Why Are Hurricanes and Typhoons More Common in the Pacific?

Typhoon Nepartak swirling over the Pacific Ocean on July 6, 2016
Typhoon Nepartak swirling over the Pacific Ocean on July 6, 2016

 Taiwan endured the impact of ferocious Typhoon Nepartak this month, a storm that crashed ashore with winds equivalent to those of a category four hurricane. The island nation, which sits off the southeastern coast of China, is a regular target for major tropical cyclones, Nepartak being the second such intense storm to come ashore there within the past year. The eastern Pacific Ocean is also hopping this summer, producing one tropical cyclone every couple of days so far this month. Meanwhile, the Atlantic has been dead quiet. This is a common pattern during the summer, and it raises a natural question: Why are hurricanes and typhoons more common in the Pacific Ocean than the Atlantic Ocean?

Tropical cyclones go by many names around the world, and the terminology can get confusing. Once a tropical cyclone strengthens to the point where it has gale-force winds—39 mph or greater—it becomes a tropical storm. A storm that reaches tropical storm strength usually gets its own name to help us quickly identify it in forecasts and warnings.

Once a tropical storm begins producing sustained winds of around 75 mph, we call the storm a typhoon in the western Pacific near Asia and a hurricane in the oceans on either side of North America. A “typhoon” and a “hurricane” are the same kind of storm, they just go by different names.

The Atlantic Ocean sees its fair share of named storms each year, averaging around 11 named storms in a normal season. The eastern Pacific Ocean averages around 16 named storms every year, and the western Pacific churns out more than two dozen named storms in a normal year. There are several factors that contribute to the Pacific teeming with cyclones while the Atlantic can sometimes struggle to see rogue thunderstorms let alone anything more ominous.


Sea surface temperatures (°C) around the world on July 14, 2016. Image credit: NOAA/ESRL/PSD

Warm sea surface water is the fuel that drives tropical cyclones. If you ignore large-scale anomalies like El Niño and La Niña, the waters in the Pacific Ocean are usually warmer than those of the Atlantic Ocean, and the temperatures stay pretty toasty through almost the entire year. If you were to take a swim in the water off the coast of the northern Philippines, it would feel like you dunked yourself into a freshly drawn bath, just as it would if you took a dip in the ocean at a beach in Florida. Though parts of the Atlantic get uncomfortably warm, the expanse of hot water is much larger in the Pacific than it is in the Atlantic. The larger pool of steamy water gives more disturbances the opportunity to spin-up into major storms.

The persistent warmth of the western Pacific allows the typhoon season there to last the entire year, unlike around North America where it starts in May in the eastern Pacific and June in the Atlantic, both stretching through November. In addition to ocean currents, which have a major impact on sea surface temperatures, another significant factor in the Atlantic’s relative coolness is its proximity to land.


Deep cold fronts don’t stop at the beach when they’re finished sweeping across the United States and Canada. Some cold fronts can keep sailing long after they leave shore, traveling across vast swaths of the ocean and dipping as far south as the islands of the Lesser Antilles. The constant train of cold fronts marching out to sea during the early spring and late fall can put the kibosh on tropical cyclone formation, stabilizing and drying out the air and chilling the warm sea surface waters. The Pacific doesn’t have that common issue—most storms stay far enough north that they don’t much affect the typhoon and hurricane seasons across the basin.

Saharan dust crossing the Atlantic Ocean in June 2010. The image was stitched together from a series of images collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite during successive orbits; gray areas show gaps between satellite overpasses. Image credit: NASA Earth Observatory

Dry air is also a major problem in the Atlantic Ocean. The Saharan Air Layer (SAL) recently made the news as dust blowing off Africa’s Sahara Desert traveled across the entire ocean and made for some hazy, colorful sunsets in the southeastern United States. These puffs of dry, dusty air coming off Africa don’t only alter our sunsets, but they can have a big effect on tropical cyclones. Dry air is the arch nemesis of tropical cyclones; by their very nature, these cyclones need as much moist air as they can ingest to survive and thrive during their life cycle. Dry air that spirals into the center of a tropical cyclone can collapse the thunderstorms and cause the storm to fizzle out.

Thunderstorms that develop over Africa also serve as the nucleus for some of the worst storms the Atlantic can produce. Disturbances that drift off the African coast can quickly come to life near the Cape Verde Islands, gaining steam as they spiral west toward North America. If western Africa experiences a drought (or the SAL keeps blowing west), it can have a significant impact on the Atlantic hurricane season.

The ironic thing about tropical cyclones is that they produce some of the worst winds on Earth, yet relatively weak winds in the atmosphere can force them to dissipate. Atmospheric wind shear—strong winds that change speed and direction with height—is a death sentence to budding tropical storms. Winds blow the tops off the thunderstorms and prevent them from developing into much more than a brief pulse. Wind shear is also much greater in the tropical Atlantic than it is in the tropical Pacific, both due to regular jet stream patterns and the constant stream of low-pressure systems blowing off North America. 

What Do the Numbers and Letters on a Boarding Pass Mean?

iStock.com/Laurence Dutton
iStock.com/Laurence Dutton

Picture this: You're about to embark on a vacation or business trip, and you have to fly to reach your destination. You get to the airport, make it through the security checkpoint, and breathe a sigh of relief. What do you do next? After putting your shoes back on, you'll probably look at your boarding pass to double-check your gate number and boarding time. You might scan the information screen for your flight number to see if your plane will arrive on schedule, and at some point before boarding, you'll also probably check your zone and seat numbers.

