A tropical storm watch will likely be posted Monday for the Hawaiian Islands after Hurricane Guillermo weakened to a Category 1 hurricane with 85 mph winds and began a turn to the northwest Sunday on a track to pass near or over Hawaii on Wednesday.

Watches are posted about 48 hours ahead of a major storm’s arrival, and a warning is posted about 24 hours before a possible landfall.

At 5 p.m. Sunday, Guillermo was 725 miles east-southeast of Hilo and 935 miles east-southeast of Honolulu, moving west-northwest at 10 mph.

Hurricane-force winds extend 45 miles from the storm’s center, while tropical storm-force winds extend 140 mph, forecasters said.

Wind shear tearing at the storm began to weaken it and slow its progress Sunday, but it is still expected to have winds greater than 40 mph when it makes landfall or passes close to Hawaii later this week.

Rain and wind ahead of the storm’s center should begin to affect Hawaii late Tuesday night into Wednesday morning, said Matthew Foster, a meteorologist with the Honolulu office of the National Weather Service.

"We are anticipating heavy rainfall and winds," Foster said. High surf could also threaten lives and property.

The wind will likely be from the northeast, so windward and mauka areas will see most of the rain and wind. But leeward sections will also see some effects.

The damage from Guillermo may not be as severe as that of Tropical Storm Iselle, which hit the Big Island on Aug. 8, 2014, the eve of the primary election, with sustained winds of 60 mph and higher gusts. The storm downed trees and power lines, blocking roads and leaving thousands of people without electricity for days.

The primary election for two precincts was postponed for six days until roads could be cleared and power restored.

The current forecast for Guillermo calls for winds of about 50 mph Wednesday, decreasing to 45 mph Thursday.

But Foster said he "wouldn’t be surprised" to see downed trees and branches, and wind damage to weak structures and roofs.

Rain could be heavy enough to cause flooding.

With the impact of Iselle still fresh in their memories, residents of Pahoa, Hawaii island, were keeping close tabs on Guillermo’s progress.

"Everyone is on edge," said Michelle Williams, a clerk at Da Store on Kahakai Boulevard. "The last time, people were more casual, thinking, ‘We never get hit.’ Now you can see that more people are paying attention. They’re cutting their shrubs and anything else that might fly around. They’re real nervous."

Williams said Da Store increased its supply of bottled water, toilet paper and other items that tend to disappear from shelves during an emergency.

Yet residents’ concerns about the storm have not yet translated to a run on emergency supplies. For example, it was business as usual at Longs Drugs in Pahoa on Sunday, with no noticeable uptick in sales.

The hurricane has already prompted a high-surf advisory for the eastern shores of Oahu, Hawaii island, Kauai and Maui through 6 p.m. Thursday. Forecasters warned that the surf on those shores will be "life-threatening" Monday.

The latest track has the storm skirting just north of the Big Island on Wednesday, possibly hitting Maui County and the tip of Oahu.

However, the entire island chain is within the forecast’s so-called "cone of uncertainty."

"It is important for those in the main Hawaiian Islands not to focus too closely on the exact forecast track of the center of any tropical cyclone, including Guillermo," forecasters said. "It is still too soon to determine with any certainty which islands would most likely experience the greatest impacts from Guillermo. It is also important to note that significant impacts from tropical cyclones can extend well away from the center."

Maui County Emergency Management Officer Anna Foust said in a news release, "It’s important for everyone to take advantage of the lead time we have ahead of this storm to make their preparations. Tropical cyclones bring a triple threat of wind, heavy rains and battering surf and we need to prepare for any impacts that may occur. Secure or move inside any loose objects that may become airborne. Clean out gutters and other drainage ways that may become clogged with debris and exacerbate flooding. Stock up on your emergency kit supplies and be prepared for possible power outages."

Moderate to strong tradewinds will continue through Monday, then weaken by Tuesday as Guillermo disrupts the flow, the weather service said. Showers will increase as remnant moisture associated with former Tropical Depression 8E, which reached the islands Sunday, with the best chances of rain over windward and southeastern portions of Hawaii island.

The forecast for this week will be highly dependent on the eventual track of Guillermo, the agency said, but rain can be expected across the islands Tuesday night through Thursday night.

Crews from the Air Force Reserve’s 53rd Weather Reconnaissance Squadron — known as the Hurricane Hunters — flew through the storm twice Sunday, and data from the flights were "critical in locating the center, determining the current intensity and adjusting the wind radii (of Hurricane Guillermo)," forecasters said.

Crews flew aboard Lockheed-Martin WC-130J aircraft specially designed to withstand the rigors of hurricane conditions.

Another mission was planned for Sunday night.

In May the Central Pacific Hurricane Center said there is a 70 percent chance of a busier-than-usual hurricane season, with five to eight storms. Driving the activity in large measure is a persistent El Nino, associated with higher-than-normal sea surface temperatures in the eastern tropical Pacific.

The hurricane season in the North Pacific lasts from June 1 to Nov. 30.