2025 Season Summary

The 2025 Atlantic hurricane season was near average in activity, with a total of

13 cyclones attaining tropical depression status,
13 cyclones attaining tropical storm status,
5 cyclones attaining hurricane status, and
4 cyclones attaining major hurricane status.

Before the beginning of the season, I predicted that there would be

15 cyclones attaining tropical depression status,
13 cyclones attaining tropical storm status,
6 cyclones attaining hurricane status, and
3 cyclones attaining major hurricane status.

The average numbers of tropical storms, hurricanes and major hurricanes (over the 30 year period 1991-2020) per season are 14.4, 7.2, and 3.2, respectively. My forecasted numbers were close to the final outcome in all categories. This season fell just below average in number of tropical storms and hurricanes, but notably had several very intense hurricanes, including three category 5's. The (preliminary) total Accumulated Cyclone Energy for the 2025 season is 132.6 units, which modestly exceeded the 30-year climatological average of 122.5.

The near-average total activity during the 2025 season is consistent with the mixed bag of atmospheric and oceanic indicators discussed in the pre-season summary. As forecast, ENSO neutral conditions prevailed through the entire hurricane season, with neither an El Niño nor a La Niña event active to suppress or enhance cyclone activity. As in the previous few years, Atlantic sea temperatures were well above the 30-year average, though the anomalies did not match the extreme ones of 2023 and 2024. The impact of these high ocean temperatures mainly lay in boosting hurricanes' intensity: despite having relatively few cyclones, 2025 featured a remarkable three category 5 hurricanes: Erin, Humberto, and Melissa. This was only the second time in recorded history that the Atlantic saw more than two category 5 hurricanes, after 2005 (which had 4).

Erin and Humberto reached category 5 strength over the western tropical Atlantic, an unusual feat made possible by ocean heat content reaching values usually only seen in the Gulf of Mexico or Caribbean. Finally, exceptionally warm waters in the western Caribbean allowed Melissa to become one of the strongest tropical cyclones ever recorded, reaching peak sustained winds of 185 mph winds and a minimum pressure of 892 mb on October 28. In terms of pressure, Melissa tied for third most intense among recorded Atlantic hurricanes, and was the strongest storm globally in 2025. Its landfall in Jamaica at 892 mb was tied for the lowest ever for a landfalling hurricane with the 1935 Labor Day Hurricane in the Florida Keys.

The map above shows all tropical cyclone tracks for 2025. It's notable that, with the glaring exception of Melissa, the south and west areas of the Atlantic basin were very quiet. In particular, the continental U.S. and Mexico each had only one Atlantic tropical storm make landfall. My area-specific forecast underestimated the risk to the Caribbean islands, and overestimated it elsewhere. The fortunate fact that most hurricanes went out to sea can be chalked up in part to a persistent pattern of upper-level troughing near the U.S. southeast.

The map above illustrates the upper-atmospheric pattern during peak hurricane season (August-October), highlighting lower than normal pressures over the U.S. southeast. This pattern generated flow from the southwest pushing hurricanes northeast out to sea, away from major landmasses.

A strange feature of the 2025 season that was repeated from 2024 was a lull in activity right at the climatological peak of hurricane season! This year, no named storms formed between August 24 and September 16 (compare to last year's lull between August 13 and September 9, which was even starker compared to the overall busy season). The last time no named storms formed in this date range is 1992, and before that 1939. A combination of features was responsible, including a regime of high sea-level pressure over the subtropical Atlantic (see below).

The map above shows a consistent high pressure area over the subtropics (red) in late August through mid-September. In the northern hemisphere, air flows clockwise around such high pressure areas, so cool and dry air from the northeast Atlantic was pushed down into the tropics, stifling the development of tropical waves coming off of Africa. Coupled with a high shear environment in the Caribbean during these dates, this effectively shut down hurricane activity.

