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September 2013 Precipitation Summary
State of Hawaii
MONTH: September 2013
PREPARED: October 3, 2013
Note: This summary uses the arithmetic mean, or average, for “normal” rainfall values.
State: [Text data table for rain gages]
Trade winds prevailed during most of the days in September with speeds mainly in the moderate range. Shower areas embedded within the trades brought almost daily rainfall to the windward slopes of the state though amounts were generally low. A couple of trade wind shower areas worth mentioning include the remnant of a cold front rain band that moved across the island chain on September 13 and a trade wind disturbance which affected the area on September 24 and 25. The September 13 frontal remnant produced 1 to 3 inches of rainfall along the windward slopes of Kauai and Oahu and less than an inch on the other islands. No significant flooding problems occurred as a result of this rain event. Rainfall totals were lower for the September 24 and 25 trade wind disturbance but it did produce minor flooding when brief heavy showers occurred over the Kona slopes of the Big Island during the afternoon of September 25.
September’s most significant rainfall event waited until the last day of the month to occur. The culprit in this case was an upper level low pressure system which moved into the area north of Kauai from the northeast. Unstable conditions helped generate heavy showers and a few thunderstorms over Kauai and Oahu from the morning of September 30 into October 1. Most of the rainfall occurred along the windward sections of both islands though leeward Oahu also received some heavy rain in the afternoon of September 30. Heavy rain on Kauai occurred in several pulses, some of which produced rates greater than 3 inches per hour. Hanalei River had 3 distinct rapid rises in water level which prompted flash flood warnings. However, the river remained within its banks and Kuhio Highway remained open for the duration of the event. The only other impacts were small landslides near Lumahai and Wainiha but Kuhio Highway remained open at both locations.
Island of Kauai : [September 2013 map] [year-to-date map]
A majority of the gages on Kauai recorded near to above average rainfall for the month of September. The few sites with below average totals came from the leeward areas. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 28.63 inches (95 percent of average) and the highest daily total of 6.51 inches on September 30. The Kapahi gage had it wettest September since 1996 and the Lihue Airport, Hanalei, and Wainiha gages had their wettest September since 2005.
Most of the rainfall totals for 2013 through the end of September were in the near average range. Mount Waialeale’s 240.97 inches (82 percent of average) was the highest year-to-date rainfall total statewide by a wide margin.
Island of Oahu: [September 2013 map] [year-to-date map]
Most of the rain gages on Oahu posted near to above average rainfall totals for September. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage recorded the highest monthly total of 12.99 inches (73 percent of average) while the USGS’ Poamoho No. 1 gage had the highest daily total of 6.84 inches on September 30. Honolulu Airport’s 1.33 inches (190 percent of average) marked the highest September rainfall total at this site since 1992. Two other sites, Waianae Kawiwi and Niu Valley, had their wettest September since 2005.
Rainfall totals for 2013 through the end of September remained in the near average range for most of the gages on Oahu. The Oahu Forest NWR gage had the highest year-to-date total of 166.90 inches (103 percent of average), which was third highest in the state.
Maui County: [Maui September 2013 map] [year-to-date map] [Molokai/Lanai September 2013 map] [year-to-date map]
Most of the gages across Maui County reported below average rainfall totals for the month of September. The USGS’ Puu Kukui gage had the highest monthly total of 11.12 inches (just 50 percent of average) and the highest daily total of 1.62 inches on September 17. On Molokai, the Kamalo rain gage recorded 1.95 inches (195 percent of average), which marked the wettest September since 2005.
Rain gages across Maui County had totals for 2013 through the end of September in the near to below average range. Puu Kukui had the highest year-to-date total of 180.36 inches (64 percent of average) which was the second highest in the state. The Kihei No. 2 rain gage has recorded less than 3 inches of rainfall so far this year.
Island of Hawaii: [September 2013 map] [year-to-date map]
Most of the gages on the Big Island recorded less than 50 percent of average rainfall for the month of September. The USGS’ Saddle Quarry gage had the highest monthly total of 7.01 inches (71 percent of average) and the highest daily total of 2.09 inches on September 8. Both the Kamuela and Kamuela Upper rain gages posted their lowest September totals within data records going back to 1991. Hilo Airport had a near normal daily rainfall frequency but the average rainfall per day was less than half of normal.
All of the Big Island gages had rainfall totals for 2013 through the end of September in the near to below average range. The USGS rain gage at Kawainui Stream had the highest year-to-date total of 101.23 inches (94 percent of average). This was the eighth highest year-to-date total in the state.
Data Sources: Data used in this report are largely from National Weather Service sources including climate network weather observation stations at Lihue, 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 Hawaii Department of Land and Natural Resources, the U.S. Geological Survey, the U.S. Bureau of Land Management, the U.S. National Park Service, the Department of Defense, the U.S. Fish and Wildlife Service, and the U.S. Department of Agriculture. Averages come from the National Climatic Data Center (1981-2010 series) and the Rainfall Atlas of Hawaii (http://rainfall.geography.hawaii.edu/). Data presented here are not certified and should be used for informational purposes only.
Kevin R. Kodama
Senior Service Hydrologist
NOAA/NWS Weather Forecast Office Honolulu