Hurricane Lane a Slow-Moving, Potential Flood Disaster; Over 30 Inches of Rain Possible in Parts of Hawaii Through Saturday

This threat was summed up succinctly by The Weather Channel hurricane expert, Dr. Rick Knabb, in a tweet Thursday morning.

I despise slow-moving tropical cyclones, and #Lane will be another one for the next 2-3 days. All Hawaiian Islands are on the stronger, wetter side of the hurricane, and the terrain will enhance rainfall and bring water and debris downslope. Potential flooding disaster.

— Dr. Rick Knabb (@DrRickKnabb) August 23, 2018

A hurricane warning remains in effect for Hawaii’s Big Island, Maui and Oahu, including Honolulu, meaning that hurricane conditions are expected within the warning area.

A hurricane watch remains in effect for Kauai County. This means hurricane conditions are possible within the watch area, and a watch is typically issued 48 hours before the onset of tropical-storm-force winds that may make preparations difficult or dangerous, according to Central Pacific Hurricane Center.

Happening Now

The center of Lane is about 210 miles south-southwest of the Big Island’s Kona Coast or about 305 miles south of Honolulu, moving northwestward. Lane has weakened somewhat, but remains a powerful Category 4 hurricane.

Lane’s outer rainbands are already drenching parts of the Big Island. Rainfall rates upwards of 1 to 3 inches per hour have been occurring in these bands.

Up to 15.66 inches of rain had been reported on the Big Island at Waiakea Experiment Station over the past 24 hours. Hilo had seen over 12 inches or rain in that same 24-hour period ending early Thursday morning.

The heavy rain has caused road flooding on the Big Island, including the city of Hilo, and landslides have occurred blocking some roads.

(LATEST NEWS: Hawaii Prepares for Lane)

Rainbands from Hurricane Lane will continue to gradually overspread the rest of the Hawaiian Islands Thursday.

Forecast Track Uncertainty

Even as Lane moves toward Hawaii, its forecast track and intensity the next couple of days still remains uncertain at this rather critical time, and small changes to its track and intensity are important for some potential impacts in the Hawaiian Islands.

Perhaps the most dangerous impact from Lane won’t depend as much on its intensity or exact track, but rather may result from its slowing forward speed in the form of heavy rainfall, as we’ll detail in our impacts section below.

Lane is now moving north-northwest after reaching the edge of subtropical high pressure, which had previously been steering it.

The most critical turn for Lane is an expected left-hand turn toward the west sometime Friday or Saturday.

The key is how soon and sharp that left-hand turn is, which will determine how close the core of Lane’s strongest winds come to the islands.

If Lane moves along the southern or western portion (left side) of its forecast projected path, it would be far enough from the islands to avoid the worst wind impacts of its core but still produce flooding rainfall, strong winds, dangerous surf and rip currents.

If, however, Lane moves along the northern or eastern side (right side) of its forecast projected path, essentially making its left-hand turn later or less sharp, damaging winds from the hurricane’s core could swipe parts of the islands, in addition to torrential rain from the core and more damaging coastal flooding from both the setup of battering waves and water rise for those areas prone to water rise.

(MAPS: Interactive Hurricane Tracker)

While waters are sufficiently warm, wind shear is increasing, and this will gradually, then more rapidly weaken Lane. Once Lane weakens sufficiently, it will make that left-hand turn, steered by lower-level winds.

So, as happens qutie often, the intensity and track forecasts depend on each other.

A sooner weakening of Lane means a sooner left turn farther from the islands. A later weakening means the core of Lane would track closer to the islands before it makes a later left-hand turn.

Adding to the complexity is the potential for Lane’s circulation to be disrupted by the higher terrain of the islands.

Despite all that, Lane could still be a hurricane near or off the coast of Maui County or Oahu Friday, areas that are not accustomed to tropical storm or hurricane conditions.

Residents in Hawaii, particularly in watch and warning areas, should rush storm preparations to completion, including putting together an emergency kit and a family emergency plan. Those with vacation plans to Hawaii through Saturday should consider changing their plans.

