March 2016 Precipitation Summary

State of Hawaii

MONTH: March 2016

PREPARED: April 7, 2016

Note:  This summary uses the arithmetic mean, or average, for “normal” rainfall values.

State: [Text data table for rain gages]

Although it is in the process of weakening, the ongoing El Nino event continues to produce generally dry conditions across the Hawaiian Islands. March is usually one of the wettest months of the year for the windward slopes but most of these areas reported drier than average conditions. The landscape would have dried out further were it not for a temporary shift to a high amplitude North Pacific pattern that destabilized the atmosphere over the state during the period from March 21 through March 25. On March 21, brief heavy rainfall during the afternoon hours produced minor flooding over the east-facing slopes of the West Maui Mountains and along Highway 450 in east Molokai. Elevated water levels made Makamakaole Stream impassable along the Waihee Ridge Trail. As a result, 14 people were rescued by a Maui County Fire Department helicopter. Two individuals among the group suffered minor injuries. Another flare up of heavy rainfall the following afternoon resulted in minor flooding on windward Oahu, Lanai, and east Maui.

These events were followed by a strong upper level trough that moved over the island chain on March 24 and 25 with its attendant thunderstorms and heavy rainfall producing flash flooding on several islands. Kauai received 5 to 10 inches, mostly within a 6-hour period starting late on March 24 and into the early morning hours of March 25. Flash flooding closed Kuhio Highway at the Hanalei Bridge for several hours, damaged a theater in Waimea town, and damaged a small barge in the lower reach of Wailua River. The system appeared to weaken as it moved past Oahu resulting in rainfall totals of mostly half an inch or less. Favorable upper level conditions combined with ample daytime heating intensified shower and thunderstorm action over Maui County and the Big Island during the afternoon of March 25. Flash flooding over east Molokai resulted in a swift water rescue of 8 people from a rain-swollen Halawa Stream. On the Big Island, an intense thunderstorm over Papaikou and Pepeekeo north of Hilo forced the closure of Highway 19 for a couple of hours with flood waters as deep as about 5 feet in low-lying areas. This same thunderstorm produced wind damage to some light structures in Papaikou and a waterspout over Hilo Bay. Thunderstorms during the late afternoon hours over the North Kona, South Kohala, and North Kohala Districts briefly closed Highway 190 between mile markers 6 and 8, and Highway 270 near mile marker 12.

Conditions prior to and after the inclement weather during March 21 through 25 were rather dry overall. During early March a high pressure ridge near the island chain produced stable and dry conditions with weak large-scale winds allowing land and sea breezes to define local conditions. A weak cold front passage on March 8 signaled the start of a strong trade wind pattern that persisted until March 14 when the trades weakened ahead of another weak cold front. This second weak front pushed across the state on March 15 and was followed by moderate to fresh trade winds through March 20. Moist north winds following the March 8 and March 15 frontal passages brought enough rain to northwest Kauai to make Hanakapiai Stream impassable on both days and briefly stranded several hikers on the Na Pali Coast trail.

Light winds and another weak cold front passage on March 29 closed out the month with relatively small amounts of rainfall and no flooding issues.

Despite the brief period of heavy rains in the latter half of the month, the overall dryness during March resulted in an increase in drought intensity over portions of the state. Most of the heavy rainfall on March 24 and 25 ended up as runoff and streams quickly reverted back to below normal flow levels once the storm had passed. Additional details on drought conditions can be found on the U.S. Drought Monitor website at http://droughtmonitor.unl.edu and in the Drought Information Statement issued by the Weather Forecast Office Honolulu at http://www.weather.gov/data/HFO/DGTHFO.

