Rapid intensification is a meteorological condition that occurs when a tropical cyclone intensifies dramatically in a short period of time. The United States National Hurricane Center defines rapid intensification as an increase in the maximum sustained winds of a tropical cyclone of at least 30 knots (35 mph; 55 km/h) in a 24-hour period.
Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw modest progress in the field after weather observation networks were formed across broad regions. Prior attempts at prediction of weather depended on historical data. It was not until after the elucidation of the laws of physics and more particularly, the development of the computer, allowing for the automated solution of a great many equations that model the weather, in the latter half of the 20th century that significant breakthroughs in weather forecasting were achieved. An important domain of weather forecasting is marine weather forecasting as it relates to maritime and coastal safety, in which weather effects also include atmospheric interactions with large bodies of water.
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".
The National Hurricane Center (NHC) is the division of the United States' National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 30th parallel north in the northeast Pacific Ocean and the 31st parallel north in the northern Atlantic Ocean. The agency, which is co-located with the Miami branch of the National Weather Service, is situated on the campus of Florida International University in University Park, Florida.
In order for rapid intensification to occur, several conditions must be in place. Water temperatures must be extremely warm (near or above 30 °C, 86 °F), and water of this temperature must be sufficiently deep such that waves do not churn deeper cooler waters up to the surface. Wind shear must be low; when wind shear is high, the convection and circulation in the cyclone will be disrupted . Dry air can also limit the strengthening of tropical cyclones.
Sea surface temperature (SST) is the water temperature close to the ocean's surface. The exact meaning of surface varies according to the measurement method used, but it is between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a short distance of the shore. Localized areas of heavy snow can form in bands downwind of warm water bodies within an otherwise cold air mass. Warm sea surface temperatures are known to be a cause of tropical cyclogenesis over the Earth's oceans. Tropical cyclones can also cause a cool wake, due to turbulent mixing of the upper 30 metres (100 ft) of the ocean. SST changes diurnally, like the air above it, but to a lesser degree. There is less SST variation on breezy days than on calm days. In addition, ocean currents such as the Atlantic Multidecadal Oscillation (AMO), can effect SST's on multi-decadal time scales, a major impact results from the global thermohaline circulation, which affects average SST significantly throughout most of the world's oceans.
Wind shear, sometimes referred to as wind gradient, is a difference in wind speed or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal wind shear. Vertical wind shear is a change in wind speed or direction with change in altitude. Horizontal wind shear is a change in wind speed with change in lateral position for a given altitude.
Usually, an anticyclone in the upper layers of the troposphere above the storm must be present as well—for extremely low surface pressures to develop, air must be rising very rapidly in the eyewall of the storm, and an upper-level anticyclone helps channel this air away from the cyclone efficiently. [ further explanation needed ] Hot towers have been implicated in tropical cyclone rapid intensification, though diagnostically has seen varied skill across basins.
An anticyclone is a weather phenomenon defined by the United States National Weather Service's glossary as "a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere". Effects of surface-based anticyclones include clearing skies as well as cooler, drier air. Fog can also form overnight within a region of higher pressure. Mid-tropospheric systems, such as the subtropical ridge, deflect tropical cyclones around their periphery and cause a temperature inversion inhibiting free convection near their center, building up surface-based haze under their base. Anticyclones aloft can form within warm core lows such as tropical cyclones, due to descending cool air from the backside of upper troughs such as polar highs, or from large scale sinking such as the subtropical ridge. The evolution of an anticyclone depends on a few variables such as its size, intensity, moist-convection, Coriolis force etc.
The troposphere is the lowest layer of Earth's atmosphere, and is also where nearly all weather conditions take place. It contains approximately 75% of the atmosphere's mass and 99% of the total mass of water vapor and aerosols. The average height of the troposphere is 18 km in the tropics, 17 km in the middle latitudes, and 6 km in the polar regions in winter. The total average height of the troposphere is 13 km.
