Dangerous Category 3 Hurricane Lane is pushing ever closer to the Hawaiian Islands and has already begun unloading excessive amounts of rainfall on the Big Island and Maui. Water from both torrential rainfall, exceeding 30 inches in some places, and battering waves, up to 25 feet on the south side of the islands, are likely to pose the biggest threat.

The resulting flooding may prove devastating.

The storm’s slow forward motion “greatly increases the threat for prolonged heavy rainfall and extreme rainfall totals,” the Central Pacific Hurricane Center, based in Honolulu, said Thursday. “This is expected to lead to life-threatening flash flooding and landslides over all Hawaiian Islands.”

Rick Knabb, the Weather Channel’s hurricane expert, called Lane a “potential flooding disaster.”

The latest

On Thursday afternoon (local time), the storm was positioned about 200 miles south-southwest of Kona on the Big Island and packed sustained winds of 125 mph. Tropical-storm-force winds extend up to 140 miles from the center and are expected to affect parts of the Big Island on Thursday and especially Thursday night, when hurricane-force winds cannot be ruled out.

(Central Pacific Hurricane Center)

But torrential rainfall is proving to be the storm’s greatest menace. Already, nearly 19 inches of rain have fallen in the eastern part of the Big Island, which is under a flash-flood warning. Rainfall rates of up to 3 to 4 inches have been observed in the high terrain.

Useful link: Weather radar for Hawaii

In Hilo, about 15 inches have fallen in the last 24 hours.

Heavy rains expanded over Maui Thursday morning, where flash-flood warnings were posted at times for the island’s eastern half, and road closures were reported.

The forecast

Hurricane warnings are in effect for not only the Big Island and Maui but also Oahu, for the first time in 26 years. Kauai is under a hurricane watch.

Conditions are expected to begin deteriorating in Oahu Thursday afternoon into Friday and its Department of Emergency Management planned to sound sirens “to alert the public to the potential for flash flooding and damaging winds.”

(Central Pacific Hurricane Center)

The storm’s peak winds are forecast to gradually weaken as the storm heads closer to the islands, but it is expected to maintain hurricane strength through at least Friday. Over the weekend, Lane should weaken to a tropical storm.

The storm has some chance to make landfall on Maui or Oahu as it is pulled north Friday, and model forecasts have shown this as an increasing possibility since late Wednesday. But Lane could also pass just south of the islands, parallel to the coastline.

Group of simulations from American (blue) and European (red) computer models from Thursday. Each color strand represents a different model simulation with slight tweaks to initial conditions. Note that the strands are clustered together where the forecast track is most confident, but they diverge where the course of the storm is less certain. The bold red line is the average of all of the European model simulations, while the blue is the average of all the American model simulations. (StormVistaWxModels.com)

The exact track has implications for the wind intensity affecting the islands and how extensive the extreme rainfall becomes, but some areas will inevitably face dangerous amounts of rain and life-threatening surf, no matter the storm’s course.

“All Hawaiian Islands are on the stronger, wetter side of the hurricane, and the terrain will enhance rainfall and bring water and debris downslope,” the Weather Channel’s Knabb tweeted.

Standing tall in the tropics and intercepting the vast streams of moisture, the Hawaiian Islands’ high terrain has a history of being the recipient of some of the world’s most extreme rainfall (one location on Kaui received nearly 50 inches in 24 hours in April). In the case of Hurricane Lane, some areas may receive multiple feet of rain.

“Flooding from these heavy rains will also be possible in areas that are typically not prone to flooding,” the National Weather Service in Honolulu wrote.

Some high-resolution models show four to five feet of rain in mountainous locations if the storm tracks close to the islands and that is within the realm of possibility given the storm’s slow movement. Some models suggests bands of heavy rain could continue to pelt the islands even into Monday, after the storm has departed.

Useful link: Detailed forecast region by region over Hawaiian Islands from National Weather Service

The storm’s peak winds are on a downtrend, which should continue, but in the scenario in which the center tracks close to or over Maui and/or Oahu, hurricane-force gusts would be possible, especially in the high terrain and in the upper floors of high-rise buildings.

Should hurricane-force winds materialize, they would result in “considerable roof damage to sturdy buildings,” severe damage to mobile homes, “many large trees snapped or uprooted,” “impassable” roads, and power outages, the Weather Service said.

However, there is a higher probability of tropical-storm-force winds, which could still cause tree damage, minor structural damage and power outages.

Useful link: Local hurricane statement from National Weather Service

As the storm churns to the north-northwest, it is likely to push “large and potentially damaging surf along exposed west, south and east facing shorelines,” according to the hurricane center. The relatively slow motion of the storm will prolong these effects. Towering waves could exceed 20 feet.

The Weather Service is calling for potentially “extreme” effects from this high water, especially for low-lying areas at high tide. “Expect ocean water surging and sweeping over beaches, coastal benches, lava flows, and roadways, creating the potential for significant damage to coastal properties and infrastructure, including roadways,” it said. “Coastal evacuations and road closures are possible. Large breaking waves may affect harbor entrances and channels with significant damage possible to docks, piers, ramps, and boats.”

Preparedness and response

While tropical storms and hurricanes regularly roam the waters near Hawaii, direct effects from storms as intense as Lane are unusual, and the island chain’s population is unaccustomed to such large storms.

The last hurricane to make landfall on Hawaii was Iniki in 1992, which hit Kauai. Dot, in 1959, was the only other hurricane to strike the state’s shores in modern records, also on Kauai.

Given the hazards posed by the storm and Hawaii’s vulnerability, officials have pleaded with residents to prepare and assured their support.

“#Lane is still an extremely dangerous storm with an uncertain forecast. Stay vigilant and be ready for flooding and widespread damage,” tweeted Brock Long, who heads the the Federal Emergency Management Agency on Thursday.

“I have authorized an emergency disaster declaration to provide Hawaii the necessary support ahead of #HurricaneLane,” tweeted President Trump.

The American Red Cross of Hawaii tweeted that it is “seeking volunteers who are willing to be on call to potentially assist in staffing shelters or assessing damage.”

Gov. David Ige (D), who issued an emergency proclamation for the islands, said he will allow nonessential state employees to go on administrative leave through Friday.

Hawaii’s education department announced that all public schools will be closed Thursday and Friday.

To reduce the risk of storm damage, the Navy is sending ships from Pearl Harbor out to sea, Axios reported.

Lane: A historic hurricane in the Central Pacific

As it moved within 300 miles of the islands, Hurricane Lane became the closest Category 5 storm on record to approach Hawaii before it began to weaken. The next-closest storm of such strength to approach the islands was John in 1994.

It is only the sixth storm to reach Category 5 intensity in the Central Pacific on record, joining Patsy (1959), Emilia (1994), Gilma (1994), John (1994) and Ioke (2006).

The storm’s central pressure dropped as low as 929 millibars, making it the most-intense hurricane (as measured by pressure) since Patricia in 2015 in the eastern half of the North Pacific Ocean.