"It's a very strong, high-end tropical storm," said Chris Brenchley, Warning Coordinator for the Central Pacific Hurricane Center in Honolulu.
Ana remains south of a ridge of high pressure and encountered windshear overnight into Wednesday that kept the storm from strengthening into a hurricane, Brenchley
Windshear often helps tear storms apart as they near the Hawaiian Islands.
"We expect that windshear will be on the decrease as we go through the day and we are forecasting that Tropical Storm Ana will become a hurricane sometime later today (Wednesday) and into this evening," said Brenchley
Once upgraded to a hurricane, Ana is forecast to pass over the Hawaiian Islands as a Category 1 storm.
A Category 1 hurricane packs winds ranging from 74 mph to 95 mph.
"We are expecting Ana to maintain hurricane strength as it slowly moves across the Hawaiian Islands," Brenchley
Surf and wind are expected to begin impacting the Big Island on Friday.
The southern part of Hawaii Island is expected to see 15- to 30-foot waves.
The southeast-facing shores of the Big Island will see the largest waves associated with the system.
"The entire state is under an area where there is a threat of significant winds, strong winds, also heavy rainfall is a good possibility as Ana moves through, particularly as it begins to approach the big island," Brenchley