Some other notable facts and figures from 2025 include:

• Tropical Storm Barry's remnants contributed to a devastating flash flood event in Texas on July 4-5 several days after its dissipation
• Hurricane Erin tied for the third-largest 24-hour pressure drop recorded in an Atlantic hurricane, dropping 83 mb from 998 mb to 915 mb on August 15-16 (the number one spot still belongs to 2005's Hurricane Wilma, the strongest Atlantic hurricane on record)
• Hurricanes Humberto and Imelda came close enough together to undergo a binary interaction, which altered the course of each hurricane (see the satellite image below); in fact, the minimum distance between the centers of the cyclones on September 30, around 466 miles (405 nautical miles, 750 kilometers), was the smallest recorded between two Atlantic hurricanes during the satellite era
• Subtropical Storm Karen was named at 44.5°N, the farthest north any Atlantic cyclone had been named

The satellite image above shows the interaction between Humberto and Imelda, which had the fortunate consequence of pulling Imelda eastward out to sea before it could make landfall in the U.S.

Overall, the 2025 Atlantic hurricane season had total statistics near the recent average, hiding the fact that it also had several exceptionally strong hurricanes.

Sources: "ENSO: Recent Evolution, Current Status and Predictions" from the Climate Prediction Center, CSU Department of Atmospheric Science Real-time Tropical Cyclone Activity, CSU Summary of 2025 Tropical Cyclone Activity, "2025 Atlantic hurricane season marked by striking contrasts" from the NOAA, Yale Climate Connections: "A Cat 4 and 5 extravaganza: A look back at the 2025 Atlantic hurricane season", Hurricane Humberto Tropical Cyclone Report (NOAA),

Squares with Ascending Digits

Yesterday's date, November 22, 2025, prompted me to think about square numbers with ascending digits (in base 10). In the month-day-year abbreviation, the digits of yesterday's date form 112225, which is a square number! In particular, 112225 = 335². Interestingly, both 335 and 112225 have an ascending digit sequence. It turns out that such squares, while rare, occur infinitely often. 112225 is a member of one of several similar infinite sequences. This one begins:

25, 1225, 112225, 11122225,...

Here the nth entry of the sequence has n-1 1's, followed by n 2's, and then a single 5 at the end. These are the squares of the sequence:

5,35,335,3335,....

Let's prove this fact by induction. Clearly, it is true that 5² = 25. Assume the nth term of the bottom sequence, a_n squares to the nth of the top sequence, b_n. Then we notice:

a_n+1 = 3*10ⁿ + a_n

so that

a_n+1² = (3*10ⁿ + a_n)² = 9*10²ⁿ + 6*10ⁿ*a_n + a_n². Now the key point is that 3*a_n is just 6 more than 333...33*3 = 999...99, so that 3*a_n = 10...05 = 10ⁿ + 5, and hence 6*a_n = 20...010 = 2*10ⁿ + 10. Simplifying the above equation then gives

a_n+1² = 9*10²ⁿ + 2*10²ⁿ + 10ⁿ⁺¹ + a_n² = 1*10²ⁿ⁺¹ + 1*10²ⁿ + 1*10ⁿ⁺¹ + a_n².

Finally, we see that to get from a_n² = b_n to a_n+1², we add two 1's to the very beginning of the number (1*10²ⁿ⁺¹ + 1*10²ⁿ) and then change the final 1 in the sequence of 1's to a 2, by adding 1*10ⁿ⁺¹. This results in precisely b_n+1, as claimed.

It'd be interesting to see whether there are higher perfect powers with ascending digit sequences; perhaps that will be the subject of another post.

Hurricane Melissa (2025)

Storm Active: October 21-31

Around October 13, a tropical wave began its passage across the tropical Atlantic. The system moved quite quickly westward and reached the Windward Islands on October 19. The vigorous disturbance produced widespread heavy rainfall during its passage into the eastern Caribbean, but its high forward speed prevented a closed circulation from forming. A little farther west, the system's forward speed slowed abruptly and it was able to become more organized. It was named Tropical Storm Melissa during the morning of October 21.

