Why did Storm Milton strengthen so quickly?

More than a million people were asked to evacuate from Florida, USA, as Hurricane Milton made landfall from the west coast, Guardian reported on October 8. Milton is the third fastest intensifying storm ever recorded in the Atlantic, according to the US National Weather Service.

While many areas in the southern United States are still overcoming the consequences of superstorm Helene, which made landfall at the end of September, the rapid strengthening speed of storm Milton surprised many people. In just about a day, Milton strengthened into a level 5 storm, the strongest level on the Saffir – Simpson scale, with winds of up to 290 km/h as it moved through the Gulf of Mexico, towards central Florida.

Milton experienced “rapid intensification,” the term used for a storm whose winds increased by at least 55 km/h within 24 hours. Milton’s strengthening speed broke this benchmark with winds increasing by 145 km/h in about 25 hours, according to research organization Climate Central.

This makes Milton one of the strongest storms to ever threaten the United States. “This storm is approaching the mathematical limit of what the Earth’s atmosphere above this ocean can produce,” said Noah Bergren, a meteorologist in Florida.

A storm forms from many variables. In Milton, these variables combine to form a “nightmare.” The storm gained a large amount of energy from high sea surface temperatures in the Gulf of Mexico, which were much higher than normal. This energy translates into higher wind speeds. The Gulf of Mexico has repeatedly set temperature records this year and the sea water is likened to a bathtub in the summer. Milton’s core passes through some unusually warm waters, about 2 – 3 degrees Celsius, warmer than average for this time of year.

Milton also absorbs moisture from a very humid atmosphere. As a rule, a warmer atmosphere can contain 7% more water vapor with each additional degree Celsius. Additionally, the air is very unstable and can rise more easily, helping storms form and maintain shape.

Due to the influence of La Nina, there is not much wind shear, wind speed and direction are relatively uniform at different altitudes. So Milton can stay in very good shape, according to Kim Wood, an atmospheric scientist at the University of Arizona. “All of the above combined makes the storm more efficient in using available energy,” Wood explains.

The perfect combination of warm seas, moist air and low wind shear continues to be supported by Milton’s path through the western part of the Gulf of Mexico, which has not experienced much significant storm activity this hurricane season. When a storm passes over warm water, it absorbs much of this heat and uses it as fuel, causing the water to cool down. But on the west side of the bay, Wood said, there isn’t anything else to cool the water yet.

Milton is also a very compact storm with a highly symmetrical circular core. Meanwhile, Helene’s core took longer to coalesce and the storm was more widespread. Wind speeds inside Milton increased to 145 km/h in about 25 hours, faster than nearly any storm on record, behind only Hurricane Wilma in 2005 and Hurricane Felix in 2007.

Climate scientists have long worried that climate change could create storms that strengthen faster and reach higher peak intensity. Milton seems to be affirming this.

A study published in the journal Scientific Reports last year showed that tropical cyclones in the Atlantic are now about 29% more likely to experience “rapid intensification” than between 1971 and 1990. Another study found that the Nature is not enough to explain the increase in such storms. This means that climate change is also a cause.

Thu Thao (Theo Guardian, The Atlantic)