Hurricane Delta Fastest on Record to Rapidly Intensify From Tropical Depression to Category 4 in Atlantic Basin

Hurricane Delta underwent extraordinary rapid intensification from a tropical depression to Category 4 hurricane in less than two days' time over the Caribbean Sea, smashing an Atlantic Basin record.

Delta was first born as Tropical Depression Twenty-Six late Sunday night while it was only 75 miles south of Kingston, Jamaica.

By Monday morning, it was already Tropical Storm Delta, the 25th named storm of the 2020 Atlantic hurricane season.

(MORE: 2020 Hurricane Season Only 3 Shy of Record Storm Tally)

Then Delta shifted into beast mode, undergoing rapid intensification, a term meteorologists use to describe a tropical cyclone whose maximum sustained winds increase by at least 35 mph in 24 hours or less.

Late Monday evening, Delta became a hurricane. By late Tuesday morning, Delta flexed into a Category 4 powerhouse.

Delta went from a tropical depression to a Category 4 hurricane in just over 36 hours from Sunday night to late Tuesday morning. In that time, Delta's pressure plunged 52 millibars and its maximum sustained winds skyrocketed from 35 mph to 130.

That's the fastest tropical-depression-to-Category-4 intensification rate on record in the Atlantic Basin, according to Sam Lillo, a NOAA scientist based in Boulder, Colorado, and Tomer Burg, a PhD candidate at the University of Oklahoma.

Lillo and Burg found Hurricane Keith was the previous such record-holder, doing so in 42 hours also in the western Caribbean Sea east of Belize in late September and early October 2000.

The satellite loop of this rapid intensification was equally stunning, beginning with a disheveled mess of a tropical depression to a compact powerhouse of a hurricane.

How It Happened

The western Caribbean Sea is a region prone to rapid intensification, and the environment for Delta's rapid intensification was ideal.

The supply of very warm water not simply at the surface, but also at some depth, was greater over the western Caribbean Sea than anywhere else in the Atlantic Basin. This warm water served as a reservoir of heat and moisture for Delta to feed on.

Wind shear – the change in wind speed and/or direction with height that can rip apart a fledgling tropical storm wannabe – was noticeably absent over the area through its rapid intensification phase, before reemerging later Tuesday.

With a generally moist atmosphere in place, Delta's convection then began to wrap around its center Tuesday morning. By late that night, the GOES-East satellite was detecting lightning flashes within Delta's tiny core.

(MORE: Why Some Hurricanes Rapidly Intensify and Others Do Not)

Small tropical cyclones can concentrate the heat release in their cores, allowing for more rapid strengthening than a larger storm.

By Tuesday afternoon, Delta's eye had shrunk to only 4 nautical miles wide.

This was only slightly larger than the smallest-observed eye of any tropical cyclone on record, the 2-nautical-mile-wide "pinhole eye" in Hurricane Wilma, also in the western Caribbean Sea, on Oct. 19, 2005.

While computer forecast models predicted a much higher than normal chance of rapid intensification, Delta's tiny size was difficult to capture even by the most sophisticated high-resolution hurricane models. Thus, the ferocity of its intensification was at least somewhat underdone.

Other Rapid Intensifiers

Most recently, Hurricane Laura rapidly intensified from Category 1 to Category 4 intensity over the Gulf of Mexico before slamming into southwestern Louisiana in late August.

A number of other recent hurricanes have rapidly intensified, including Lorenzo in 2019, Florence and Michael in 2018 and Harvey in 2017.

Both hurricanes Maria in 2017 and Wilma in 2005 exploded from tropical depression to Category 5 in 54 hours, the fastest such rates on record in the Atlantic Basin.

Wilma's pressure plunged an incredible 97 millibars in 24 hours Oct. 18-19, 2005, and became the most intense Atlantic hurricane on record by pressure (882 millibars).

Hurricane Patricia in 2015 holds the global record for rapid intensification by wind speed. Its winds increased from 85 mph to 205 in just 24 hours, Oct. 22-23. Patricia's central pressure plunged 97 millibars in 24 hours as well.

Patricia set Western Hemisphere records for highest maximum sustained wind record (215 mph) and lowest surface pressure (872 millibars).

In 1983, Typhoon Forrest's pressure plunged an incredible 100 millibars in 24 hours – a record intensification rate by pressure anywhere on Earth – while over the Philippine Sea.

These rapidly intensifying tropical cyclones could become more common in a warming world, according to a recent study by Kerry Emanuel, an MIT scientist.

By 2100, the chance of a hurricane's winds increasing by 70 mph or greater in 24 hours right before landfall is expected to be once every 5 to 10 years, according to Emanuel. That's an increase from a rate of once every 100 years in the late-20th-century climate.

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