Monthly Precipitation
State of Hawaii Summary

The following excerpts are taken from the NOAA NWS Honolulu Forecast Office's Monthly Precipitation Summaries.

July: Trade winds prevailed through most of April at mainly moderate levels. Trade shower activity during the first two weeks of the month brought daily rainfall to the east-facing slopes of the islands, though totals were mostly less than an inch and no significant flooding problems occurred. The airmass over the island chain stabilized for the period from April 15 to 25 with many sites reporting little or no rainfall. The trades broke down on April 26 as a weak, late-season cold front moved slowly across the state on April 27 and 28 before dissipating near the Big Island and Maui on April 29. Most rain gages recorded less than a quarter of an inch during the frontal passage.

August: Rainfall during August across several areas of the state dropped off considerably from July’s totals. The largest decreases occurred on Kauai and Oahu where most gages recorded totals well below the August normals. A couple of heavy rain events, described below, helped save the island chain from more widespread rainfall deficits...A surface low pressure trough associated with the remnant of Tropical Depression One-C helped bring heavy rains to the Big Island from August 6 through August 10...the second bout of heavy rains took place on August 28 through August 30 as a low pressure system moved westward to the north of the island chain....the remnant of Hurricane Fernanda brushed the Big Island and Maui on August 19 but did not produce any significant flooding.

September: After a rather dry August, rainfall increased dramatically over many areas of the state as a result of several upper level low pressure systems convecting tropical low level moisture.The first significant heavy rain event occurred from September 13 through 15 and affected primarily the north- and east-facing slopes of Kauai, Oahu, Maui, and the Big Island...On September 22 and 23, another upper level low dropped in to the north of the Hawaiian Islands bringing another round of unstable conditions over the state. This same upper low brought about the demise of Hurricane Jova due to the unfavorable levels of vertical wind shear. The heaviest rains occurred over the Koolau Range on Oahu during the late afternoon of September 23...The third significant event involved yet another unseasonably strong upper level low pressure system and the low level remnant of Hurricane Kenneth which moved into the Big Island on September 30. Like with Hurricane Jova, the upper level low played a key role in weakening Kenneth with strong vertical shear, but also brought very unstable conditions. Heavy rains commenced on September 30 and continued through the night of October 1. The rains of September 30 affected the Big Island, Maui, and Oahu but did not produce significant flooding.

Kevin R. Kodama, Senior Service Hydrologist
National Weather Service Forecast Office, Honolulu, Hawaii