The water filling station line was growing, and Walmart was already out of propane when Imua Kahoonei tried to stock up in Kailua-Kona a day ahead of Tropical Storm Lala. The storm is forecast to become a hurricane before hitting Hawaii on Saturday afternoon.

He did load up on Oreos, waffles and a pack of seaweed wrap for Spam musubi, a local staple of sushi rice and marinated lunch meat wrapped in nori. It all went into the trunk of his Tesla before he tried his luck at the Home Depot down the street.

Despite the lack of propane, Mr. Kahoonei, 55, said he was calm. Preparing for a storm is par for the course on the Big Island, even if Hawaii rarely gets a full hurricane.

Depending on Lala’s exact track, the core of the storm could roll directly over Hawaii County, on Hawaii’s largest and easternmost island, where about 210,000 people live. The outer bands were already causing rain and a few power outages on the island early Saturday morning. Officials warned residents to prepare for extensive power outages, dangerous flooding and possible evacuations as the brunt of the storm hits.

“We have not had a direct-hit hurricane since the late 1800s,” Kimo Alameda, the mayor of Hawaii County, said in an interview on Friday afternoon. “We are preparing as if that is going to happen, which means all hands on deck.”

The county will operate 13 evacuation shelters, the mayor said, and is distributing bags of sand for residents to stack outside of their homes to help protect from flooding. Mr. Alameda urged tourists to hunker down, and asked that surfers heed warnings and avoid venturing into the ocean swells, no matter how tempting.

“We don’t want their excitement to lead to a rescue situation,” he said.

Across the island, residents stocked up on what they considered the essentials. Steve Macomber, 66, loaded up a cooler in the bed of his red pickup with a bag of ice for his beer, which he planned to drink as he waited out the storm.

Having lived on the island his whole life, he said, much of his emergency prep was already in place. He usually keeps four or five propane tanks filled at home, and he has relied on a gas-powered generator that he bought in 2011, after a catastrophic earthquake in Japan threatened Hawaii with a tsunami.

Mr. Macomber said his home, which sits on high ground, was retrofitted to withstand hurricane winds after Hurricane Iniki in 1992. That was the last hurricane to make a direct hit on the state.

Others felt as if they had more on the line. Javier Rodriguez worked up a sweat on Friday as he loaded chips and canned salsa into his truck.

He had been up since 4 a.m., he said, battening down his house on a coffee farm, where he lives with his parents.

The farm was still recovering from the winter weather system known as a Kona low, which flooded his crops in March and dealt a blow to his business. Mr. Rodriguez said he was also still shaken from a recent earthquake that rocked the island.

“It’s been a bad year,” he said. “Three big events that normally don’t happen here, all happening within a year — it’s brought a lot of extra costs and stress.”