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There are several types of wind hazards that affect Maui County. These include trade winds and thunderstorm wind events. Hurricanes tropical storms, and Kona Storms are also wind events that have the potential to impact Maui County, but due to special hazards associated with these types of events, they are listed as a separate hazard.
High wind definitions can vary by region. In general, high wind events are those events greater than normal averages and have damage potential. Wind events are common throughout the United States, including the Hawaiian Islands. Local National Weather Service Centers can issue a high wind advisory, watch, or warning. At the Honolulu Weather Forecast Office, a wind advisory is issued when sustained winds of 30 to 39mph and/or frequent gusts up to 50mph or greater are occurring or imminent. For summit areas the sustained wind range is 45 to 55mph and/or frequent gusts of 55 to 65mph. Wind advisories may be in effect for 6 to 12 hours.
A High Wind Watch is issued when sustained winds exceeding 40mph and/or frequent gusts over 60mph are likely to develop in the next 24 to 48 hours. For summit areas, high wind watches are issued when sustained winds are expected to exceed 56mph and/or frequently gust over 66mph. A High Wind Warning is issued when these same wind speeds are occurring or imminent. Wind warnings may be issued up to 24 hours ahead of the onset of high winds.
Trade Winds: Trade winds are the most common winds over Hawaiian waters. These persistent winds blow 70% of the time from a northeast to east-northeast direction and generally range from 10 to 25mph. Occasional extreme events reach 40 to 50mph when the sub-tropical high-pressure cell north of the islands intensifies. Trade winds occur up to 90% of the time in summer (June through August) and 50% of the time in winter (December through January).
On the Island of Maui, trade winds appear to be stronger when passing through the isthmus between the West Maui Mountains and Haleakalā. Wind speeds may be higher at locations such as Māʻalaea and north Kīhei than along the island’s north shore. This increase in wind speed is the result of wind funneling, which occurs when wind passes between two mountains or into a valley. North Pacific high- pressure systems can cause gusty trade wind episodes over Hawaiian waters, which can last for days.
Thunderstorms: Thunderstorms are associated with high wind because wind is typically one component of thunderstorms. Thunderstorms are very dangerous because of their ability to generate tornadoes, hailstorms, strong winds, flash flooding, and damaging lightning. Three conditions need to occur for a thunderstorm to form. First, there needs to be moisture present to form clouds and rain. Second, it needs unstable air, such as warm air that can rise rapidly (this often referred to as the “engine” of the storm). Third, thunderstorms need lift, which comes in the form of cold or warm fronts, sea breezes, mountains, or the sun’s heat. When these conditions occur simultaneously, air masses of varying temperatures meet, and a thunderstorm is formed. These storm events can occur singularly, in lines, or in clusters. Further, they can move through an area very quickly or linger for several hours.
High winds, including thunderstorm wind, can impact the entire county. Maui County is capable of experiencing winds up to 160 miles per hour. However, south-facing shorelines are at greatest risk to wind events, along with the north shore as winds accelerate down the north slopes of Haleakalā.
Previous wind events were gleaned from the 2015 Maui County Hazard Mitigation Plan, as well as from NOAA’s NCEI Storm Events Database, which was investigated for past high wind and thunderstorm wind events reported in Maui County. From 1970 to 2004, the 2015 Maui County Hazard Mitigation Plan reported 67 high wind events, totaling almost $2.5 million in damages, and resulting in five injuries and 3 fatalities.
Wind extent can be measured in terms of speed, reported in knots. Within Maui County, the strongest wind speed reported during a windstorm event was 72 knots (83mph). It should be noted that stronger wind events are possible in the county.
Future Probability
Extreme wind is recognized as a regular occurrence in Maui County. With 94 wind events reported in Maui County in 50 years, the county experienced approximately two reported wind events each year, although it is likely that wind events have gone unreported, especially if they did not result in damage, injuries, or deaths. Further, the county is in a location that experiences approximately six thunderstorm days per year. However, climate change impacts may decrease the frequency of some future wind events, as climate change is associated with a documented decrease in trade winds in Maui County. Based on the above factors and available information regarding the location of past wind events, an annual probability of Highly Likely (greater than 90% annual chance) was assigned for high windstorm events in all community planning areas in Maui County.
All of Maui County is vulnerable to high windstorms due to the topography and movement of weather fronts through the area. During a time of extreme heat and high winds, the wildfire threat would significantly increase. Specific impacts to buildings, infrastructure, life safety, public heath, and the economy from lightning are described below.
Buildings and Infrastructure: All current and future buildings in Maui County (including critical facilities) are considered at-risk to high wind events. High wind has the potential to blow shingles, siding, awnings, and other features off buildings. Falling trees and tree limbs can damage structures and block roadways, demonstrated by the 2019 windstorm that caused downed trees to block Hāna Highway and Kula Highway. Objects picked up by wind can be hurled through the air, damaging structures and breaking windows when contact is made. In some cases, structures can be blown off foundations. In addition, mobile homes are considered at a higher risk to severe wind. Proper anchoring can make mobile homes more resilient to severe wind.
Severe winds can cause damage to critical infrastructure, including communications infrastructure, utility poles, and above ground power lines can be blown down.
Health and Safety: Severe winds can result in serious life safety impacts. People outside during severe wind events may be struck by falling trees and limbs, or by objects falling off buildings or being hurled through the air. While high windstorms are unlikely to result in an evacuation, wind advisories, watches and warnings may be issued for sustained winds and gusts of certain speeds (see Description subsection for warning thresholds specific to Maui County). Watches and warnings may be issued several days to several hours ahead of an event. Certain areas, such as Haleakalā National Park, may close to visitors during high wind events.
Economic Impacts: Communication lines, antennas, and towers can suffer damage from wind and downed branches/trees. Damages to buildings, roads, and vehicles can be costly. Businesses interruptions can occur due to power outages. Flights may be delayed or canceled due to severe wind events.
Climate Change Impacts: Climate change is projected to have various impacts of wind events in Maui County. While trade winds have decreased as temperatures have warmed over the last several decades, how future climate change conditions will impact trade winds and monsoon winds in Maui County is unclear. Increases in severe storm events may increase the severity and/or frequency of high wind events in Maui County.
