Akoni (2019)

A small tropical cyclone formed from a cluster of thunderstorms along the monsoon trough and was first classified as a tropical depression at 1200 UTC on 4 September 2019 near 140°W, about 1,200 nautical miles east-southeast of the Island of Hawai‘i. The system moved west-southwest across the far eastern central Pacific and was upgraded to Tropical Storm Akoni by 1800 UTC on 5 September. Akoni maintained tropical-storm strength for about 12 hours, then weakened as its thunderstorms became disorganized and it encountered dry air. It became a remnant low by 1200 UTC on 6 September and opened into a trough about 500 nmi south-southeast of the Big Island before dissipating.

Akoni did not make any landfalls. It remained well southeast of the Hawaiian Islands throughout its life and posed no threat of coastal impacts that required watches or warnings.

The peak intensity was 35 knots (40 mph) with a minimum central pressure of 1004 mb, reached around 1800 UTC on 5 September. That peak intensity is the highest the cyclone attained and is equivalent to a minimal tropical storm.

There were no reports of storm surge or rainfall impacts tied to Akoni in the report. No coastal surge heights or rainfall totals at specific named locations were recorded or reported in connection with this storm.

No casualties or damage were reported. The storm produced no known direct or indirect deaths and no notable destruction.

Akoni was notable because its formation was not expected: it was not highlighted in NHC’s Tropical Weather Outlooks prior to genesis and most global models did not predict tropical-cyclone formation. Only one official forecast was issued by NHC for Akoni; that forecast’s track and intensity errors were small in some measures, and CPHC’s official intensity forecasts performed well compared with guidance.