Back-to-back tropical threat for Hawaii, impacts to start this weekend

Hawaii’s Big Island could face a new wave of flooding rain and power outages, with a tropical depression poised to become a tropical storm. Impacts could spread westward through the island chain.

A new tropical threat is brewing for Hawaii about a week after Hurricane Lala brought torrential rain, flash floods, mudslides and damaging winds. A tropical rainstorm southeast of the islands has intensified into a tropical depression and could strengthen further into a tropical storm before approaching Hawaii this weekend.

With strengthening anticipated, the next name on the Central Pacific storm list is Moke.

How much of an impact the storm will have on the Big Island and the rest of the island chain in terms of rain- and wind-related issues will depend on its organization, strength and how close it tracks to the island.

"We referred to the area of interest as a tropical rainstorm to raise public awareness and for planning purposes," AccuWeather Lead Hurricane Expert Alex DaSilva said on Wednesday.

At 5 a.m. HST Thursday, the National Hurricane Center dubbed the storm a tropical depression with a closed circulation and maximum sustained winds of 35 mph.

AccuWeather meteorologists believe the depression will intensify into a tropical storm as it nears Hawaii, with the center projected to pass just south of the islands.

"It appears the core of the storm will pass farther south of Hawaii than Lala did, perhaps 150-200 miles south of the Big Island," DaSilva said. "Lala passed about 30 miles south of the southern tip of the Big Island last weekend."

At this early stage, a general several inches to a foot or more of rain is likely on the Big Island, with the potential for more. The initial AccuWeather Local StormMax™ rainfall is 24 inches.

“The rainfall amounts are going to be largely dependent on the storm track, which could move farther south and largely miss the islands,” DaSilva said. “That doesn't mean there wouldn't be significant impacts to land, though, as this is a rather large system."

The ground also remains saturated in some areas, especially on the Big Island, after multiple feet of rain from Lala, and erosion and mudslides have damaged infrastructure. Top-heavy trees in wet soil may be more prone to falling, even if winds are weaker than they were during Lala.

So far, this storm is much larger in terms of the extent of clouds, showers and thunderstorms, compared to Lala. As a result, there could still be drenching downpours capable of producing flash flooding well to the north, despite a more southerly track.

Should the storm become more compact, there could be less rain or no rain at all farther north across the islands.

However, problematic rainfall appears highly likely over at least the southern part of the Big Island, with the potential for significant impacts from rain there and farther north and northwest across the island chain.

Weighing the odds and anticipating the greatest threat to be from torrential rain, flash flooding and mudslides, the AccuWeather RealImpact™ Scale for Hurricanes is a 1 for Hawaii with this storm.

"At this time, the earliest showers and thunderstorms from the system are expected to spread across the Big Island on Sunday and then extend westward from there," DaSilva said.

Wind gusts strong enough to cause tree damage and power outages are possible on the Big Island.

Some increase in wind shear and dry air from high pressure northeast of Hawaii could lead to fluctuation in the strength of the new storm later this weekend to next week.

Lala lives on as a central Pacific hurricane

Meanwhile, Lala strengthened significantly since departing Hawaii, becoming a major hurricane earlier in the week. Lala has since lost some wind intensity, and as of Thursday night, Hawaii time, Lala was a Category 2 hurricane with maximum sustained winds of 100 mph.

"We expect Lala to remain mainly a threat to shipping over the North Pacific during the next week or so due to mountainous seas, heavy squalls and powerful winds," DaSilva said. "Lala will pass well east of Midway Atoll late this week and this weekend."

Lala will send some long-period swells eastward to Hawaii into this weekend, which will cause heavy surf in some west-facing shorelines.

Lala could approach parts of Alaska's Aleutian Islands later next week as a tropical wind and rainstorm.

AccuWeather meteorologists are monitoring three additional potential areas of development in the Pacific. The first area has a high risk of tropical development from Aug. 22-24.

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