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Look Up Once in a While: Climate Update in 9 Pacific Island National Parks

August 27, 2012

Climate and weather influence every aspect of ecosystem health. For example, warmer ocean temperatures affect coral growth, and therefore, whole reef ecosystems. Climate/weather variations affect how invasive species spread, and influence the composition of terrestrial plant communities. Precipitation directly impacts groundwater dynamics, freshwater animals, and water quality. Insects are affected by changes in temperature, precipitation, and seasons which, in turn, affect bird communities. In short, climate affects everything. The primary goal of climate monitoring is to determine the status and trends of weather patterns and long-term climate regimes so managers can make informed decisions about resources.

Climate is generally mild on equatorial Pacific islands. Weather patterns in the national parks are largely controlled by island topography and events like El Niño/La Niña Southern Oscillation. Two seasons prevail in Hawaii; the April through October dry season, and the November through March wet season. The wet season in American Samoa is from October through April and from July through November in the Marianas (Saipan and Guam).

In 2010, data was collected from 18 weather stations in or near parks across the Pacific Island Network. Many of the national park units in the Pacific islands contain multiple and various types of weather stations (COOP and/or RAWS stations). These stations take different measurements but are becoming increasingly standardized as the National Park Service installs new and replaces older models. Although weather measurements are not consistent among all parks, data collection and integration is improving each year. Measured variables typically include temperature, precipitation, wind speed and direction, humidity, solar radiation, barometric pressure, fuel temperature, and fuel moisture.

climate table 2010

This table approximates the average temperature and precipitation for all of the weather stations in each park. These figures compare 2010 data with long-term “normal” conditions derived from historical data. Therefore, “69%” preciptation and “Less than 1°F warmer” temperature were the 2010 weather conditions as compared to the long-term average conditions for that park unit. *The 3°F cooler average temperature was taken from three lower elevation stations, whereas the 12°F cooler average was recorded at the summit of Mauna Loa.


The 2010 October through April wet season in Hawaii was the driest in 30 years. The northern area of Kohala on the Big Island was classified in the exceptional drought category; the first time any area in the state has been classified as such.

Most parks in the Pacific Island Network were substantially drier and somewhat cooler than normal with the exception of the National Park of American Samoa. American Memorial Park and War in the Pacific National Historical Park were also drier, but slightly warmer than normal.

Rainfall and temperature data for the islands in the PACN showed strong El Niño conditions until April 2010 with a transition to La Niña conditions as spring progressed.

In Hawaii, late wet season rain fell at nearly normal monthly rates and abated drought conditions in most areas. A record single-day rainfall total of 5.41 inches fell at the Honolulu International Airport on Sunday, December 19th, breaking the old record of 5.28 inches set in 1955. This one day event pushed the annual total much closer to normal conditions.

The number of tropical cyclones in the North Pacific Basin during 2010 was far fewer than has ever been recorded, making 2010 a very remarkable year.

 So don’t forget to look up all once in a while. The weather may surprise you.


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