A weird lack of Northern Hemisphere tropical cyclones so far in 2025 » Yale Climate Connections

Flash floods have been front and center in this month’s U.S. weather picture, while tropical cyclones have been mostly lying low, as we discussed in our July 18 Eye on the Storm post. The year’s fourth named storm of the Atlantic season has only low odds of developing this week from a bubbling disturbance in the tropical Atlantic, and it looks unlikely to become a serious threat to land even if it does get organized.

It’s not just the Atlantic that’s been quiet. Each of the four basins of the Northern Hemisphere that generate tropical cyclones — the Atlantic, Northeast Pacific, Northwest Pacific, and North Indian Oceans — is now running below average on accumulated cyclone energy, or ACE, a function of peak wind speeds and storm longevity. For the hemisphere as a whole, the total ACE to date is the third-lowest in records dating back more than half a century.

The graph above shows Northern Hemisphere ACE for each year from January 1 through July 21, starting with 1971, the first year of reliable data from the Northeast Pacific. The ACE to date of 45.5 is only about 41% of the climatological average for the period 1991-2020. The only years with lower ACE at this point were 1977 (23.0) and 1998 (39.1).

The table below, from the Real-Time Global Tropical Cyclone Activity page maintained by Colorado State University, shows how each basin on Earth is faring on various measures of tropical cyclone activity. The Northern Hemisphere hasn’t been slack in producing named storms: the total of 16 thus far is actually at the year-to-date average. It’s just that the systems that do develop haven’t been surviving long or intensifying much. The cumulative longevity of each named storm (or “named storm days” in the table below) is only about two-thirds of average. As for hurricane-strength systems — which are called typhoons in the Northwest Pacific and severe cyclonic storms in the North Indian Ocean — their cumulative longevity is a mere 27% of average.

Surprising at it may seem, given how active the Atlantic has been over the past 30 years, the total number of tropical cyclones on Earth hasn’t increased in recent decades, although the strongest hurricanes, typhoons, and cyclones are getting more intense on average.

In its 2021 assessment, the Intergovernmental Panel on Climate Change concluded that these trends are liable to continue:

• “the proportion of Category 4-5 TCs [tropical cyclones] will very likely increase globally with warming”
• “it is likely that … the global frequency of TCs over all categories will decrease or remain unchanged”

Though they’re in a minority, a few researchers have found evidence in high-resolution modeling for a potential global increase in tropical cyclone numbers, including Kerry Emanuel of the Massachusetts Institute of Technology.

Looking region by region at 2025 thus far

Sea surface temperatures are the third-warmest on record for mid-July for the planet as a whole, not far behind the record-smashing years of 2023 and 2024. From the subtropics well into the midlatitudes of the Northern Hemisphere, the temperatures are sizzling relative to average. The Arctic Oscillation has been in a positive mode for most of the northern spring and early summer. This reflects the polar jet stream being displaced farther north than usual, helping midlatitude waters to heat up more readily while allowing flood-producing thunderstorm complexes to loiter across the United States.

In the deep tropics, where most tropical cyclones take shape, there’s a mix of above- and below-average areas.

Given that the storm-making basins of the hemisphere are so far-flung, it’s possible that this year’s unusually low ACE is being influenced by multiple regional factors that happen to be aligned.

In the basins that affect North America, “We’ve generally had pronounced sinking motion over the eastern North Pacific and Atlantic the past couple of weeks that has suppressed storm chances in both basins,” CSU’s Phil Klotzbach said in an email. Before July, the Northeast Pacific had been the hemisphere’s main tropical-cyclone-producing region, spawning five named systems from late May to late June. The most damaging was Hurricane Erick, which rocketed to Category 4 strength before making a Cat 3 landfall along Mexico’s southern Pacific coast. Erick caused at least 23 deaths and inflicted around USD 250 million in damage.

The Northwest Pacific got off to its third-latest start on record with the formation of Tropical Storm Wutip on June 11. Only two of the basin’s seven named storms to date have achieved typhoon status. Typhoon Danas moved north of the Philippines before making an unusual west-coast landfall in Taiwan on July 6 as a Category-3-equivalent. Danas caused more than USD 100 million in damage and took four lives. This past weekend, Tropical Storm Wiphi briefly reached minimal typhoon status (Cat 1 equivalent) while passing just south of Hong Kong. Wipha was on track to make a second landfall and move through northern Vietnam on Tuesday, most likely as a tropical storm.

India’s monsoon arrived more than a week early this year, and it’s been a strong one, dumping about 10% more rain than average over the past month. Tropical cyclones in the North Indian Ocean are strongest and most numerous in the pre- and post-monsoon periods, so the early arrival of the 2025 monsoon did its part to help keep the basin free of any named storms so far this year. The quietest season on record in the North Indian Ocean, 1993, produced just two named storms, one in mid-November and one in early December.

As for what’s on the horizon, weaker-than-average trade winds have led to substantial warming across the tropical Atlantic this month, Klotzbach noted. Meanwhile, stronger-than-usual trade winds have cooled the Northeast Pacific. Together, says Klotzbach, these trends may work to support tropical activity in the Atlantic toward August.

Wind shear has also suppressed activity in the Caribbean Sea — a common state of affairs in July, when the eastern Caribbean most often earns its “hurricane graveyard” nickname. “That pattern looks to finally be breaking down as we get into early August,” Klotzbach says. “This could lead to busier times in the Atlantic.”