Hurricane Walaka

Hurricane Walaka
Category 5 major hurricane (SSHWS/NWS)
Hurricane Walaka at peak intensity south of Johnston Atoll on October 2
Formed September 29, 2018
Dissipated October 9, 2018
(Extratropical after October 6)
Highest winds 1-minute sustained: 160 mph (260 km/h)
Lowest pressure 920 mbar (hPa); 27.17 inHg
Fatalities None
Damage Unknown
Areas affected Johnston Atoll, Northwestern Hawaiian Islands, Alaska, British Columbia
Part of the 2018 Pacific hurricane season

Hurricane Walaka (/wɑːlɑːkɑː/ ua-la-ka; Hawaiian: ʻwalaka meaning "ruler of the army") was one of the most intense Pacific hurricanes on record. By minimum pressure, Walaka is the second-strongest tropical cyclone in central Pacific, alongside Hurricane Gilma in 1994, and is only surpassed by Hurricane Ioke in 2006. The nineteenth named storm, twelfth hurricane, eighth major hurricane, and second Category 5 hurricane of the 2018 Pacific hurricane season, Walaka originated from an area of low pressure that formed over a thousand miles south-southeast of Hawaii on September 25. The National Hurricane Center tracked the disturbance for another day or so before it moved into the Central Pacific Basin. The Central Pacific Hurricane Center monitored the disturbance from that time until September 29, when the system organized into Tropical Storm Walaka. Walaka gradually strengthened, becoming a hurricane on October 1. Walaka then began to rapidly intensify, reaching Category 5 intensity by early on October 2. An eyewall replacement cycle caused some weakening of the hurricane, though it remained a powerful storm for the next day or so. Afterward, less favorable conditions caused a steady weakening of the hurricane, and Walaka became extratropical on October 6, well to the north of the Hawaiian Islands.

Although the hurricane did not impact any major landmasses, it passed very close to the unpopulated Johnston Atoll as a strong Category 4 hurricane, where a hurricane warning was issued in advance of the storm. Four scientists there intended to ride out the storm on the island, but were then evacuated before the storm hit. Walaka then neared the far Northwestern Hawaiian Islands, but weakened considerably as it did so. Damage, if any, from the storm is currently unknown.

Unrelated to Walaka, Typhoon Kong-Rey developed and intensified into a Category 5-equivalent around the same time Walaka reached its peak intensity, marking the first time since 2005 where two tropical cyclones of Category 5 strength spanned the Pacific basin.

Meteorological history

Map plotting the track and the intensity of the storm, according to the Saffir–Simpson scale

Walaka originated from a trough of low pressure that the National Hurricane Center (NHC) first noted on September 22. At the time, the NHC forecasted a low-pressure area to form in the far western portion of the east North Pacific within a few days.[1] Early on September 25, a trough of low pressure formed approximately 1,600 miles (2,575 km) south-southeast of Hilo, Hawaii.[2] The NHC continued to monitor the disturbance for another day or so until it moved into the Central Pacific Hurricane Center's (CPHC) area of responsibility on September 26 at 12:00 UTC.[3] The CPHC monitored the disturbance for another few days until the system organized into Tropical Storm Walaka on September 29 at 21:00 UTC.[4] Environmental conditions, including low wind shear, high sea surface temperatures and ample moisture supported steady – perhaps even rapid – intensification into a powerful hurricane.

Most intense Pacific hurricanes[5]
HurricaneYearPressure
hPainHg
1 Patricia 2015 872 25.75
2 Linda 1997 902 26.64
3 Rick 2009 906 26.76
4 Kenna 2002 913 26.96
5 Ava 1973 915 27.02
Ioke 2006
7 Marie 2014 918 27.11
Odile
9 Guillermo 1997 919 27.14
10 Gilma 1994 920 27.17
Walaka 2018
Listing is only for tropical cyclones in the Pacific Ocean
north of the equator and east of the International Dateline

Over the next twelve hours, the system showed little change in intensity before quickly strengthening into a strong tropical storm, as a strong central dense overcast became established.[6][7] Over the next twelve hours, Walaka gradually strengthened, becoming a hurricane at 03:00 UTC on October 1.[8] Explosive intensification then ensued as a small, well-defined eye formed, with Walaka reaching major hurricane status early that morning.[9] Rapid intensification culminated at 00:00 UTC on October 2, when the storm peaked as a Category 5 hurricane, with 1-minute sustained winds of 160 mph (260 km/h) and a central pressure of 920 mbar (27.17 inHg).[10] This made Walaka the second-most intense hurricane in the Central Pacific by pressure (behind Hurricane Ioke in 2006), and the second Category 5 hurricane recorded in the same year – Lane was the other storm of such intensity.

Soon afterward, Walaka began to undergo an eyewall replacement cycle, which subsequently caused weakening and the eye became less defined.[11] For the next day or so, Walaka remained a powerful hurricane as it turned northwards due to a ridge of high pressure to its northeast.[12] However, as the hurricane moved into a less favorable environment on October 4, Walaka began to lose its intensity again.[13] Later that day, Walaka fell below major hurricane status as it travelled north, away from the Northwestern Hawaiian Islands.[14] At this time, it was noted that Walaka's low-level circulation center was exposed in the southwest quadrant due to strong wind shear.[15] Weakening accerlated the next day as almost all deep convection was being sheared away, and Walaka weakened into a tropical storm on October 4.[16] At 09:00 UTC on the next day, it was noted that Walaka was beginning to transition into an extratropical system as it continued north, under the influence of deep southwesterly flow.[17] At 15:00 UTC on October 6, Walaka transitioned into an extratropical cyclone 1,085 miles (1,740 km) north-northwest of Honolulu, Hawaii.[18] Afterward, Walaka's extratropical remnant rapidly weakened while accelerating northeastward, reaching the Gulf of Alaska on October 8. On October 9, Walaka's remnant was absorbed by another frontal system over British Columbia.

