Winds with gusts of 40 mph, 20-foot waves in rough ocean conditions, and up to 12 inches of rain are possible on all islands this weekend when Tropical Storm Ana reaches Hawaii.

Tropical Storm Ana was about 340 miles south-southeast of Hilo and 530 miles southeast of Honolulu at 11 p.m. Thursday, moving west-northwest at 14 mph.

The storm’s winds increased to 65 mph at the Thursday night report. The winds had dropped to 60 mph overnight because of wind shear. But the Central Pacific Hurricane Center expects Ana to gradually strengthen through Friday until it briefly becomes a category 1 hurricane with 75 mph winds as it passes about 120 miles south of the Big Island.

Previously expected to pass about 85 miles south of the Big island, officials at the National Weather Service adjusted the forecast track of Ana westward even as the storm nudged closer toward the isles turning to a west-northwest direction.

The tropical storm force winds extend 60 miles from the center. But even if Ana does not hit directly hit the Big Island, the storm will likely still bring heavy rain, high winds and rough surf.

Hawaii Island and Maui County leeward waters are under a tropical storm watch. The Big Island will also be under a flash flood watch from noon Friday until 6 p.m. Sunday.

A tropical storm warning is now in effect for offshore Hawaiian waters, and National Weather Service officials plan to upgrade it to a hurricane warning Friday afternoon because of stormy seas.

Surf from Ana has already started arriving on the Big Island.

Hawaii County Civil Defense is advising coastal residents of Punaluu, Kalapana, Kapoho and Pohoiki to move to higher ground.

The Civil Defense agency reported surf of 5 to 10 feet at Isaac Hale Park. The weather service said waves of up to 20 feet are possible Friday night during the closest approach of Ana to the Big Island, and surf of 15 feet could hit the Kona Coast on Saturday as the storm moves past South Point.

At noon, forecasters said the chances of tropical storm conditions in Hilo Friday were 26 percent, 54 percent at South Point and 43 percent at Kailua-Kona, slightly lower than during the 5 a.m. forecast.

The storm is being steered by a high pressure ridge, which has kept its direction to the west. But the ridge is moving and weakening and forecasters expect the storm to gradually shift to the northwest — toward Hawaii.

Another weather system moving toward the state is expected to bring wind shear and weaken Ana over the weekend as it approaches Oahu and Kauai.

But the storm is still expected to be packing tropical storm force winds as it moves south of Oahu late Saturday night and potentially hits Kauai on Sunday.

The Big Island should start to see winds and rains from the storm Friday afternoon. The storm should move near Maui County Saturday morning.

The forecast for southern shores of Oahu, including Honolulu, calls for scattered showers and potentially heavy rain, including thunderstorms Friday afternoon and evening as rains bands ahead of the center of the storm reach the island. Tropical storm conditions are possible Saturday with frequent showers and a chance of thunderstorms. 

Saturday night and Sunday could bring gusts of 40 mph as the storm makes its closest pass to Oahu. Forecasters say there is a 100 percent chance of rain.

The rainy conditions could continue into Tuesday, as the storm moves off to the northwest.

Forecasters caution that people should not pay too much attention to the actual track of the storm.

“We don’t want people to focus on that black track (line), but take into consideration that cone of uncertainty,” said Eric Lau, a meteorologist with the National Weather Service. “It could be to the left or the right of that line.”

Any area within the forecast cone could be in the path of the storm, Lau said.

Lau said even if Ana doesn’t reach hurricane strength of 75 mph, the winds can still down power lines and cause a lot of damage. Heavy rain could cause flooding, and storm surge can also cause damage along the coast.

“Even a 40 mph wind is pretty strong,” Lau said. “Torrential rains would be cause for flash flooding, especially for people in low-lying areas.”

The weather service and civil defense officials say people should have their emergency kits stocked and be ready for the storm.

“People should be prepared for potential impacts,” Lau said. “It could potentially be a dangerous storm.”