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Update: Global Tropical Cyclone Activity Less Than One Third of Average in 2017; Nearing Record Late First Typhoon
Published: July 14, 2017
Tropical cyclone activity so far in 2017 continues to languish well below average through mid-July, despite recent hurricanes in the eastern Pacific basin.
(MORE: Hurricane Central)
According to Colorado State University atmospheric scientist Dr. Phil Klotzbach, the northern hemisphere's ACE (Accumulated Cyclone Energy) index, a measure of tropical cyclone activity, through July 14 is less than one-third of the average year-to-date total.
The ACE index is calculated by adding each tropical storm, hurricane or typhoon's wind speed through its life cycle.
Long-lived, intense hurricanes/typhoons 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.
Atlantic, East Pacific: Not That Quiet
Don't blame the Atlantic Basin for the slump.
An average Atlantic hurricane season doesn't see the first named storm form until the second week of July, according to the National Hurricane Center.
June typically doesn't feature intense, long-lived Atlantic hurricanes, but rather short-lived tropical depressions or storms. This is partly due to a more restricted region of development, stronger wind shear and drier air compared to later months.
In July, Tropical Depression Four made an attempt to become "Don", but faced both shearing winds and ample dry air typical of the zone between Africa and the Lesser Antilles early in the season.
(MORE: Notorious July Hurricanes)
Despite this, through July 14, eastern Pacific ACE, again combining both intensity and longevity of all named storms, was still about 25 percent below the season-to-date average.
The first three named storms in this basin were short-lived tropical storms, and Dora only maxed out as a Category 1 hurricane for a little over 24 hours.
The Real Drought Source: The Western Pacific Basin
If you haven't heard the word "typhoon" in a while, it's because there hasn't been one yet in 2017, and we're nearing a record-long wait for the year's first.
Through mid-July, there have been only three tropical storms – Muifa in late April, Merbok in mid-June, Nanmadol in early July – in 2017, so far in the western Pacific basin.
According to Dr. Klotzbach, this is about half the average named storms-to-date (5 to 6). Typically, three to four typhoons have developed by mid-July of an average year, Klotzbach calculated. One to two of those typhoons would have reached at least Category 3 intensity in a typical year, as well.
Since 1950, only three years had a later "first typhoon": 1998 (August 3), 1995 (July 18) and 1977 (July 19).
Given only three tropical storms lasting a combined 5.5 days, the western Pacific's ACE index was a scant 8 percent of average. As of July 11, only three other years started quieter in the basin, according to Klotzbach.
"One of the reasons for suppression of the NW Pacific TC season to date is that we've generally had sinking motion across most of the basin since early May," said Klotzbach.
Stronger than average trade winds, blowing east-to-west near the Philippines, Taiwan, and the South China Sea, have also been in place since May, Klotzbach said. This increases wind shear which tends to either prevent tropical cyclones from forming or rip apart those that have formed.
2016 Déjà Vu?
Interestingly, we were at roughly this same point of inactivity as July began last year.
The Atlantic hurricane season's peak months of August and September still lie ahead. If it hadn't been for January oddball Alex, all Atlantic hurricanes in 2016 would've formed from August on, including Matthew.
The bottom line is that it's still very early.
"We're only about 15 percent of the way through the Northern Hemisphere tropical cyclone season from a climatological perspective," Klotzbach said.
Despite the slow start, 2016's tropical cyclone activity ended up a tad above average, according to Klotzbach.
Despite fighting a hostile environment, several meteorologists noted the strength and procession of tropical waves marching westward off west Africa in late June and early July resembled what you typically see during the heart of the hurricane season.
Don't be fooled by a relatively benign start to any tropical cyclone season. After all, in June 2015, we were tracking a record active start of northern hemisphere tropical cyclones.
Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7. Follow him on Facebook and Twitter.
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