Hurricane Elida on July 25, 2002 near maximum intensity

Category 5 hurricanes are tropical cyclones that reach Category 5 intensity on the Saffir-Simpson Hurricane Scale. They are the most catastrophic hurricanes that can form. They are rare in the eastern Pacific Ocean and generally form only once every several years. In general, Category 5's 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.

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, which formed east of the dateline but did not reach Category 5 intensity until after crossing the dateline.

Contents

[edit] Statistics

Saffir-Simpson Hurricane Scale
TD TS 1 2 3 4 5

A Category 5 hurricane sustained winds of greater than 135 knots (155.4 mph/250.0 km/h).[1] Sustained winds refers to a one-minute average measured 10 metres (32 ft 9.7 in) above the ground. Short gusts can be up to 50% higher than the sustained winds.[2] 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.[3]

Between the 1959 and 2006 seasons inclusive, only 12 hurricanes have reached and were recorded as a Category 5. There are no known Category 5 storms occurring before 1959. It is possible that some earlier storms reached Category 5 over open waters, but the strongest winds were not measured.[4]

[edit] Lists of Category 5 Pacific hurricanes

[edit] Listed in chronological order

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 then re-strengthening.

Before the advent of reliable geostationary satellite coverage in 1966, the number of eastern Pacific tropical cyclones was significantly underestimated.[5] It is therefore possible that there are Category 5's other than those listed, but they were not reported and therefore not recognized. However, the lack of Category 5's during the late 1970s, 1980s, and early 1990s, is certain.[4]

Hurricane Linda at record peak intensity
Name Season Max. 1 min. average sustained wind
knots km/h mph
1950s
Patsy 1959 150 280 175
"Mexico" 1959 140 260 160
1970s
Ava 1973 140 260 160
1990s
Emilia 1994 140 260 160
Gilma 1994 140 260 160
John 1994 150 280 175
Guillermo 1997 140 260 160
Linda 1997 160 300 185
2000s
Elida 2002 140 260 160
Hernan 2002 140 260 160
Kenna 2002 145 270 165
Ioke 2006 140 260 160

[edit] Listed by date in season

Hurricanes have reached Category 5 intensity during every month from June to October. The earliest Category 5 has formed in a season is June 7, by 1973's Hurricane Ava. The latest Category 5 to form in a season is the 1959 Mexico hurricane, which reached peak intensity on October 27. Hurricanes Ava, Gilma, Guillermo, Linda, and Kenna are the most intense storms to form in their respective months. There have been no May, November, or off-season Category 5's.[4]

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.[4] Hurricane Ioke was tied for the longest-lasting Category 5 hurricane recorded, spending 42 hours at that strength,[6] while hurricanes John and Linda had the longest time spent consecutively at that intensity.[4]

Hurricane Hernan off the coast of Mexico
Name Date attained Date lost Time as a Category 5
Ava June 7 June 8 12 hours
Emilia July 19 July 20 18 hours
July 20 July 21
Gilma July 24 July 25 18 hours
Elida July 25 July 25 6 hours
Guillermo August 4 August 5 12 hours
John August 22 August 24 42 hours
Ioke August 24 August 25 42 hours
August 26 August 26*
Hernan September 1 September 1 12 hours
Patsy September 6 September 6 6 hours
Linda September 12 September 13 42 hours
Kenna October 24 October 25 18 hours
"Mexico" October 27 October 27 6 hours
*Ioke did not lose Category 5 status on August 26, however, it moved into the Western North Pacific, and thus was no longer considered a hurricane, but rather a typhoon.

For its first time as a Category 5, Emilia was at that intensity for 6 hours; the second time was for 12 for a total of 18 hours.[7] For its first time as a Category 5, Ioke was at that intensity for 18 hours; the second time was 24 additional hours east of the dateline, giving a total of 42 hours.[4]

[edit] Listed by minimum pressure

Microwave radar in the tail of a C130 during a flight into Hurricane Ava
Name Lowest Pressure
Millibars Inches of Mercury
Linda 902 26.6
Kenna 913 27.0
Ava ≤915 ≤27.0
Guillermo 919 27.1
Gilma ≤920 ≤27.2
Ioke 920 27.2
Elida 921 27.2
Hernan 921 27.2
Emilia 926 27.3
John ≤929 ≤27.4
"Mexico" ≤958 ≤28.3
Patsy unknown unknown

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[8] and Ava,[9] the central pressure was measured by hurricane hunter aircraft flying into the storm. In the case of the 1959 Mexico hurricane, the best central pressure reading was measured after landfall.[4] Because of the estimation of central pressures, it is possible that other storms more intense than these have formed.[10]

The reason for estimating the pressure is the fact that most of these storms did not threaten land.[11] As Kenna was threatening land, its pressure was measured by a dropsonde.[8] Hurricane Ava never threatened land.[4] However, it was flown into to test equipment and conduct research.[9]

Before 1997, the means for estimate pressure from satellite imagery was not available. Older storms have incomplete pressure readings taken by ships, land-based observations, or recon aircraft. Ava's minimum known pressure was measured when it was a Category 4, for example.[4] 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.[12]

Note 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 2001's Hurricane Juliette. Juliette's lowest pressure was 923 millibars.[4]

[edit] Climatology

Hurricane Guillermo, the first of two Category 5's during the 1997 season

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 5's cluster in single seasons. The effects of El Niño are most significant in the central Pacific (140°W to the dateline).[13]

The general lack of Category 5's 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 unfavourable for tropical cyclones.

