Tropical cyclones, known as hurricanes in the Central Pacific, threaten the Hawaiian Islands. The official Central Pacific hurricane season runs annually from June 1st through November 30th, although storms can form outside this window. The Central Pacific Hurricane Center (CPHC) in Honolulu tracks and issues advisories for tropical cyclones moving into the region between 140 degrees West longitude and the International Date Line. These powerful storms, characterized by strong winds, heavy rainfall, and dangerous storm surges, present a genuine, though relatively infrequent, risk to the archipelago.
Frequency and Classification of Hawaiian Storms
The statistical probability of a tropical storm or hurricane passing within 60 miles of the Hawaiian Islands in any given year is low, but the threat is constant during the summer and fall months. Historically, the state has a 25.2% chance of experiencing a tropical cyclone in a single year. An average season sees about four to five tropical cyclones track through the CPHC’s area of responsibility.
The classification system used for these Pacific storms is the same as the Atlantic system, based on maximum sustained wind speeds. Tropical depressions have winds below 39 miles per hour, while tropical storms range from 39 to 73 miles per hour. A storm becomes a hurricane when its sustained winds reach 74 miles per hour, categorizing it on the Saffir-Simpson Hurricane Wind Scale. Most storms that approach the islands tend to weaken significantly, often arriving as tropical storms or depressions rather than full-fledged hurricanes.
The Protective Role of Geography and Ocean Currents
Several natural environmental factors work together to steer or weaken tropical cyclones before they can make landfall. One significant factor is the presence of the semi-permanent Pacific High pressure system, a large area of high atmospheric pressure located north of Hawaii. This system often acts as a steering mechanism, pushing approaching storms toward the south and away from the main islands.
Tropical cyclones attempting to reach the islands from the east or south must cross areas with increased vertical wind shear. Vertical wind shear refers to the change in wind speed or direction with altitude; strong shear disrupts the vertical structure of a hurricane, inhibiting its ability to strengthen. Furthermore, as storms move west toward the archipelago, they often encounter a natural boundary of cooler sea surface temperatures. Since hurricanes require warm water for fuel, passing over these cooler patches strips the storm of its energy, causing it to rapidly weaken or dissipate.
Notable Hurricanes and Their Island Impacts
Despite the natural protective mechanisms, the islands have experienced destructive direct hits. Hurricane Iwa, a Category 1 storm in November 1982, passed just west of Kauaʻi and Niʻihau, causing widespread damage on both islands and also impacting Oʻahu. The storm surge and high winds resulted in an estimated $250 million in damage at the time, making it the most destructive hurricane in the state’s recorded history until 1992.
Hurricane Iniki, which struck Kauaʻi in September 1992, remains the most powerful and devastating storm to hit the islands in modern history. It made landfall as a Category 4 hurricane with sustained winds of 145 miles per hour, causing approximately $3.1 billion in damage and destroying over 1,300 homes, primarily on Kauaʻi. Iniki demonstrated that the danger varies significantly between islands, with the north-western islands like Kauaʻi being historically more vulnerable.
Even storms that do not make a direct hit can cause significant damage, primarily through heavy rain, coastal flooding, and high surf. For instance, Hurricane Lane in 2018 dropped massive amounts of rain on the Big Island and Maui, causing devastating flooding and landslides, even though the storm itself weakened significantly before its closest approach. The historical record shows that every major island in the chain has experienced damaging impacts from tropical cyclones, highlighting the need for continual vigilance.
Essential Safety and Preparedness Steps
Because the Hawaiian Islands are isolated, large-scale evacuation is not a practical option, making preparation a local responsibility for every resident and visitor. A key first step is to track official weather alerts from the Central Pacific Hurricane Center.
Residents should assemble a comprehensive emergency kit containing enough supplies to be self-sufficient for a minimum of two weeks. The kit should include:
- A gallon of water per person per day
- Non-perishable food
- A battery-powered radio
- Flashlights
- A first-aid kit
Securing property involves trimming dead or weak tree branches, reinforcing garage doors, and securing or moving any outdoor items that could become dangerous projectiles in high winds. Developing a family communication plan, including an out-of-state contact, is also important if local communication lines are down.