List of Category 5 Atlantic hurricanes

Hurricane Isabel viewed from space

This is a list of all recorded Atlantic hurricanes that have reached Category 5, the highest classification of tropical cyclone intensity on the Saffir-Simpson Hurricane Scale. Category 5 storms are the most catastrophic hurricanes that can form, and occur only about once every three years on average in the Atlantic basin. Only four times — in the 1960, 1961, 2005 and 2007 hurricane seasons — have multiple Category 5 hurricanes formed. Only in 2005 have more than two Category 5 storms formed, and only in 2007 has more than one made landfall at Category 5 strength.^[1]

Statistics

Tracks of all known Category 5 Atlantic hurricanes

A Category 5 hurricane has sustained winds greater than 135 knots (155.4 mph; 250.0 km/h). "Sustained winds" refers to the average wind speed observed over one minute at 10 metres (32 ft 9.7 in) above ground, which is the standard height windspeed is measured at to avoid interference by obstacles and obstructions. Brief gusts in hurricanes are typically up to 50 percent higher than sustained winds.^[2] Because a hurricane is (usually) a moving system, the wind field is asymmetric, with the strongest winds on the right side (in the Northern Hemisphere), relative to the direction of motion. The highest winds given in advisories are those from the right side.^[3]

Between 1924 and 2007, 32 hurricanes have been recorded at Category 5 strength. No Category 5 hurricanes were observed officially before 1924. It can be presumed that earlier storms reached Category 5 strength over open waters, but the strongest winds were not measured. The anemometer, a device used for measuring wind speed, was invented in 1846. However, during major hurricane strikes the instruments as a whole were oftentimes blown away, leaving the hurricane′s peak intensity unrecorded. For example, as the Great Beaufort Hurricane of 1879 struck North Carolina, the anemometer cups were blown away when indicating 138 mph (222 km/h).^[4]

An ongoing reanalysis of weather data is ongoing by researchers who may upgrade or downgrade other Atlantic hurricanes currently listed at Categories 4 and 5.^[5] For example, the 1825 Santa Ana hurricane is suspected to have reached category-5 strength.^[6] Furthermore, paleotempestological research aims to identify past major hurricanes by comparing sedimentary evidence of recent and past hurricane strikes. For example, a “giant hurricane” significantly more powerful than Hurricane Hattie (category 5) has been identified in Belizean sediment, having struck the region sometime before 1500.^[7]

Officially, the decade with the most Category 5 hurricanes is 2000-present, with 8 Category 5 hurricanes occurring thus far this decade, Hurricanes Isabel (2003), Ivan (2004), Emily (2005), Katrina (2005), Rita (2005), Wilma (2005), Dean (2007), Felix (2007). The previous decade with the most Category 5 hurricanes was the 1960s, with six occurring between 1960 and 1969. (Ethel, Donna, Carla, Hattie, Beulah, and Camille)^[1]

Lists of Category 5 Atlantic hurricanes

Listed in chronological order

Hurricane Ivan as a Category 5

This is a list of all of the Category 5 hurricanes in the order in which they formed.

Before the advent of reliable geostationary satellite coverage in 1966, the number of tropical cyclones in the Atlantic Ocean was underestimated. It is therefore probable that there are additional Category 5s other than those listed, but they were not reported and therefore not recognized.^[8]

Wind speeds are rounded to the nearest five units. Many older estimates are unreliable because measurement equipment would often be destroyed or damaged in the extreme conditions present in a Category 5 hurricane.^[9]

Listed by date in season

Hurricane Emily, the earliest Category 5

Hurricanes have reached Category 5 intensity during every month from July through October. The earliest-forming Category 5 storm was Hurricane Emily while the latest-forming Category 5 was Hurricane Hattie. Hurricanes Emily, Allen, Gilbert, and Wilma were the most intense storms to form in their respective months.^[1]

Six Atlantic hurricanes—Allen, Andrew, Isabel, Ivan, Dean and Felix—have reached Category 5 intensity on more than one occasion; that is, by reaching Category 5 intensity, weakening to a Category 4 or lower, and then becoming a Category 5 again. Such hurricanes have their dates shown together. However, no Atlantic hurricane has reached Category 5 intensity more than three times, as Allen, Isabel and Ivan each reached that intensity on three separate occasions. Andrew, Dean and Felix are the only other storms to have reached Category 5 on multiple occasions, each doing it twice ^[10]. Hurricane Allen holds the record for most overall time spent as a Category 5, while Hurricanes Dog and Ivan hold the record for most time spent consecutively as a Category 5.^[1]

