The storm moved erratically northward until becoming a hurricane on November 23 when it began accelerating to the northeast in response to strong upper-level flow from the north.

The first significant hurricane to hit the Hawaiian Islands since statehood in 1959, Iwa severely damaged or destroyed 2,345 buildings, including 1,927 houses, leaving 500 people homeless.

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.

[1] Though very late in the season, warm temperatures to the south of the Hawaiian Islands due to the strongest El Niño in many years allowed the disturbance to develop into Tropical Storm Iwa on November 19 while located about 970 miles (1,560 km) southwest of the southernmost point in Hawaii.

[1][2] 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 (140 km/h) late on November 23 while located 245 miles (394 km) southwest of Waimea on the island of Kauaʻi.

The acceleration of the hurricane concentrated the energy of its swells, resulting in high waves and storm surge across the Hawaiian Islands, though primarily near the path of the center.

[12] The heaviest rainfall reported from the island chain was from the Intake Wainiha 1086 site, where 20.33 inches (516 mm) was measured.

Strong waves sank or grounded several small vessels on the southwestern coast of Kauaʻi,[2] with 44 of the 45 boats at Port Allen being sunk.

[18] Rough seas killed a person on a Navy Destroyer the USS Goldsborough DDG-20 in Pearl Harbor when the seaman hit a stanchion,[1] with four others injured on the ship.

The storm surge washed sand into streets in Waikīkī and flooded cars in areas of basement parking.

Gusty winds shattered glass windows in the Honolulu International Airport, injuring several passengers.

[22] On November 28, five days after the hurricane struck, President Ronald Reagan declared the islands of Kauaʻi, Niʻihau, and Oʻahu as a disaster area.

Army and Air Force planes delivered 20,000 Thanksgiving rations to the thousands left in temporary shelters.

The United States military also airlifted generators to Kauaʻi due to several days of power outages.