Madeline is expected to travel over or near the Big Island on Wednesday, carrying heavy rain and strong winds, according to the US National Weather Service.
Its current path in the central Pacific could coincide with Obama's planned visit to Hawaii for the kickoff of the World Conservation Congress, a major meeting including thousands of heads of state, scientists and policy makers.
At 0900 GMT, Madeline was 1,220 kilometers east of Hilo, Hawaii.
Forecasters said, however, that models show a great deal of uncertainty about the path of Madeline, which they are tracking closely.
More From This Section
The International Union for the Conservation of Nature stages the World Conservation Congress every four years at a different location around the globe. This year it runs from September 1-10.
Obama is scheduled to address the gathering on September 1.
The US leader is also expected to travel to Midway Atoll, inside a newly named protected area, where Obama burnished his environmental bona fides last week by establishing the world's largest marine reserve, home to thousands of rare sea creatures in the northwestern Hawaiian islands.
Gaston is the first major hurricane of the Atlantic season, the National Hurricane Center.
Gaston, packing top sustained winds of 185 kilometers per hour, was stationary about 575 miles from Bermuda, the Miami-based NHC said at 0900 GMT today.
The storm was not an immediate threat to land, and was expected to remain near its current strength, picking up speed as it travels toward the northeast over the next couple of days, forecasters said.