Melissa's evolution was difficult to forecast. On the one hand, the cyclone sat over a deep area of very warm water and had plenty of moisture to work with in the atmosphere. On the other, it was constantly beset by strong shear out of the west. As a result, Melissa continually developed areas of extremely strong thunderstorms which were consistently displaced east of the center. Oftentimes the low-level circulation of Melissa outpaced the convective mass, but this swirl would dissipate as the center reformed farther east. At the same time, due to Melissa being wedged between two mid-level ridges, steering currents were very weak and the cyclone did little more than meander for days. Overall it made a little progress north and west between its naming and October 24. Though the system remained away from land, rain on the outskirts of the storm caused torrential rains over portions of Hispaniola.

Around that time, though, wind shear began to gradually diminish and the system's structure changed. Organized outer bands developed and a central dense overcast appeared on the 25th. After these elements were in place, rapid intensification began. Melissa reached hurricane strength that afternoon and major hurricane strength just 9 hours afterward. By that time, an eye began to clear out. On October 26, the storm briefly paused deepening at category 4. Meanwhile, it had assumed a slow westward track, pushed by a weak mid-level ridge to the north. It tracked south of Jamaica and tropical storm conditions occurred along the southern coast of the island in outer bands.

Early on October 27, Melissa's satellite presentation became even more symmetric and the area of extremely intense thunderstorms around the eyewall grew, extending even higher into the atmosphere. This prompted an upgrade to category 5 intensity. Melissa was the third category 5 of the season after Erin and Humberto. This made 2025 only the second season on record with three or more category 5 hurricanes, after 2005, which featured four.

Over the next day, an approaching trough over eastern North America eroded the ridge that was steering Melissa and began to pull the cyclone, causing it to turn toward the north-northeast. This set it on a path toward Jamaica. It was, meanwhile, moving over some of the highest ocean heat content waters in the world. Though already a category 5, Melissa continued strengthening, avoiding the usual fluctuations in intensity that arise from eyewall replacement cycles common to powerful cyclones. During the morning of October 28, a few hours before Melissa's center made landfall in western Jamaica, the hurricane reached its extreme peak intensity. At its peak, the storm had estimated sustained winds of 185 mph and a minimum central pressure of 892 mb. It made landfall at this peak soon after.

Melissa's strength set a number of records. The 892 mb mark tied the Labor Day Hurricane of 1935 for most intense at landfall by minimum pressure in a recorded Atlantic huricane. This same pressure mark tied for third lowest ever recorded in an Atlantic hurricane, behind only Gilbert of 1988 and Wilma of 2005. The winds of 185 mph tied with several other hurricanes for second highest recorded in the Atlantic, behind only Allen of 1980. The wind damage wrought by the storm was catastrophic in western Jamiaca where the center passed through. The mountainous terrain did disupt Melissa enough to weaken it to a category 3 hurricane by the time it emerged back over water early that evening.

The storm had a brief resurgence in strength late on the 28th as a large eye redeveloped on satellite, and it was upgraded back to a category 4. Soon after that, though, wind shear out of the southwest began to disrupt Melissa's core again, and it weakened back to a category 3 at landfall in eastern Cuba in the early morning hours of October 29. The system continually accelerated northeastward, crossing quickly into the Atlantic and passing among the southeastern Bahamas as a category 1 that afternoon. Despite some shear, it managed to intensify slightly again over the western Atlantic to category 2 strength. The remaining core convection became displaced from the center on October 30, but Melissa was still a formidable cyclone as it rocketed by just west of Bermuda that evening.

Melissa transitioned to a post-tropical system during the morning of October 31. That night, the storm passed just east of Newfoundland, still packing hurricane-force winds. Ex-Melissa continued northeastward over the northern Atlantic until it merged with another low.

The image above shows Melissa at peak intensity just before its record landfall in Jamaica during the morning of October 28.

The hot waters of the southwest Caribbean sea allowed Melissa to become one of the most powerful hurricanes in recorded history. The storm's most devastating impacts were in western Jamaica, but it also caused damage in Haiti, eastern Cuba, the Bahamas, and Bermuda.

