State of Hawaii

MONTH: September 2008

PREPARED: October 2, 2008

State: [Text data table for rain gages]

Trade winds persisted through most of September with speeds generally in the light to moderate range across the main Hawaiian Islands. The weakness in trade wind speeds enabled land and sea breezes to dominate local wind patterns on many days. An upper level low pressure system near Kauai helped destabilize the local airmass to help support brief heavy afternoon showers over portions of Kauai as well as central and west Oahu from September 11 through September 14. A second, more persistent upper level low settled in near Kauai from September 21 through 25 but was able to trigger heavy showers only during the late afternoon hours of September 21 over the Kona slopes. No significant damages were reported from any of these rain events.

On September 30, a weak cold front swept across the state and deposited around 0.25 to 0.50 inches of rain in several areas and as much as 1 to 2 inches over some of the upper slopes. This frontal passage was noteworthy in that it was unusually early. Normally, the first frontal passage of the wet season across Hawaii occurs during the latter half of October.

Organized tropical weather systems did not play a significant role in shaping September rainfall across the island chain. In fact, east Pacific tropical cyclone activity turned out to be rather subdued which did not even allow for tropical system remnants to provide enhanced shower activity in any area of the state.

Rather than flooding, drought conditions continue to define hydrology-related issues across the State of Hawaii. Every county has at least one location with some level of voluntary or mandatory water use conservation measure in place. Effects of the drought so far have been greatest on the agriculture sector, especially in the cattle industry where some ranchers have reported stocking rates reduced by at least 50 percent, very poor pasture conditions, and even livestock deaths. Reservoir supplies remain extremely low in east Oahu and west Molokai and mandatory restrictions of 30 and 20 percent continue for users of irrigation water from Waimanalo and Kualapuu Reservoirs, respectively. The ongoing drought prompted the U.S. Department of Agriculture to declare the State of Hawaii a primary disaster area on August 1 for agriculture interests.

Island of Kauai : [September 2008 map] [Year-to-date map]

Rain totals from the Kauai gages provided mixed signals for the month of September. Many of the gages such as Hanalei, Lihue Airport, and Port Allen reported below normal totals. However, interspersed among those sites are gages indicating above normal totals such as Hanapepe (159 percent of normal), Kapahi (129 percent of normal), and Lihue Variety Station (115 percent of normal). The U.S. Geological Survey’s Mount Waialeale gage reported the highest monthly total statewide (20.18 inches) but this amount was somewhat below the September normal. This site also recorded the highest daily total on the island with 2.92 inches on September 11 associated with showers enhanced by an upper level low.

Rain totals for 2008 through the end of September remained below normal at most locations on Kauai. The Mount Waialeale gage recorded 236.70 inches (76 percent of normal) so far this year and continued to lead all totals statewide. The Kalaheo and Port Allen gages had the totals closest to normal at 80 and 88 percent of normal, respectively.

Island of Oahu: [September 2008 map] [Year-to-date map]

Most windward Oahu gages reported near to above normal rainfall for September, but leeward sites mainly reported below normal totals. Kalaeloa Airport provided one of the leeward area exceptions with 352 percent of normal rainfall off of a 1.76 inch total. Of this total, 1.59 inches occurred in 2 days, September 11 and 14. In fact, the 0.78 inches recorded between 3 PM and 5 PM HST on September 14 exceeded the September normal value of 0.50 inches. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage recorded the highest monthly total on the island at 12.33 inches (83 percent of normal) which was second highest in the state. The Nuuanu gage recorded the highest daily total of 2.14 inches on September 12. A University of Hawaii Dept. of Meteorology faculty member reported 1.57 inches in about an hour on September 14 deep in Palolo Valley.

Rain totals for 2008 through the end of September remained below normal at most locations on the island of Oahu. The only exception was the USGS gage at the South Fork Kaukonahua Stream site which has recorded 90 percent of normal rain so far this year. The Oahu Forest NWR total of 99.08 inches (65 percent of normal) stayed at sixth highest statewide.

Maui County: [Maui September 2008 map] [Year-to-date map] [Molokai/Lanai September 2008 map] [Year-to-date map]

Most locations across Maui County recorded below normal rain totals for the month of September. A few locations recorded above normal amounts, including Molokai Airport which saw 284 percent of normal rainfall from a monthly total of 1.99 inches. The West Wailuaiki gage recorded the highest county total of 7.02 inches (59 percent of normal). The USGS’ Puu Kukui gage usually records the highest Maui County total but this site’s September total came in second highest at 6.71 inches (29 percent of normal). The Puu Kukui gage has not seen normal rainfall since the end of February, though it did manage to record the highest daily total of 1.19 inches on September 23.

Most of the Maui County rain totals for 2008 through the end of September remained in the below normal range. The Puu Kukui gage’s 150.54 inches (52 percent of normal) maintained its position as the second wettest spot in the state so far for 2008.

Island of Hawaii: [September 2008 map] [Year-to-date map]

Once again, all of the Big Island gages recorded below normal monthly rain totals with most amounts in the range of 30 to 60 percent of normal. The Pahoa gage posted the highest monthly total of 5.04 inches (55 percent of normal) while the Honaunau gage recorded the highest daily total of 1.81 inches on September 30. The windward side of the Big Island continued to see a near normal frequency of rain days but the amount of rain occurring per day was well below normal. For example, the Hilo Airport gage normally reports 5 days with at least 0.50 inches of rain but September 2008 included only one such day, 0.55 inches on the 20th. Hilo Airport’s 4.27 inches (47 percent of normal) also marked the lowest September total since 1995.

Most of the Hilo and Puna totals for 2008 through the end of September remained in the near normal range but the ongoing dryness has pushed some sites into the below normal range. Waiakea Uka’s 104.63 inches (78 percent of normal) led all Big Island totals and ranked fourth 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