215 mph, the strongest hurricane on record in either the eastern Pacific or the Atlantic, and the Hurricane Center's report acknowledged that its forecasts "failed to explicitly show rapid intensification until it was actually occurring." Patricia weakened almost as fast and came ashore on a lightly populated stretch of the Jalisco coast. In 2018, the forecasts for Hurricane Willa called for rapid strengthening from the very first advisory, but not for the roughly 70 mph it gained in a single day. Then came Otis. Early on October 24, 2023, Otis was a 65-mph tropical storm south-southeast of Acapulco, and the forecast issued about 22 hours before landfall called for an 85-mph Category 1 hurricane at the coast. Instead it gained about 104 mph in 21 hours and came ashore at Acapulco a little before 1 a.m. local time on October 25th as a Category 5 with winds of about 160 mph, the strongest eastern Pacific landfall since the Hurricane Center took over the region in 1988. Less than four hours before landfall, the forecasters wrote, "A nightmare scenario is unfolding for southern Mexico this evening."

Mexico's government counted at least 52 deaths, with 32 more people missing, and the Hurricane Center's report cautions that the final toll could be much higher. More than 98 percent of homes in Acapulco were damaged, and estimated losses of $12 billion to $16 billion made Otis the costliest tropical cyclone on record for Mexico. The report states that the extreme intensification "was not anticipated by NHC forecasters or the intensity guidance suite." Satellite-based estimates lagged the real winds. The one Air Force Reserve Hurricane Hunter flight showed forecasters that no model had the storm right, but only after the intensification was well underway, and the report notes how sparse observations over the eastern Pacific are, especially for small storms like Otis.

The tools have improved since, and some of that shows in Rachel's own forecasts. NOAA's newest hurricane model, known as HAFS, went into operation in June 2023. It zooms in to a resolution of 1.2 miles on the parts of a storm that matter most, and NOAA says it predicts rapid intensification better than earlier models, though it was already running when Otis formed four months later. On September 29th, a NOAA research plane flew into Rachel and launched a small uncrewed aircraft into the layer of air just above the sea, where a hurricane's winds meet the water, and that day's track forecast blended an AI model from Google DeepMind with the traditional ones. The Hurricane Center's review of the 2025 season, the first in which it used AI models in real time, found record accuracy for its eastern Pacific intensity forecasts two and three days out. It also called that season's storms easier than normal to forecast and rapid intensification one of the biggest challenges the center faces. Progress is being measured in knots, not in certainty.

The trend that matters most for coastlines is where the fast strengthening happens. A 2023 study in Nature Communications found that rapid-intensification events within 400 kilometers, about 250 miles, of a coastline tripled worldwide between 1980 and 2020, from fewer than five a year in the 1980s to about 15, while the count over open ocean showed no significant change. The west coast of Mexico was among the places where increases appeared, and the authors used climate models to argue that ocean warming has amplified the shift. They also concede that 41 years may be too short to demonstrate a long-term trend, and the Congressional Research Service notes that scientific questions remain. A storm that intensifies in the open ocean is a meteorological event. One that does it within 200 miles of Acapulco is a test of how quickly a city can board up, evacuate, and move its boats.

Which brings the story back to Rachel, whose forecasters saw its jump coming a day out, and whose core stayed well offshore. Its forecasts still teach a habit worth keeping. The category in an advisory describes what a hurricane is. The discussion underneath describes what it might become. About 22 hours before Otis reached Acapulco, its discussion noted that a statistical index gave the storm about a 1 in 4 chance of rapid strengthening over the next day. One in four is not a long shot, and in the eastern Pacific it has a way of arriving overnight.