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Nora to Add to Record-Breaking Central Pacific Tropical Activity

Tropical Storm Nora is headed to the Central Pacific Basin, where unusually warm waters have already led to a record 13 tropical systems this hurricane season.

Nora is expected to strengthen into a hurricane by the end of the weekend, but will eventually curve well away from Hawaii, with the main impacts being to shipping interests in its lifetime.

AccuWeather meteorologists will be monitoring the strength of Nora in the event it gets stronger than currently expected and sends dangerous swells to Hawaii.

Even in the event that no impacts are felt on Hawaii, Nora will still go into history books as the record 14th tropical system (either a depression, storm or hurricane) to roam the waters of the Central Pacific Basin this year.

Never before since reliable record-keeping began in the late 1960s has there been that many tropical systems in the Central Pacific. The previous highest tally was 11 during the years 1992 and 1994.

This number includes systems that either developed in the Central Pacific or tracked westward from the Eastern Pacific. The border of the Central Pacific Basin lies from 140 degrees west longitude to the International Date Line.

The Central Pacific is typically not an active basin with four to five organized systems observed on average every year, compared to the 15 named storms (which does not even count tropical depressions) that form on average in the Eastern Pacific annually.

In normal years, tropical systems in the Eastern Pacific will take a more northwestward than westward track, eventually weakening due to cooler waters before reaching the Central Pacific.

With warmer-than-normal ocean water in place, a record number of systems have been able to form this year in the Central Pacific or track far enough westward from the Eastern Pacific.

"The warmer the water, the more the air will rise and lead to increased storminess," stated AccuWeather Meteorologist Ben Noll.

While the strong El Niño that is unfolding is a major contributing factor, Noll stated that it is not the only reason for the warm waters.

"The combination of the strong El Niño and a strongly positive Pacific Decadal Oscillation (PDO) have resulted in exceptional warmth in the sea-surface temperatures that extend from Baja California to Hawaii," he said.

A positive PDO refers to anomalously warm waters off the west coast of the United States.

"In fact, September featured the warmest sea-surface temperatures in history near Hawaii, smashing the previous record by 0.9 degrees C [roughly 1.4 degrees F]," Noll said in referencing research by Eric Blake from the National Hurricane Center.

Despite the increase in tropical activity, Hawaii has so far escaped a direct hit this year.

Nearly half of the systems that roamed the Central Pacific, including Guillermo, Kilo, Ignacio and Jimena, passed close enough to put residents and visitors on heightened alert for rough surf and, in some cases, flooding downpours.

There was one beneficial aspect to the tropical rain that Hawaii received over the summer, drought relief.

Three months ago, about two-thirds of the state was either abnormally dry or in the midst of a drought. Thursday's report from the United States Drought Monitor indicated that number has been erased with Hawaii now drought-free.

Presently, Hawaii will not face another tropical threat in the near future as a dip in the jet stream will steer Nora back to the northeast over the open waters of the Pacific.

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Nora has the potential to enter record books again next week if it crosses 140 degrees west longitude for a second time and re-enters the Eastern Pacific Basin, a feat no organized tropical cyclone has done since at least 1970.

There are no other immediate tropical threats to Hawaii, but AccuWeather meteorologists will continue to monitor any possibility due to the unusually warm waters and with hurricane season not officially over until the end of November.

However, tropical activity should diminish later this month.

According to AccuWeather Meteorologist Anthony Sagliani, "By late October, winds aloft usually become too hostile for tropical systems to form or maintain themselves over the Central Pacific."