Western Pacific storms
© The Weather Channel
IR Satellite: The West Pacific three storms.
Hurricane season may be quiet in the Atlantic for now, but the Pacific Ocean is pulling off an impressive feat.

At some point this week, you could see not one, not two, but as many as five tropical cyclones spinning in the Pacific Basin. Although it's not unheard of to see multiple storms at the same time, five is impressive on any scale.

Three tropical cyclones -- Chan-hom, Linfa and Nangka -- formed in the western Pacific within three days of each other last week. Two of those became typhoons, and all three remain active.

That's busy enough, but it doesn't end there.

Tropical Depression Four-E formed Tuesday night well east-southeast of Hawaii.

Another disturbance over 1,000 miles southwest of Hawaii now has a good chance of developing into a tropical depression.

If that happens, that's how you'll see five tropical cyclones active at one time in the Pacific Ocean.

The current satellite image shows all five systems lined up like a string of pearls.
Pacific storms
© The Weather Channel
How Unusual?

Multiple tropical cyclones in the Pacific is not totally rare, given the year-round potential of the western Pacific Ocean.

On average, 36 tropical cyclones form each year in the northwestern Pacific and southwestern Pacific basins, combined. Another 16-17 form each year in the central and eastern north Pacific basin.

In mid-March 2015, four tropical cyclones at once spun in the western Pacific.

In a search through the reliable historical record, hurricane expert and Colorado State University seasonal forecaster Phil Klotzbach said the Pacific Ocean once had six tropical cyclones at once.

"That was in 1974 (August 26) when Ione, Joyce, Kirsten, Lorraine, Maggie and Polly were present at the same time," said Klotzbach.

Record Pacific storms
© Phil Klotzbach, NHC
Five active tropical cyclones in the eastern Pacific Ocean at 5 a.m. PDT on August 26, 1974. Tropical Depression Dolly near Guam was the sixth active Pacific tropical cyclone that day.
All but Tropical Depression Polly were in the eastern Pacific Ocean that day. Polly was a tropical depression at the time northeast of Guam.

Klotzbach said the last time there were as many as five active tropical cyclones simultaneously in the Pacific Ocean was from September 21-23, 2005 when Jova, Kenneth, Max were in the eastern Pacific, while Damrey and Saola spun in the western Pacific.

In the Atlantic Basin, four simultaneous hurricanes has only happened twice.

Most recently, this occurred September 25-27, 1998. Hurricane Georges was heading toward a Gulf Coast landfall while Hurricanes Ivan, Jeanne (not the Ivan and Jeanne you remember from 2004) and Karl meandered harmlessly in the central Atlantic Ocean.

Atlantic four hurricanes
Infrared satellite image of four hurricanes at once in the Atlantic Basin on Sep. 26, 1998.
On August 22, 1893, four hurricanes were also active in the Atlantic. One of these was the killer Sea Islands hurricane, which claimed between 1,000 and 2,000 lives in Georgia and South Carolina.

Incredibly, there have been five active Atlantic tropical cyclones at one time, from September 11-12, 1971. According to the National Hurricane Center, no more than two were of hurricane strength at any one time.

Why Did This Happen?

To answer why we had so many at once, we need to delve into several other factors.

Areas near the equator don't get cold fronts. The only changeable weather over a relatively short period of time is a roughly 30-60 day wet/dry cycle triggered known as the Madden-Julian Oscillation. The MJO is essentially a wave of energy in the atmosphere that propagates eastward around the Earth near the equator once every 30-60 days.

By a "wave," we mean the MJO has a phase where upward motion in the atmosphere is strong, helping to boost the formation of clouds and thundershowers, and a suppressive phase, helping to squelch precipitation.

In this case, a strong MJO was supporting strong upward motion, clouds and thundershowers in the western Pacific Ocean, as the "west-Pac trio" was just about to get going.

This strong upward motion, as with all MJOs, would eventually push east, giving a boost to thunderstorm clusters in the central Pacific pushing into early July.

The second factor was a strong burst of westerly near-surface winds near the equator in the western Pacific Ocean.

WSI operational scientist Dr. Michael Ventrice noted this would be the strongest such burst on record in the summer for the western and central Pacific.

Eric Blake, hurricane specialist at the National Hurricane Center, later noted this westerly wind burst was on track for a July record.

Generally speaking, the trade winds typically blow from a southeasterly direction south of the equator, and a northeasterly direction north of the equator.

Keeping in mind winds flow clockwise around low-pressure systems in the Southern Hemisphere, this westerly wind burst near the equator can give a boost to any fledgling areas of low pressure trying to form.

Finally, contributing to the low-level warmth and humid air needed to fuel convection, are impressive sea-surface temperature anomalies in the region where the two central Pacific systems are located.

Blake tweeted Tuesday parts of the eastern Pacific Ocean were seeing record warm sea-surface temperatures.

El Niños tend to lead to more eastern and central Pacific storms due to reduced wind shear, which would otherwise rip active or developing tropical cyclones apart.

More storms move west from the eastern Pacific basin into the central Pacific basin during El Niños, as well.