State of Hawaii

MONTH: April 2012

PREPARED: May 4, 2012

State: [Text data table for rain gages]

After an unsettled March, the atmospheric pattern over the Hawaiian Islands was rather stable throughout most of April with a majority of the days involving trade winds in the moderate to fresh range. Showers embedded within the low level trade wind flow mainly affected windward slopes while leeward areas remained dry. Weak cold fronts brought enhanced rainfall mainly to the windward slopes on April 8 and April 22 through 23 with some sites recording around an inch of rain in a day. There were no significant flood events during the month as most areas had below normal rainfall totals.

The end of April marked the completion of the 2011-2012 wet season in the Hawaiian Islands. Overall, the October 2011 through April 2012 rainfall totals for the west half of the state were higher than the east half. Data from key rain gages across the island chain indicated that the 2011-2012 wet season ranked as the 18 th wettest in the last 30 years. A weak to moderate La Nina in the tropical Pacific played a role in determining the wet season weather patterns which affected the state. Historically, La Nina events have shown a tendency to produce wetter than normal conditions in the Hawaiian Islands. However, recent La Nina events appear to be trending toward drier conditions though it is unclear why this is happening.

October 2011 - April 2012 wet season rainfall maps: [Kauai] [Oahu] [Molokai/Lanai] [Maui] [Big Island]

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

Most of the rain gages on Kauai recorded below normal rainfall totals for the month of April. The U.S. Geological Survey’s (USGS) Mount Waialeale gage had the state’s highest monthly total of 30.45 inches (81 percent of normal). This site also had the highest daily total of 3.98 inches on April 22 during the passage of a weak cold front.

Lihue Airport had its second-driest April on record with only 0.37 inches (16 percent of normal). The record low April rainfall total is 0.32 inches from 1992. Only a month before, Lihue Airport had its second-wettest March with 18.17 inches so it is interesting how quickly conditions have changed.

Most of the gages on Kauai had near to above normal rainfall totals for 2012 through the end of April. Mount Waialeale’s 159.22 inches (128 percent of normal) topped all other year-to-date totals in the state by a very wide margin.

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

Most of the rain gages on Oahu measured below normal rainfall totals for the month of April. Many of these totals were less than 50 percent of normal. The U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge (NWR) gage had the highest monthly total of 17.64 inches (85 percent of normal) and the highest daily total of 2.54 inches from the April 8 cold front.

Most of the gages on the slopes of the Koolau Range had near to above normal rainfall totals for 2012 through the end of April. Most of the west Oahu gages had below normal totals. The Oahu Forest NWR gage had the highest year-to-date total of 80.21 inches (110 percent of normal) which ranked sixth highest statewide.

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

All of the gages in Maui County had below normal monthly rainfall totals for April and most were less than 50 percent of normal. The USGS gage on Puu Kukui had the highest monthly total of 22.54 inches (59 percent of normal) and the highest daily total of 3.98 inches on April 10. Ulupalakua Ranch posted just 0.16 inches (8 percent of normal) which made it the driest April since 1976.

All of the gages in Maui County had below normal rainfall totals for 2012 through the end of April. The Puu Kukui gage had the highest year-to-date total of 84.42 inches (63 percent of normal) which ranked fifth highest in the state.

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

Most of the Big Island’s gages recorded below normal rainfall totals for the month of April. Windward sites were largely in the 40 to 70 percent of normal range and leeward sites were mostly less than 30 percent of normal. The USGS’ gage at Kawainui Stream had the highest monthly total of 14.73 inches (95 percent of normal) and the highest daily total of 2.41 inches of April 23 associated with a weak cold front.

Most of the windward Big Island gages had near normal rainfall totals for 2012 through the end of April. Most of the leeward gages maintained rainfall deficits with year-to-date totals well below 50 percent of normal. The Glenwood gage’s 57.74 inches (70 percent of normal) was the highest amount of rainfall on the Big Island so far in 2012.

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