Tropical Storm Iselle unleashes over a foot of rain on Big Island

The Big Island’s strongest tropical storm on record, Iselle, will likely be remembered for its rain, rather than its wind.

Several locations on the Big Island’s eastern, windward side have recorded over 8 inches of rain.  The highest totals have surpassed a foot.

The Saddle Road Quarry near Hilo has logged 14.6 inches so far and the rain has filled the gauge at a one inch per hour clip over the last 12 hours.

Rainfall totals through 8:45 a.m. local time (2:45 p.m. ET) (NWS)

What’s remarkable is that on the leeward side of the Big Island around Kona, on the West Coast, a mere 0.04 inches of rain has fallen.  This is classic example of the rain shadow effect, in which the mountains in between the coasts squeeze out all of the rain coming in from the east, leaving mere morsels for western parts of the island.

Here’s a look at doppler estimated rainfall totals from the Big Island’s east coast, which shows widespread totals exceeding 4 inches:

(National Weather Service)
Doppler estimated rainfall totals through 9 a.m. local time (3 p.m. ET) (National Weather Service)

Heavy rain continues to douse the eastern and northern sections of the island, so these totals will increase.


Watch: Long radar loop of Iselle’s rain on Big Island from landfall to present


Winds have been strong – gusting in the 30-60 mph range near sea level – but not quite violent.  Maximum sustained winds at landfall were near 60 mph and have dropped to 50 mph as of the latest advisory as the storm has weakened.

Hilo Airport recorded a peak gust of 54 mph.

The strongest winds have occurred in the mountainous terrain.  Earlier today, AccuWeather reports a wind gust of 66 mph was logged at Volcano National Park.  Near the remote summit of Mauna Kea, at an altitude of nearly 14,000 feet, winds reached the 60-80 mph range, according to data from an automated weather sensor published online.  The National Weather Service reports a 91 mph peak gust there.

Wind speed recorded near the summit of Mauna Kea on Hawaii’s Big Island. (Mauna Kea Weather Center)

The gusty winds have knocked out power to roughly 21,000 customers, writes Mark Berman at Post Nation.

Link: List of peak wind gusts

Temperature extreme

Here’s an interesting Iselle-related tidbit: As it approached the Big Island Thursday and the winds out ahead of it swept over the mountains,  a strong downsloping wind current developed on the eastern (leeward) side of the island.  The sinking air resulted in compressional heating giving temperatures a big boost.  Kona’s temperature soared to 95 – appearing to tie its all-time record high set in  1989.  You might think it would get hotter than this along the coast of Hawaii, but ocean breezes tend to moderate the climate there, with highs mainly in the 80s.

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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