Heavy Rainfall - Oct 31 to Nov 2, 2006

Heavy Rainfall For Much of Hawaii

October 31-November 2, 2006

Andy Nash & Kevin Kodama

Summary:

Heavy rainfall across much of Hawaii during the period was the result of two systems. The first being left over moisture from an old front that pooled along the windward sides of the islands. The light easterly wind flow helped push the moisture over windward sections of the islands, resulting in some showers on October 30. By October 31, the destabilized further as an upper level trough of low pressure moved toward Hawaii. The more unstable conditions resulted in locally heavy rainfall that persisted into the afternoon hours of November 1. The excessive rains produced flooding over portions of windward Kauai and Oahu and triggered a significant landslide that closed Oahu's Pali Highway. As the upper level low pushed across the state on November 2, it once again triggered the development of a cluster of thunderstorms near Oahu during the late morning. These thunderstorms brought one last round of flooding to portions of Oahu and then to Molokai and Maui during the afternoon as it slid southeast down the island chain. Such heavy rain events due to the combination of an old front, or shearline, and an upper level low pressure are not uncommon and happen several times a year. Click here to read a summary of heavy rainfall in late 2003 under similar circumstances.

Rainfall amounts during the period were quite large, especially along windward sections of Kauai and Oahu, with some locations receiving well over 15 inches of rainfall. Some locations received over 3 inches in just a matter of 1 or 2 hours.

Radar Estimated Rainfall:

Notes:

Color scale -Blue <1" Greens 1 to 2 1/2" Orange 2 1/2 to 5" Red 5 to 10" Purple 10 to 15" White >15"

The black circles are areas that are too close to the radar for accurate rainfall estimations to be made.

Kauai Oahu Molokai/Lanai Maui

Selected Rainfall Amounts (in inches) from 8am October 30 to 8am November 3:

Significant Storm Reports:

October 31

245 pm - Oahu - Flooding closes Kapaa Quary Road near Kaneohe

545 pm - Oahu - Small landslide along Kapaa Quary Road

November 1

1045 am- Oahu - Landslide closes the Pali Highway

1215 pm - Kauai - Hanalei River overflows and closes the Kuhio Highway

November 2

1230 pm - Maui - Waterspouts occur in Maalaea Bay

130 pm - Oahu - Flooding of Waikane Stream forces the closure of Kamehameha Highway

215 pm - Maui - Flooding in and around Kahului to Paia closes several roads

215 pm - Molokai - Flooding closes Highway 450 between mile markers 4 and 13.

250 pm - Maui - Flooding in and around Kihei closes several roads

Watch/Warning/Advisory Summary:

During the period, the Forecast Office issued a number of watches, warnings and advisories primarily for the flood threat, although the upper level system responsible for the unsettled weather also brought strong winds to the highest summits. Winds over 50 mph were measured on Mauna Kea.

Flash Flood Warnings - Total 13 (Kauai 3, Oahu 4, Molokai 4, Maui 2)

Flood Advisories - Total 22 (Kauai 2, Oahu 12, Molokai 2, Lanai 1, Maui 2, Big Island 3)

Flood Watch - In effect from early morning November 1 until late on November 2.

High Wind Warning - For Mauna Kea and Mauna Loa summits on the Big Island

Wind Advisory - Total 2 (Haleakala on Maui and Mauna Kea/Mauna Loa on the Big Island)