Pewa — 2013

Pewa formed as a tropical depression on August 16, 2013, near 9.2°N, 172.0°W, about 545 miles south-southwest of Johnston Atoll, becoming the first tropical cyclone of the year in the central Pacific. It strengthened gradually while moving west-northwest across the International Date Line, then turned northwest. Pewa briefly reached typhoon strength in the western North Pacific before weakening over open ocean; it dissipated on August 25, near 28.4°N, 166.2°E, about 1625 miles east of Tokyo, Japan. Pewa made no landfalls. Its strongest winds were 75 mph, with a minimum central pressure of 987 millibars, at 13.9°N, 178.0°E, about 855 miles west-southwest of Johnston Atoll on August 19. That intensity is equivalent to Category 1 on the Saffir-Simpson scale; in the western North Pacific, the storm was classified as a typhoon. The report lists no storm-surge or rainfall measurements. Pewa remained over the open ocean, and no surface observations of tropical-storm-force or stronger winds were reported. There were no reported deaths, injuries, or damage. Pewa formed during a rare burst of activity: the same broad weather system produced three central Pacific tropical cyclones in about three days. Pewa was the first tropical cyclone to form in the central Pacific since Tropical Storm Omeka in December 2010. Forecasters initially gave Pewa only a 10% chance of developing within 48 hours, increasing that estimate to nearly 100% by August 16. Track forecasts increasingly missed the storm’s path at longer ranges because it moved farther north than expected. The report notes that a track-model consensus beat the official track forecasts at every forecast period; official intensity forecasts were better than most guidance during the first 48 hours.