Tropical Storm Olivia made landfall Wednesday morning on Hawaii's island of Maui, bringing with it flooding, rains and 45-mph winds as it moves over the state's main islands.
A tropical storm warning was in effect for the island of Oahu and Maui County.
The storm was moving west at 10 mph, the Central Pacific Hurricane Center said.
"Tropical storm #Olivia continues to weaken but we're not out of the woods," Honolulu Mayor Kirk Caldwell tweeted Tuesday evening. "We expect to feel the first effects of the storm this morning," an emergency proclamation Caldwell signed Wednesday said.
Olivia is forecast to weaken during the next 48 hours but will remain a tropical storm for the "next day or so," the hurricane center said. Flash-flood watches remain for all four Hawaiian counties. Maui and Honolulu counties have high-surf warnings.
"Remember that wind gusts can be much stronger near higher terrain, and in the upper floors of high-rise buildings," the center said. "Winds can also be especially gusty through gaps between mountains and where winds blow downslope."
Residents were warned to prepare for an increase in rain over portions of the main islands. The storm is expected to produce 5 to 10 inches of rain, though some areas could see as much as 15 inches.
The rainfall may produce "life-threatening flash flooding," the hurricane center said.
Large swells from the storm also could "result in dangerously high and potentially damaging surf, mainly along exposed east facing shores," the center said.
Gov. David Ige has requested a presidential emergency declaration for federal assistance.
The letter also asked for "direct federal support from Department of Defense assets for strategic airlift between the islands; temporary power generation at evacuation centers; technical assistance related to points of distribution and debris management action planning."
The Hawaii Tourism Authority warned that severe weather effects could extend statewide and said visitors and residents should ensure they have an adequate supply of food, water, medications and essential goods.
All post offices and public schools in Maui County were closed Wednesday, with a number of other Hawaiian schools and universities also closed, CNN affiliate KHON in Honolulu reported.
Olivia follows Hurricane Lane, which dropped more than 50 inches of rain last month on Hawaii, the second-highest rainfall total from a tropical cyclone in the United States since 1950.