Western Pacific Tropical Cyclone Activity Sees Record Year to Date

Tropical cyclone activity in the western North Pacific Ocean basin continues at a record pace this year, a leading atmospheric scientist said Monday.

According to Dr. Phil Klotzbach, lead author of tropical season forecasts at Colorado State University, the ACE (Accumulated Cyclone Energy) index of 257 units through Aug. 17 shatters the previous record active start to the year set in 2002 of about 227 units.

The ACE index is calculated by adding each tropical storm, hurricane or typhoon's wind speed through its life cycle.

Long-lived, intense hurricanes have a high ACE index. Short-lived, weak tropical storms, a low ACE index. The ACE of a season is the sum of the ACE for each storm and takes into account the number, strength and duration of all the tropical storms in the season.

With typhoons Goni and Atsani in the Pacific now, this number will skyrocket.

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These ACE index values in the western North Pacific Ocean are more than two and a half times the year-to-date average, and exceeds those from all of 2014 (254), according to Dr. Ryan Maue, atmospheric scientist at WeatherBell, who tracks global ACE index values.

Seventeen storms, 12 of which reached typhoon (equivalent to hurricane) status, have flared up so far in 2015 in the northwest Pacific basin. This includes Typhoon Halola, which migrated westward from the central Pacific basin. 

When adding the eastern North Pacific basin, Klotzbach said the 12 Category 4 or 5 tropical cyclones this year through Tuesday, Aug. 18, set a year-to-date record for the Northern Hemisphere, smashing the previous record of seven such intense tropical cyclones tied in 2014, according to records dating to 1971. 

Klotzbach said the previous earliest date this occurred -- 12 Category 4 or 5 northern hemisphere tropical cyclones -- was on September 13. Incredibly, three-quarters of all Northern Hemisphere hurricanes or typhoons so far in 2015 have been at least Category 4 strength, according to Klotzbach.

This is impressive since the Atlantic basin had yet to produce a single hurricane, much less one of that intensity.

The Pacific tropical activity can be attributed, in part, to impressively warm ocean water. 

"The high ACE values we've seen in the northeast and northwest Pacific basins are consistent with El Nino," Klotzbach said in early June.

El Nino is an anomalous, yet periodic, warming of the central and eastern equatorial Pacific Ocean. For reasons still not well understood, every 2 to 7 years, this patch of ocean warms for a period of 6 to 18 months.

(MORE: Strong El Nino Likely | Atlantic Season Outlook)

The eastern Pacific basin typically sees an increase in named storms during a moderate to strong El Nino thanks to diminished vertical wind shear.

The opposite is true in the Atlantic basin, since wind shear tends to increase in a moderate to strong El Nino, particularly in the Caribbean Sea.

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