This does not mean that a Category 5 cannot form outside of an El Niño event. The entire year of 1959 was neither an El Niño or a La Niña, but had two Category 5's and was the deadliest pacific hurricane season ever recorded in history. Most of 1973 was during a La Niña, which reduces tropical cyclone activity in the eastern Pacific.[14]

[edit] Landfalls

Hurricane Kenna, one of only two Category 5 Pacific hurricanes to make landfall at any intensity

Of all of the Category 5 Pacific hurricanes, the only ones to make landfall were the 1959 Mexico hurricane and Hurricane Kenna. The 1959 storm was the only one to make landfall as a Category 5, as Kenna had weakened to a Category 4 at the time of its landfall. These are the strongest and third strongest landfalls by east Pacific tropical cyclones, respectively—the second strongest was 1976's Hurricane Madeline.[8]

In addition to those two systems, Hurricanes John, Linda and Ioke all threatened land for a while. John had minimal impact on Johnston Atoll and caused heavy surf in Hawaii.[7] Linda was briefly forecast to approach southern California, and it passed close to Socorro Island near peak intensity.[15] Ioke had minor effects on Johnston Atoll as well.[6]

The reason for the lack of landfalls is that tropical cyclones in the northern hemisphere usually travel to the west.[16] 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.

[edit] See also

Tropical cyclones portal

[edit] Notes

  1. ^ "The Saffir-Simpson Hurricane Scale". National Hurricane Center (2007-08-17). Retrieved on 2008-09-14.
  2. ^ Chris Landsea. "Subject: D4) What does "maximum sustained wind" mean ? How does it relate to gusts in tropical cyclones?". FAQ: Hurricane, Typhoons, and Tropical Cyclones. Atlantic Oceanographic and Meteorological Laboratory Hurricane Research Division. Retrieved on 2006-01-04.
  3. ^ Chris Landsea. "Subject: D4) What does "maximum sustained wind" mean ? How does it relate to gusts in tropical cyclones?". FAQ: Hurricane, Typhoons, and Tropical Cyclones. Atlantic Oceanographic and Meteorological Laboratory Hurricane Research Division. Retrieved on 2006-01-04.
  4. ^ a b c d e f g h i j "Eastern North Pacific Tracks File 1949-2007" (plaintext). National Hurricane Center (2008-03-21). Retrieved on 2008-09-14.
  5. ^ Chris Landsea (2002-06-11). "Subject: E10) What are the average, most, and least tropical cyclones occurring in each basin?". FAQ: Hurricane, Typhoons, and Tropical Cyclones. Atlantic Oceanographic and Meteorological Laboratory Hurricane Research Division. Retrieved on 2006-01-04.
  6. ^ a b Andy Nash, Tim Craig, Sam Houston, Roy Matsuda, Jeff Powell, Ray Tanabe, & Jim Weyman. "2006 Tropical Cyclones Central North Pacific". Central Pacific Hurricane Center. Retrieved on 2008-09-14.
  7. ^ a b "The 1994 Central Pacific Tropical Cyclone Season". Central Pacific Hurricane Center. Retrieved on 2008-09-14.
  8. ^ a b c James Franklin (2002-12-26). "Tropical Cyclone Report Hurricane Kenna". National Hurricane Center. Retrieved on 2008-09-14.
  9. ^ a b F.J. Hoelzl (1973-06-06). "wea01151, NOAA's National Weather Service (NWS) Collection". NOAA Photo Library. National Oceanic and Atmospheric Administration. Retrieved on 2008-09-14.
  10. ^ Max Mayfield (1997-10-02). "Preliminary Report Hurricane Guillermo". National Hurricane Center. Retrieved on 2008-09-16.
  11. ^ Neal Dorst. "Subject: H2) Who are the "Hurricane Hunters" and what are they looking for?". FAQ: Hurricane, Typhoons, and Tropical Cyclones. Atlantic Oceanographic and Meteorological Laboratory Hurricane Research Division. Retrieved on 2006-01-04.
  12. ^ Jim Gross (1989-08-30). "Preliminary Report Hurricane Dalilia" (GIF). National Hurricane Center. Retrieved on 2006-01-04.
  13. ^ Chris Landsea. "Subject: G2) How does El Niño-Southern Oscillation affect tropical cyclone activity around the globe?". FAQ: Hurricane, Typhoons, and Tropical Cyclones. Atlantic Oceanographic and Meteorological Laboratory Hurricane Research Division. Retrieved on 2006-01-04.
  14. ^ "Cold and Warm Episodes by Season". Climate Prediction Center. Retrieved on 2006-01-04.
  15. ^ Max Mayfield (1997-10-25). "Preliminary Report Hurricane Linda". National Hurricane Center. Retrieved on 2006-01-04.
  16. ^ Chris Landsea. "Subject: G8) Why do hurricanes hit the East coast of the U.S., but never the West coast?". FAQ: Hurricane, Typhoons, and Tropical Cyclones. Atlantic Oceanographic and Meteorological Laboratory Hurricane Research Division. Retrieved on 2008-09-14.

[edit] References