Preparations and impact

Johnston Island

On September 30, a hurricane watch was issued for Johnston Atoll.[19] Early on the next day, the hurricane watch was upgraded to a hurricane warning.[20] A crew of four scientists on the isolated Johnston Atoll planned on riding out the storm in an evacuation shelter, until the United States Fish and Wildlife Service sought an emergency evacuation on October 1. On the next day, the United States Coast Guard flew a plane from Kalaeloa Airport to evacuate the personnel.[21][22] The hurricane warning for Johnston Atoll was discontinued on October 3 as Walaka moved away.[23]

Northwestern Hawaiian Islands

Early on October 2, a hurricane watch was issued for the Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef.[24] Late on the same day, the hurricane watch for Frigate Shoals to Maro Reef was upgraded to a hurricane warning. Additionally, a tropical storm warning was issued for Nihoa to French Frigate Shoals.[25] Also on that day, seven researchers studying Hawaiian monk seals and green sea turtles on French Frigate Shoals were evacuated to Honolulu.[26] On October 4, the hurricane warning for the Papahanaumokuakea Marine National Monument was lowered to a tropical storm warning,[27] and all of them were eventually discontinued early on the next day, as Walaka weakened and moved away from the islands.[28]

See also

References

  1. ↑ Zelinsky, David. NHC Graphical Outlook Archive. National Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  2. ↑ Zelinsky, David. NHC Graphical Outlook Archive. National Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  3. ↑ Houston, Sam. CPHC Graphical Outlook Archive. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  4. ↑ Wroe, Derek. Tropical Storm Walaka Advisory Number 1. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  5. ↑ National Hurricane Center; Hurricane Research Division; Central Pacific Hurricane Center. "The Northeast and North Central Pacific hurricane database 1949–2017". United States National Oceanic and Atmospheric Administration's National Weather Service. A guide on how to read the database is available here.
  6. ↑ Jelsema, Jon. Tropical Storm Walaka Advisory Number 3. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  7. ↑ Jelsema, Jon. Tropical Storm Walaka Advisory Number 4. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  8. ↑ Powell, Jeff. Hurricane Walaka Advisory Number 6. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  9. ↑ Jelsema, Jon. Hurricane Walaka Intermediate Advisory Number 7A. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  10. ↑ Kodama, Kevin. Hurricane Walaka Intermediate Advisory Number 9A. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  11. ↑ Jelsema, Jon. Hurricane Walaka Discussion Number 12. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 3 October 2018.
  12. ↑ Brenchley, Chris. Hurricane Walaka Intermediate Advisory Number 17A. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 4 October 2018.
  13. ↑ Brenchley, Chris. Hurricane Walaka Advisory Number 18. Central Pacific Hurricane Center (Report). Retrieved 4 October 2018.
  14. ↑ Houston, Sam. Hurricane Walaka Advisory Number 20. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 4 October 2018.
  15. ↑ Houston, Sam. Hurricane Walaka Discussion Number 20. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 4 October 2018.
  16. ↑ Jelsema, Jon. Tropical Storm Walaka Advisory Number 23. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 6 October 2018.
  17. ↑ Houston, Sam. Tropical Storm Walaka Discussion Number 27. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 6 October 2018.
  18. ↑ Sam Houston (October 6, 2018). "Post-Tropical Cyclone Walaka Discussion Number 28". Honolulu, Hawaii: Central Pacific Hurricane Center. Retrieved October 7, 2018.
  19. ↑ Jelsema, Jon. Tropical Storm Walaka Forecast/Advisory Number 4. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  20. ↑ Powell, Jeff. Hurricane Walaka Forecast/Advisory Number 6. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 2 October 2018.
  21. ↑ David McGee (October 2, 2018). "Hurricane Walaka Threatens Seabirds With Direct Hit on Johnston Atoll in Pacific". Newsweek. Retrieved October 8, 2018.
  22. ↑ "Coast Guard evacuates Fish and Wildlife crew off Johnston Atoll ahead of Hurricane Walaka". Coast Guard News. October 2, 2018. Retrieved October 8, 2018.
  23. ↑ Houston, Sam. Hurricane Walaka Advisory Number 16. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 5 October 2018.
  24. ↑ Kodama, Kevin. Hurricane Walaka Advisory Number 10. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 3 October 2018.
  25. ↑ Brenchley, Chris. Hurricane Walaka Advisory Number 13. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 3 October 2018.
  26. ↑ "7 Researchers Evacuated From Pacific Atoll as Storm Nears". The New York Times. Associated Press. October 3, 2018. Retrieved October 12, 2018.
  27. ↑ Houston, Sam. Hurricane Walaka Advisory Number 20. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 5 October 2018.
  28. ↑ Wroe, Derek. Hurricane Walaka Advisory Number 21. Central Pacific Hurricane Center (Report). National Oceanic and Atmospheric Administration. Retrieved 5 October 2018.

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