State of Hawaii

MONTH: March 2012

PREPARED: April 5, 2012

State: [Text data table for rain gages]

An unsettled atmospheric pattern over the central North Pacific intensified in early March and produced damaging severe weather and significant flooding across several islands that will be remembered for quite some time. There were two weather systems which affected the state from March 2 through 9. The first involved an upper level trough coupled with a slow moving cold front that mainly affected Kauai and Oahu. Heavy rainfall initiated on the evening of March 2 along the windward and upper slopes of the Koolau Mountains of Oahu caused by island-scale effects in southeasterly low level winds. Rainfall totals of 7 to 11 inches over the upper Koolaus produced elevated stream levels but no reports of damage. The focus of significant weather shifted to Kauai on the afternoon of March 3 as the initial pulses of heavy rain began to impact the eastern two-thirds of the island. At 4 PM HST the Hanalei gage registered the start of what would be 76 hours of continuous rainfall at this site, followed a few hours later by the closing of Kuhio Highway at the Hanalei Bridge as Hanalei River overflowed its banks. Multiple spikes in Hanalei River’s flow kept the highway inundated and isolated the town of Hanalei for almost 3 days. Flash flooding also caused numerous road closures in other areas of Kauai including Kapaa, Haena, Kalihiwai, Wailua, and Koloa. With flooding ongoing over Kauai, heavy rainfall hit Oahu again during the early morning hours of March 5, this time over the east half of the island. In Honolulu, water levels in Manoa Stream rose 6 feet in an hour and covered a nearby property with about a foot of water. On the windward side, Kamehameha Highway was shut down in both directions as Waikane Stream overflowed its banks. One of the thunderstorms that moved over east Oahu in the mid-morning briefly dropped hail stones with a maximum size of 1.5 inches. Conditions finally stabilized on March 6 allowing recovery efforts to begin. Kauai’s rainfall totals from 8 AM HST on March 3 to 2 PM HST on March 6 ranged from 10 to 25 inches over the east-facing slopes to over 35 inches on the north-facing slopes. Oahu totals ran from 5 to more than 15 inches on the eastern half of the island over the same time frame.

The atmosphere did not provide much time for recovery. In the early morning hours of March 8, an approaching upper level low pressure system began to destabilize the airmass again over the island chain. Thunderstorms developed north of Maui County along the remnant of the above-mentioned cold front and produced heavy rainfall over the windward slopes of Haleakala and the eastern half of Molokai. The east Molokai rainfall was particularly intense and produced flash flooding which closed Kamehameha V Highway at four locations and Maunaloa Highway at Kaunakakai Gulch for several hours. Later that day, a strong afternoon thunderstorm near Kamuela on the Big Island produced minor flooding and dropped 1-inch diameter hail. The weather event peaked in the early morning hours of March 9 when strong thunderstorms fired up on the windward slopes of Maui, Molokai, Oahu, and Kauai. A severe thunderstorm over east Maui produced 1.75-inch hail, damaging winds and intense rainfall over the lower slopes from Nahiku to Hana. A recording gage at Honomaele measured 12.6 inches of rain in 6-hours from 10:45 PM HST March 8 to 4:45 AM HST March 9, which included 6.3 inches in a one-hour period from 12:45 AM to 1:45 AM, and 2 inches in the 15-minute period from 1:00 AM to 1:15 AM. This is believed to be the highest officially measured one-hour rainfall total since the December 14, 1991 Anahola, Kauai flash flood (maximum one-hour rainfall of 6.7 inches). Flash flooding closed several roads in the area, including Hana Highway, for several hours.

On Kauai, heavy rainfall flared up a little before midnight on March 9 near Hanalei then evolved into a large area encompassing the northeast half of the island. Coming so soon after nearly 3 feet of rain, runoff occurred hard and fast resulting in a rise of Hanalei River’s water level by 6 feet within 90 minutes. Kuhio Highway was once again closed at the Hanalei Bridge and would remain closed all day. Flash flooding closed several roads in Kilauea, Kalihiwai, and Wailua, and damaged Kapahi Bridge in Kapaa. Dime-size hail was also reported to have broken a window in Kapaa.

