State of Hawaii
Seasonal Precipitation Summary

October marked the beginning of Hawaii’s rainy season. Despite several moderate rain events throughout the month of October, more than 75 percent of the state was under moderate drought or worse conditions. In mid-November, the north Pacific weather pattern shifted to more winter-like conditions. Heavy rains over east Molokai on the morning of November 18 produced flash flooding that forced the brief closure of the Kamehameha V Highway. As the system shifted eastward, heavy rainfall moved over to Maui where minor flooding occurred along the slopes of the West Maui Mountains and windward Haleakala. On November 21, a kona low, or subtropical cyclone, developed northwest of the state and produced about 1 to 4 inches of widespread rainfall over Kauai, Oahu, and Molokai. Fortunately, most of the rainfall occurred at light to moderate intensities over prolonged periods, which was able to soak into the ground and help bring meaningful drought relief. Despite the wet conditions in the west half of the state, the Big Island remained drier than normal overall through November and the area under severe drought spread eastward.

Like November, the month of December began with relatively stable conditions and little rainfall across the state. However, a significant shift in the weather pattern over the north Pacific resulted in wet conditions across most of the Hawaiian Islands from December 10 through the remainder of 2008. A series of strong kona lows and short wave troughs brought episodes of heavy showers and thunderstorms to the state, resulting in several instances of flooding across Kauai and Oahu. The first in a series of heavy rain events occurred over Kauai and Oahu on December 10 - 11. An intense area of rain moved into central and northeast Oahu with peak rain rates in excess of 4 inches per hour. According to the U.S. Geological Survey (USGS), several streams in central and windward Oahu set new peak flow records during the storm. Flooding produced severe damage to homes, infrastructure, and farm lands with losses easily running into the range of millions of dollars. A second round of serious flooding occurred December 12 – 13 over southwest Kauai. The shortwave trough also helped generate a severe thunderstorm with a rare tornado which moved over the Pakala area of south Kauai on December 13. The band of heavy rainfall shifted eastward and reached Oahu during the mid-afternoon hours, where two boys had to be rescued after being swept downstream in a flash flood near Waianae.

Additional individual rainfall station information and specific island information for Hawaii can be found in the Monthly Precipitation Summaries.

Hawaii Rainfall Summary for Select Stations, 4th Quarter 2008

Climate Outlook: The following is in excerpt from the Climate Prediction Center’s official Seasonal Outlook Discussion for Hawaii ...

“NCEP models predict above normal temperatures for Honolulu and Lihue for February 2009. Above normal precipitation is expected for Hawaii for February 2009. NCEP models predict a tendency for above normal temperature from March-April-May to June-July-August 2009 at Hilo - and from February-March- April to June-July-August 2009 at Kahului, Honolulu and Lihue. Models also predict above normal precipitation for Hawaii from February-March-April to May-June-July 2009.”