The eye is a region of mostly calm weather at the center of strong tropical cyclones. The eye of a storm is a roughly circular area, typically 30–65 km (20–40 miles) in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather and highest winds occur. The cyclone's lowest barometric pressure occurs in the eye and can be as much as 15 percent lower than the pressure outside the storm.
The United States National Hurricane Center previously defined rapid deepening of a tropical cyclone, when the minimum central pressure decreased by 42 millibars (1.240 inHg) over a 24-hour period. However it is now defined as an increase in the maximum sustained winds of a tropical cyclone of at least 30 knots (35 mph; 55 km/h) in a 24-hour period.
Explosive cyclogenesis is the rapid deepening of an extratropical cyclonic low-pressure area. The change in pressure needed to classify something as explosive cyclogenesis is latitude dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by 24 mbar (hPa) or more in 24 hours. This is a predominantly maritime, winter event, but also occurs in continental settings, even in the summer. This process is the extratropical equivalent of the tropical rapid deepening. Although their cyclogenesis is totally different from that of tropical cyclones, bombs can produce winds of 74–95 mph, the same order as the first categories of the Saffir-Simpson scale and give heavy precipitation. Even though only a minority of the bombs become so strong, some have caused significant damage.
An annular tropical cyclone is a tropical cyclone that features a normal to large, symmetric eye surrounded by a thick and uniform ring of intense convection, often having a relative lack of discrete rainbands, and bearing a symmetric appearance in general. As a result, the appearance of an annular tropical cyclone can be referred to as akin to a tire or doughnut. Annular characteristics can be attained as tropical cyclones intensify; however, outside the processes that drive the transition from asymmetric systems to annular systems and the abnormal resistance to negative environmental factors found in storms with annular features, annular tropical cyclones behave similarly to asymmetric storms. Most research related to annular tropical cyclones is limited to satellite imagery and aircraft reconnaissance as the conditions thought to give rise to annular characteristics normally occur over water well removed from landmasses where surface observations are possible.
Hurricane Linda was the second-strongest eastern Pacific hurricane on record. Forming from a tropical wave on September 9, 1997, Linda steadily intensified and reached hurricane status within 36 hours of developing. The storm rapidly intensified, reaching sustained winds of 185 mph (295 km/h) and an estimated central pressure of 902 millibars (26.6 inHg); both were records for the eastern Pacific until Hurricane Patricia surpassed them in 2015. The hurricane was briefly forecast to move toward southern California, but instead, it turned out to sea and lost its status as a tropical cyclone on September 17, before dissipating on September 21. Linda was the fifteenth tropical cyclone, thirteenth named storm, seventh hurricane, and fifth major hurricane of the 1997 Pacific hurricane season.
The 1992 Pacific hurricane season was the most active Pacific hurricane season on record, featuring 27 named storms, and the second-costliest Pacific hurricane season in history, behind only the 2013 season. The season also produced the second-highest ACE value on record in the basin, surpassed by the 2018 season. The season officially started on May 15 in the eastern Pacific, and on June 1 in the central Pacific, and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean. However, these bounds were easily exceeded when Hurricane Ekeka formed on January 28 and again a couple months later with Tropical Storm Hali.
The 1989 Pacific hurricane season officially started on May 15, 1989, in the eastern Pacific, and 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 17 storms and 9 hurricanes formed, which was near long-term averages. Four hurricanes reached major hurricane status on the Saffir-Simpson Hurricane Scale.
Tropical Storm Zeta was a very late-developing tropical storm over the central Atlantic that formed after the 2005 Atlantic hurricane season had officially ended and continued into January 2006. Becoming a tropical depression at approximately midnight on December 30 (UTC), it became the record-breaking thirtieth tropical cyclone of the 2005 Atlantic hurricane season and after intensifying into Tropical Storm Zeta six hours later, it became the season's twenty-seventh named storm. Zeta was one of only two Atlantic tropical cyclones to span two calendar years.
