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|Category 5 major hurricane (SSHWS/NWS)|
|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|
|Areas affected||Johnston Atoll, Northwestern Hawaiian Islands, Alaska, British Columbia|
|Part of the 2018 Pacific hurricane season|
Hurricane Walaka (// 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. East Island in the French Frigate Shoals suffered a direct hit and was completely destroyed.
Walaka originated from a trough of low pressure that the National Hurricane Center (NHC) first forecasted on September 22. The NHC forecasted a low-pressure area to form in the far western portion of the east North Pacific within a few days. Early on September 25, a trough of low pressure formed approximately 1,600 miles (2,575 km) south-southeast of Hilo, Hawaii. 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. The CPHC monitored the disturbance for another few days until the system organized into Tropical Storm Walaka on September 29 at 21:00 UTC. Environmental conditions, including low wind shear, high sea surface temperatures and ample moisture supported steady – perhaps even rapid – intensification into a powerful hurricane.
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. Over the next twelve hours, Walaka gradually strengthened, becoming a hurricane at 03:00 UTC on October 1. Explosive intensification then ensued as a small, well-defined eye formed, with Walaka reaching major hurricane status early that morning. 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). 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. Unrelated to Walaka, Typhoon Kong-rey developed and intensified into a Category 5-equivalent super typhoon around the same time Walaka reached its peak intensity, marking the first time since 2005 when two tropical cyclones of Category 5 strength existed simultaneously in the Northern Hemisphere.
Soon afterward, Walaka began to undergo an eyewall replacement cycle, which subsequently caused weakening, and the eye became less defined. For the next day or so, Walaka remained a powerful hurricane as it turned northward, due to a ridge of high pressure to its northeast. However, as the hurricane moved into a less favorable environment on October 4, Walaka began to lose its intensity again. Later that day, Walaka fell below major hurricane status as it travelled north, away from the Northwestern Hawaiian Islands. At this time, it was noted that Walaka's low-level circulation center was exposed in the southwest quadrant due to strong wind shear. Weakening accelerated the next day as almost all deep convection was being sheared away, and Walaka weakened into a tropical storm on October 4. 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. At 15:00 UTC on October 6, Walaka transitioned into an extratropical cyclone 1,085 miles (1,740 km) north-northwest of Honolulu, Hawaii. 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.
On September 30, a hurricane watch was issued for Johnston Atoll. Early on the next day, the hurricane watch was upgraded to a hurricane warning. 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. The hurricane warning for Johnston Atoll was discontinued on October 3 as Walaka moved away.
Early on October 2, a hurricane watch was issued for the Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef. 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. Also on that day, seven researchers studying Hawaiian monk seals and green sea turtles on French Frigate Shoals were evacuated to Honolulu. On October 4, the hurricane warning for the Papahanaumokuakea Marine National Monument was lowered to a tropical storm warning, and all of them were eventually discontinued early on the next day, as Walaka weakened and moved away from the islands.
A powerful storm surge accompanied the hurricane as it traversed the French Frigate Shoals. The small, low-lying East Island suffered a direct hit and was completely destroyed, with sediment scattered across coral reefs to the north. The island served as one of the major nesting locations for the endangered green sea turtles, and critically endangered Hawaiian monk seals. An estimated 19 percent of 2018's sea turtle nests on the island were lost; however, all adult females tending the nests left before the storm. Approximately half of Hawaii's green sea turtles nested on the island, and Charles Littnan—director of the National Oceanic and Atmospheric Administration's protected species division—stated it would take years for the implications of the island's loss to be fully understood.
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