Two Fun Factorizations

I recently came across the following pair of numbers, quite close to one another, and with similar-looking prime factorizations:

4061 = 31*131
4069 = 13*313

We can explain the proximity of these two numbers by expanding the products as follows:

4061 = (3*10 + 1*1)(1*100 + 3*10 + 1*1) = 3*1000 + 9*100 + 1*100 + 3*10 + 3*10 + 1*1 4069 = (1*10 + 3*1)(3*100 + 1*10 + 3*1) = 3*1000 + 9*100 + 1*100 + 3*10 + 3*10 + 3*3

Notice that only the last terms are different, leading to the difference 3*3 - 1*1 = 8 between the two numbers.

The same sort of argument shows that products of the aba...ba*ba and bab...ab*ab differ only by a*a - b*b, where a and b are any two digits. However, a computer search yields no other examples where all of these numbers are prime, besides the above, up to at least a googol.

Tropical Storm Lorenzo (2025)

Storm Active: October 13-15

On October 10, a tropical wave entered the Atlantic from Africa. The wave was vigorous and developed fairly quickly, leading to the naming of Tropical Storm Lorenzo on October 13. At the time, it was located around 1000 miles west of Cabo Verde. This was fairly late in the season for a tropical cyclone to form in the "Main Development Region" of the tropical Atlantic between Africa and the Lesser Antilles.

Lorenzo experienced significant shear out of the southwest, preventing it from intensifying much as it moved northwestward. Even after shear lessened the next day, the storm entered an area of dry mid-level air that stifled convective developement. Without moist unstable air to drive its circulation, Lorenzo began to spin down quickly. It curved toward the north-northeast and steadily weakened before dissipating on October 15.

The image above shows Lorenzo on October 14.

Lorenzo did not affect any land areas as a tropical cyclone.

Subtropical Storm Karen (2025)

Storm Active: October 9-10

Around October 8, a non-tropical low pressure system formed well to the northwest of the Azores. The low quickly separated from the surrounding fronts and developed a tiny warm core, embedded in a larger upper-level trough. These characteristics, along with gale force winds, led to the designation of Subtropical Storm Karen late on October 9. This was the northernmost formation by an Atlantic tropical or subtropical cyclone on record, at 44.5°N.

Besides this impressive statistic, Karen did not lead a very notable existence. The small area of convection near the center was snuffed out the following afternoon when the storm moved even farther north over yet colder waters. By that evening, the system was declared post-tropical.

The image above shows Karen as a subtropical storm on October 10.

Karen carved out a warm core inside a larger system and managed to maintain subtropical cyclone status for a day before becoming post-tropical.

Tropical Storm Jerry (2025)

Storm Active: October 7-11

On October 3, a late season tropical wave entered the Atlantic basin. It moved quickly toward the west-northwest and steadily organized. By October 6, the wave had a very impressive satellite signature, featuring a broad area of spin and concentrated thunderstorm activity. The next day, it was named Tropical Storm Jerry. Jerry was still over a thousand miles east of the Lesser Antilles, but was moving quickly toward the west-northwest. Despite a strong start, the storm actually became less organized after it was named. By the next day, shear opposite to its forward motion had displaced all thunderstorm activity east-southeast of the center. Nevertheless, it managed to strengthen some through the evening of October 8.

Jerry approached the Leeward Islands the next day. The center made its closest approach to land during the evening of the 9th, but the accompanying rains peaked over the islands only overnight and into the next morning, since convection was so removed from the center. The storm wasn't strong, but did cause widespread flooding for the northeasternmost Caribbean islands. Only on the 10th did Jerry lift north away from the Leewards. The cyclone's center was very poorly defined, with a pronounced elongation in the northwest-southeast direction. The cyclone was never able to recover from this poor organization and lost its circulation on October 11, degenerating into a trough of low pressure.

The image above shows Jerry just east of the Leeward Islands on October 9. The center of circulation ultimately missed the islands, but Jerry's passage dragged an area of heavy rain, displaced south and east of the center, across those areas over the following day.

Jerry dissipated shortly after its brush of the Caribbean.

