The Coast Guard said today it has placed two new weather buoys off Kaua'i and O'ahu that will give more precise readings on how large waves will be and what island shores they will hit.

For example, the new device 120 miles northwest of Kaua'i may allow meteorologists to limit a high surf advisory just to O'ahu's North Shore when the older buoy model would have indicated massive waves for both West O'ahu and the North Shore.

"It will help us fine tune our forecasts," said Bob Burke, a meteorologist at the Honolulu office of the National Weather Service.

Residents of the Big Island's west coast will likely find the buoy particularly helpful during the winter.

Forecasters should be able to distinguish between seasonal west-northwest swells, which can send waves crashing onto coastal roads in Kailua-Kona, and northwest swells which are blocked by the other islands in the archipelago.

The National Oceanic and Atmospheric Administration old buoy off Kaua'i, replaced last Thursday, only measured the height and period of waves, not the direction.

"It's going to give a more accurate picture of what's coming in," said Lt. Ian Brosnan, a spokesman for the Coast Guard cutter Kukui, which placed the machines in the ocean. "It will be nice to know more accurate wave height and wave direction."

Like older models, the new machine will also feed data on sea temperatures, humidity, and wind speed.

The Kukui also replaced a buoy about 200 miles southwest of O'ahu yesterday, although this device does not give data on wave direction.

The buoys also will supply key data that will allow the weather service to provide early hurricane warnings, the Coast Guard said.