State of Hawaii

MONTH: February 2009

PREPARED: March 3, 2009

State: [Text data table for rain gages]

Trade winds were unusually persistent during February with the only breaks occurring on February 7 and from February 10 through 12. The month started with a weak shear line pushing across the island chain on February 1 and 2 before stalling just east of the Big Island. Remnant showers then returned back to the state in the trades on February 3. This shear line produced the most significant rainfall of the month including 4 to 7 inch totals over the windward slopes of Maui and the Big Island. A stream mouth clogged by sand and rocks created a backwater effect and some minor flooding in Waipio Valley on February 3.

On February 7, a brief break in the trades allowed local land and sea breezes to occur with deep convection forming over west Oahu and the Big Island interior. Short-lived heavy showers produced minor flooding and even quarter-inch hail. Moderate trades returned on February 8 and 9 only to weaken once again as a strong upper level trough induced a low-level surface trough that affected island weather from February 10 to 12. Heavy afternoon showers and thunderstorms occurred on all 3 days with the Kapolei area of Oahu and the South Kohala District of the Big Island seeing the strongest activity. The Kapolei thunderstorm produced brief but intense rainfall that prompted a flash flood warning but did not produce significant damage. However, this thunderstorm did produce a tornado which caused property damage and some injuries.

From February 13 through the end of the month, a rather strong and unusually persistent blocking high pressure pattern became established over the north central Pacific resulting in uninterrupted moderate to fresh trade winds with speeds occasionally pushing up into the fresh to strong range. These trade winds brought in cooler, drier air from the northeast with rainfall generally limited to daily totals of less than 1 inch primarily along windward slopes. A weak shear line moved over the state on February 18 and 19 causing a brief enhancement in trade wind showers to the tune of 1 to 2 inches in 24-hours.

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

Most of the rain gages on Kauai recorded below normal totals for the month of February. The Kapahi gage recorded the sole monthly total greater than normal (7.90 inches, 116 percent of normal). This site also recorded Kauai’s highest daily total of 3.21 inches on February 12 during heavy afternoon showers. The U.S. Geological Survey (USGS) gage on Mount Waialeale posted the highest monthly total on Kauai (23.92 inches, 69 percent of normal) but was tied with the West Wailuaiki gage on Maui for the highest total statewide. This is rather unusual since the Mount Waialeale monthly total normally far exceeds any other total in the island chain. The persistence of trade winds coupled with the drier, stable airmass resulted in below normal rainfall at all leeward gages with totals less than 50 percent of normal.

Most of the gages across Kauai have recorded below normal rainfall totals for 2009 through the end of February. The Mount Waialeale total of 46.31 inches (64 percent of normal) leads all year-to-date totals statewide. Most of the remaining sites have totals in the range of 30 to 60 percent of normal.

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

Most of the gages on Oahu recorded below normal rain totals for the month of February and several totals were below 10 percent of normal. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage recorded the highest monthly total of 18.88 inches (116 percent of normal) while the highest daily total of 5.90 inches came from the USGS’ Poamoho No. 2 gage on February 12. The lowest rainfall totals, all less than 0.10 inches for the entire month, came from gages clustered around the leeward coast from Waianae to Kalaeloa. Honolulu Airport’s 0.25 inches marked the driest February since the 0.07 inches recorded in the year 2000.

Most of the gages on Oahu have recorded below normal rainfall for 2009 through the end of February. The Oahu Forest NWR site is the sole exception with a near normal total of 28.73 inches which is third highest in the state. Most of the remaining locations have totals in the range of 30 to 60 percent of normal.

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

Most of the gages across Maui County recorded below normal totals with the only exceptions being the USGS gages at West Wailuaiki (23.92 inches, 159 percent of normal) and Oheo Gulch (7.19 inches, 93 percent of normal). The West Wailuaiki total matched the Mount Waialeale value for the highest statewide total in February 2009. Several sites posted totals at less than 20 percent of normal, including 0.00 inches at Kihei and 0.04 inches at Lahainaluna (1 percent of normal).

Most of the Maui County gages have recorded below normal totals for 2009 through the end of February though wetter conditions in January have allowed several gage totals to remain at near to above normal levels. Notable amounts include 32.68 inches at West Wailuaiki (104 percent of normal) and 22.62 inches at Kaupo Gap (102 percent of normal). On the opposite end of the spectrum, the gage at Lahainaluna has recorded only 1.86 inches (26 percent of normal).

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

Most of the gages from windward Kohala to the Puna District recorded above normal rainfall during the month of February. Piihonua’s 17.38 inches (123 percent of normal) topped all other Big Island gages and ranked fourth highest statewide. The highest daily total came from the Laupahoehoe gage with 6.71 inches recorded on February 3 as a shear line remnant moved back onto the Hamakua Coast. Honokaa’s 14.32 inches (199 percent of normal) marked the highest monthly total for this location since May 2006. The area has been hit hard by drought conditions over the past year. Remaining gages across the Big Island posted mostly below normal totals. A notable exception was the gage at Pohakuloa Kipuka Alala which recorded a monthly total of 1.95 inches (98 percent of normal). A large fraction of this total occurred during thunderstorms on February 7 which deposited 0.94 inches in a 2-hour period (2 PM to 4 PM).

Most of the windward Big Island gages have recorded near to above normal totals for 2009 through the month of February. In the leeward areas, most of the gages have posted below normal totals in the range of 30 to 60 percent of normal. The Piihonua total of 24.85 inches (81 percent of normal) ranks first among Big Island gages and is tied for fifth statewide.

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