 | ||
Category 5 hurricanes are tropical cyclones that reach Category 5 intensity on the Saffir-Simpson Hurricane Scale. They are by definition the strongest hurricanes that can form on planet Earth. They are rare in the eastern Pacific Ocean and generally form only once every several years. In general, Category 5s form in clusters in single years. Landfalls by such storms are rare due to the generally westerly path of tropical cyclones in the northern hemisphere.
Contents
The term "hurricane" is used for tropical cyclones in the Pacific Ocean, north of the equator and east of the international date line. A Category 5 Pacific hurricane is therefore a tropical cyclone in the north Pacific Ocean that reached Category 5 intensity east of the international dateline. Identical phenomena in the north Pacific Ocean west of the dateline are called "typhoons" or "super typhoons". Category 5 super typhoons generally happen several times per season, so cyclones of that intensity are not exceptional for that region. This difference in terminology therefore excludes storms such as Super Typhoon Paka and Super Typhoon Oliwa of 1997, and Super Typhoon Genevieve of 2014, which formed east of the dateline but did not reach Category 5 intensity until after crossing the dateline.
Statistics
A Category 5 hurricane is defined as having sustained windspeeds of at least 137 knots (158 mph; 254 km/h) over a one-minute period 10 metres (33 ft) above the ground. As a tropical cyclone is moving, its wind field is asymmetric. In the northern hemisphere, the strongest winds are on the right side of the storm (relative to the direction of motion). The highest winds given in advisories are those from the right side.
Since the 1959 season, only 15 hurricanes are known to have reached Category 5 intensity. There are no known Category 5 storms occurring before 1959. It is possible that some earlier storms reached Category 5 over open waters, but they were never recognized because they never affected land and remained at sea.
Category 5 Pacific hurricanes
This lists all of the Category 5 hurricanes in the order in which they formed. Only 1994's Hurricane Emilia and 2006's Hurricane Ioke have reached Category 5 intensity more than once; that is, by weakening into a Category 4 or weaker storm and later re-strengthening to a Category 5 storm.
Before the advent of reliable geostationary satellite coverage in 1966, the number of eastern Pacific tropical cyclones was significantly underestimated. It is therefore very possible that there are additional Category 5 hurricanes other than those listed, but they were not reported and therefore not recognized. However, the lack of Pacific Category 5 hurricanes during the late 1970s, 1980s, and early 1990s, is certain.
The minimum central pressure of these storms is, for the most part, estimated from satellite imagery using the Dvorak technique. In the case of Kenna, Ava, and Patricia, the central pressure was measured by hurricane hunter aircraft flying into the storm. Because of the estimation of central pressures, it is possible that other storms more intense than these have formed.
The reason for estimating the pressure (in lieu of direct measurements) is the fact that most of these storms did not threaten land. As Kenna and Patricia were threatening land, their pressures were measured by Hurricane Hunters using dropsondes. While Hurricane Ava never threatened land, it too was flown into by Hurricane Hunters to test equipment and conduct research.
Older storms have incomplete pressure readings, since there were no satellite-based estimates; the only observations were taken by ships, land-based observations, or reconnaissance aircraft when available. Ava's minimum known pressure was measured when it was a Category 4 hurricane, for example. John and Gilma have incomplete pressures because the Central Pacific Hurricane Center, in general, did not publish pressure on systems in the central Pacific (140°W to the dateline) at the time. However, it should be noted that this list is not identical to the list of most intense Pacific hurricanes. The most intense known Category 4 storm in the eastern Pacific was 2014's Odile. The lowest pressure of this storm was 918 millibars, lower than that of some Category 5's, such as Guillermo.
Hurricanes have reached Category 5 intensity during every month from June to October. The earliest Category 5 to form in a season is 1973's Hurricane Ava, which formed on June 7. The latest Category 5 to form in a season is Hurricane Kenna, which reached peak intensity on October 24. Hurricanes Ava, Gilma, Ioke, Linda, and Patricia are the most intense storms to form in their respective months. There have been no May, November, or off-season Category 5 hurricanes.
Two Pacific hurricanes are known to have reached Category 5 intensity multiple times: Emilia and Ioke. Both did it twice, and Ioke reached Category 5 status a third time as a typhoon while in the western Pacific. Hurricane Ioke was tied for the longest-lasting Category 5 hurricane recorded, spending 42 hours at that strength, while hurricanes John and Linda had the longest time spent consecutively at that intensity.
Climatology
In the eastern Pacific, Category 5 hurricanes usually occur only in El Niño years. During El Niño years, conditions are more favorable for tropical cyclones because of warmer sea surface temperatures and reduced wind shear. This is why Category 5s cluster in single seasons. The effects of El Niño are most significant in the central Pacific (140°W to the dateline).
The general lack of Category 5s in non warm-ENSO years is because of there being limited space for development. The prevailing ocean currents of the area carry warm water to the west. As there is no large piece of land to block the water and cause it to "pile up" like in the Atlantic, the area suitable for all tropical cyclones is small. Farther out to sea, while waters are still warm, wind shear limits the development of tropical cyclones in the waters south of Hawaii. This makes an otherwise ideal region unfavorable for tropical cyclones.
This does not mean that a Category 5 hurricane cannot form outside of an El Niño event. The entire year of 1959 was neither an El Niño or a La Niña, but it had one Category 5 hurricane (Patsy). Most of 1973 was during a La Niña, which reduces tropical cyclone activity in the eastern Pacific, yet Hurricane Ava, a Category 5 hurricane, formed in June of that year. The 2009, 2010, 2014, and 2015 seasons are the only pairs of seasons in which a Category 5 hurricane formed in consecutive years (Rick and Celia, and Marie and Patricia, respectively).
Landfalls
Of all of the Category 5 Pacific hurricanes, the only ones to make landfall at any intensity were Hurricane Kenna, Hurricane Rick, and Hurricane Patricia. None made landfall as Category 5 hurricanes; Patricia and Kenna had weakened to Category 4 at the time of their landfalls, and Rick was a tropical storm at its landfall. Patricia was the strongest landfall among Pacific hurricanes; 1976's Hurricane Madeline and 1992's Hurricane Iniki are tied as the second strongest storms at landfall, both of which didn't reach Category 5 strength, but made landfall as stronger Category 4 storms than Kenna. Originally, a hurricane in 1959 was thought to have struck Manzanillo at Category 5 intensity, but a reanalysis in 2016 indicated the storm had peaked as a Category 4 hurricane, and made landfall with the same winds as Kenna. Patricia was also originally thought to have made landfall as a Category 5 hurricane near Manzanillo before post-season analysis in 2016.
In addition to these three systems, Hurricanes John, Linda, and Ioke all threatened land for a while. John and Ioke had minimal impact on Johnston Atoll and John caused heavy surf in Hawaii. Linda was briefly forecast to approach southern California, and it passed close to Socorro Island near peak intensity.
The reason for the lack of landfalls is that tropical cyclones in the northern hemisphere usually travel to the west. In the Atlantic, this sends hurricanes towards North America. In the eastern Pacific, this sends tropical cyclones out into the open ocean to dissipate over waters too cool to support them or in environments with high wind shear. Hawaii, the only heavily populated island chain in the eastern Pacific, is protected from most hurricanes by a subtropical ridge and is small enough to avoid being hit simply due to low odds.