Windward Oahu received moving bands of moderate to heavy rainfall late on March 8 and into the early hours of March 9. However, heavy showers and thunderstorms that developed from about 3:00 AM HST remained nearly stationary and eventually spread to encompass the area from Punaluu to Kailua. The peak rain rate recorded was at Waihee Pump where 2.48 inches fell between 5:00 AM and 5:30 AM. By 6:00 AM, the stationary area had evolved into two separate thunderstorm cells, one covering the area from Kahuku to Kahana and a stronger one over the Kailua and Kaneohe Marine Base areas. Flash flooding once again shut down Kamehameha Highway at Waikane Stream, several homes were damaged along or near Kaneohe Bay Drive, and properties and roads in Laie were covered by several feet of water. The thunderstorm over Kailua reached severe criteria with many reports of hail larger than one inch. The largest hail stone was 4.5 inches which easily set a new state record for size. Following the hail, a waterspout moved onshore in Lanikai then moved into the Enchanted Lakes area as an EF-0 tornado, causing property damage but fortunately no serious injuries. In addition to the new state record for hail size, the occurrence of significant hail on three islands within a 6-hour period is quite remarkable.

Following the exit of the upper level low to the west, the rest of March mainly consisted of trade winds in the fresh to strong range. Periods of trade wind showers mostly affected the windward slopes with no significant flooding problems.

Island of Kauai : [March 2012 map] [Year-to-date map]

Most of the rain gages on Kauai had above normal rainfall totals for the month of March. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the state’s highest monthly total of 64.11 inches (169 percent of normal), which also made it the wettest March since 2006 for this site. Wainiha’s 55.35 inches (424 percent of normal) and Hanalei’s 52.66 inches (603 percent of normal) set new monthly rainfall records by a wide margin. Wainiha’s previous record was 39.39 inches in March 1982 while Hanalei’s previous record was 28.82 inches in March 2006. The 4-day (March 3 through 6) total of 36.96 inches at Wainiha is more than many sites receive in a year.

All of the gages across Kauai had near to above normal rainfall totals for 2012 through the end of March. Mount Waialeale’s 128.77 inches (148 percent of normal) led all other year-to-date totals in the state by a very wide margin.

Island of Oahu: [March 2012 map] [Year-to-date map]

All of the gages on Oahu had near to above normal rainfall for the month. At many locations it was the wettest March since the so-called “40 days of rain” in 2006. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total of 48.49 inches (258 percent of normal) while the USGS’ Moanalua rain gage had the highest daily total of 11.22 inches on March 2.

Most of the Oahu gages on the slopes of the Koolau Range had near to above normal rainfall totals for 2012 through the end of March. Most of the west Oahu gages have had near to below normal rainfall. The Oahu Forest NWR gage had the highest year-to-date total of 62.57 inches (120 percent of normal) which ranked fifth highest statewide.

Maui County: [Maui March 2012 map] [Year-to-date map] [Molokai/Lanai March 2012 map] [Year-to-date map]

Most of the gages in Maui County had near to above normal monthly rainfall totals. With a total of 42.96 inches (112 percent of normal), the USGS gage on Puu Kukui had its wettest March since 2004. On Molokai, the Makapulapai gage on the Kalaupapa Peninsula recorded 6.18 inches (122 percent of normal) which was the highest monthly total since December 2007.

Despite the increase in rainfall, all of the gages in Maui County continued to have below normal totals for 2012 through the end of March. Puu Kukui had the highest year-to-date total of 61.88 inches (65 percent of normal), which was sixth highest in the state.

Island of Hawaii: [March 2012 map] [Year-to-date map]

Once again, storm systems have managed to avoid dropping rainfall along the south and west portions of the Big Island leaving March totals below 50 percent of normal at many locations. Windward gages continued to have near to above normal totals. The Glenwood gage picked up the most rainfall during the month with 20.54 inches (82 percent of normal). The USGS’ gage at Kawainui Stream had the highest daily total of 3.77 inches on March 7.

Most of the windward Big Island gages had near normal totals for 2012 through the end of March. However, most of the leeward gages continued to increase rainfall deficits with most year-to-date totals well below 50 percent of normal. The Glenwood gage had the highest year-to-date total with 43.26 inches (72 percent of normal).

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