The remnants of former Tropical Depression Fifteen-E are showing signs of organization about 800 miles southeast of Hawaii Island, and forecasters expect a tropical depression to form south or southeast of the islands by the middle to latter part of the week. The Central Pacific Hurricane Center's tropical weather outlook said environmental conditions were forecast to become more conducive for development as the system moves generally westward.

Development odds rose sharply on Monday. An early-morning outlook put the chance of formation at 20 percent within 48 hours and 80 percent within seven days, and by Monday afternoon the center had raised those odds to 60 percent and 90 percent, according to Big Island Now. If the system becomes a tropical storm, it would be named Nolo.

The main concern is rain, not wind. The National Weather Service's extended forecast calls for multiple days of heavy rain beginning Wednesday evening on the Hilo side of Hawaii Island and by Friday evening on the Kona side. No watches or warnings had been issued as of Monday, and the track and timing remain uncertain.

A Rain Threat Aimed at Communities Still Recovering

The risk is highest in Kaʻū, the southeastern district where Pahala, Naalehu and Waiohinu were heavily damaged by Hurricane Lala in August. Darryl Oliveira, Hawaii County's acting Civil Defense administrator, told the Hawaii Tribune-Herald that "the rainfall seems to be the most concerning element" of the system. He said some areas could see 3 to 4 inches, with the potential for more than 7 to 10 inches in the same areas.

Oliveira said those communities have not seen new mudslide damage since Lala, but recent heavy rain has repeatedly closed Highway 11 and other Kaʻū roads because of flooding. He noted the county is watching how storm timing could affect students getting home from school.

AccuWeather forecast 4 to 8 inches of rain for the Big Island, with 8 to 12 inches possible on eastern slopes and even heavier totals possible. AccuWeather meteorologist Peyton Simmers warned that the system could slow dramatically or even stall south of the islands, funneling moisture over the same areas and turning the event into a prolonged rainstorm lasting into the weekend.

Forecast Uncertainty Remains High

The difference between a soaking and a disaster comes down to track and speed. AccuWeather noted that even a relatively small shift could dramatically change how much rain falls. A path closer to Hawaii Island would raise rainfall and flood risk sharply, while a track farther south could keep totals much lower. Residents should treat current numbers as possibilities, not a forecast of what will fall on a specific neighborhood.

Two other storms are active but pose no current threat to Hawaii. Tropical Storm Odalys, well east of the Central Pacific basin, was expected to strengthen into a hurricane over open water, and Hurricane Polo was intensifying off southwestern Mexico.

Lala's Damage Still Shapes Local Risk

Lala passed just south of Hawaii Island as a Category 1 hurricane on Aug. 15 without making landfall. It still brought rainfall totals above 20 inches to parts of the island, with a storm maximum of 43.55 inches at Laupāhoehoe, northwest of Hilo, according to NASA's Earth Observatory. Floods downed trees, damaged bridges, and knocked homes off their foundations.

That history raises the stakes. Soils in parts of Kaʻū remain vulnerable, some roads and drainage systems are still damaged, and families displaced by Lala may have fewer resources to prepare. The state is also still recovering from Hurricane Lowell's damage on Kauai earlier this month.

Why El Niño Keeps Sending Storms Toward Hawaii

The busy season was anticipated. In May, NOAA's 2026 Central Pacific hurricane outlook gave a 70 percent chance of an above-normal season, with 5 to 13 tropical cyclones forecast in a basin where a near-normal season has 4 or 5. The agency said strong El Niño conditions are typically associated with dramatically elevated activity in the central Pacific.

El Niño warms waters in the equatorial Pacific and tends to reduce the wind shear that tears storms apart in this region, giving systems more chances to form and survive near Hawaii. NOAA has stressed that seasonal outlooks describe overall activity, not where or when storms will strike land.

Residents on Hawaii Island, especially in Kaʻū, Puna and the Hilo area, should review evacuation routes, clear gutters and storm drains, secure outdoor items and prepare for possible road closures and outages. Keep medications, water, food, and chargers on hand for several days. Never cross flooded roads or streams, which can rise within minutes. Follow instructions from Hawaii County Civil Defense and the NWS in Honolulu, and sign up for county alerts.

Homeowners should check coverage now. Flood losses are generally covered through the National Flood Insurance Program or private flood policies, not standard homeowners insurance, and new NFIP policies usually take 30 days to take effect.

The Central Pacific Hurricane Center updates its outlook regularly and will begin advisories if a depression forms. The key questions are whether the system forms by midweek, how close it tracks to Hawaii Island, and whether it stalls.

What Readers Want to Know

What is former Depression 15-E?

It is the remnant of Tropical Depression Fifteen-E, which formed in the eastern Pacific earlier this month. Forecasters expect it to reorganize into a tropical depression south or southeast of Hawaii by the middle to latter part of this week.

Will it be named?

If it strengthens into a tropical storm in the Central Pacific, it would be named Nolo.

When could rain reach Hawaii Island?

The NWS extended forecast calls for heavy rain beginning Wednesday evening on the Hilo side and by Friday evening on the Kona side, depending on the track.

How much rain is possible?

Hawaii County officials cited 3 to 4 inches in some areas and possibly more than 7 to 10 inches locally. AccuWeather forecast 4 to 8 inches, with 8 to 12 inches possible on eastern slopes.

Which communities face the greatest risk?

Kaʻū communities such as Pahala, Naalehu and Waiohinu, which were heavily damaged by Hurricane Lala, along with other flood-prone areas on the island's windward side.

Are there any watches or warnings?

None had been issued as of Monday, Sept. 21. Check the Central Pacific Hurricane Center and NWS Honolulu for updates.

Why is Hawaii seeing so many storms this year?

A strong El Niño has warmed Pacific waters and made conditions more favorable for storms near Hawaii, as NOAA's above-normal Central Pacific outlook anticipated.