State of Hawaii

MONTH: September 2007

PREPARED: October 3, 2007

State: [Text data table for rain gages]

Trades continued unabated throughout most of September bringing frequent showers to windward slopes of the state. The strength of the trades generally registered at moderate levels during the first half of the month then increased to fresh to strong levels as stronger than normal areas of high pressure moved into the region far north of the Hawaiian Islands. A low level remnant of former Tropical Depression 13-E provided the sole disruption in the trade winds as it passed just to the north of the main Hawaiian Islands on September 28 and 29. Most of the remnant’s associated rainfall passed north of the island chain but residents and visitors did not miss out on the increased humidity and the veering of low level winds to a southeasterly direction.

An area of deep tropical moisture, drawn northward by a middle and upper level trough northwest of the state, brought enhanced shower activity to the windward slopes on September 14 and 15. The 1 to 3 inches of rain over the windward Koolau Range on Oahu produced some minor flooding but no significant damage.

The boost in trade wind rainfall helped improve water supply conditions over portions of the state, especially in the Upcountry Maui area which depends on water sent from the windward slopes of Haleakala through a series of ditches. Residents and farmers in Upcountry Maui have been under a mandatory 10 percent cutback in water use since June 13. Drought conditions also continued over east Oahu where a mandatory 30 percent reduction in water use has been in place since September 6 for farms utilizing the Waimanalo Irrigation System.

Island of Kauai : [September 2007 map] [Year-to-date map]

Most of the rain gages on Kauai recorded near to above normal rainfall during September. The highest available total of 9.87 inches (143 percent of normal) came from the Hanalei River gage. Mount Waialeale probably had a higher September total but a problem with the automated gage resulted in the unavailability of data from this site. Very difficult access to the Waialeale gage may mean that the data will be unavailable for several months.

Lihue Airport’s 0.44 inches (16 percent of normal) was not the lowest total on the Garden Island, but it did set a new record for the driest September at that location. The previous record was 0.45 inches set in 1975. Two other points are worth mentioning; this is the second consecutive month where the all-time monthly record was broken and about 3 miles away, the Lihue Variety Station gage recorded 3.89 inches (88 percent of normal).

Most of the gage totals for 2007 through the end of September remain in the below normal range. Kapahi and Wailua are the wettest of the available locations at 45.53 and 46.07 inches, respectively.

Island of Oahu: [September 2007 map] [Year-to-date map]

Many of the gages situated on the slopes of the Koolau Range recorded near to above normal totals for September. The upslope gages had the highest amounts with Poamoho 2 leading all totals island wide at 13.88 inches. The Oahu Forest National Wildlife Refuge (NWR), Manoa Lyon, and Nuuanu Upper gages also posted totals greater than 10 inches. As for daily rainfall, the Oahu Forest NWR gage recorded the highest total of 3.13 inches on September 15 as a shower area from the deep tropics moved across the state. Measurable rainfall occurred on most days, especially in the interior slopes of the Koolaus. A National Weather Service forecaster observed measurable rain at his residence in upper Palolo Valley on 28 of 30 days and the Manoa Lyon and Nuuanu gages recorded rain on 27 of 30 days. While many of the Koolau gages reported ample rain, several of the lower elevation Koolau sites, especially those on the east end of the island, indicated a continuation of well below normal rainfall. These sites include the Kaneohe Marine Corps Base (10 percent of normal), Kamehame (17 percent of normal), and Hawaii Kai Golf Course (17 percent of normal). Many West Oahu residents saw very dry conditions with most locations recording less than 25 percent of normal September rainfall.

Most of the gage totals across Oahu continue to fall in the below normal range for 2007 through the end of September. The Oahu Forest NWR total of 124.09 inches (82 percent of normal) leads all totals island-wide but slips from second to fourth in the state behind Mount Waialeale, Puu Kukui, and West Wailuaiki.

Maui County: [Maui September 2007 map] [Year-to-date map] [Molokai/Lanai September 2007 map] [Year-to-date map]

Maui County saw its usual wide range of rainfall conditions, from 0 ( Lanai 1 and Kihei) to 235 (Mahinahina) percent of normal. Rainfall at Puu Kukui measured 30.83 inches (133 percent of normal), the highest county-wide and the first time since May 2006 that its total exceeded 30 inches and reached the near to above normal range. Puu Kukui also recorded the highest daily total of 5.94 inches on September 18. The frequent trade showers pushed the West Wailuaiki total of 20.58 inches to a well above normal level and helped bring much needed water to Upcountry Maui reservoirs. In contrast, central Maui gages indicated continued very dry conditions with Kahului Airport and Waikapu Country Club showing less than 10 percent of normal rainfall. Most of Molokai and Lanai had below normal rainfall, the exception being Makapulapai on the Kalaupapa Peninsula which recorded 115 percent of normal rainfall as a result of exposure to frequent trade wind showers.

Most of the gages in Maui County have totals in the below normal range for 2007 through the end of September. Only West Wailuaiki and Oheo Gulch have totals in the near to above normal range. Puu Kukui’s 140.86 inches leads all Maui County totals and is second highest statewide but registers only at 49 percent of normal for the year-to-date.

Island of Hawaii: [September 2007 map] [Year-to-date map]

Frequent trade showers helped push most of the windward Big Island totals into the near to above normal range for September. The Glenwood total of 13.40 inches topped all other totals island-wide, though it was the Piihonua gage in upper Hilo that recorded the highest daily total, 2.19 inches on September 19. Totals from the Kau, North and South Kona, and leeward North and South Kohala Districts fell into the near to below normal range. The Kealakekua gage recorded 7.74 inches, most of which occurred during 3 afternoons, September 1, 10, and 22, with about 2 inches each day.

Despite the increase in trade wind showers, rain totals at most locations remain at below normal levels for 2007 through the end of September. The exceptions are Keahole Airport and Glenwood at 97 and 95 percent of normal, respectively. Most of the remaining totals are in the range of 30 to 70 percent of normal. Glenwood’s 114.18 inches for the year-to-date leads all Big Island totals and is fifth highest in the state.

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