Island of Kauai : [March 2016 map] [year-to-date map]

Due to the heavy rain event straddling March 24 and 25, most of the gages on the southwest half of Kauai posted above average monthly rainfall totals. The U.S. Geological Survey’s (USGS) Mount Waialeale gage recorded the highest monthly total of 19.10 inches (50 percent of average). Their North Wailua Ditch rain gage a couple miles away had the highest daily total of 6.30 inches on March 24 during the previously described flash flood event. The occurrence of a flash flood event embedded within a period of overall dryness has generated some interesting statistical anomalies. At Mount Waialeale, it was the driest March since 2001. On the other hand, the March 24-25 event resulted in Hanapepe recording its highest March rainfall total since 2002. During an 11-minute span, this site recorded 0.67 inches as thunderstorms rumbled across Kauai’s southern slopes. The Waimea Heights gage a few miles to the west received 3.76 inches from 10 PM on March 24 through 1 AM on March 25.

The heavy rain event helped push rainfall totals at a few locations into the near average range for 2016 through the end of March, but most sites still showed below average totals. The Kilohana gage had the highest year-to-date total of 34.11 inches (71 percent of average) though Mount Waialeale was close to catching up with 33.89 inches (39 percent of average).

Island of Oahu: [March 2016 map] [year-to-date map]

Oahu missed out on the bulk of the late-March storm action. Thus, nearly all of the gages across the island recorded below average monthly rainfall totals with most amounts at less than 50 percent of average. The USGS’ Poamoho No. 1 gage had the highest monthly total of 10.01 inches (47 percent of average) and the highest daily total of 4.08 inches on March 14. The Palolo Fire Station and Manoa Lyon Arboretum gages posted their lowest March totals on record and the Moanalua gage had its lowest total since 1993.

Prior to February 2016 the U.S. Fish and Wildlife Service’s Oahu Forest National Wildlife Refuge gage often had the highest monthly total on Oahu. This station was relocated farther downslope to better support fire weather monitoring which is its primary function. This move placed it in a lower average rainfall zone so there is currently a much lower likelihood of this site having the highest monthly rainfall total on Oahu for any given month.

All of the gages on Oahu had below average rainfall totals for 2016 through the end of March with most amounts at less than 50 percent of average. The USGS’ Poamoho No. 1 rain gage had the highest year-to-date total of 21.17 inches (38 percent of average).

Maui County: [Maui March 2016 map] [year-to-date map] [Molokai/Lanai March 2016 map] [year-to-date map]

Most of the gages across Maui County reported below average rainfall totals for the month of March. The USGS’ West Wailuaiki rain gage had the highest monthly total of 20.38 inches (70 percent of average) and the highest daily total of 4.52 inches on March 19. Puu Kukui, another USGS site, often has the highest monthly total in Maui County but instead had its driest March on record.

Most of the gages in Maui County had below average rainfall totals for 2016 through the end of March. The Puu Alii gage had the highest year-to-date total in the county with 30.71 inches (88 percent of average).

Island of Hawaii: [March 2016 map] [year-to-date map]

March rainfall totals on the Big Island were below average at most of the gages with more than half of them at less than 50 percent of average. Most of the totals in the near to above average range were from the Hamakua and Kohala sections of the island. The Natural Resources Conservation Service’s Island Dairy station had the highest monthly total of 25.34 inches (128 percent of average) and the highest daily total of 7.81 inches on March 12. Totals from the Mauna Loa Observatory and Honaunau were the lowest March values since 1998, which was also a strong El Nino year. Glenwood, in the Puna District, had its lowest March total since 2003.

Most of the Big Island gages had below average rainfall totals for 2016 through the end of March. The USGS’ rain gage at Kawainui Stream had the highest available year-to-date total of 33.74 inches (85 percent of average). The Island Dairy site may have a higher year-to-date total but was not available for comparison because of an incomplete data record for January.

Data Sources: Data used in this report are largely from National Weather Service sources including climate network weather observation stations at Lihue, 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 Hawaii Department of Land and Natural Resources, the U.S. Geological Survey, the U.S. Bureau of Land Management, the U.S. National Park Service, the Department of Defense, the U.S. Fish and Wildlife Service, and the U.S. Department of Agriculture.  Averages come from the National Climatic Data Center (1981-2010 series) and the Rainfall Atlas of Hawaii (http://rainfall.geography.hawaii.edu/).  Data presented here are not certified and should be used for informational purposes only.

Kevin R. Kodama
Senior Service Hydrologist
NOAA/NWS Weather Forecast Office Honolulu