Heavy rainfall from Moke still expected to begin late Saturday on Big Island

Little changed between early evening and late night Friday for Tropical Storm Moke, as it continued on a west-northwest track, moving about 8 mph, with its center still forecast to pass south of the Big Island this weekend and then the smaller Hawaiian Islands early next week.

Moke was about 545 miles southeast of Hilo as of the 11 p.m. storm advisory from Central Pacific Hurricane Center. It still had maximum sustained winds of 45 mph with higher gusts.

Tropical storm force winds extended outward from the storms center up to 175 miles.

However, given the expected track south of the islands and compact nature of the storm, likelihood of tropical storm watches or warnings being necessary for the main Hawaiian Islands remains very low.

“The enhanced pressure gradient north of Moke, combined with moisture associated with the cyclone interacting with the island terrain, will likely produce gusty winds and periods of heavy rainfall across portions of the state,” the 11 p.m. update said.

Key messages from late Friday night update

Rainfall and flooding

Heavy rainfall associated with Moke remains forecast to begin impacting the Big Island late Saturday, with rain spreading westward across the remainder of the Hawaiian Islands from Sunday into Monday.

Rainfall totals of 5 to 10 inches, with maximum amounts of up to 15 inches in some areas, are expected around the Big Island, focused mainly in windward and southeast areas of the island.

That brings the threat of life-threatening flooding and mudslides, especially in areas of steep terrain and over locations that only a week ago were hit hard by Hurricane Lala, including Kaʻū communities such as Nāʻālehu, Pāhala and Waiʻōhinu.

A flood watch will be in effect from late Saturday night through Monday afternoon for the Big Island.

Meanwhile, rainfall total of 1 to 2 inches, with maximum amounts of 4 inches, are forecast for eastern Maui and 1 to 2 inches of rain are possible for the remainder of the state.

Winds and surf

The strongest winds associated with Moke are expected to pass south of the Hawaiian Islands, but strong gusty winds are likely, particularly in areas within and downslope of higher terrain.

Swells generated by the storm are expected to impact exposed east- and south-facing shores of the state, with the possibility of life-threatening surf and rip current conditions this weekend and early next week.

Impacts from Moke could be aggravated in locations still recovering from Hurricane Lala, particularly in areas where soils remain saturated.

More from the forecast

A low- to mid-level ridge is forecast to strengthen north of Moke during the next few days, which should steer the cyclone west-northwestward at a slightly faster forward speed.

“This motion is expected to take the core of Moke south of the main Hawaiian Islands,” said the Central Pacific Hurricane Center update.

Moderate southwesterly vertical wind shear continues to displace the deepest convection north of the low-level circulation center, where convection has expanded in coverage and cloud-top temperatures cooled during the past several hours.

Despite those developments, gradual strengthening of the tropical storm during the next day or two is still forecast.

“Thereafter, dry mid-level air is expected to become increasingly entrained into the circulation while vertical wind shear remains unfavorable late this weekend into early next week,” said the 11 p.m. update.

Moke will then begin to steadily weaken as it passes well south of the smaller Islands.

Residents of Hawai‘i should continue to closely monitor Moke’s forecast and watch information from the National Weather Service forecast office in Honolulu for local forecasts, including any advisories, watches or warnings issued.

Hawai‘i County preparations

Hawaiʻi County urges residents and visitors to be ready for the forecasted heavy rainfall and flooding starting late Saturday night. Because the ground remains saturated from the inundation by Lala, it won’t take much more rain to cause additional flooding.

Hawaiʻi County Civil Defense reminds island residents and businesses:

• Take the time left to make any additional preparations for possible severe weather.
• Consider relocating to a safer location before storm conditions begin if the area you are in is prone to flooding or you location is unsafe.
• Shelters will be designated as safe places, if necessary. Shelter locations would then be provided in future messages.

Hawai‘i Department of Transportation preparations

Crews on all islands are preparing facilities and working to remove vegetation from streams and saturated hillsides in preparation for heavy rainfall from Tropical Storm Moke.

Crews also are removing debris washed into streams by Lala and all previous storms at mileposts 50, 51.5, 53.5, 54.5 and 56.5. All bridges along Māmalahoa Highway (Highway 11) in Ka‘ū impacted by Lala were inspected and are structurally sound and safe.

Residents and responders are notified that there could be single-lane closures with alternating traffic control at these points on the highway.

Crews reinspected drainage, trimmed trees to remove potential hazards, secured equipment, tied down or relocated aircraft and topped off emergency power generators at Hilo International and Ellison Onizuka Kona International airports.