Tropical Rainstorm Olana bringing dangerous flash flood risks to Hawaii
Olana will bring torrential rain to Hawaii through Thursday night, threatening flash flooding, landslides and road washouts, even in areas that are usually dry.
It has already been a wet summer in Hawaii, and more rain is on the way. See why O‘ahu and Maui face the heaviest downpours, with over 2 feet possible on some mountain peaks.
Former Tropical Storm Olana poses a significant threat to Hawaii as it brings a rare swath of torrential downpours, reaching trade wind rain-shadowed areas on the islands this week. Flash flooding, landslides and road washouts will be ongoing risks to residents and visitors from Olana as a tropical "rainstorm."
Days before Olana officially became a tropical storm, AccuWeather meteorologists designated the developing system a tropical rainstorm to alert people in Hawaii to the potential for dangerous flooding. AccuWeather continues to use that designation to emphasize the threat of torrential rainfall after Olana lost its tropical storm status.
Because of the heavy rain and the flash flooding, landslides and road washouts it will cause, Olana is a 1 on the AccuWeather RealImpact™ Scale for Hurricanes in Hawaii.
The six-point scale has ratings from less than 1 to 5. It considers wind, flooding rain and storm surge, as well as total damage and economic loss.
Although Olana developed far west of Hawaii, winds higher in the atmosphere are carrying moisture associated with the storm eastward across the islands.
The moisture arriving from the west will bring heavy rain to south- and west-facing shores and mountain slopes, including areas that are typically drier under northeast trade wind showers and from more typical tropical downpours that move in from the east.
"Moisture associated with Olana will bring heavy rain to Hawaii through Thursday night, Hawaii Standard Time," according to AccuWeather Lead Hurricane Expert Alex DaSilva. "General rainfall totals of 1-2 inches are expected across the islands, with 4-8 inches in parts of the island chain from Maui to O'ahu."
Rainfall could reach 8-12 inches in Maui’s higher elevations, with an AccuWeather Local StormMax™ of 30 inches in an isolated location.
Where downpours linger on saturated soil, rainfall rates of 1-3 inches per hour can accelerate and worsen the flash flood, debris flow and washout risk. Never drive through a flooded road, even if the water appears shallow. Water can rise quickly, and the pavement beneath it may have washed away.
Weather conditions are forecast to improve somewhat late this week across the islands as the plume of intense tropical moisture slices off to the east. However, the rain will not completely go away.
"Showers will become more evenly distributed across the islands from Friday through the weekend, rather than concentrating on south- and west-facing slopes," said AccuWeather Senior Meteorologist Adam Douty.
"Lingering tropical moisture can still fuel downpours and localized flash flooding through the weekend," AccuWeather Senior Meteorologist Brett Anderson cautioned.
"High pressure building over the islands from the north-central Pacific should bring drier conditions next week," Anderson added. "However, northeast trade winds will continue to bring occasional showers to north- and east-facing slopes."
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