Nolo’s flood forecast overlaps Hurricane Lala’s repair zone on Hawaiʻi Island

For anyone deciding whether an offshore hurricane is an inland problem, Nolo’s wind category is not the most useful number. The more immediate concern is a forecast for as much as 16 inches of rain over parts of eastern and southern Hawaiʻi Island—including communities where roads, channels and hillsides were damaged by Hurricane Lala six weeks earlier.

At 8 p.m. Friday, Nolo was nearly stationary about 150 miles south-southeast of South Point, with sustained winds of 105 mph. Its center was forecast to remain well south of the main islands. Even so, the Central Pacific Hurricane Center advisory called for 8 to 12 inches of rain across eastern and southern Hawaiʻi Island, with isolated totals of 16 inches. Hawaiʻi County was under a tropical-storm warning and hurricane watch.

The distinction matters: a storm’s category describes wind near its core, not the amount of water a particular slope, gully or road crossing will receive. By Friday night, the National Weather Service in Honolulu reported that Nolo’s outer rainbands were beginning to reach the island’s southeastern slopes. Gusts exceeding 50 mph had been observed on Hawaiʻi Island and Maui, but the expected overnight flooding remained a forecast, not a report of widespread new damage.

What Lala left behind

Lala provides a sobering comparison, but not a simple prediction. During that August storm, rain fell at generally 2 to 4 inches an hour across the hardest-hit areas. Hawaiʻi Island totals reached 15 to 30 inches across Hāmākua, Hilo, Puna and Kaʻū, with isolated measurements above three feet. Much of it arrived within roughly 15 hours, according to the National Weather Service’s August rainfall summary.

Flooding and landslides around Pāhala and Nāʻālehu damaged homes, roads, bridges and other infrastructure, and fatalities were reported. One gauge at Nene Cabin recorded 30.50 inches on August 15.

Nolo’s forecast maximum of 16 inches is lower than that single observed Lala total. But those figures should not be treated as a statewide before-and-after score: one is a forecast maximum, the other a measurement at a particular site. Flood consequences depend on where the heaviest bands linger, how quickly the rain falls and what lies downhill.

USGS observations after Lala help explain the mechanism. On southern Hawaiʻi Island, runoff entered steep, deeply cut gullies containing abundant soil and rock. The confined flow gained energy; sediment was deposited when it emerged from the channels and slowed. Investigators also saw indications that material accumulated around some culverts and road underpasses. In other words, the danger was not simply wet ground sliding everywhere. Water and debris were concentrated by the shape—and sometimes the obstruction—of drainage routes.

The clearest overlap is on the repair map

The available records do not establish that every watershed stayed saturated from Lala through late September. Nor do they show that streams remained continuously high. The defensible carryover is more concrete: damaged infrastructure, altered channels and debris still available to move.

Hawaiʻi’s transportation department listed continuing storm-damage work along multiple Route 11 segments around Pāhala, Punaluʻu and Honuʻapo for September 26 through October 2. Those repair sites sit within the southern district covered by Nolo’s heavier rainfall forecast.

There are protective changes, too. Local reporting from Kaʻū said county crews had cleared culverts and channels and used material from Lala to build berms near Waiʻōhinu, Nāʻālehu and Pāhala. But a county water official also warned that substantial debris remained upslope and could be mobilized by renewed flooding. The work may reduce risk without eliminating it.

How to read the next update

Three observations will say more about inland danger than a change in Nolo’s category:

1. Rainfall location and duration: Are successive bands repeatedly crossing the same eastern or southern slopes?
2. Local warnings and road conditions: Are flood alerts or closures appearing around specific gullies, bridges and Route 11 repair areas?
3. Measured water response: Are nearby stream and rain gauges rising sharply, rather than merely recording brief showers?

That is also the evidence needed to tell whether conditions are worsening or easing. Nolo does not have to repeat Lala’s extraordinary rainfall to cause trouble where drainage routes and roads are still being repaired. But Lala’s destruction, by itself, is not proof that every part of the island entered this storm saturated.