2025 North Atlantic Hurricane Season halftime recap: Calm before the storm?

Authors: James Cosgrove, Associate Director - Analytics and Modeling, Moody's; Jeff Waters, Director - Product Management, Moody's

September 10 marked the climatological peak of the North Atlantic hurricane season. Though in the basin itself, it told a very different story, with a day without active tropical cyclones or disturbances.

Here, we recap the adverse conditions that have limited tropical storm activity so far this year and examine the forecasts for the remainder of the season, which continue to call for average or above-average activity.

A quiet first half punctuated by Category 5 Erin

The North Atlantic hurricane season officially began on June 1, but over three weeks had passed before Andrea, the first tropical storm of the season, formed over the central North Atlantic on June 23—the latest start to the hurricane season since Arthur formed on July 1, 2014.

Tropical Storm Barry formed a few days later, on June 28, in the Bay of Campeche and made landfall as a tropical storm in Tampico, Mexico, the following day. The next week, on July 4, Tropical Storm Chantal formed off the southeastern U.S. coast and made landfall in South Carolina two days later. Then, after a month of inactivity, on August 4, Tropical Storm Dexter formed off the U.S. East Coast, headed out to the open water of the North Atlantic, and dissipated.

The standout event of the 2025 season thus far has been Major Hurricane Erin. Developed from an easterly wave off West Africa in mid-August, Erin gradually intensified as it crossed the tropics towards the Caribbean, and on August 15, Erin became the first (and so far, only) hurricane of the season.

On August 16, Erin underwent a period of extreme rapid intensification from a Category 1 hurricane to a Category 5 major hurricane. Erin’s center fortunately tracked north of the Caribbean Leeward Islands and the Greater Antilles with its destructive core and hurricane-force winds remaining offshore, though the system’s outer winds and rainbands did produce minor impacts on some Caribbean islands.

Erin then weakened in intensity but grew in size as it curved north and carved a path between Bermuda and the U.S. East Coast. Some minor coastal impacts were reported along parts of the North Carolina and Mid-Atlantic coasts and Bermuda. By August 22, Erin eventually accelerated into the far northern North Atlantic without any direct landfalls.

Erin’s explosion of activity was followed by the formation of Tropical Storm Fernand on August 23, the sixth named storm of the year. Formed over the open waters of the North Atlantic, Fernand then dissipated several days later with no land impacts.

The basin remained eerily quiet as September began. Remarkably, for the first time since 1939, no tropical cyclones developed in the North Atlantic between August 28 and September 15—an extraordinary occurrence during the climatological peak of hurricane season.

Figure 1: 2025 North Atlantic Hurricane Season. Source: National Hurricane Center.

By this stage of the season, an average year will have produced approximately nine named storms, of which four will have normally attained hurricane intensity, and around two of those will have reached major hurricane intensity. The count for 2025 (so far) stands at seven named storms, and only one of these storms—Erin—reached hurricane and major hurricane status. So, what is behind this quiet first half of the season, and will the pre-season forecasts that called for an active season still hold?

Where have the storms gone?

Despite the above-average sea surface temperatures (SSTs) that would typically favor heightened activity, the 2025 hurricane season has been governed by a combination of local and large-scale atmospheric factors that have hindered tropical cyclone development and intensification more than expected.

Tropical cyclones require moisture and atmospheric instability; without these crucial ingredients, storms struggle to develop and intensify. Throughout this year’s hurricane season, the North Atlantic has been much ‘drier’ and more stable than average, driven largely by outbreaks of Saharan dust and drier air that has been advected from the subtropics over the basin’s main development region.

Much of the North Atlantic was subject to low-frequency subsidence (sinking air at the surface) throughout July, August, and early September. This not only stabilized the atmosphere but is also thought to have suppressed the West African monsoon and the development and intensity of easterly waves.

Figure 2: Vertical instability in the tropical North Atlantic (blue points and line) has run below average (black line) throughout the season thus far, signifying more stable conditions in the basin. Source: NOAA.

Vertical wind shear, the change of wind speed or direction with height, and higher surface-level air pressure have also periodically stabilized the atmosphere and suppressed tropical activity across the basin, especially in the Caribbean Sea and the Gulf.

It was these factors combining for the majority of the season that have hindered storm development thus far. But Erin’s intensification into a Category 5 major hurricane in mid-August is a warning: when the North Atlantic was not suppressed by one of these factors, the underlying conditions in the basin were supportive of heightened activity. So, with this in mind, what might the rest of the season have in store?

What does the remaining season have in store?

Ahead of the 2025 season, there was a strong consensus among numerous meteorological agencies and groups that activity was likely to be average to above-average. These pre-season forecasts reflected the combined influence of several key seasonal oceanic and atmospheric factors that typically influence intraseasonal hurricane activity in the basin.

