Iselle (2014)

Iselle formed from a tropical wave in the eastern Pacific and became a tropical depression on July 31, 2014 about 825 nautical miles south-southwest of Baja California. It strengthened to a tropical storm within six hours and became a hurricane by August 2. Iselle rapidly intensified and reached its peak intensity on August 4 as it moved westward near 140°W, then gradually weakened as it moved into the central Pacific and toward the main Hawaiian Islands. The system weakened to a tropical storm by early August 8 and became a remnant low by August 9, dissipating over the open Pacific on August 10.

The only landfall occurred on August 8, 2014 when Iselle’s center crossed the Kau coast of the Island of Hawaii just east of Pahala at about 1230 UTC. By the time of landfall the cyclone had weakened to a tropical storm with maximum sustained winds estimated near 50 kt (about 58 mph) and an estimated central pressure of 1001 mb.

Iselle’s maximum intensity was estimated at 120 kt (about 138 mph) and a minimum central pressure of 947 mb on August 4, making it a Category 4 hurricane at peak intensity in the eastern Pacific well before reaching Hawaii.

Storm surge at the nearest tide station (Hilo) reached about 0.8 ft above normal tide levels, but very large waves produced much higher total water levels locally. In the small community of Kapoho on the Island of Hawaii, waves estimated near 25 ft combined with about 2 ft of surge to produce total water levels of 8–10 ft above ground, causing extensive coastal flooding. Rainfall was heaviest on the Island of Hawaii, with much of the east and southeast slopes receiving 6–10 inches and isolated higher amounts; the greatest recorded rainfall was 15.25 inches at the Kulani NOAA Weather Radio site. Other notable totals included about 12.86 inches at the Pali2 station and widespread 2–5 inch totals on east-facing slopes of other islands.

Iselle caused one confirmed direct death: a hiker drowned on August 8 in Kauai’s Na Pali Coast State Park while attempting to cross a swollen stream. The storm produced significant wind and flood damage, especially on the Island of Hawaii where large numbers of shallow-rooted albizia trees were toppled, causing major damage to homes, roads, and electrical infrastructure (over 33,000 customers lost power at peak). Federal disaster assistance was designated for Hawaii and Maui counties; media and agency assessments estimated statewide losses between about $148 million and $325 million, with reports of 11 homes destroyed and about 50 homes damaged on the Island of Hawaii and substantial agricultural losses (for example, an estimated $53 million loss to the papaya industry).

Noteworthy aspects include Iselle’s annular structure and rapid intensification to Category 4 well east of Hawaii, plus the weakening caused by increasing wind shear and interaction with the high terrain of the Island of Hawaii before landfall. Track forecasts were unusually accurate (errors below recent averages through 72 hours), but intensity forecasts underestimated the rapid intensification and annular behavior, leading to larger-than-normal intensity forecast errors.