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July 2013 Precipitation Summary
State of Hawaii
MONTH: July 2013
PREPARED: August 5, 2013
Note: This summary uses the arithmetic mean, or average, for “normal” rainfall values.
State: [Text data table for rain gages]
The main weather event during the month of July was the westward passage of tropical cyclone Flossie just to the north of the main Hawaiian Islands. Flossie moved into the state’s offshore waters as a weakening tropical storm early on July 29, then was declared a tropical depression at 5 PM HST that afternoon. Further weakening occurred overnight which resulted in Flossie being declared a post-tropical cyclone at 5 AM HST on July 30. Thunderstorms and heavy showers within a trailing rain band southeast of the low pressure center brought wet conditions to portions of the state. The highest rainfall totals did not occur on the Big Island as expected but on the island of Maui during a period of explosive thunderstorm development which produced totals of 1 to 2 inches with peak amounts greater than 5 inches over a time frame of a couple of hours. Flash flooding near Wailea and Kihei caused some property damage and road closures but no serious injuries. Lightning caused more problems than the flooding with several power outages on Maui and Molokai, property damage from a strike to a roof in Kahului, and a possible lightning-related injury in Haiku. Despite the presence of very tall thunderstorms over the Big Island, event rainfall totals were modest by tropical standards at mainly less than an inch with a peak total of nearly 3 inches. Event totals on Oahu and Kauai were similar to the Big Island’s.
A week before Flossie’s arrival, a low pressure trough near the surface moved across state in conjunction with an upper level low pressure system north of the island chain. The combination of these low pressure systems created an unstable airmass which produced thunderstorms and heavy showers over the Koolau Range on Oahu during the night of July 22. Rainfall totals of 1 to 3 inches produced minor flooding without any reports of significant damage.
Outside of these weather systems, trade winds dominated the weather scene with speeds mainly in the moderate to fresh range. Rainfall occurred daily, but totals were generally below average due to very stable conditions. If not for the passage of Flossie, July would have been a very dry month at many locations and possibly record-breaking at some.
Island of Kauai : [July 2013 map] [year-to-date map]
Most of the rainfall totals on Kauai were in the near to above normal range for the month of July. Several leeward sites had totals well above normal, mainly due to the Flossie’s trailing rain band in southerly to southeasterly low level winds. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the highest monthly total of 33.01 inches (85 percent of average) and the highest daily total of 5.88 inches on July 30 associated with the remnant of Flossie. The total from Waialeale marked its wettest July since 2005.
Rainfall totals for 2013 through the end of July were in the near average range at most of the gages on Kauai. Mount Waialeale’s 194.69 inches (86 percent of average) was the highest in the state.
Island of Oahu: [July 2013 map] [year-to-date map]
Most of the rain gages on Oahu recorded below average rainfall totals for the month of July despite the nearby passage of Flossie’s remnant circulation and deep tropical moisture. Many sites along the Koolaus had totals in the range of 40 to 70 percent of average. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total of 12.84 inches (70 percent of average). The highest daily total of 3.00 inches came from the USGS’ Moanalua gage in the upper Koolau slopes on July 22. Gages at Wheeler Army Airfield, Ahuimanu Loop, and at Manoa’s Lyon Arboretum posted their lowest July totals since 2006.
Rainfall totals for 2013 through the end of July were in the near normal range for most of the gages on Oahu. The Oahu Forest NWR gage had the highest year-to-date total of 137.29 inches (110 percent of average), which was third highest statewide.
Maui County: [Maui July 2013 map] [year-to-date map] [Molokai/Lanai July 2013 map] [year-to-date map]
Tropical cyclone Flossie provided a dry season boost in rainfall over many of the leeward gages in Maui County. While the actual totals were not very high, the percent of average values were extremely high in some cases because of the low July rainfall averages. The most notable examples were Kepuni at 1267 percent of average (4.18 inches observed, July average 0.33 inches) and Kula 1 at 450 percent of average (3.96 inches observed, July average 0.88 inches). Interestingly, the highest monthly total was 9.41 inches at the USGS’ Puu Kukui gage but this was only 28 percent of the average and marked the lowest July total at this location since 1987. Other significant totals included Waikapu Country Club’s 1.31 inches, making it the wettest July in 20 years of record, and Kaunakakai Mauka’s 0.74 inches, which was the highest July total since 2003.
Gages across Maui County have recorded rainfall totals in the near to below average range for 2013 through the end of July. Puu Kukui’s year-to-date total of 148.24 inches (66 percent of average) was the highest in the county and remained second highest in the state.
Island of Hawaii: [July 2013 map] [year-to-date map]
Most of the gages on the Big Island had below average rainfall totals for the month of July. Flossie’s rainfall helped push a few leeward totals into the above average range, not so much because of high observed amounts but due to low July averages. Windward gages had consistently low monthly totals with most at less than 50 percent of average. The highest monthly total was 10.46 inches (78 percent of average) from the USGS rain gage at Kawainui Stream. This site also had the highest daily total of 2.80 inches on July 29 as Flossie passed north of the Big Island.
Rainfall totals for 2013 through the end of July remained in the near to below average range across the Big Island. The rain gage at Kawainui Stream had the highest year-to-date total of 82.21 inches (90 percent of average) which was eighth highest statewide.
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