The brown ocean effect is an observed weather phenomenon involving some tropical cyclones after landfall. Normally, hurricanes and tropical storms lose strength when they make landfall, but when the brown ocean effect is in play, tropical cyclones maintain strength or even intensify over land surfaces. [1] Australia is the most conducive environment for this effect, where such storm systems are called agukabams. [2]
One source of the brown ocean effect has been identified as the large amount of latent heat that can be released from extremely wet soils. [1] [3] [4] A 2013 NASA study found that, from 1979-2008, 45 of 227 tropical storms either gained or maintained strength after making landfall. [5] The press release stated, "The land essentially mimics the moisture-rich environment of the ocean, where the storm originated." Originally, research devoted to extratropical cyclones, storms that first derive energy from the warm ocean waters and later from the conjecture of various air masses, explained the intensification of storms after landfall. [6] However, as research into these storms persists, Andersen and Shepherd, the two leading scientists behind the NASA study, discovered that some of these storms were not transitioning from warm-core to cold-core but were actually maintaining their warm-core dynamics, while ultimately outputting a greater measure of rainfall. [6]
In order for the brown ocean effect to take place, three land conditions must be met: "First, the lower level of the atmosphere mimics a tropical atmosphere with minimal variation in temperature. Second, soils in the vicinity of the storms need to contain ample moisture. Finally, evaporation of the soil moisture releases latent heat, which the team found must measure at least 70 watts averaged per square meter." [6] Storm systems impacted by the brown ocean effect gave rise to a new sub-category of tropical storm type called Tropical Cyclone Maintenance and Intensification Event or TCMI. [6] Another study concluded that latent surface heat flux from land surfaces actually have the potential to be larger than from the ocean, albeit for brief periods only. [7] Andersen and Shepherd are also examining the effects of climate change on TCMIs, looking into the potential intensification of these storms due to increase or decrease in the degree of wetness and dryness in areas susceptible to these systems. [6]
In the North Indian Ocean, countless cases of brown ocean-type tropical depressions forming over the subcontinent of India have been reported. The IMD has been known to issue advisories for these systems, while the JTWC usually does not, due to the common lack of intensity and structure to these systems. The most recent example of a brown ocean-type system has been characterized in Cyclone Tauktae, as it maintained its intensity despite making a landfall.
In 1972, Hurricane Agnes formed as a tropical depression over the Yucatán Peninsula. It made landfall in Florida as a Category 1 hurricane, and quickly collapsed into a tropical depression. However, it reintensified into a tropical storm over central North Carolina.[ citation needed ]
In 1973, an African easterly wave completed tropical cyclogenesis into a tropical depression while still inland over Guinea, some hours before the system's center crossed over from the African mainland to the Atlantic Ocean, where it later developed into Tropical Storm Christine.[ citation needed ]
In 1978, a tropical depression formed a few miles away from the coast of Texas and developed into Tropical Storm Amelia over Texas and caused flooding. Amelia slightly strengthened over land before weakening and fizzling out, however it maintained strength and even came as close as developing an eye like feature, as well as having bursts of convection.[ citation needed ]
2005's Tropical Storm Arlene made landfall near Pensacola, Florida. Due to the brown ocean effect, it remained a tropical depression and it held its intensity and structure for two more days as it traversed inland, where it finally dissipated near Flint, Michigan.[ citation needed ]
2005’s Hurricane Katrina made its first landfall in Florida on August 25 on the southern end of the peninsula. It held its intensity and only weakened slightly. [ vague ]
Tropical Storm Erin of 2007 is an example of the effect, when the storm intensified over central Texas, eventually forming an eye over Oklahoma. [1] [3] [4] Tropical Storm Erin gained even more traction as it travelled across the plains, a rare feat as most tropical storms weaken as they go farther inland. [4] Andersen states "Until events like Erin in 2007, there was not much focus on post-landfall tropical cyclones unless they transitioned. Erin really brought attention to the inland intensification of tropical cyclones." [6]
Tropical Storm Fay upon landfall over the Florida mainland strengthened to near hurricane strength and briefly forming an eye-like feature before weakening. The cause of this was the waterlogged terrain of South Florida specifically Lake Okeechobee and the Everglades. [8]
Another possible case is Tropical Storm Bill of 2015, when saturated soil conditions from the 2015 Texas–Oklahoma flood and tornado outbreak sustained the system for a longer period of time. [9]
In 2016, Tropical Depression Eleven made landfall in Eastern Florida. While over land, it became the first tropical cyclone to reach tropical storm strength while over Florida, where it was named Julia .
