State of Hawaii

MONTH: April 2008

PREPARED: May 2, 2008

State: [Text data table for rain gages]

Trade winds at mainly moderate to fresh levels persisted through the first 3 weeks of the month before breaking down on April 23. A surface trough embedded within the trade flow moved westward across the state on April 9 bringing enhanced shower activity on the windward slopes of the island chain. Minor flooding occurred on the Big Island, Maui, and Lanai with maximum rain totals in the range of 1 to 3 inches. On April 10, an upper level trough southwest of the state helped enhance showers over windward areas of Kauai and produced some minor flooding problems.

On April 23, a large low pressure system in the North Pacific pushed the subtropical ridge of high pressure southward over the Hawaiian Islands. This shift in weather pattern resulted in light large-scale winds allowing local land and sea breezes to take hold. Unstable upper level conditions on April 25 and 26 helped support heavy showers and isolated thunderstorms over the islands with the heaviest rainfall occurring over Oahu during the afternoon of April 25. Rain rates of 1 to 2 inches per hour produced minor flooding problems over the Kailua and Waimanalo areas. Trades resumed on April 27 and reached fresh to strong levels on April 30.

Island of Kauai : [April 2008 map] [Year-to-date map]

Most of the rain gages on Kauai recorded below normal rain totals for the month of April. Only the Makaha Ridge, Port Allen, and Hanapepe gages indicated near to above normal monthly amounts. Most of the remaining gages posted totals at less than 50 percent of normal. The U.S. Geological Survey’s (USGS) gage at Mount Waialeale recorded a statewide leading total of 19.17 inches but this amount registered at only 49 percent of normal. This site also recorded the highest daily total of 2.07 inches on April 12 under moderate trade wind conditions. On the afternoon of April 17, the Port Allen gage posted a 1-hour total of 1.46 inches which accounted for more than half of its total for the entire month.

Rain totals for 2008 through the end of April remained in the near to below normal range at all gages on Kauai. The Mount Waialeale total of 118.79 inches (81 percent of normal) leads all totals statewide. Lihue Airport continues to have dry conditions with only 4.52 inches (31 percent of normal) so far this year, marking the lowest January through April total since 1993 (3.53 inches).

Island of Oahu: [April 2008 map] [Year-to-date map]

Nearly all of the gages on Oahu posted below normal totals with more than half of the sites at less than 50 percent of normal. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage recorded the highest monthly total of 8.36 inches (40 percent of normal) which was 4th highest in the state. However, the Manoa Lyon Arboretum gage posted the highest daily total of 2.01 inches on April 6. During a heavy rain episode on April 25, the gage at the Olomana Fire Station recorded 1.05 inches in 30-minutes and 1.31 inches for the day. This daily total at Olomana accounted for nearly half of the 3.08 inches recorded at this location over the entire month.

Rain totals for 2008 through the end of April remain in the near to below normal range at all locations on Oahu. The Oahu Forest NWR gage has the highest total of 48.76 inches (67 percent of normal). For Honolulu Airport, archive data indicate that the 0.91 inches recorded so far this year marks the lowest January through April total on record. The previous record was 1.33 inches during January through April 1983, a strong El Nino year. According to the NOAA Climate Prediction Center, conditions in the tropical Pacific are considered to be in a La Nina state.

Maui County: [Maui April 2008 map] [Year-to-date map] [Molokai/Lanai April 2008 map] [Year-to-date map]

While most gages across Maui County recorded below normal rain totals, Upcountry gages at Kula and Ulupalakua Ranch indicated well above normal rainfall amounts for April. At both locations, heavy afternoon showers on April 9 and 26 generated more than half of the monthly totals. The highest monthly total county-wide, and second highest in the state, was 12.25 inches (56 percent of normal) at the USGS’ West Wailuaiki gage. The USGS gage on Puu Kukui recorded the highest daily total of 2.39 inches on April 12. For the second consecutive month, Kahului Airport set a new record for the lowest monthly rainfall with its April 2008 total of 0.03 inches beating the previous record of 0.06 inches set in April 1990.

Most Maui County gages continue to show below normal totals for 2008 through the end of April. West Wailuaiki and Oheo Gulch are the only sites showing near normal totals so far this year. Puu Kukui’s 82.14 inches (59 percent of normal) leads all totals county-wide and is second highest statewide.

Island of Hawaii: [April 2008 map] [Year-to-date map]

Most of the Big Island gages recorded below normal rain totals for the month of April with many showing less than 50 percent of normal rainfall. The Pahoa gage had the highest monthly total of 8.06 inches (58 percent of normal), which was a bit unusual since the Glenwood gage in upper Puna usually posts the highest value. The highest daily total, 2.47 inches on April 9, came from the Pahala gage as a result of thunderstorms triggered by a passing surface low pressure trough.

Gages in Hilo, Puna, and most of Kau continue to show near to above normal rain totals for 2008 through the end of April, mainly as a result of the heavy early February rains. Totals in the Hamakua area have slipped into the below normal range joining the ranks of the gages in Kohala and Kona. Waiakea Uka’s 72.02 inches (104 percent of normal) leads all Big Island totals and ranks third 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