Hawaii Forecast Impacts

Here is a break down of potential impacts from Lane.

Rainfall Flood Threat

• Regardless of the exact track, bands of heavy rain will hammer the Hawaiian Islands through Saturday.
• These heavy rainbands may occur both well ahead and for some time after the closest approach of the center of Lane.
• Moist winds up the slopes of the hills and mountains on Lane’s northern and eastern flanks could lead to prolific rainfall, potentially unleashing deadly, destructive flash flooding and landslides.
• According to the Central Pacific Hurricane Center, isolated maximum rainfall totals of more than 30 inches are possible, particularly over south- and/or eastward-facing slopes.

High Wind Threat

• At least tropical-storm-force winds (39 to 73 mph) are expected in most areas of the islands.
• These tropical-storm-force winds are most likely to begin later Thursday in Maui County, late Thursday night in Oahu and late Friday in Kauai County.
• There is a small chance of hurricane-force winds (74 mph or higher) in parts of the islands, particularly along the western or southern coasts.
• Small changes in the track and intensity forecast will make the difference between the core of Lane’s strongest winds affecting at least parts of the islands or remaining offshore.
• Regardless, the combination of heavy rain and strong winds could down more trees than strong winds alone.

High Surf/Coastal Flood/Storm Surge Threats

• Large swells generated by Lane will spread across the Hawaiian Islands Thursday.
• Dangerous surf conditions and rip currents are expected, especially on exposed west-, south-facing coasts, including those typically not accustomed to large waves, such as Waikiki Beach, Maui and the Kona Coast.
• The surf could be damaging in spots.
• Coastal flooding – possibly more locally significant storm-surge flooding if the core of Lane moves close enough – is also expected but depends on the exact track of Lane.
• Water levels may rise by as much as 2 to 4 feet above normal tide levels along south- and westward-facing coasts near where the center of Lane passes, according to the Central Pacific Hurricane Center.

Tornadoes

• As always with hurricanes and tropical storms affecting land, a threat of waterspouts and tornadoes is in play, particularly in discrete cells embedded in outer rainbands.
• Given these are embedded in Lane’s rainbands, they may develop quickly and move rapidly.
• You may not be able to see a tornado before it arrives.
• Take shelter immediately if the National Weather Service issues a tornado warning for your area.

Hawaii Hurricane History

Lane is the strongest hurricane to track within 300 miles of Hawaii, according to NOAA’s historical database. While 1994’s Hurricane John had stronger maximum sustained winds, Lane’s lowest pressure was lower than John’s, and John only came within 319 miles from South Point on the Big Island.

According to NOAA’s best track database, there is no record of a hurricane track within 65 nautical miles of either Maui or Honolulu since statehood.

There have been three notable hurricanes that struck the western island of Kauai during that time: landfalls of Iniki in 1992 and Dot in 1959 and an eyewall brush with Iwa in 1982.

(MORE: How Unusual are Hawaii Hurricanes)

Three of the previous Category 5 central Pacific hurricanes occurred in 1994 during a hurricane season that featured a central Pacific flavor of El Niño called Modoki El Niño. Modoki El Niños occur when the warmest pool of water compared to average occurs in the central Pacific rather than in the eastern Pacific.

Warmer water allows tropical cyclones to readily intensify. A Modoki El Niño opens the window for strong hurricanes in the central Pacific as long as atmospheric conditions such as wind shear and humidity are also favorable.

Check back with us at weather.com for the latest on Lane and its potential impacts in Hawaii.

Recap of Lane So Far

Lane formed as a tropical storm in the eastern Pacific on Aug. 15 and became a hurricane the next day.

Tuesday evening, Hurricane Lane joined an exclusive company of central Pacific Category 5 hurricanes, the first since Ioke in 2006, only the second on record within 350 miles of Hawaii(John in 1994 was the other) and the most intense North Pacific hurricane east of the International Date Line since Patricia in 2015.

https://weather.com/storms/hurricane/news/2018-08-22-hurricane-lane-hawaii-forecast