One possible case in the southern hemisphere is Tropical Cyclone Kelvin in 2018. Shortly after making landfall over Western Australia, Kelvin developed a clear eye and continued strengthening despite moving over the Great Sandy Desert, where most tropical cyclones rapidly weaken. The strengthening was assisted by the affected areas already experiencing record or near-record rainfall due to the preceding Cyclones Hilda, Joyce, and Low 11U passing over the same area in the months leading up to Kelvin.
Tropical Storm Alberto of 2018 is another example of the brown ocean effect. The storm sustained its strength as a Tropical Depression after landfall, lasting for an additional three days after its landfall. Alberto became one of only eleven cyclones to reach Lake Huron as a tropical depression. [10]
One possible case is Tropical Storm Claudette. Claudette formed just prior to landfall on southern Louisiana on June 19, 2021, possibly from the moist soils from recent flooding. The system weakened to a tropical depression before it restrengthened back to a tropical storm inland over North Carolina on June 21, 2021. [11]
The very powerful Hurricane Ida of 2021, which struck Louisiana, continued to maintain Category 4 winds some four hours after landfall, a further example of this effect. [12] [13]
Cyclone Ellie of 2022-2023 maintained tropical depression status days after landfall and even restrengthened into a tropical storm for a short amount of time over Western Australia.
Hurricane Helene of 2024 was able to move quickly through Florida, Georgia, and the Carolinas due to the brown ocean effect. [14]
The 1995 Atlantic hurricane season was a very active Atlantic hurricane season, and is considered to be the start of an ongoing era of high-activity tropical cyclone formation. The season produced twenty-one tropical cyclones, nineteen named storms, as well as eleven hurricanes and five major hurricanes. The season officially began on June 1 and ended on November 30, dates which conventionally delimit the period of each year when most tropical cyclones develop in the Atlantic basin. The first tropical cyclone, Hurricane Allison, developed on June 2, while the season's final storm, Hurricane Tanya, transitioned into an extratropical cyclone on November 1. The very active Atlantic hurricane activity in 1995 was caused by La Niña conditions, which also influenced an inactive Pacific hurricane season. It was tied with 1887 Atlantic hurricane season with 19 named storms, which was later equalled by the 2010, 2011, and 2012 seasons.
The 1961 Atlantic hurricane season was a very active Atlantic hurricane season, with an accumulated cyclone energy (ACE) total of 189, the highest since 1950 and until being surpassed by 1995. The season, however, was an average one in terms of named storms. The season featured eight hurricanes and a well above average number of five major hurricanes. It was previously thought that the season had a record-tying seven major hurricanes, before the Atlantic hurricane reanalysis project downgraded two storms in 2019. Two Category 5 hurricanes were seen in 1961, making it one of only eight Atlantic hurricane seasons to feature multiple Category 5 hurricanes in one season. The season started on June 15, and ended on November 15. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The first system, an operationally unclassified tropical depression, formed offshore east Central Florida on June 10, but dissipated a few days later. Next, Hurricane Anna developed in the eastern Caribbean Sea near the Windward Islands on July 20. It brought minor damage to the islands in, as well as wind and flood impacts to Central America after striking Belize as a hurricane. Anna caused one death and about $300,000 (1961 USD) in damage. Activity went dormant for nearly a month and a half, until Hurricane Betsy developed on September 2. Betsy peaked as a Category 4 hurricane, but remained at sea and caused no impact.