Hurricane Imelda (2025)

Storm Active: September 27-October 2

Around September 16, the first of a pair of tropical waves entered the Atlantic basin from the east. Unlike its successor, which would become Hurricane Humberto, the leading wave did not generate much thunderstorm activity for much of its journey across the tropical Atlantic. It first attracted notice on September 21, when this activity increased markedly as it approached the Leeward Islands. The system remained too disorganized to consolidate into a tropical cyclone, but it brought significant rainfall across the Caribbean. It first impacted the Leewards on the 23rd, Puerto Rico the next day, and the Dominican Republic on the 25th. After that time, the disturbance slowed down and turned toward the north. Less land interaction and favorable atmospheric conditions allowed it to establish a circulation over the next couple of days. Eventually, the system was designated Tropical Depression Nine a little off the northern coast of east Cuba.

Despite achieving tropical cyclone status, the depression was very still broad and disorganized at first, with mid-level spin displaced from the low-level center. It began to build a dense area of convection near the developing center on the 28th. That afternoon, it was upgraded to Tropical Storm Imelda. Around the same time, the center began to move northward through the Bahamas, bringing tropical storm conditions to some of the islands. Imelda deepened steadily over the next few days and winds increased. By the time it exited the Bahamas on September 29, it was a strong tropical storm. It was upgraded to a hurricane during the morning of September 30.

Imelda did not have the traditional appearance of a hurricane on satellite imagery; some dry air was present near the center and convection did not completely surround it. Nevertheless, it continued strengthening. That day it also took a sharp turn toward the east-northeast. This was due to an approaching trough near the U.S. east coastline and a binary interaction with Hurricane Humberto to Imelda's northeast. As the two cyclones approached each other, the Fujiwhara effect caused them to rotate in a counterclockwise direction around the "center of gravity" between the two. This center of gravity was recurving northeast, so Humberto's eastward progress slowed some, while Imelda was yanked quickly eastward out to sea away from land.

Imelda closed off a circular eyewall and continued to intensify. During the morning of October 1, the cyclone reached its peak intensity as a category 2 hurricane with 100 mph winds and a minimum central pressure of 966 mb. After that time, wind shear increased due to the encroaching trough, but Imelda managed to temporarily maintain its strength due to a favorable trough interaction. This meant it was still near peak intensity when the center of circulation passed within a handful of miles of a direct landfall of Bermuda late on October 1. The center's passage just south of the island brought hurricane-force winds to Bermuda for a few hours, before Imelda sped off to the east.

After that, the storm began to weaken and lose its remaining tropical characteristics. During the morning of October 2, Imelda transitioned to a post-tropical cyclone. Its remnants arced northeastward over the open north Atlantic until they dissipated several days later.

The image above shows Imelda on October 1 at peak intensity. The island of Bermuda is visible at right, directly in the hurricane's path.

Imelda took a sharp turn eastward around September 30, preventing it from affected mainland North America. Nevertheless, the storm brought significant impacts to the Bahamas and Bermuda.

Hurricane Humberto (2025)

Storm Active: September 24-October 1

On September 18, a vigorous tropical wave entered the tropical Atlantic ocean from the west African coastline. It tracked west-northwestward and steadily organized until it was designated Tropical Storm Humberto northeast of the Lesser Antilles on September 24. Despite some wind shear out of the west early on, Humberto steadily strengthened from formation. On the 25th, spiral bands and a central core appeared on satellite imagery. The storm became a hurricane the next morning. Meanwhile, the storm's forward speed slowed significantly due to weak steering currents.

Atmospheric conditions soon improved further over the storm. On September 26, Humberto rapidly intensified. An eye appeared and cleared out extremely quickly; within an 18 hour period, the storm went from a minimal hurricane to a strong category 4 hurricane. Overnight, an eyewall replacement cycle briefly halted strengthening, but the system rebounded surprisingly quickly. September 27 brought an even more symmetric eye surrounded by a larger ring of extremely cold cloud tops. This coincided with Humberto reaching its peak strength as a category 5 hurricane, with maximum sustained winds of 160 mph and a minimum central pressure of 918 mb. Humberto was the second category 5 hurricane of the season, after Hurricane Erin. This made 2025 the second consecutive year with multiple category 5 Atlantic hurricanes, due to the formation of Beryl and Milton in 2024. Such an event only occurred once before on record, during the 1932-1933 seasons.

