Typhoon Nepartak Ends Record-Long Quiet Period for Northwest Pacific

Since the beginning of the year, the Northwest Pacific Ocean has been eerily quiet, with nary a tropical system forming in a region that normally sees more storm activity than any other.

After a record 200 days without a tropical cyclone developing in the basin, Super Typhoon Nepartak burst onto the scene over the weekend, and is poised to bring damaging winds and torrential rains to China, Taiwan and possibly parts of Japan and the Korean Peninsula.

The slow start and subsequent reversal are due to climate patterns — particularly El Niño — that can impact the weather over large swaths of the planet. How those patterns change as the Earth warms from the continual addition of heat-trapping greenhouse gases to the atmosphere could affect future storm activity in the region.

A large chunk of global tropical cyclone activity each year typically occurs in the Northwest Pacific, where such storms are called typhoons. The very deep stores of warm ocean waters, which fuel the convection that drives tropical systems, are one of the main reasons for the large share of storms.

But the last tempest in the region that reached at least tropical storm strength was Melor in mid-December. Since then, nothing has been able to get going, culminating in the longest storm-free stretch for the region on record. The previous record was the 198 typhoon-free days that began in  late 1972, Weather Underground reported.

The July 3 formation of Nepartak also marked the second latest start to any typhoon season, Weather Underground said, behind only the July 8 start of the 1998 season. In 1973, the first storm didn’t occur until July 1.

What do all of these years have in common? They saw the waning of some of the strongest El Niño events on record.

While El Niño tends to ramp up tropical cyclone activity across the whole North Pacific as it forms and nears its peak — because of warmer ocean waters and more favorable winds — it tends to suppress activity in the Northwest Pacific as it wanes and leads to dry, subsiding air there.

Nepartak was able to form because of the influence of another climate phenomenon called the Madden-Julian Oscillation, or MJO. It features alternating areas of enhanced and suppressed rainfall that moves from west to east across the globe over the course of weeks. The MJO can reinforce or counteract other climate influences, like El Niño.

In this case, the MJO led to rising air in the Northwest Pacific, Philip Klotzbach, a hurricane researcher at Colorado State University, said in an email. That shift in atmospheric patterns combined with very warm waters helped the seed of Nepartak grow and strengthen into what is now a major typhoon, with winds of about 150 mph.

Favorable water temperatures and winds are expected to continue as Nepartak heads toward Taiwan and China; it is forecast to strengthen into a Category 5 storm with winds above 165 mph.

The exact path the storm will take is uncertain, but its winds and expected torrential rains could cause considerable damage in the areas it blows over. Rain is a particular concern in Taiwan where mountainous terrain works to wring even more rain out of storms.

Nepartak doesn’t likely herald a reversal in the Northwest Pacific typhoon season, as not only is the MJO fleeting in nature, but seasons after a major El Niño tend to be quieter overall, Klotzbach said.

For the 1973, 1983, 1988, and 1998 typhoon seasons — the most recent ones that came after a strong El Niño —  the total amount of energy from all storms those seasons was about 60 percent of normal, Klotzbach said.

One of the big questions moving forward is how the continual warming of the planet might impact climate patterns like El Niño and the MJO. Some studies have suggested that the Pacific will enter a more permanent El Niño-like state, while others suggest it will seesaw between more extreme El Niños and La Niñas.

While the effects on typhoons from that aspect are uncertain, another recent study suggests a more direct impact: the warming of the upper layers of the ocean could mean more intense typhoons overall in the future.