Tropical Storm Helene was a long-lived tropical cyclone that oscillated for ten days between a tropical wave and a 70 mph (110 km/h) tropical storm. It was the twelfth tropical cyclone and eighth tropical storm of the 2000 Atlantic hurricane season, forming on September 15 east of the Windward Islands. After degenerating into a tropical wave, the system produced flooding and mudslides in Puerto Rico. It reformed into a tropical depression on September 19 south of Cuba, and crossed the western portion of the island the next day while on the verge of dissipation. However, it intensified into a tropical storm in the Gulf of Mexico, reaching its peak intensity while approaching the northern Gulf Coast.
Hurricane Wilma was the most intense tropical cyclone in the Atlantic basin on record, with an atmospheric pressure of 882 hPa. Wilma's destructive journey began in the second week of October 2005. A large area of disturbed weather developed across much of the Caribbean Sea and gradually organized to the southeast of Jamaica. By late on October 15, the system was sufficiently organized for the National Hurricane Center to designate it as Tropical Depression Twenty-Four.
The 2011 Pacific hurricane season was a below-average Pacific hurricane season and was the first season since 2009 that featured no depressions or named storms in the month of May. It had six major hurricanes which was above average for a Pacific hurricane season. The season officially started on May 15, 2011, for the eastern Pacific, and started on June 1, 2011, for the central Pacific, both of which ended on November 30, 2011. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. A total of 11 named storms were observed, which is below average.
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 started on May 15 in the eastern Pacific, and on June 1 in the central Pacific, and ended on November 30; these dates conventionally delimit the period during which most tropical cyclones form in the northeastern Pacific Ocean. However, with the formation of Tropical Storm Aletta on May 14 the season slightly exceeded these bounds.
Hurricane Emilia was, at the time, the strongest tropical cyclone on record in the Central Pacific Ocean, and the second of such to be classified as a Category 5 hurricane – the highest rating on the Saffir–Simpson hurricane wind scale. However, hurricanes Gilma later that year, Ioke in 2006, and hurricanes Lane and Walaka in 2018 later reached lower barometric pressures in the Central Pacific. The fifth named storm and the first of three Category 5 hurricanes of the 1994 hurricane season, Emilia developed from an area of low pressure southeast of Hawaii on July 16. Tracking westward, the initial tropical depression intensified into a tropical storm several hours after tropical cyclogenesis. Subsequently, Emilia entered the Central Pacific Ocean and moved into the area of responsibility of the Central Pacific Hurricane Center (CPHC).
The 2009 Pacific hurricane season was the most active Pacific hurricane season since 1994. The season officially started on May 15 in the East Pacific Ocean, and on June 1 in the Central Pacific; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. However, the formation of tropical cyclones is possible at any time of the year.
Hurricane Gilma was one of the most intense Pacific hurricanes on record and the second of three Category 5 hurricanes during the active 1994 Pacific hurricane season. Developing from a westward tracking tropical wave over the open waters of the eastern Pacific Ocean on July 21, the pre-Gilma tropical depression was initially large and disorganized. Gradual development took place over the following day before rapid intensification began. By July 23, the storm intensified into a hurricane and later a Category 5 storm on July 24. As Gilma reached this intensity, it crossed into the Central Pacific basin, the fourth consecutive storm to do so.
Hurricane Adrian was an intense, albeit short-lived early-season category 4 hurricane that took part during the 2011 Pacific hurricane season. Adrian originated from an area of disturbed weather which had developed during the course of early June, off the Pacific coast of Mexico. On June 7, it acquired a sufficiently organized structure with deep convection to be classified as a tropical cyclone, and the National Hurricane Center (NHC) designated it as Tropical Depression One-E, the first one of 2011. It further strengthened to be upgraded into a tropical storm later that day. Adrian moved rather slowly; briefly recurving northward after being caught in the steering winds. After steady intensification, it was upgraded into a hurricane on June 9. The storm subsequently entered a phase of rapid intensification, developing a distinct eye with good outflow in all quadrants. Followed by this period of rapid intensification, it obtained sustained winds fast enough to be considered a major hurricane and reached its peak intensity as a category 4 hurricane that evening.
