Tropical Storm Hilda is expected to intensify and become a hurricane late tomorrow or early Thursday as it approaches the state.

On its current track, Hilda will be a hurricane as it passes far to the south of the Islands later this week. But forecasters said residents probably won't notice any changes in the weather as Hilda blows by.

"It shouldn't have too much impact on the Islands," said Pete Donaldson, National Weather Service forecaster. "There wouldn't be much surf either."

Unlike this season's two previous hurricanes, Felicia and Guillermo, Hilda is gaining strength as it moves south of the state. Felicia and Guillermo got stronger as they crossed the Eastern Pacific, but fizzled out as the storms entered Hawaiian waters.

Donaldson said there is no simple formula to predict whether a storm will get stronger or weaker as it nears the Islands. He said the Central Pacific Hurricane Center relies on a "super computer" that gathers and analyzes data to come up with a forecast track.

Generally, Donaldson said, cooler ocean waters north of the state, coupled with stronger vertical windshears, weaken a storm. Warmer waters, such as those found south of Hawai'i, will help to sustain a tropical cyclone.

But Donaldson cautioned that every storm is different.

"There usually tends to be more windshear farther up north when you get farther away from the deep tropics," Donaldson said. "But that varies from time to time and that varies pretty rapidly from one day to the next or even a shorter timeframe than that."

At 11 p.m. yesterday, Hilda was about 585 miles southeast of Hilo and 795 miles from Honolulu and was moving west at 9 mph. The storm had maximum sustained winds of 60 mph and tropical storm-force winds extended 75 miles from Hilda's center.