State of Hawaii

MONTH: September 2009

PREPARED: October 2, 2009

State: [Text data table for rain gages]

Trade winds dominated the weather pattern over and around the State of Hawaii during the month of September. On September 11, 14 through 15, and 20 through 23, low pressure systems in the North Pacific pushed the low level subtropical ridge closer to Hawaiian Islands. This resulted in light trade winds that allowed land and sea breezes to dominate local weather conditions. The rest of the days in the month had trades at mainly moderate to fresh levels with embedded showers primarily affecting windward slopes. Although windward areas experienced rainfall on most days, amounts were relatively light overall and there were no flooding problems reported statewide.

Island of Kauai : [September 2009 map] [Year-to-date map]

All of the rain gages across Kauai recorded near to below normal rainfall during the month. Leeward areas were particularly dry with several sites indicating totals at less than 50 percent of normal. The U.S. Geological Survey’s (USGS) gage on the summit of Mount Waialeale recorded 20.85 inches (74 percent of normal) which was the highest monthly total statewide. The highest daily total, also recorded by the Mount Waialeale gage, was 3.36 inches on September 6. A closer look at the data from Lihue Airport showed that the daily rainfall frequency was near normal (15 days observed versus a normal of 16 days) but the amount per day was below normal (2 days with at least 0.10 inches versus a normal of 6 days).

Most of the gages on Kauai have recorded below normal rainfall for 2009 through the end of September. Mount Waialeale’s 223.15 inches (71 percent of normal) leads all statewide totals by a wide margin.

Island of Oahu: [September 2009 map] [Year-to-date map]

Most of the rain gages on Oahu recorded less than 50 percent of normal rainfall during the month of September. At several windward locations such Punaluu Pump, Luluku, and Ahuimanu Loop, it was the driest September since 2002. The highest monthly total, 11.27 inches, was recorded by the U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage. This gage also posted the highest daily total of the month, 2.11 inches on September 25.

Most of the gage totals on Oahu were in the below normal range for 2009 through the end of September. The exceptions were from the windward Koolau area from Hakipuu to Waimanalo which continued to show near to above normal totals despite the dryness during the past month. The Oahu Forest NWR total of 138.83 inches (91 percent of normal) was the highest on the island and ranked fourth statewide.

Maui County: [Maui September 2009 map] [Year-to-date map] [Molokai/Lanai September 2009 map] [Year-to-date map]

Data from across Maui County exhibited the more familiar wide range of conditions from no measurable rain at Kihei, Waikapu, and Lahainaluna to 123 percent of normal at West Wailuaiki, and 300 percent of normal at Kaunakakai. The USGS gage at Puu Kukui posted the highest monthly total of 14.75 inches (64 percent of normal). The highest daily total of 2.06 inches came from the USGS’ West Wailuaiki gage on September 6. At Kula Branch Station, the monthly total of 0.07 inches marked the driest September at this location since 1979.

Most of the Maui County gages have recorded below normal rain totals for 2009 through the end of September. The West Wailuaiki gage has the highest county-wide total of 157.65 inches (105 percent of normal) among all available gages. Most of the remaining gage totals were in the 50 to 80 percent of normal range.

Island of Hawaii: [September 2009 map] [Year-to-date map]

Several windward Big Island gages reported near to above normal rainfall for September, including the Mountain View gage which had the highest monthly total of 12.46 inches (116 percent of normal). The persistent trades helped bring in a higher than normal frequency of rain days during the month with Hilo Airport logging 28 days at 0.01 inches or greater rainfall versus a normal of 23 days. However, the observed average daily rain of 0.23 inches was below the normal average of 0.30 inches. In contrast, leeward gages mostly recorded well below normal amounts. At Kapapala Ranch in Kau, the 0.45 inches recorded during the month marked the driest September since 1976.

Most of the windward Big Island gages have recorded near to above normal totals for 2009 through the end of September. Leeward gages remained mostly in the range of 40 to 70 percent of normal. Glenwood’s 118.52 inches (99 percent of normal) led all Big Island totals and remained at fifth highest statewide.

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