The 1968 Atlantic hurricane season was a below average hurricane season during which only nine nameable storms developed. The season officially began on June 1 and lasted until November 30, dates which conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. Of the named storms, five strengthened into hurricanes; none however intensified into a major hurricane. Only four other seasons since the start of the satellite era—1972, 1986, 1994, and 2013—did not feature a major hurricane. The first system, Hurricane Abby, developed in the northwestern Caribbean on June 1. Abby moved northward and struck Cuba, bringing heavy rainfall and flooding to western portions of the island. Making landfall in Florida on June 4, Abby caused flooding and spawned four tornadoes, but left behind little damage. Overall, the hurricane resulted in six deaths and about $450,000 (1968 USD) in damage. In late June, Tropical Storm Candy brought minor flooding and spawned several tornadoes across portions of the Southern United States. Overall damage from the cyclone reached approximately $2.7 million. 1968 featured two simultaneously active tropical storms during the month of June, a phenomenon that would not occur again until 2023.
The 1969 Atlantic hurricane season was the most active Atlantic hurricane season since the 1933 season, and was the final year of the most recent positive Atlantic multidecadal oscillation (AMO) era. The hurricane season officially began on June 1, and lasted until November 30. Altogether, 12 tropical cyclones reached hurricane strength, the highest number on record at the time; a mark not surpassed until 2005. The season was above-average despite an El Niño, which typically suppresses activity in the Atlantic Ocean, while increasing tropical cyclone activity in the Pacific Ocean. Activity began with a tropical depression that caused extensive flooding in Cuba and Jamaica in early June. On July 25, Tropical Storm Anna developed, the first named storm of the season. Later in the season, Tropical Depression Twenty-Nine caused severe local flooding in the Florida Panhandle and southwestern Georgia in September.
The 1957 Atlantic hurricane season featured one of the longest-travelling tropical cyclones in the Atlantic basin, Hurricane Carrie. Nevertheless, the season was generally inactive, with eight tropical storms – two of which went unnamed – and three hurricanes, two of which intensified further to attain major hurricane intensity. The season officially began on June 15 and ended on November 15, though the year's first tropical cyclone developed prior to the start of the season on June 8. The final storm dissipated on October 27, well before the official end of the season. The strongest hurricane of the year was Carrie, which reached the equivalent of a Category 4 hurricane on the Saffir–Simpson hurricane scale on two separate occasions in the open Atlantic; Carrie later caused the sinking of the German ship Pamir southwest of the Azores, resulting in 80 deaths.
The 1949 Atlantic hurricane season was the last season that tropical cyclones were not publicly labeled by the United States Weather Bureau. It officially began on June 15, and lasted until November 15. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The first storm, a tropical depression, developed in the northern Gulf of Mexico on August 14. The final system, Tropical Storm Sixteen, dissipated in the southwestern Caribbean Sea on November 5. It was a fairly active season, featuring 16 tropical storms and seven hurricanes. Two of these strengthened into major hurricanes, which are Category 3 or higher on the Saffir–Simpson hurricane wind scale.
The 1941 Atlantic hurricane season was the period in 1941 in which tropical cyclones formed in the Atlantic Basin. It was a relatively inactive hurricane season, with only six known storms. It officially began on June 16, 1941, and lasted until November 1, 1941. These dates delimit the period of each year when most tropical cyclones tend to form in the Atlantic basin. Of the six cyclones, four attained hurricane status, and three became major hurricanes. The active season had an abnormally late start; the first system formed on September 11, nearly three months after the official beginning date. The season was also short-lived, as all six storms developed in rapid succession. On September 23, three hurricanes existed simultaneously in the Atlantic basin.
The 1920 Atlantic hurricane season featured tropical storms and hurricanes only in the month of September. The first system, a hurricane, developed on September 7 while the last, a tropical depression, transitioned into an extratropical cyclone on October 27. Of note, four of the six cyclones co-existed with another tropical cyclone during the season.
