The National Weather Service has issued a flood watch for Hawaii Island and Maui County as an expected tropical cyclone forms just southeast of the state.

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A three-day rainfall forecast from the National Hurricane Center shows the potential for over 20 inches of rain for much of east and southeast Hawaii Island, including Ka‘u district and other areas that were devastated by Hurricane Lala flooding in August.

“A potential tropical cyclone is expected to bring heavy rain to the eastern end of the state over the coming days,” says the flood watch, which lasts from Wednesday afternoon through Saturday afternoon. “The track of this potential storm is uncertain, but heavy rain is likely.”

This afternoon, the remnants of former Tropical Depression 15-E, were located several hundred miles southeast of Hawaii and reforming into a potential cyclone. The National Hurricane Center says the system has a 90% chance of tropical cyclone formation over the next 48 hours.

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If it reaches tropical storm strength, it will be named Nolo.

“Heavy rain on the north side of a developing tropical system (the future Nolo) should develop Wednesday afternoon,” forecasters said. “Windward and southeast Big Island and windward Maui are the most likely to experience heavy rain. However, other islands in Maui County are at risk as well, and therefore are included in the watch. Very high rainfall rates, which can cause flash flooding, are possible within the entire watch area.”

Flood-prone roads and other low-lying areas may be closed due to runoff and overflowing streams, officials said. Urban areas may also receive significant flooding and property damage due to rapid runoff, they added.

Forecasters said the exact track of the impending storm will be highly uncertain until it forms into a cyclone.

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