Tropical Storm Iselle made landfall along the southeastern coast of Hawaii’s Big Island early Friday morning bringing some fairly strong winds and big waves. However, it was the potential of torrential rainfall and possible flash flooding that was of greatest concern. So far, this has not materialized in any significant way, at least for Hawai'i's Big Island.
Although the final reports are not yet available it would appear that the rainfall may not have been as dramatic as expected given the topography of the island and the slug of moisture that Iselle tossed upon it. So far (as of 8 a.m. HST on Friday August 8th), the top amount reported has been 14.51” at Kulani (elevation 5,050’). Below is map of some other rainfall reports from across the island (not final totals):
A sketchy map of some rainfall reports on the Big Island as of early Friday morning. Note the lack of precipitation along the western shores where the rain shadow of Mauna Kea and Mauna Loa holds sway. This map, of course, will be updated later today or Saturday. Map from The Weather Channel (as of about 4 a.m. HST).
Rainfall reports for the Big Island as of 8 a.m. HST. By this time the rainfall had, for the most part, ended along the eastern shores including Hilo where a total of 3.34” was reported: not really a substantial amount for this normally very wet location and where 27.24” once fell in 24 hours (on November 1-2, 2000). Table from NWS-Honolulu. You can follow this link for updated rainfall reports for all locations in the state of Hawaii.
The heaviest rains have occurred on the windward slopes of the volcanoes and, at sea level locations, along the southeastern coastline. This is, climatologically, the norm year around as the map below illustrates.
A rough map of the Big Island’s annual average precipitation. There are few gauges in the region of heaviest rainfall along the steep slopes of the mountains just west of Hilo. Map from Hawai’i-Guide.com.
According to the rainfall atlas produced by the Geography Department of the University of Hawaii-Manoa the wettest location on the Big Island is a site known as Makakanaloa 2 located at 2,675’ elevation (19.810°N, 155.191° W) 13 miles northwest of Hilo and where an average of 7613 mm (299.72”) of rainfall accumulates each year. The gauge here was operated under the supervision of the State Division of Forestry from 1934-1953. The driest location, according to the rain atlas, is the Mauna Kea Observatory (13,631’) with an annual average precipitation (which includes snowfall) of just 207 mm (8.15”). Amazingly, the summit site is only about 18 miles west of the wettest site mentioned above.
Christopher C. Burt
Weather Historian
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