State of Hawaii

MONTH: July 2009

PREPARED: August 5, 2009

State: [Text data table for rain gages]

Trade winds persisted through most of July at moderate to fresh levels. A break in the trade wind pattern occurred from July 22 through 23 as a surface trough moved westward across the state. Very moist low level conditions coupled with a subtropical jet stream in the upper levels over the island chain helped produce heavy rainfall over the Big Island and Maui on July 22 and over Kauai on July 23. The July 22 rainfall (1 to 4 inches) produced minor flooding over the windward slopes of Haleakala and the West Maui Mountains on the island of Maui. On July 23, heavy rainfall with totals of 3 to 6 inches occurred over the northeast half of Kauai. Hanalei River overflowed its banks twice forcing the closure of Kuhio Highway near the Hanalei Bridge for several hours both times.

Meanwhile, consistent trades meant that conditions remained dry over leeward areas of the state. The Maui County Board of Water Supply continued its request for a 5 percent and 10 percent cut-back in water use for Upcountry and Central Maui residents, respectively. Dry conditions in the leeward areas of the Big Island have also been adversely impacting livestock operations.

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

Rain gages in the northeast half of Kauai recorded near to above normal rainfall totals for the month of July. Gages in the southwest half posted below normal totals, mainly in the range of 40 to 70 percent of normal. The U.S. Geological Survey (USGS) gage on the summit of Mount Waialeale logged 29.07 inches of rain (88 percent of normal), the highest July total statewide. Thunderstorms on July 23 produced very heavy rainfall over portions of north and east Kauai. Over north Kauai, the USGS gage at the Hanalei River recorded 2.77 inches during the 3-hour period from 7 AM to 10 AM. In east Kauai, the gage at Kapahi registered 1.00 inches in 15-minutes (12:15 PM to 12:30 PM) and 2.66 inches during the 3-hour period from 11 AM to 2 PM.

Despite the heavy rains, most of the gages on Kauai continued to show below normal totals for 2009 through the end of July. A majority of the year-to-date totals were in the range of 40 to 70 percent of normal. Mount Waialeale’s year-to-date total of 165.47 inches (67 percent of normal) was the highest statewide amount by a wide margin.

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

Many of the rain gages in the central Koolau slopes and from Kaneohe to Waimanalo recorded near to above normal rainfall during the month of July. Most of the remaining gages posted below normal totals. Gages at Kalaeloa and Waianae Boat Harbor did not record any measurable rainfall. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage recorded the highest monthly total of 18.06 inches (120 percent of normal) while the gage at the St. Stephens Seminary posted the highest daily total of 4.74 inches on July 23.

Most of the Oahu rain gage totals remained in the below normal range for 2009 through the end of July. Some of the locations in windward Oahu, such as Waimanalo and Maunawili, have received near to above normal rainfall. The Oahu Forest NWR total of 106.65 inches (88 percent of normal) was the highest on the island and ranked fourth in the state.

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

Rain gages along the windward slopes of Haleakala and the West Maui Mountains recorded near to above normal rainfall during the month of July. However, totals from the leeward areas indicated a continuation of very dry conditions including no measurable rainfall at Kihei and Waikapu. The USGS gage at Puu Kukui recorded the highest monthly total of 23.58 inches (70 percent of normal) while the highest daily total came from the West Wailuaiki gage where 4.36 inches of rain fell on July 22.

Most of the Maui County gages continued to show below normal rain totals for 2009 through the end of July. The USGS’ West Wailuaiki gage maintained its county-wide lead with 124.61 inches (105 percent of normal) recorded in 2009. Puu Kukui, normally the second wettest spot in the state, has received only52 percent of normal rainfall so far this year and ranked third statewide.

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

Most of the windward Big Island gages recorded near to above normal rainfall during the month of July. Afternoon thunderstorm activity on July 22 helped bring needed rainfall over some of the leeward and interior areas and pushed some of the monthly totals into above normal levels. Examples of these sites include Pali 2 (508 percent of normal) and Pohakuloa Kipuka Alala (191 percent of normal). At the Pohakuloa Kipuka Alala site, the 1.06 inches recorded on July 22 accounted for more than half of the 1.91 inches for the month.

Windward Big Island gages have recorded near to above normal totals for 2009 through the end of July. Most of the leeward gage totals remained within the range of 40 to 70 percent of normal. The Glenwood gage’s 102.02 inches (103 percent of normal) passed the Piihonua gage for the highest rainfall total so far this year and ranked fifth 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