Hurricane Dora was the strongest tropical cyclone in the northeastern Pacific in 2011. Dora developed from a tropical wave south of Honduras on July 18. Moving northwestward in favorable conditions, the system quickly intensified to tropical storm status and attained hurricane intensity the next day. Rapid intensification ensued shortly thereafter, bringing the storm to its peak intensity on July 21 as a Category 4 hurricane, with a minimum barometric pressure of 929 mbar and maximum sustained winds of 155 mph (250 km/h). However, the storm's path into an area with cool sea surface temperatures and wind shear caused Dora to quickly deteriorate and weaken. By July 24, Dora had degenerated into a remnant low-pressure area west of the Baja California Peninsula. Dora brought stormy conditions to the southwestern Mexico coast and the Baja California Peninsula throughout its existence. Remaining off the coast from its formation to dissipation, Dora's effects on land were slight. However, the outer rainbands of the hurricane caused flooding and mudslides in southern Mexico and Guatemala, while rough surf toppled a lighthouse and damaged 60 restaurants along the coast. The hurricane's remnants contributed to heightened shower and thunderstorm activity across New Mexico and Arizona in late July.
Hurricane Ophelia was the most intense hurricane of the 2011 Atlantic hurricane season. The seventeenth tropical cyclone, sixteenth tropical storm, fifth hurricane, and third major hurricane, Ophelia originated in a tropical wave in the central Atlantic, forming approximately midway between the Cape Verde Islands and the Lesser Antilles on September 17. Tracking generally west-northwestward, Ophelia was upgraded to a tropical storm on September 21, and reached an initial peak of 65 mph (100 km/h) on September 22. As the storm entered a region of higher wind shear it began to weaken, and was subsequently downgraded to a remnant low on September 25. The following day, however, the remnants of the system began to reorganize as wind shear lessened, and on September 27, the National Hurricane Center once again began advisories on the system. Moving northward, Ophelia regained tropical storm status early on September 28, and rapidly deepened to attain its peak intensity with maximum sustained winds of 140 mph (220 km/h) several days later. The system weakened as it entered cooler sea surface temperatures and began a gradual transition to an extratropical cyclone, a process it completed by October 3.
Hurricane Mitch's meteorological history began with its origins over Africa as a tropical wave and lasted until its dissipation as an extratropical cyclone north of the United Kingdom. Tropical Depression Thirteen formed on October 22, 1998, over the southwestern Caribbean Sea from a tropical wave that exited Africa on October 10. It executed a small loop, and while doing so intensified into Tropical Storm Mitch. A weakness in a ridge allowed the storm to track slowly to the north. After becoming disorganized due to wind shear from a nearby upper-level low, Mitch quickly intensified in response to improving conditions which included warm waters and good outflow. It became a hurricane on October 24 and developed an eye. After turning to the west, Mitch rapidly intensified, first into a major hurricane on October 25 and then into a Category 5 on the Saffir-Simpson Hurricane Scale the next day.
Hurricane Raymond was the only major hurricane in the eastern Pacific in 2013 and briefly threatened the southwestern coast of Mexico before recurving back out to sea. The seventeenth named storm and eighth hurricane of the annual cyclone season, Raymond developed from a tropical wave on October 20 south of Acapulco, Mexico. Within favorable conditions for tropical cyclone development, Raymond quickly intensified, attaining tropical storm intensity and later hurricane intensity within a day of cyclogenesis. On October 21, the hurricane reached its peak intensity with winds of 125 mph (205 km/h). A blocking ridge forced the hurricane to the southwest, while at the same time Raymond began to quickly weaken due to wind shear. The following day, the tropical cyclone weakened to tropical storm status. After tracking westward, Raymond reentered more favorable conditions, allowing it to intensify back to hurricane strength on October 27 while curving northward. The hurricane reached a secondary peak intensity with winds of 105 mph (165 km/h) several hours later. Deteriorating atmospheric conditions resulted in Raymond weakening for a final time, and on October 30, the National Hurricane Center (NHC) declared the tropical cyclone to have dissipated.