Aside from these key nuggets of information, the other letters and numbers on your boarding pass might seem like gobbledygook. If you find this layout confusing, you're not the only one. Designer and creative director Tyler Thompson once commented that it was almost as if "someone put on a blindfold, drank a fifth of whiskey, spun around 100 times, got kicked in the face by a mule … and then just started puking numbers and letters onto the boarding pass at random."

Of course, these seemingly secret codes aren't exactly secret, and they aren't random either. So let's break it down, starting with the six-character code you'll see somewhere on your boarding pass. This is your Passenger Name Reference (or PNR for short). On some boarding passes—like the one shown below—it may be referred to as a record locator or reservation code.

A boarding pass
Piergiuliano Chesi, Wikimedia Commons // Public domain

These alphanumeric codes are randomly generated, but they're also unique to your personal travel itinerary. They give airlines access to key information about your contact information and reservation—even your meal preferences. This is why it's ill-advised to post a photo of your boarding pass to social media while waiting at your airport gate. A hacker could theoretically use that PNR to access your account, and from there they could claim your frequent flier miles, change your flight details, or cancel your trip altogether.

You might also see a random standalone letter on your boarding pass. This references your booking class. "A" and "F," for instance, are typically used for first-class seats. The letter "Y" generally stands for economy class, while "Q" is an economy ticket purchased at a discounted rate. If you see a "B" you might be in luck—it means you could be eligible for a seat upgrade.

There might be other letters, too. "S/O," which is short for stopover, means you have a layover that lasts longer than four hours in the U.S. or more than 24 hours in another country. Likewise, "STPC" means "stopover paid by carrier," so you'll likely be put up in a hotel free of charge. Score!

One code you probably don’t want to see is "SSSS," which means your chances of getting stopped by TSA agents for a "Secondary Security Screening Selection" are high. For whatever reason, you've been identified as a higher security risk. This could be because you've booked last-minute or international one-way flights, or perhaps you've traveled to a "high-risk country." It could also be completely random.

Still confused? For a visual of what that all these codes look like on a boarding pass, check out this helpful infographic published by Lifehacker.

Have you got a Big Question you'd like us to answer? If so, send it to bigquestions@mentalfloss.com.

Does Having Allergies Mean That You Have A Decreased Immunity?


Tirumalai Kamala:

No, allergy isn't a sign of decreased immunity. It is a specific type of immune dysregulation. Autoimmunity, inflammatory disorders such as IBS and IBD, and even cancer are examples of other types of immune dysregulation.

Quality and target of immune responses and not their strength is the core issue in allergy. Let's see how.

—Allergens—substances known to induce allergy—are common. Some such as house dust mite and pollen are even ubiquitous.
—Everyone is exposed to allergens yet only a relative handful are clinically diagnosed with allergy.
—Thus allergens don't inherently trigger allergy. They can but only in those predisposed to allergy, not in everyone.
—Each allergic person makes pathological immune responses to not all but to only one or a few structurally related allergens while the non-allergic don't.
—Those diagnosed with allergy aren't necessarily more susceptible to other diseases.

If the immune response of each allergic person is selectively distorted when responding to specific allergens, what makes someone allergic? Obviously a mix of genetic and environmental factors.

[The] thing is allergy prevalence has spiked in recent decades, especially in developed countries, [which is] too short a time period for purely genetic mutation-based changes to be the sole cause, since that would take multiple generations to have such a population-wide effect. That tilts the balance towards environmental change, but what specifically?

Starting in the 1960s, epidemiologists began reporting a link between infections and allergy—[the] more infections in childhood, [the] less the allergy risk [this is called hygiene hypothesis]. Back then, microbiota weren't even a consideration but now we have learned better, so the hygiene hypothesis has expanded to include them.

Essentially, the idea is that the current Western style of living that rapidly developed over the 20th century fundamentally and dramatically reduced lifetime, and, crucially, early life exposure to environmental microorganisms, many of which would have normally become part of an individual's gut microbiota after they were born.

How could gut microbiota composition changes lead to selective allergies in specific individuals? Genetic predisposition should be taken as a given. However, natural history suggests that such predisposition transitioned to a full fledged clinical condition much more rarely in times past.

Let's briefly consider how that equation might have fundamentally changed in recent times. Consider indoor sanitation, piped chlorinated water, C-sections, milk formula, ultra-processed foods, lack of regular contact with farm animals (as a surrogate for nature) and profligate, ubiquitous, even excessive use of antimicrobial products such as antibiotics, to name just a few important factors.

Though some of these were beneficial in their own way, epidemiological data now suggests that such innovations in living conditions also disrupted the intimate association with the natural world that had been the norm for human societies since time immemorial. In the process such dramatic changes appear to have profoundly reduced human gut microbiota diversity among many, mostly in developed countries.

Unbeknownst to us, an epidemic of absence*, as Moises Velasquez-Manoff evocatively puts it, has thus been invisibly taking place across many human societies over the 20th century in lock-step with specific changes in living standards.

Such sudden and profound reduction in gut microbiota diversity thus emerges as the trigger that flips the normally hidden predisposition in some into clinically overt allergy. Actual mechanics of the process remain the subject of active research.

We (my colleague and I) propose a novel predictive mechanism for how disruption of regulatory T cell** function serves as the decisive and non-negotiable link between loss of specific microbiota and inflammatory disorders such as allergies. Time (and supporting data) will tell if we are right.

* An Epidemic of Absence: A New Way of Understanding Allergies and Autoimmune Diseases Reprint, Moises Velasquez-Manoff

** a small indispensable subset of CD4+ T cells.

This post originally appeared on Quora. Click here to view.