three landfalls in one weekend » Yale Climate Connections

Oscar is the third named storm to make landfall on a Caribbean island in 2024. The others:

• Hurricane Beryl hit Carriacou, Grenada, on July 1 as a high-end Category 4 hurricane, causing catastrophic damage and killing at least five people in the Lesser Antilles.
• Hurricane Ernesto passed through the Leeward Islands on Aug. 13-14 as a tropical storm with 45-65 mph winds, causing $150 million in damage, but no fatalities, according to Gallagher Re.

Another “shortie” for the Atlantic

Nadine lasted just 12 hours as a tropical storm, making it the fourth named storm of the 2024 Atlantic hurricane season to last two days or less at tropical storm or hurricane strength (a “shortie”). The others were Alberto (one day), Chris (six hours), and Gordon (two days). The number of these short-lived storms has been increasing markedly in recent decades. As we wrote in a lengthy 2021 post, this increase is likely to be substantially inflated by observing system changes over time. 

Similarly, Oscar was an extremely small hurricane with an eye as small as 3.5 miles in diameter; it thus could have easily gone unreported in the days before routine satellite monitoring. Oscar’s compact size also allowed it to spin up and gain strength much more easily than a larger storm could have.

Nadine and Oscar were the first two named Atlantic storms of 2024 to develop on the same date. They arrived just after a remarkable burst of late-season activity highlighted by the catastrophic U.S. landfalls of Category 4 Helene and Category 5 Milton and the impressive open-ocean trek of Category 4 Kirk.

A late-season flurry of activity

Despite the mysterious pause in activity during the peak portion of the season in late August and early September, tropical cyclone activity in the Atlantic in 2024 has been above-average in all categories, and way above average for number of hurricanes (see Bluesky post below).

With the addition of Nadine and Oscar, the Atlantic has had 15 named storms, 10 hurricanes, four major hurricanes, and an accumulated cyclone energy, or ACE, index of 143. The averages for this date are 13 named storms, six hurricanes, three major hurricanes, and an ACE index of 110. The long-term averages for the period 1991-2020 for an entire season were 14.4 named storms, 7.2 hurricanes, 3.2 major hurricanes, and an ACE index of 123.

So while the Atlantic hurricane season of 2024 hasn’t been quite as hyperactive as many seasonal forecasters had expected, it certainly ranks head and shoulders above a typical season in terms of both potency and impact, and we may yet see one or more additional systems before year’s end.

Placid Pacific, frenzied Atlantic: This year’s clumping of tropical activity

After the catastrophic one-two punch of Helene and Milton – and given the record warmth swaddling most of the world’s oceans – it’d be easy to assume that the planet was bristling with hurricanes and typhoons over the past several months. But as it happens, it’s mainly the Atlantic that’s been on the active side.

The other three oceanic basins that generate Northern Hemisphere tropical cyclones – the Northwest Pacific, Northeast Pacific, and the North Indian – have all been running well below seasonal averages in activity to date. Here’s a look at accumulated cyclone energy (ACE) as of October 20, as compared to the year-to-date averages for 1991-2020, as compiled by Colorado State University (CSU):

Atlantic:  143.9 (avg. 109.5) = 31% above average
Northeast Pacific:  59.9 (avg. 124.6) = 52% below average
Northwest Pacific:  119.3 (avg. 233.8) = 51% below average
North Indian:  3.3 (avg. 12.1) = 73% below average

The North Pacific usually produces more than twice the tropical activity of the North Atlantic. So not even this year’s blockbuster Atlantic storms like Beryl, Helene, Kirk, and Milton have been enough to compensate for the quiet Pacific. The entire Northern Hemisphere’s total ACE through October 20 of 326.4 is less than two-thirds of the long-term average up to this point. Even if the 2024 total were to increase by 10% by December 31, it would still end up as the Northern Hemisphere’s second quietest year in the 45 years of reliable satellite data tracked by CSU.

It’s not unusual at all for some Northern Hemisphere basins to be quite active while others are on the slow side. Features like the El Niño–Southern Oscillation tend to enhance activity in some basins while suppressing it in others. This often leaves the hemispheric average not far from normal even when a basin or two is active or even hyperactive. When the tropical Pacific is moving toward La Niña during northern summer and autumn, as is now the case, conditions tend to favor tropical activity in the North Atlantic and reduce it across the North Pacific – which is exactly what’s happened, albeit in an especially dramatic way.