New tropical rainstorm threatens Hawaii with flooding, mudslides
A slow-moving tropical rainstorm will raise the risk of prolonged downpours, flooding and mudslides across Hawaii, with the greatest impacts expected on the Big Island.
A developing tropical rainstorm could approach Hawaii this weekend, bringing the risk of life-threatening flash flooding and more than a foot of rain in the highest elevations of the Big Island.
A new tropical rainstorm has formed about 700 miles to the southeast of the Big Island of Hawaii and is forecast by AccuWeather to bring flooding rain and mudslides across portions of the islands beginning Wednesday (HST). Life-threatening conditions could unfold.
This image, captured on Tuesday morning, Sept. 22, 2026, shows a large disorganized area of showers and thunderstorms centered about 700 miles to the southeast of the Big Island of Hawaii. (AccuWeather Enhanced RealVue™ Satellite)
AccuWeather meteorologists dubbed the batch of showers and thunderstorms a tropical rainstorm on Monday to raise awareness and help the public and officials plan for what could be a significant and dangerous event for the islands.
The rainstorm is forecast to gain organization as it tracks westward this week. It could strengthen into a tropical depression or tropical storm by late week as it nears Hawaii. As this rainstorm is in the central Pacific basin, the next name on the list is Nolo.
Later this week and over the weekend, the rainstorm's forward speed is forecast to slow dramatically south of Hawaii. Its slow movement will allow tropical moisture to flow toward the islands for an extended period, increasing the duration of heavy rain and the likelihood of serious flooding, mudslides, and washouts.
Due to the impacts of prolonged torrential downpours, this tropical rainstorm is a 1 on the AccuWeather RealImpact™ Scale for Hurricanes in Hawaii. If the rainstorm stalls near the islands, flooding and mudslides could be much more severe across portions of the islands.
As of daybreak Tuesday, Hawaii time, there were no National Weather Service flood watches in effect for the islands. Nor were there any tropical storm watches in effect from the National Hurricane Center.
Unlike the Saffir-Simpson Hurricane Wind Scale, which accounts for wind speed only, the AccuWeather RealImpact™ Scale for Hurricanes considers a broader range of factors, including wind speed, flooding rain, storm surge and economic damage and loss.
A wide swath of 1-2 inches of rain is forecast from northern Kaua'i through western portions of the Big Island, with higher totals of 2-4 inches stretching from the northern shores of Moloka'i to the Big Island.
Rain across the islands is expected to be heaviest across the Big Island, where a widespread 4-8 inches is forecast. Areas near Hilo and along the southeastern slopes could receive 12-18 inches as tropical downpours occur across mountainous terrain.
"If the storm keeps moving slowly along, we are looking at about three days of drenching rain with focus on the Big Island," AccuWeather Chief Meteorologist Jon Porter said. "However, if the storm stalls, we could be looking at five or six days with persistent drenching rain."
Repeated tropical downpours over the mountainous terrain may produce locally higher amounts. The AccuWeather Local StormMax™ from Wednesday through Monday is 38 inches.
Flooding downpours and mudslides are expected to pose the greatest threat across the Big Island, with a lower but still notable risk extending to Maui and Oah'u. Rapidly rising streams, flooded roads and debris flows could make travel dangerous, especially in steep terrain.
Areas still recovering from damage caused by Hurricane Lala may be especially vulnerable to additional flooding and mudslides.
Wind gusts of 40 to 60 miles per hour can occur across Hawaii and Maui counties from Tuesday night to next Monday.
Winds to this magnitude, combined with the heavy and persistent rainfall, can result in downed trees and localized power outages. The AccuWeather Local StormMax™ is 95 mph.
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The new rainstorm follows an unusually active and destructive hurricane season near Hawaii. Over the last two months, hurricanes Lala and Lowell passed nearby, causing significant damage from flooding, destructive waves, coastal inundation and strong winds.
Late-season close approaches are unusual around Hawaii. On average, fewer than one tropical system per year passes within 100 miles of the main islands, and many years have none. Only four tropical cyclones on record have passed within 100 miles of the islands during October, November or December.
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