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|Category 4 major hurricane (SSHWS/NWS)|
|Formed||September 1, 2018|
|Dissipated||September 19, 2018|
|(Remnant low after September 13)|
|Highest winds||1-minute sustained: 130 mph (215 km/h) |
|Lowest pressure||951 mbar (hPa); 28.08 inHg|
|Damage||$25 million (2018 USD)|
|Part of the 2018 Pacific hurricane season|
Hurricane Olivia was the first tropical cyclone to make landfall on Maui and Lanai in recorded history. The fifteenth named storm, ninth hurricane, and sixth major hurricane of the 2018 Pacific hurricane season, Olivia formed southwest of Mexico on September 1. The depression slowly organized and strengthened into Tropical Storm Olivia on the next day. Olivia then began a period of rapid intensification on September 3, reaching its initial peak on September 5. Soon after, Olivia began a weakening trend, before re-intensifying on September 6. On the next day, Olivia peaked as a Category 4 hurricane, with winds of 130 mph (215 km/h) and a minimum central pressure of 951 mbar (28.08 inHg). Six hours later, Olivia began another weakening trend that resulted in the hurricane being downgraded to Category 1 status on September 8, east of the 140th meridian west. On September 9, Olivia entered the Central Pacific Basin. Over the next couple of days, Olivia prompted the issuance of Tropical Storm Watches and Warnings for Hawaii County, Oahu, Maui County, and Kauai County. Olivia weakened into a tropical storm on September 11, before making brief landfalls in northwest Maui and Lanai on the next day, becoming the first tropical cyclone to impact the islands in recorded history. Tropical storm-force winds mainly affected Maui County and Oahu. Torrential rains affected the same area from September 11 to 13, causing flash flooding. Olivia caused a total of US$25 million in damages. Olivia was downgraded to a tropical depression on September 13 while continuing to head west. Due to wind shear disrupting Olivia's convection, the system weakened into a remnant low on September 14. Olivia crossed into the West Pacific Basin on September 19 as a remnant low, before dissipating later that day.
Olivia originated from a disturbance that formed over the southwest Caribbean Sea on August 26. The disturbance tracked westward and crossed over Central America, where it entered the Northeastern Pacific Ocean a few days later. A broad area of low pressure formed several hundred miles southwest of Mexico on August 30. The National Hurricane Center (NHC) continued to monitor the disturbance as it moved west-northwest for the next couple of days and gradually became more organized. At 00:00 UTC on September 1, the NHC declared that the low had become Tropical Depression Seventeen-E approximately 425 miles (680 km) southwest of Manzanillo, Mexico. Initially, due to north-northeasterly vertical wind shear, the nascent depression only strengthened slowly. The depression intensified into Tropical Storm Olivia on September 2, after obtaining gale-force sustained winds  For the next several days, the system would travel west to west-northwest under the influence of a subtropical ridge that extended from central Mexico across the eastern Pacific.
Over the next day and a half, Olivia changed little in strength as wind shear continued to impinge on the system. Late on September 3, however, a central dense overcast developed over Olivia's center of circulation and an inner core began to form, preceding a period of rapid intensification. By 00:00 UTC on September 4, Olivia had strengthened into a hurricane, and reached Category 2 status on the Saffir–Simpson scale twelve hours later. At 18:00 UTC on September 4, Olivia reached Category 3 status and thus became the sixth major hurricane of the season. Six hours later, Olivia reached its initial peak intensity, with maximum sustained winds of 125 mph (195 km/h). Shortly after, however, Olivia began a weakening trend, falling below Category 3 status at 12:00 UTC on September 5. Eventually, Olivia bottomed out as a low-end Category 2 hurricane, before beginning to re-intensify on September 6. Olivia regained major hurricane status by 12:00 UTC that day, and peaked as a Category 4 hurricane at 00:00 UTC on September 7, with winds of 130 mph (215 km/h) and a minimum pressure of 951 mbar (hPa; 28.08 inHg). At that time, the NHC noted that Olivia was "an outstanding example of an annular hurricane", with a sharp eye surrounded by a single ring of intense convection. Six hours later, Olivia began another weakening trend as sea surface temperatures decreased and cloud tops around the eye warmed. By 06:00 UTC on September 8, Olivia had weakened to a Category 1 hurricane. At 03:00 UTC on September 9, the Central Pacific Hurricane Center (CPHC) took over the responsibility of monitoring and issuing advisories on Olivia after the hurricane crossed the 140th meridian west and entered the central Pacific.
Early on September 11, Olivia weakened to a tropical storm, after encountering strong wind shear. Late on the same day, Olivia's low level circulation center separated from the deep convection, resulting in a significant increase in forward speed. Olivia rapidly weakened as it approached Hawaii, before making brief landfalls over Maui and Lanai, the first such instance in recorded history, on September 12, at 19:10 UTC and 19:54 UTC respectively, with sustained winds of 45 mph (75 km/h). At 09:00 UTC on September 13, as Olivia was pulling away from Hawaii, the system weakened into a tropical depression. After wind shear continually disrupted Olivia's convection, the system degenerated into a post-tropical remnant low on September 14. On September 19, Olivia's remnant low crossed the International Date Line, entering the West Pacific Basin. The Joint Typhoon Warning Center (JTWC) stated that there was a possibility of redevelopment. Soon afterward, Olivia quickly lost all of its convection and dissipated, due to wind shear.
On September 10, in anticipation of Olivia's landfall in Hawaii, tropical storm watches were issued for Hawaii County, Oahu, and Maui County including the islands of Maui, Molokai, Lanai, and Kahoolawe. At 15:00 UTC, the tropical storm watches for Hawaii County and Maui were changed to tropical storm warnings. At 03:00 UTC on September 11, the watch for Oahu was changed to a tropical storm warning. Additionally, tropical storm watches were issued for Kauai County including the islands of Kauai and Niihau due to the uncertainty of the track. At 21:00 UTC the watches for Kauai and Niihau were changed to tropical storm warnings after the track shifted northward. At 09:00 UTC on September 12, as the path of Olivia became clearer, the warnings for Kauai and Niihau were discontinued. On September 9, Governor David Ige signed an emergency proclamation declaring the counties of Hawaii, Maui, Kalawao, Kauai, and Honolulu as disaster areas. On September 12, all public schools and post offices were closed in Maui with numerous schools and universities closed elsewhere.
Olivia was the second tropical cyclone to affect Hawaii in 2018, with Hurricane Lane having affected the state a few weeks earlier. Tropical storm-force winds mainly affected Maui County and Oahu. Peak winds of 55 mph (89 km/h) were observed in Lanai Airport, and peak winds of 46 mph (74 km/h) were observed in Kuaokala. Many trees were downed and numerous power outages occurred in Maui. Widespread rains in Maui County and Oahu from September 11–13 caused numerous instances of flash flooding, with the worst felt in areas along the slopes of the West Maui Mountains. Brief road closures occurred in Oahu on the night of September 12 as a result of the flash floods. In Maui County, rainfall totals reached a maximum of 12.93 in (328 mm) in West Wailuaiki, while on Oahu, rainfall totals peaked at 10.31 in (262 mm) at the Lyon Arboretum in Manoa. In Honolulu, the water level of a dam rose by about 4 to 5 feet after heavy rainfall from Olivia affected the area, prompting officials to consider evacuations. Additionally, a sewage pipe overflowed, sending over 30,000 gallons (113,562 L) of raw sewage into Kapalama Stream and Honolulu Harbor. Overall, Olivia caused a total of US$25 million in damages.
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