Hurricane Genevieve, also referred to as Typhoon Genevieve, was the fourth-most intense tropical cyclone of the North Pacific Ocean in 2014. A long-lasting system, Genevieve was the first one to track across all three northern Pacific basins since Hurricane Dora in 1999. Genevieve developed from a tropical wave into the eighth tropical storm of the 2014 Pacific hurricane season well east-southeast of Hawaii on July 25. However, increased vertical wind shear caused it to weaken into a tropical depression by the following day and degenerate into a remnant low on July 28. Late on July 29, the system regenerated into a tropical depression, but it weakened into a remnant low again on July 31, owing to vertical wind shear and dry air.
Hurricane Patricia was the most intense tropical cyclone ever recorded in the Western Hemisphere and the second-most intense worldwide in terms of barometric pressure. It also featured the highest one-minute maximum sustained winds ever recorded in a tropical cyclone. Originating from a sprawling disturbance near the Gulf of Tehuantepec in mid-October 2015, Patricia was first classified a tropical depression on October 20. Initial development was slow, with only modest strengthening within the first day of its classification. The system later became a tropical storm and was named Patricia, the twenty-fourth named storm of the annual hurricane season. Exceptionally favorable environmental conditions fueled explosive intensification on October 22. A well-defined eye developed within an intense central dense overcast and Patricia grew from a tropical storm to a Category 5 hurricane in just 24 hours—a near-record pace. The magnitude of intensification was poorly forecast and both forecast models and meteorologists suffered from record-high prediction errors.
The 2018 Pacific hurricane season produced the highest accumulated cyclone energy (ACE) value on record in the Eastern Pacific basin. With 23 named storms, it was the fourth-most active season on record, tied with 1982. The season officially began on May 15 in the eastern Pacific, and on June 1 in the central Pacific; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin, as illustrated when the first tropical depression formed on May 10.
Hurricane Olivia was the first tropical cyclone to make landfall on Maui and Lanai in recorded history. The fifteenth named storm, ninth hurricane, and sixth major hurricane of the 2018 Pacific hurricane season, Olivia formed southwest of Mexico on September 1. The depression slowly organized and strengthened into Tropical Storm Olivia on the next day. Olivia then began a period of rapid intensification on September 3, reaching its initial peak on September 5. Soon after, Olivia began a weakening trend, before re-intensifying on September 6. On the next day, Olivia peaked as a Category 4 hurricane, with winds of 130 mph and a minimum central pressure of 951 mbar. Six hours later, Olivia began another weakening trend that resulted in the hurricane being downgraded to Category 1 status on September 8, east of the 140th meridian west. On September 9, Olivia entered the Central Pacific Basin. Over the next couple of days, Olivia prompted the issuance of Tropical Storm Watches and Warnings for Hawaii County, Oahu, Maui County, and Kauai County. Olivia weakened into a tropical storm on September 11, before making brief landfalls in northwest Maui and Lanai on the next day, becoming the first tropical cyclone to impact the islands in recorded history. Tropical storm-force winds mainly affected Maui County and Oahu. Torrential rains affected the same area from September 11 to 13, causing flash flooding. Olivia caused a total of US$25 million in damages. Olivia was downgraded to a tropical depression on September 13 while continuing to head west. Due to wind shear disrupting Olivia's convection, the system weakened into a remnant low on September 14. Olivia crossed into the West Pacific Basin on September 19 as a remnant low, before dissipating later that day.
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