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Strengthening Nepartak ends record tropical cyclone drought in western North Pacific

A record was set in the tropical northwestern Pacific Ocean as the basin entered its longest stretch of time without a named tropical cyclone.

The new record of 199 days ended on Sunday with the development of Tropical Storm Nepartak. The lack of tropical systems occurred from Dec. 17, 2015 to July 2, 2016.

The previous record was 198 days which occurred from Dec. 15, 1972 to June 30, 1973 and also from Dec. 22, 1997 to July 7, 1998.

Strengthening Tropical Storm Nepartak will track to the northwest through the coming week, likely strengthening into a typhoon by Tuesday or Wednesday.

Residents of Taiwan, eastern China, South Korea and Japan, including the Ryukyu Islands, are being put on alert for impacts from the tropical system during the latter part of the week.

Flooding rainfall will accompany Nepartak along its path. The risk of damaging winds and rough surf will heighten as it strengthens.

While the worst of the impact are expected to pass to the north of Taiwan, cities in northern parts of the country should remain alert for impacts. This includes Taipei and Keelung.

In the Ryukyu Islands, the Yaeyama and Miyako Islands will have the highest chance for significant impacts from high wind and flooding rainfall. Further to the north in Okinawa, squally showers and thunderstorms are most likely.

Once in the East China Sea late this week, Nepartak is expected to curve to the north and northeast, potentially bringing impacts to South Korea and the southern mainland of Japan over the weekend. While weakening is expected during this time, Nepartak could still be a typhoon or strong tropical storm.

Nepartak is not expected to be followed by a flurry of tropical activity.

"The window for development looks to slam shut by next weekend," AccuWeather Senior Meteorologist Jason Nicholls said. "Then, I do not see much opportunity [for further development] until late July."

The current five longest stretches, including this year, without a named tropical system in the western Pacific Basin all occurred during transitions from El Niño to La Niña phase of El Niño-Southern Oscillation (ENSO).

El Niño is defined by above-average sea-surface temperatures in the eastern and central equatorial Pacific Ocean. These sea-surface temperatures cycle from warm to cool, relative to average, over a several-year period.

When the sea-surface temperatures in the same area of the Pacific Ocean are lower than average for a few months, a La Niña pattern has developed.

These below-normal sea-surface temperatures can have significant impacts on tropical development in the western Pacific Ocean. meteorologists are currently predicting a below-normal season for the western Pacific basin with 19 tropical storms and 10 typhoons. This is significantly below the historical averages for the basin.

"This will be one of the least active years on record," AccuWeather Tropical Expert Meteorologist Dan Kottlowski. "The record [for least tropical activity in the western Pacific Ocean] is 14 tropical storms and nine typhoons in 2010."

Areas predicted to have the greatest threat from tropical cyclones over the remainder of this summer include the Philippines, Taiwan and China. This threat is likely to shift toward Japan later in the season.

Despite a well below-normal forecast for tropical cyclones in the western Pacific Ocean, people should not let their guard down as a single strike from a powerful cyclone can cause great destruction and loss of life.

Content contributed to this story by Senior Meteorologist Kristina Pydynowski.