Weather forecasters and government officials were in forewarning mode Thursday as Hawaii Island prepares for a potential second round of damaging wind and rain within a week.

As of 5 p.m. Thursday, Tropical Depression Two-C was about 815 miles southeast of Hilo, packing maximum sustained winds of 35 mph and moving to the northwest at 14 mph. The tropical depression is expected to drop 5 to 10 inches of rainfall, with 15 inches possible — while residents of Ka‘u continue to dig themselves out of the flooding debris caused by Hurricane Lala.

“Grounds in Hawaii are very porous. They drain very fast. But they’re still saturated. And with this rain, we could have more flooding damage, and that’s what we’re focused on,” National Weather Service meteorologist John Bravender said Thursday during a press conference hosted by Gov. Josh Green in Honolulu.

Bravender said that after Lala, “it’s an event to have another tropical cyclone form just like this.”

The cyclone is expected to become Tropical Storm Moke (pronounced Mow-kay) when maximum sustained winds are 40 mph. That is likly to occur soon, because the storm is “expected to strengthen and move towards the islands in the next couple of days,” Bravender said.

“This is not the same as Lala. It looks like the track is going to be a little bit further south, and the wind field is not as large, so hopefully it won’t be as damaging. However, there could be a lot of rain with it … especially for southeastern sections of the Big Island,” he added.

The forecast track early Thursday evening projected a tropical storm passing south of Hawaii Island early Sunday morning — although high winds and rain are likely to hit the island on Saturday.

“This is down a little bit from our early estimates, thinking it might become a hurricane,” Bravender said. “But now, it looks like it could be a high-end tropical storm. … But as we see during events like these, we can have strong, gusty winds localized by our island terrain that can be very damaging. With this passing south of us, think of it like an enhanced trade wind type of pattern where we have strong, gusty winds in those areas that typically see those strong winds.”

Green said officials are focused on “helping families get the support and resources they need now and ensuring our state is ready for what may come next.”

“I am grateful to every responder, community partner, donor and individual resident, giving of themselves and stepping forward to support our people,” said Green.

Green announced donations from three billionaires with significant ties to the islands: $1 million each from Salesforce CEO Mark Benioff and Dell CEO Michael Dell, both of whom have Big Island residences, and a $3 million donation and up to 50,000 items of clothing from Tadashi Yanai, the UNIQLO founder and Fast Retailing CEO who owns the Kapalua Bay and Kapalua Plantation golf courses on Maui.

“$5 million came in immediately to jump-start us,” Green said. “These are resources that can do things that, on occasion, government can’t wade into … or immediate actions that we want to get started. For example, we’re going to rent a bunch of rooms to help people have a place to go. That’s important, because they may want to be away from the storm before it comes.”

In a statement, Mayor Kimo Alameda on Thursday urged the public “to take this new storm seriously and prepare for its expected arrival on Saturday.”

“The exact impacts aren’t clear, but that much rain falling on saturated ground could cause more flooding and landslides, so be prepared to move to shelter early,” Alameda said.

County workers have been consulting with NWS throughout the week about the developing storm and making plans to reduce its impacts. Civil Defense urged everyone on Hawaii Island to review their emergency plans, check and replenish supplies, and stay informed.

“The impacts from this storm could fall heavily across Puna and Ka‘u, which are recovering from the flooding and wind damage caused by Lala,” said Darryl Oliveira, acting Civil Defense administrator. “Don’t wait for flooding to develop – if you are at risk, get to a safer shelter before the new storm arrives.”

Calling the forecast “a ton of rain,” Green said Ka‘u’s schools and hospital could be affected by additional flooding, and those who’ve had their power restored could lose it again.

“That’s why we’re really posturing now to get ready for this — presumably late Saturday or early Sunday,” he said.

Email John Burnett at john.burnett@hawaiitribune-herald.com.