The 1909 Atlantic hurricane season was an average Atlantic hurricane season. The season produced thirteen tropical cyclones, twelve of which became tropical storms; six became hurricanes, and four of those strengthened into major hurricanes. The season's first storm developed on June 15 while the last storm transitioned into an extratropical cyclone on November 14. The most notable storm during the season formed in late August, while east of the Lesser Antilles. The hurricane devastated the Lesser Antilles, the Greater Antilles, and Mexico, leaving around 4,000 fatalities and more than $50 million (1909 USD) in damage.
The 1989 Pacific hurricane season was a near normal season. It officially started on May 15, 1989, in the eastern Pacific, and on June 1, 1989, in the central Pacific, and lasted until November 30, 1989. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean. A total of 18 storms and 9 hurricanes formed, which was near long-term averages. Four hurricanes reached major hurricane status on the Saffir–Simpson scale.
The 1981 Pacific hurricane season was a slightly below average Pacific hurricane season. The season officially started on May 15 in the eastern Pacific basin and June 1 in the central Pacific basin. Both basins' seasons ended on November 30; these dates conventionally delimit the period during which most tropical cyclones form in the northeastern Pacific Ocean. The first tropical cyclone of the season was designated on May 30, and the final storm of the season, Hurricane Otis, dissipated on October 30. The season produced fifteen named storms and a total of eight hurricanes, which was near normal. However, the total of one major hurricane was below the average of three.
The 1906 Atlantic hurricane season was an average season. It featured twelve tropical cyclones, eleven of which became storms, six became hurricanes and three became major hurricanes. The first storm of the season, a tropical storm in the northern Caribbean, formed on June 8; although it struck the United States, no major impacts were recorded. July saw a period of inactivity, with no known storms. However, in August, the streak of inactivity ended with two storms, including a powerful hurricane. September brought three storms, including a deadly hurricane, with catastrophic impacts in Pensacola and Mobile. October included three storms, with a powerful hurricane that killed over 200 people. The final storm of the season impacted Cuba in early November and dissipated on November 9. The season was quite deadly, with at least with 381 total recorded deaths.
The 1905 Atlantic hurricane season featured five known tropical cyclones, two of which made landfall in the United States. The first system was initially observed near the Windward Islands on September 6. The last system to dissipate, the fourth storm, transitioned into an extratropical cyclone on October 11, while located well southeast of Newfoundland. These dates fall within the period with the most tropical cyclone activity in the Atlantic. Between October 5 and October 10, the fourth and fifth system existed simultaneously.
The 1902 Atlantic hurricane season featured five known tropical cyclones, three of which made landfall in the United States. The first system was initially observed in the northwestern Caribbean on June 12. The last system dissipated on November 6 while located well southeast of Newfoundland. These dates fall within the period with the most tropical cyclone activity in the Atlantic. None of the systems existed simultaneously.
The 2007 Atlantic hurricane season was the first season since 2003 to feature tropical activity both before and after the official bounds of the season. There were an above-average number of named storms during the season – 15, however many storms were weak and short-lived. Despite the predominance of weak systems, this was the first season on record to feature more than one Category 5 landfalling hurricane. This would not happen again until 2017. It produced 17 tropical cyclones, 15 tropical storms, six hurricanes, and two major hurricanes. It officially started on June 1 and ended on November 30, dates which conventionally delimit the period during which most tropical cyclones form in the Atlantic Ocean, although as shown by Subtropical Storm Andrea and Tropical Storm Olga in early May and early December, respectively, the formation of tropical cyclones is possible at any time of the year. The first system, Subtropical Storm Andrea, developed on May 9, while the last storm, Tropical Storm Olga, dissipated on December 13. The most intense hurricane, Dean, was, at the time, the third most intense landfalling Atlantic storm on record. It was the second on record in which an Atlantic hurricane, Felix, and an eastern Pacific hurricane, Henriette, made landfall on the same day. September had a then record-tying eight storms, until it was surpassed in 2020. However, the strengths and durations of most of the storms were low.
