The remnants of a tropical depression that wind shear tore apart more than a week ago are reorganizing southeast of Hawaii, and forecasters say the system could become a tropical cyclone again around midweek as it heads toward Hawaii Island. As of Monday, Sept. 21, the Central Pacific Hurricane Center gave the system a 60 percent chance of forming within 48 hours and a 90 percent chance within seven days, Big Island Now reported. If it becomes a tropical storm, it will be named Nolo.

Hawaii County Civil Defense said Monday that the system may bring flooding rain and high winds to Hawaii Island as early as Wednesday, and that those conditions could linger into the weekend. The National Weather Service's extended forecast calls for multiple days of heavy rain starting Wednesday evening on the Hilo side and by Friday evening on the Kona side, according to the Hawaii Tribune-Herald. As of Monday evening, no tropical storm watch or flood watch had been issued for the islands.

The greatest concern sits in Kaʻu. Pahala, Naalehu and Waiohinu were heavily damaged when Hurricane Lala passed close to the south in August, and the ground there remains saturated. Repeated rain has already closed Highway 11 and other Kaʻu roads in recent weeks.

A Storm Getting a Second Life

"Zombie storm" is not an official term. The Weather Channel used it because the system formed as Tropical Depression Fifteen-E more than a week ago, then fell apart as it moved west into strong wind shear. Its leftover circulation kept drifting west and has now reached an area with less shear, giving it a second chance to develop.

AccuWeather placed the disturbance about 800 miles southeast of the Big Island on Monday and expects it to track west to northwest this week. The Weather Channel said models agree it has the potential to at least reach tropical storm strength.

The moisture is the bigger story. In its Monday afternoon forecast discussion, the NWS office in Honolulu said deep tropical air would move over the Big Island starting Wednesday, with precipitable water values above 2 inches. That air mass will likely reach Maui County, perhaps Wednesday night into Thursday, while it remains unclear whether it will reach Oahu and Kauai. "A flood watch will likely be issued before Wednesday," forecasters wrote, according to Big Island Video News.

The same discussion said rainfall from Wednesday morning to Saturday morning could exceed 10 inches on the windward Big Island and 3 inches on the leeward side, with more than 4 inches on windward Maui, while cautioning that the forecast may change considerably. Winds are expected to increase across the eastern end of the state regardless of the exact track, most likely Thursday into Friday.

Three Paths, and Why a Near Miss Still Matters

The Weather Channel laid out three possible outcomes. In its most likely scenario, the storm keeps moving west, slows to a crawl, turns north and then steers away before making landfall, much as Hurricane Lala did. In a second scenario, the northward turn is sharp enough to bring a landfall, most likely on the Big Island, which the network called the worst outcome. In a third, a dip in the jet stream steers the system away early and keeps the worst weather offshore, similar to Tropical Storm Moke.

These are a private forecaster's scenarios, not official products. The Weather Channel said the first two paths could bring substantial rain to the Big Island, and that totals could be measured in feet rather than inches under the worst case.

Other estimates are lower but still significant. AccuWeather forecast 4 to 8 inches of rain, with 8 to 12 inches possible along eastern slopes of the Big Island. AccuWeather meteorologist Peyton Simmers said the biggest concern is how slowly the storm could move, since a stall south of the islands would keep feeding moisture over the same areas into the weekend.

Darryl Oliveira, the county's acting Civil Defense administrator, told the Tribune-Herald that some areas could see 3 to 4 inches, with the same areas possibly exceeding 7 to 10 inches. "We're watching it, especially for those flood-prone areas down southeast," he said.

A near miss can still flood neighborhoods. When soil is already soaked, more of each inch of rain runs straight into streams, gulches and roads, which is why modest totals have been enough to close Highway 11 in Kaʻu.

Flood-Prone Communities and the Week Ahead

Residents of Kaʻu, windward communities from Hilo through Puna, and anyone who lives near streams, low-water crossings or steep slopes face the greatest risk. Oliveira said the county is watching closely for rain that hits while students are in school, because road closures can affect their trips home. Visitors driving Saddle Road or the coastal highway should expect sudden closures.

The storm fits a pattern that has made 2026 unusually punishing for Hawaii. The Weather Channel counts this as potentially the fourth system this season to at least graze the state, after Lala, Moke and Lowell. Fox Weather said the rapidly strengthening El Niño has helped produce 18 named storms across the Central and Eastern Pacific so far this season. El Niño tilts the odds toward a busier Central Pacific season, but it does not cause any single storm.

The practical steps are straightforward. Hawaii County Civil Defense asked residents to use this time to develop personal, family, and business emergency plans. Households should clear gutters and drainage ditches, move vehicles and valuables away from flood-prone areas, charge phones and batteries, and photograph property for insurance records. Flood policies through the National Flood Insurance Program generally take 30 days to take effect, so a new policy would not cover this storm.

Never drive or walk through flowing water, and do not cross flooded roads even if they look shallow. Follow evacuation or shelter instructions from Hawaii County Civil Defense.

Many Hawaii households are still recovering from earlier storms. Nature World News previously reported on Kauai's power restoration and Hawaii's request for disaster aid after Hurricane Lowell.

The next milestones are whether a tropical depression forms around midweek and whether the NWS in Honolulu issues a flood watch before Wednesday. The central uncertainty is the storm's track and speed near the islands, especially whether it stalls south of the Big Island. Residents should check updated forecasts at least twice a day through the weekend.

Developing Story Timeline

Sept. 21, 2026, HST: Hawaii County Civil Defense issues its first message on the system, and formation odds reach 90 percent within seven days.

Mid-September 2026: Tropical Depression Fifteen-E forms, then falls apart in strong wind shear while moving west.

Early September 2026: Hurricane Lowell, which peaked at Category 5, brings impacts mainly to the western islands.

August 2026: Hurricane Lala passes close to the south of the Big Island, damaging Kaʻu communities, and Tropical Storm Moke follows with additional rain.

What Readers Want to Know

What is a "zombie storm"?

It is an informal name for a tropical system that falls apart and later regenerates. Tropical Depression Fifteen-E weakened in strong wind shear more than a week ago, and its remnants are now reorganizing over calmer conditions southeast of Hawaii.

Is there a watch or warning for Hawaii right now?

As of Monday evening, Sept. 21, HST, no tropical storm watch or flood watch had been issued. The NWS in Honolulu said a flood watch will likely be issued before Wednesday.

When could rain reach the Big Island?

Civil Defense said impacts could begin as early as Wednesday. The NWS extended forecast shows heavy rain starting Wednesday evening on the Hilo side and by Friday evening on the Kona side.

How much rain could fall?

Estimates vary with the track. The NWS in Honolulu said totals could exceed 10 inches on the windward Big Island from Wednesday to Saturday, and AccuWeather forecast 4 to 8 inches with 8 to 12 inches on eastern slopes. The Weather Channel warned that its worst-case scenario could bring totals measured in feet.

Which areas face the greatest flood risk?

Kaʻu communities such as Pahala, Naalehu and Waiohinu, which Hurricane Lala damaged in August, face the highest risk. Windward Hilo and Puna, and any area near streams or low-water crossings, are also vulnerable.

Will the storm make landfall?

It is too early to know. The Weather Channel's most likely scenario keeps the center offshore, but a stall or a sharper northward turn would raise the risk for the Big Island.

What should residents do now?

Review family emergency plans, clear drainage, charge devices and sign up for county alerts. Follow Hawaii County Civil Defense for any evacuation or shelter guidance.