HONOLULU, United States (AFP) — A strengthening tropical storm named Lala is set to hit Hawaii’s Big Island with hurricane force gales on Saturday, bringing dangerous winds, rainfall and heavy surf.

The governor of the United States (US) Pacific island state declared a state of emergency as the storm barrelled towards the archipelago, packing winds that could gust up to 85 miles (137 kilometers) an hour.

A hurricane warning was in effect for Hawaii County, which covers the Big Island, and a tropical storm warning held for the islands of Maui, Molokai and Kahoolawe to its northwest. Lower grade tropical storm watches were in place for other islands.

The National Oceanic and Atmospheric Administration (NOAA) said rainfall of up to 12 inches (30 centimetres) was expected across Maui and the Big Island, with up to 25 inches in certain pockets of the latter, and storm surge of 1-3 feet.

Rough conditions could persist into Sunday.

Governor Josh Green proclaimed a state of emergency to ensure the state and its counties “have sufficient resources to clear debris, secure infrastructure, and take other measures to prepare.”

Honolulu Mayor Rick Blangiardi said Friday his adminstration had spent days preparing the area for the impact of the storm, and urged residents to be ready.

“I am asking everyone to finish your preparations today. Don’t wait for the weather to deteriorate,” he said.

“Stay informed, stay away from dangerous areas, and make sure your family knows what to do if conditions worsen.”

Hawaii’s emergency management agency recommended residents clear gutters and drains and move valuables off the ground, seal gaps in doors and remove tree limbs that threaten their properties.

“Stay away from beaches and coastal areas where rough surf and rip currents could sweep you away,” it added.

Hawaii was menaced by Hurricane Fausto last month, before the storm weakened and skirted north of the island chain.

The state was last hit by a “major” hurricane — meaning Category 3, 4, or 5 on the Saffir-Simpson scale — in 1992, when Hurricane Iniki caused at least six deaths and billions of dollars in damage.

The storm comes as a powerful El Nino has formed in the central equatorial Pacific Ocean, with temperatures already so high that NOAA now predicts a 69 percent chance of a “historic event that would exceed the strength of previous El Nino events dating back to 1950” when it peaks between October-December.

El Nino, a natural climate pattern when sea surface temperatures in the central and eastern Pacific Ocean become unusually warm, tends to promote hurricane activity in the Pacific while suppressing it in the Atlantic.

Human-caused climate change can amplify El Nino’s impacts because a warmer ocean and atmosphere increase the availability of energy and moisture for extreme weather events, such as heat waves and heavy rainfall.