As a popular vacation destination, the Hawaiian islands are well known for their predictable and relatively mild weather year round. However, there are wide variations in the weather depending on the exact location in the island chain. Also, there are some unique hazards to aviation operations caused by Hawaii’s location and geography that one must become acquainted with before operating an aircraft in the 50th state. One can encounter trade winds and their associated weather, temperature inversions and their effects, volcanic eruptions, high winds, heavy rain, and tropical cyclones.
The Hawaiian archipelago lies within the band of 0º- 30ºN Latitude, which is the region of global circulation where the northeasterly trade winds are located (Lester 7-5). These prevailing northeasterly winds cause unique rainfall patterns throughout the islands. In the waters surrounding Hawaii, an average of 25-30 inches of rain falls per year. However, Hawaii’s orography and trade winds cause the islands to have up to 15 times greater rainfall than the surrounding ocean (Price 54-55). The warm, moist air from the Pacific is brought to the islands’ windward mountains, which then cause the air to rise, cool, and condense to form clouds and rain. This effect often causes extreme rainfall numbers of up to 9-11 m/yr in many northeast-facing, windward areas of the islands (Giambelluca and Nullet 209). Along windward facing ridges in the northern parts of the islands, lifting air is common whenever the prevailing trade winds are blowing across the ridge. For sailplane pilots, this produces beneficial ridge lift. For powered airplane operators, however, this can create turbulence across ridges, especially when the wind speed is high.
The so-called trade wind inversion has a large impact on Hawaiian weather. This temperature inversion is the result of sinking air on the eastern part of the subtropical high pressure area. This sinking air is adiabatically warmed and sits atop the cooler ocean air forming a temperature inversion ("Subtropical High”). This inversion causes the cloud heights in the Hawaiian region to be limited. Because of the stable layer (typically a -1.6ºC lapse rate) and decreased moisture at the inversion, cloud tops rarely reach above this inversion. The result of this is that thunderstorms and clouds with extensive vertical development are uncommon in the Hawaiian islands. However, if the inversion layer weakens or disappears, thunderstorms may appear (Leopold 88, 91). Even in mountainous areas where upslope lifting can occur, clouds are still often capped at the inversion. This causes mountains in the region to have drier summits and wetter slopes (Giambelluca and Nullet 209). Even though thunderstorms are rare in Hawaii due to the temperature inversion, they still occur and can cause extreme difficulties to the unaware pilot.
One of the more obvious hazards to aviation operations in the Hawaiian islands is volcanic activity. It is an island...