Listed by minimum pressure

The minimum pressure of the more recent systems was measured by recon aircraft using dropsondes, or by determining it from satellite imagery using the Dvorak technique. For older storms, pressures are often incomplete. The only readings came from ship-reports, land-observations, or aircraft reconnaissance. None of these methods can provide constant pressure measurements. Thus, sometimes the only measurement can be from when the hurricane was not a Category 5. Consequently, the lowest measurement is sometimes unrealistically high for a Category 5 hurricane.

These pressure values do not "match-up" with the wind readings. This happens because the wind speed of a hurricane depends on both its size and how rapidly the pressure drops as the hurricane's center approaches. Thus, a hurricane in an environment of high ambient pressure will have stronger winds than a hurricane in an environment of low ambient pressure, even if they have identical central pressures.^[11]

This listing is not entirely identical to the list of most intense Atlantic hurricanes. Some modern Category 5 hurricanes have readings higher than some "weaker" Category 4 hurricanes. The most intense Atlantic hurricane not to reach Category 5 intensity was Hurricane Opal with a pressure of 916 millibars.^[12] This value is lower than the minimum pressure of some Category 5s with reliable pressure readings, such as Hurricane Andrew. Below Opal's intensity, this listing is identical to the list of most intense Atlantic hurricanes. Above it, some Category 4s would be included.

Eye of Hurricane Katrina from a Hurricane Hunter flight

Climatology

An October Category 5 that hit Cuba in 1924

A total of thirty-two Category 5s have been recorded in the Atlantic basin. One was in July, seven in August, twenty in September, and four in October. There have been no officially recorded June, November or off-season Category 5 hurricanes.

The July and August Category 5s reached their high intensities in both the Gulf of Mexico and the Caribbean Sea. These are the areas most favourable for tropical cyclone development in those months.^[13]

September sees the most Category 5 hurricanes. This coincides with the climatological peak of the Atlantic hurricane season, which occurs in early September.^[14] September Category 5s reached their strengths in any of the Gulf of Mexico, Caribbean Sea, and open Atlantic. These places are where September tropical cyclones are likely to form.^[13] Many of these hurricanes are either Cape Verde-type storms, which develop their strength by having a great deal of open water; or so-called "Bahama busters", which intensify over the warm Loop Current in the Gulf of Mexico.^[15]

All four October Category 5s reached their intensities in the western Caribbean, a region where Atlantic hurricanes strongly gravitate toward late in the season.^[13] This is due to the climatology of the area, which sometimes has a high-altitude anticyclone which promotes rapid intensification late in the season, as well as warm waters. Originally, there were only 3 category 5's discovered in October, but reanalysis found out that a Hurricane in 1924 also reached that intensity during the month, so four Category 5's developed in October.^[16]

Landfalls

Hurricane Camille, a landfalling Category 5

All Atlantic Category 5 hurricanes except Dog, Easy, and Cleo have made landfall at some location at some strength. Most Category 5 hurricanes in the Atlantic make landfall because of their usual proximity to land in the Caribbean and Gulf of Mexico, where the usual synoptic weather patterns carry them towards land, as opposed to the westward, oceanic mean track of Eastern Pacific hurricanes.^[17] Thirteen of the storms made landfall while at Category 5 intensity.^[1]

Many of these systems made landfall shortly after weakening from a Category 5. This weakening can be caused by dry air near land, shallower waters due to shelving, interaction with land, or cooler waters near shore.^[18]

The hurricanes are listed in chronological order with their landfalls indicated. Because they never made landfall, Hurricanes Dog, Easy, and Cleo are not included.

The 2007 season is the only one in recorded history to have more than one Category 5 storm make landfall at that intensity.^[1]

See also

Tropical cyclones portal

• List of Atlantic hurricanes
• List of Atlantic hurricane seasons
• List of Category 5 Pacific hurricanes

References

• Unisys Archive accessed March 14, 2006
• The Great Zo's Category 5 research page accessed March 14, 2006

External links

• NHC web site