Hurricane Iwa - Meteorological History

Meteorological History

A very active trough of low pressure persisted along the equator in the middle of November, with westerly surface winds and windspread convection located along the trough from 140° W to 140° E. An organized circulation developed near Palmyra Atoll on November 18, and steadily developed as it drifted westward. Though very late in the season, warm temperatures to the south of the Hawaiian Islands due to the strongest El Nino in many years allowed the disturbance to develop into Tropical Storm Iwa on November 19 while located about 970 miles (1,760 km) southwest of the southernmost point in Hawaii. The storm tracked slowly northward after forming and initially remained a weak tropical storm. After turning to the northeast, Iwa began slowly intensifying, and on November 23 after turning to the north-northwest Iwa strengthened into a hurricane while located 580 miles (930 km) southwest of the southern tip of Hawaii.

Shortly after becoming a hurricane, Iwa turned and accelerated to the northeast in response to strong upper level flow to its north. The hurricane possessed sufficient moisture, instability, and upper divergence for continued intensification, and Iwa reached peak winds of 90 mph (145 km/h) late on November 23 while located 245 miles (395 km) southwest of Waimea on the island of Kauai. Its forward speed increased to 30 to 40 mph, and Iwa passed just north of the island of Kauai on November 23 (November 24 in UTC). The right semicircle of the storm extended across Kauai and Oahu, with gusts from 100 to 120 mph (161 to 193 km/h). After passing Hawaii, the convection of Iwa rapidly deteriorated as it gradually lost tropical characteristics. Late on November 24, the hurricane degenerated into a tropical storm, and on November 25 Iwa became an extratropical cyclone while located about 600 miles (965 km) northeast of Hawaii.