What are my risks?

• Do I live in a flood prone area?
• Where have stream floods been recorded on Maui?
• Where have high waves been recorded on Maui?

Do I live in a flood prone area?

For information on flooding in your neighborhood, refer to a Flood Insurance Rate Map (FIRM). These maps are computed water surface elevations that are combined with topographic mapping data to develop flood hazard maps. They provide information on areas subject to flooding. They are used to guide future development away from flood-prone areas and to regulate development that is proposed to occur within such areas.

Even so, updates to these maps have not kept up with development in Maui County. Each year, numerous properties not officially mapped as “flood prone” are flooded.

Call your Flood Coordinator for information about flooding. Or, ask your regional librarian to see the Flood Insurance Rate Map for your community.

Where have stream floods been recorded on Maui?

Click to enlarge

Stream flooding on Maui is not only common, but is also the very agent responsible for making it famous as the Valley Island.

Annual rainfall is greatest (360 inches) at the summit of west Maui and nearly as high (280 inches) along the eastern flanks of east Maui just below the trade wind inversion. Rainfall is lowest (<15 inches) in the vicinity of Kihei and Lahaina.

Flooding in areas around Lahaina and Kihei are in part a result of the abrupt transition in slope at the coastline and the behavior of flash flooding. Many flash floods in these areas occurred after heavy rainfall in higher elevations - in some cases equaling the average annual maximum, like in December 1988.

The north central portion of Maui and the Hana coast have the greatest stream flooding histories. Nearly once a decade, water sheets into the urban centers of Kahului and Wailuku (e.g., November 1950 and 1960). Along the road to Hana temporary road closures are common due to flash floods and mudslides from the steeper slopes of East Haleakala.

In addition, the Lahaina region and Kihei are vulnerable to standing surface water flooding. This may interrupt transportation and damage low elevation buildings. Standing surface water develops after intense rainfall events where poor soil permeability and urbanization prevent adequate drainage and temporarily disrupting transportation.

Where have high waves been recorded on Maui?

Click to enlarge

Waves from north and northwest swell tend to be highest on an annual basis and generally occur between October and March. Wave heights associated with these swells range between 5-10 feet (Kaanapali) and 10-20 feet (Honolua Bay, Waihee to Paia).

Occasionally, waves of 25 feet and greater occur over the deep offshore reefs of the North Shore. Two of the largest wave events occurred February 1993 and January 1998, when waves reached heights of 30 and 40 feet, respectively.

The southern shores of Maui are partly protected from south swell in summer by the islands of Kahoolawe and Lanai. Even so, wave heights range between 4 and 6 feet and, at times, reach 8-10 feet. During winter months, Kona Storm waves can reach 5 feet.

Trade wind waves, usually between 3 and 4 feet, impact the eastern shores 70% of the time.

In the summer months, tropical storms and hurricanes can generate wave heights of 10-20 feet along any portion of coast on Maui. Hurricanes Susan, Ignacio, and Estelle generated 10-15 foot waves along the north and east shores. Along the west shore, Hurricane Emilia caused wave heights of 6-10 feet.

Fortunately for Maui, much of its coastline has wide fringing reefs that dissipate wave energy offshore of its northern and western shores, where wave heights are highest.

Also, relative to the other islands, there are only a few locations where development along the shore is subject to direct impact by high waves. Unfortunately, however, areas important for tourism and commerce such as Lahaina, Kaanapali, Honokowai, Olowalu, Kihei, and Kahului are sited on low coastal plains, and so experience periodic wave overwash, causing rapid erosion and temporarily disrupting transportation.