While 2025 has gotten off to a slow start due to the factors aforementioned, several meteorological agencies and groups released updated forecasts in August that continue to suggest the season will likely conclude with near-average or slightly-above-average activity, meaning that the second half of the season will likely be more active than the first.

On August 7, the U.S. National Oceanic and Atmospheric Administration (NOAA) slightly lowered its seasonal forecast compared to its initial late-May release, but still called for an average to above-average season. Its updated forecast calls for 13 to 18 named storms (previously 13 to 19), of which five to nine are expected to become hurricanes (previously six to 10), and of those, two to five are expected to become major hurricanes (previously three to five).

The Accumulated Energy (ACE) index is forecast to be 90 to 160 percent of the median (previously 95 to 180 percent). These numbers include those storms that have already formed and the ACE that has already accumulated thus far.

Furthermore, NOAA’s update slightly decreased the probability of an above-normal season from 60 percent to 50 percent, slightly increased the odds for a near-normal season from 30 percent to 35 percent, and slightly increased the likelihood of a below-normal season from 10 percent to 15 percent.

Similarly updated forecasts from Colorado State University, Tropical Storm Risk, the U.K. Met Office, and the European Centre for Medium-Range Weather Forecasting (ECMWF) continue to call for a near-average to slightly above-average season with some minor changes in the ranges of tropical storms, hurricanes, major hurricanes, and ACE compared to pre-June 1.

As September 10 marked the climatological midpoint of the hurricane season, there’s a long way to go before the hurricane season officially concludes on November 30, and the season’s activity can be fully evaluated. Needless to say, the longer the basin remains quiet and struggles to generate storms, the more likely the season’s final storm count will conclude below the pre-season forecasts.

As always, further updates from Moody’s RMS™ Event Response will help explain how the rest of the season unfolds over the coming months. 

The short- to medium-range forecasts indicate that marginally more favourable conditions for development are expected in the second half of September across the main development region and tropical North Atlantic as an enhanced phase of the Madden-Julian Oscillation (MJO) enters the basin; Tropical Storm Gabrielle formed on September 17 over the open water of the central tropical North Atlantic and is no immediate risk to land, but its course will be monitored closely over the coming days.

In the Pacific, El Niño–Southern Oscillation (ENSO)-neutral conditions remain present with sea surface temperatures near or below average across most of the tropics. A transition from ENSO-neutral to a more hurricane-promoting La Niña phase is likely in the next few months (October to December); it remains to be seen whether this transition happens soon enough to impact and influence the hurricane season.

If La Niña conditions were to develop in the Pacific through the fall, this could result in a more active end to the North Atlantic hurricane season; La Niña conditions are typically associated with increased activity (double the amount) in November when compared to ENSO-neutral and especially when compared to Novembers with El Niño conditions.

Remember that 2024 saw the North Atlantic enter a mid-season slumber around the peak month of the season. But conditions in the basin remained favorable, sea surface temperatures in the Pacific trended cooler toward La Niña, and once the hurricane-hindering factors waned, the basin was able to produce 11 storms past mid-September, including Helene and Milton, which caused devastating impacts in the U.S. A back-loaded second half of 2025 is not out of the question, too.

What does this mean for the industry?

Regardless of how active or inactive the rest of the season may be, what’s key to hurricane risk for the industry is ultimately decided by the trajectory, path, and landfall of individual tropical cyclones relative to exposures at risk. These variables are dependent on both broad-scale and local synoptic factors at the time of a storm’s formation and are not possible to skillfully forecast in monthly timelines. It’s important to monitor how the next few months unfold, as regardless of overall activity and storm count, it can only take one landfalling event to make a season costly or memorable.

With over 20 U.S. landfalling hurricanes since 2017, the industry is no stranger to hurricane risk and the increasing complexity of event losses. Every event serves as a unique reminder of the multifaceted nature of hurricane risks facing the insurance industry, with factors such as population increases in coastal areas, social inflation, construction inflation, and regulatory mandates influencing the overall event losses.

From exposure analytics to managing financial implications, Moody’s RMS Event Response provides support for every time-critical decision during a real-time event. Frequently released, detailed accumulation layers and stochastic event selections, both pre- and immediately post-landfall, enable exposure and portfolio analysis to inform decisions and prepare for potential losses as the event unfolds.

Moody’s HWind clients also receive enhanced analytics with access to real-time and historical wind field analyses in the western North Atlantic, Eastern North Pacific, and Central Pacific Basins, and real-time wind, storm surge, and precipitation forecasting products for the North Atlantic Basin.

These real-time forecasting products are made directly available to the Risk Modeler™ and ExposureIQ™ applications on the Moody’s Intelligent Risk Platform™. Moody’s RMS Event Response continues to support clients by ensuring a timely and comprehensive view of anticipated industry event loss.

The Moody’s RMS Event Response team ensures clients are well informed of global tropical cyclone activity with regular updates on the Support Center. Follow Moody’s – Insurance Solutions social media channels on LinkedIn for updates throughout the rest of the season.