The 1975 Pacific hurricane season officially started May 15, 1975, in the eastern Pacific, and June 1, 1975, in the central Pacific, and lasted until November 30, 1975. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeast Pacific Ocean.
The 2012 Pacific hurricane season was a moderately active Pacific hurricane season that saw an unusually high number of tropical cyclones pass west of the Baja California Peninsula. The season officially began on May 15 in the eastern Pacific Ocean, and on June 1 in the central Pacific (from 140°W to the International Date Line, north of the equator; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in these regions of the Pacific Ocean. However, the formation of tropical cyclones is possible at any time of the year. This season's first system, Tropical Storm Aletta, formed on May 14, and the last, Tropical Storm Rosa, dissipated on November 3.
The 2020 Atlantic hurricane season was the most active Atlantic hurricane season on record, in terms of number of systems. It featured a total of 31 tropical or subtropical cyclones, with all but one cyclone becoming a named storm. Of the 30 named storms, 14 developed into hurricanes, and a record-tying seven further intensified into major hurricanes. It was the second and final season to use the Greek letter storm naming system, the first being 2005, the previous record. Of the 30 named storms, 11 of them made landfall in the contiguous United States, breaking the record of nine set in 1916. During the season, 27 tropical storms established a new record for earliest formation date by storm number. This season also featured a record ten tropical cyclones that underwent rapid intensification, tying it with 1995, as well as tying the record for most Category 4 hurricanes in a singular season in the Atlantic Basin. This unprecedented activity was fueled by a La Niña that developed in the summer months of 2020, continuing a stretch of above-average seasonal activity that began in 2016. Despite the record-high activity, this was the first season since 2015 in which no Category 5 hurricanes formed.
During 2022, tropical cyclones formed in seven major bodies of water, commonly known as tropical cyclone basins. Tropical cyclones were named by various weather agencies when they attained maximum sustained winds of 35 knots. During the year, 133 systems formed, of which 87 were named. The strongest storm to form was Typhoon Nanmadol, with minimum pressure of 910 hPa (26.87 inHg). The deadliest tropical cyclone was Tropical Storm Megi, which caused 214 fatalities in the Philippines, while the costliest was Hurricane Ian, which had an estimated damage total of at least $113.1 billion after affecting Trinidad and Tobago, Venezuela, Colombia, the western part of the Greater Antilles and Southeast United States.
During 2023, tropical cyclones formed in seven major bodies of water, commonly known as tropical cyclone basins. They were named by various weather agencies when they attained maximum sustained winds of 35 knots. Throughout the year, a total of 115 systems formed, with 79 of them being named. The most intense storm this year was Typhoon Mawar, which had a minimum pressure of 900 hPa (26.58 inHg). The deadliest tropical cyclone of the year was Storm Daniel, which killed at least 5,591 people in Libya, Greece, Turkey, and Bulgaria. Meanwhile, the costliest tropical cyclone was Typhoon Doksuri which caused at least $28.4 billion (USD) worth of damage in China, the Philippines and Taiwan, becoming the costliest on record outside the Atlantic Ocean basin. Among this year's systems, thirty became major tropical cyclones, of which ten intensified into Category 5 tropical cyclones on the Saffir–Simpson scale (SSHWS). This year, for the first time on record, at least one such Category 5 system formed in each tropical cyclone basin: Typhoons Mawar, Saola, and Bolaven in the western Pacific Ocean, Hurricanes Jova and Otis in the eastern Pacific, Hurricane Lee in the Atlantic, Cyclone Mocha in the North Indian Ocean, Cyclone Freddy in the southwest Indian Ocean, Cyclone Ilsa in the Australian region, and Cyclone Kevin in the South Pacific. The accumulated cyclone energy (ACE) index for the 2023, as calculated by Colorado State University (CSU) was 857.4 units, which was above the 1991-2020 mean of 770.2 units.