Heavy downpours foreceast as Niala weakens

Tropical Storm Niala continues to weaken as it tracks westward, but forecasters warn of potential flash flooding as the system passes the Big Island.

As of 5 p.m. Saturday, the storm was 245 miles southeast of Hilo and moving west at 8 mph. Maximum sustained winds were near 65 mph.

Strong vertical wind shear is disrupting thunderstorm activity within Niala and causing the storm to lose strength, National Weather Service senior forecaster Jon Jelsema said Saturday. He said the weather service has “pretty good confidence it’ll pass south of the island.”

That doesn’t mean residents are in the clear, though. A tropical storm watch for Hawaii Island is still in effect, with a flash flood watch in effect through Monday.

“Tropical storms in general have quite a bit of increased moisture in them,” Jelsema said. “So with the system passing to the south we’re increasing the moisture targeting at the higher terrain.”

The moist air has nowhere to go but up, leading to torrential rain and flash flood conditions.

Niala also is expected to bring high surf conditions to the island, particularly along the southeastern shores.

According to the most recent weather service advisory, most of the rain is expected to fall on the windward side, but “all portionals of the island should be ready for heavy rain.”

It is the 11th tropical storm to form in the Central Pacific this season, tying with 1992 and 1994 for busiest year on record.

“We’ve still got quite a bit of hurricane season yet to come,” Jelsema said. The season ends in late November.

Email Ivy Ashe at iashe@hawaiitribune-herald.com.