During this episode of strengthening, Humberto's heading meandered a little, but the subtropical ridge generally pushed it west-northwestward at a slow but steady pace. Although conditions remained favorable a bit longer, another outer eyewall soon formed and disrupted the storm's internal structure, causing it to weaken back to a category 4 by the 28th. The core continued to evolve, but the storm remained a category 4 until the following evening, when shear increased markedly. This shear was associated with an approaching trough and in part due to the increasing proximity between Humberto and Imelda, which was approaching from the southwest. This shear destroyed the hurricane's core and exposed the center, leading to rapid weakening. By the afternoon of September 30, Humberto was down to category 1 strength, though it maintained an area of strong storms northeast of the center.

Meanwhile, the hurricane recurved toward the north and then sharply turned toward the east in the mid-latitue westerly flow. Humberto met a quick demise soon after: its circulation was absorbed into the approaching front during the morning of October 1.

The image above shows the impressive satellite signature of Humberto at its peak intensity as a category 5 hurricane on September 27.

Humberto did not affect any land areas as a tropical cyclone.

Note: Opertionally, the minimum pressure of Humberto was reported as 924 mb. Due to lack of aircraft reconnaissance at that time, there was some uncertainty in this figure. Post-season analysis indicated that subsequent in-situ measurements revealed a lower pressure than expected through typical wind-pressure models, so the estimated peak intensity was adjusted to the more intense 918 mb.

Hurricane Gabrielle (2025)

Storm Active: September 17-25

A tropical wave entered the Atlantic ocean around September 12 and moved slowly westward over the next several days. It produced a significant amount of thunderstorm activity but remained quite disorganized. The system was eventually designated Tropical Depression Seven on September 17. At the time, it was a little past halfway from Africa to the Windward Islands. Despite achieving tropical depression status, the cyclone was still a mess, with almost all convection displaced east of the center. Furthermore, the center itself was a warring group of vorticies rotating around one another. Later that day, the center reformed further north, coaxed poleward by an upper-level low over the subtropics. The storm's winds also increased enough that it was upgraded to Tropical Storm Gabrielle.

Gabrielle evened out to a more steady west-northwest heading on the 18th and consolidated its circulation, but struggled to produce thunderstorm activity. For most of the day, it was little more than a naked swirl. That evening, it began to put up a better fight against westerly wind shear and storm activity blossomed in the eastern semicircle. Nevertheless, atmospheric conditions remained hostile through the next day. It was only on the 20th that shear lessened and Gabrielle was able to start intensifying again. The storm spent the next few days curving around the western edge of the subtropical ridge, first turning toward the north and toward the east. This path kept it east of Bermuda, too far to cause any direct impacts to the island. This was fortunate, because Gabrielle strengthened significantly.

On the 21st, it was upgraded to a hurricane. Shortly after that, the cyclone's satellite presentation improved markedly. An eye quickly cleared out and became more symmetric. Gabrielle vaulted to major hurricane strength by the morning of September 22. That afternoon it reached its peak intensity as a category 4 hurricane, with maximum winds of 140 mph and a central pressure of 948 mb. The storm accelerated toward the east-northeast and encountered gradually increasing wind shear as well as decreasing ocean heat content. This began a decaying trend, though it remained a significant hurricane.

Gabrielle began to lose tropical characteristics late on September 24 as the central core collapsed and it weakened to a category 1 hurricane. By this time, the storm was speeding eastward toward the central Azores. During the afternoon of September 25, a few hours before arriving at the islands, Gabrielle transitioned to a post-tropical cyclone. This did not prevent the cyclone from bringing strong winds, storm surge, and brief heavy rains to the Azores; during the storm's passage, hurricane-force gusts were recorded at sea level as well as hurricane-force sustained winds at higher elevations. A fully extratropical ex-Gabrielle exited the island chain toward the east by the next morning. Its remnants passed near the coast of Portugal before dissipating days later.

The image above shows Gabrielle as a category 4 hurricane on September 22.

Gabrielle did not directly impact any land areas as a tropical cyclone, but did make a direct hit on the Azores shortly after losing tropical characteristics.