MONTHLY PRECIPITATION SUMMARY

State of Hawaii

MONTH: January 2011

PREPARED: February 4, 2011

State: [Text data table for rain gages]

A high amplitude weather pattern that dominated the north Pacific during December 2010 continued into January 2011. This pattern pushed four cold fronts into the island chain during the period from January 6 through 16. The January 6 front was rather weak and deposited less than an inch of rain in most areas with isolated totals in the 1 to 2 inch range. The following week brought a much more active weather pattern and much higher rainfall totals. On January 10, a cold front swept across Kauai and Oahu bringing a brief period of heavy rains. The relatively quick forward movement of the frontal rain band limited rainfall totals to less than one inch on both islands. However, the rain band slowed near Maui and briefly became more active which resulted in higher rainfall accumulations over south Maui from Maalaea to Kihei. Rock and mud slides closed Honoapiilani Highway near Maalaea during the early evening hours of January 10. Overflowing culverts also deposited mud and debris onto properties along Hauoli St. to the northeast of Maalaea Harbor.

After the January 10 cold front, a stronger front reached Kauai on January 12, depositing 2 to 4 inches of rain before moving on to Oahu. The frontal rain band became more active just west of Oahu in the late afternoon hours of January 12 and proceeded to move slowly southeastward across the island as a nearly continuous line of heavy rainfall. Flash flooding occurred in several locations in the Waianae area and within Kaukonahua Stream near Waialua. Emergency managers reported several water rescues from the flooding in Waianae. Several gage totals over west and central Oahu were within the 6 to 11 inch range over 24-hours. The maximum total of 10.68 inches in 24-hours occurred at the Palehua gage on the south-facing slope of the Waianae Mountains. The most noteworthy values from the Palehua data were the maximum short-duration totals of 7.63 inches in 6 hours, 6.23 inches in 3 hours, and 3.65 inches in 1 hour. All of these short-duration totals exceeded the 1-percent annual probability level for the Palehua gage site. After reaching central Oahu, the frontal rain band accelerated which resulted in lower rainfall accumulations over east Oahu. The front moved across Molokai during the early morning hours of January 13 with heavy rainfall causing a rock and mud slide on the Kamehameha V Highway near Kawela. Shortly afterward, a saturated Maui had its turn with heavy rains forcing the closure of Honoapiilani Highway west of Maalaea for the second time in a week. South Kihei Road was also closed again due to flooding problems. The cold front weakened quickly as it crossed Maui County and never reached the Big Island.

The last cold front during this active weather pattern reached Kauai on January 16. Rainfall totals ranged from 1 to 4 inches and flash flooding over northwest Kauai briefly closed Kuhio Highway near Haena. Shower activity associated with the front weakened considerably after passing Kauai and dropped less than 1 inch of rain on Oahu and less than half an inch on Maui County. The front dissipated before reaching the Big Island. On January 18 and 19, a cold upper level low pressure system brought unstable conditions to the Big Island and Maui but heavy rainfall did not materialize. This weather system did, however, produce snow down to the 8000 ft level allowing Haleakala to receive a relatively rare coat of white over its upper elevations.

More stable conditions settled in over the state and trade winds resumed for the first time in more than 2 weeks on January 20. A weak front dissipated near Kauai on January 26 and did not produce significant rainfall. The last cold front of the month reached Kauai on January 30 and moved quickly down the island chain. Heavy rainfall briefly occurred along the leading edge of the cold front rain band but its rapid movement prevented notable accumulations and did not result in any significant flooding problems.

The heavy rainfall in January did not appreciably affect the Big Island and severe to extreme drought persisted for another month over the leeward and interior sections of the island. For more information on the drought, please refer to the latest Drought Information Statement at: http://www.weather.gov/data/HFO/DGTHFO

Island of Kauai : [January 2011 map]

Most of the rain gages on Kauai recorded near to below normal rainfall for the month of January. The U.S. Geological Survey’s (USGS) Mount Waialeale gage recorded the island’s highest monthly total of 14.37 inches (38 percent of normal) and the highest daily total of 4.17 inches from the cold front passage on January 12. The high amount of cold front activity during the month resulted in the occurrence of the highest rain totals over the northwest quadrant of the island.

Island of Oahu: [January 2011 map]

Rain gages over the western half of Oahu received near to above normal rainfall totals for the month of January. Most of the rainfall at these sites occurred during the January 12 cold front passage. In contrast, most of the gages in the east half of Oahu registered near to below normal monthly totals. The Schofield South gage recorded the highest monthly total of 13.49 inches (180 percent of normal). More than two-thirds of this total fell on the night of January 12. The Palehua gage had the highest daily total, also during the January 12 heavy rain event. Refer to the “State” section above for more details.

Maui County: [Maui January 2011 map] [Molokai/Lanai January 2011 map]

Most of the gages in Maui County recorded near to above normal rainfall totals for the month of January. The USGS’ Puu Kukui gage posted the state’s highest monthly total of 16.58 inches but this was only 55 percent of normal for this site. In recent years, the Puu Kukui monthly totals have often been below the previously established normal values. Updated normal values will be published later this year and will likely reflect a significant decrease in what defines “normal” rainfall.

Island of Hawaii: [January 2011 map]

The significant weather systems affecting the state during January mostly dissipated prior to reaching the Big Island. As a result, all of the gages across the island posted below normal rainfall for the month of January with most of the totals at less than 50 percent of normal. The highest monthly total was 8.76 inches (74 percent of normal) from the USGS’ Kawainui Stream site.

Data Sources: Data used in this report are largely from National Weather Service sources including climate network weather observation stations at Lïhue, Honolulu, Kahului, and Hilo, the Hydronet state network of automated rain gages, and selected Cooperative Observer sites. Additional data come from automated rain gages operated by the State of Hawai‘i Department of Land and Natural Resources, the US Geological Survey, the US Bureau of Land Management, the US National Park Service, the Department of Defense, and the US Fish and Wildlife Service. Data presented here are not certified and should be used for information purposes only.

Kevin R. Kodama
Senior Service Hydrologist
NOAA/NWS Weather Forecast Office Honolulu