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The science of how Hurricane Patricia became so colossal

BY   October 23, 2015 at 6:07 PM EST
Hurricane Patricia as viewed from the International Space Station. Photo by Scott Kelly/NASA

Hurricane Patricia as viewed from the International Space Station. Photo by Scott Kelly/NASA

In early July, six cyclones struck the Pacific Ocean at once, marking the first time in a decade that this ocean has hosted five or more weather events with tropical storm strength. The following month, two storms with super-typhoon intensity — Goni and Atsani — marched across the Pacific in the same week — that hasn’t happened since 1997.

Now, Hurricane Patricia, the strongest storm ever recorded in the western Hemisphere, is churning across the Pacific on its way to Mexico, raising a number of questions:

Is El Niño responsible for these storm patterns? Partly, but not totally.

Is Patricia the worst storm ever in the Western Hemisphere? Depends on what you’re measuring.

How bad will Patricia be? By some measures, potentially as bad as hurricane Katrina.

And why is Patricia called a hurricane, not a typhoon, if it’s in the Pacific? Because of an arbitrary decision in 1945.

Let me explain.

Did El Niño cause Patricia?

In a word, no. You can’t attribute a single weather event to global climate change or El Niño.

But El Niño has contributed to the storm’s intensity, said Accuweather meteorologist Dan Kottlowski.

 

Water temperatures in the Eastern Pacific and along the West Coast are warmer than normal. In fact, Kottlowski said, off the coast of Mexico, the water temperatures are by far some of the warmest that have ever been measured since meteorological buoys and satellites began covering the area in the 1970s.

El Niño has also reinforced Patricia and other storms in the Pacific Basin by lowering wind shear.

Cyclones form when ocean temperatures reach 80 degrees Fahrenheit, which heats the air just above the water. That air rises into the cooler portions of the atmosphere, moving massive amounts of air and creating strong winds. The rising humid air also spawns the giant clouds of a cyclone.

Wind shear occurs when winds move at different speeds at different heights. For example, if there is no wind on the ground but 100 mile per hour winds at the top of the Empire State Building, then you’d say that location has high wind shear. If winds are moving at the same speed, then there is no wind shear.

Cyclones love conditions when there is little wind shear, and that’s what El Niño has done to the northern Pacific Ocean. One readout for this potency is accumulated cyclone energy, or ACE.

“We use what’s called ACE to calculate the energy expelled by tropical cyclones in a year,” Kottlowski said. “That value has been phenomenal this year, much higher than normal. Right now, it’s near a record amount.”

In fact, according to Slate’s Eric Holthaus, “Patricia is now very close to the theoretical maximum strength for a tropical cyclone on planet Earth.” El Niño is also triggering droughts in eastern Africa.

Ironically, El Niño and wind shear have combined to create a weaker than usual hurricane season in the Atlantic Ocean and Caribbean Sea, according to Kottlowski.

If you’ve ever played with a spinning top, you know that if you tilt the top, it will fall over, Kottlowski said: “It’s the same thing with the atmosphere. What it’s basically doing is all the thunderstorms are getting blown off to the right or the left.”

Spinning top

The fast-moving winds from the west and resulting wind shear are cutting tropical storms to ribbons.

“In the Atlantic Basin, it’s pretty typical when there’s an El Niño that you don’t see as many storms developing. I looked at a graph of the shear across the Caribbean. It’s probably the strongest shear that we’ve seen across the Caribbean. That’s why there have been fewer storms,” Kottlowski said.

Is Patricia the worst storm to ever hit the Western Hemisphere?

The only way to know the true strength of a hurricane is by making measurements inside the storm, which is typically done with weather buoys in the water or by reconnaissance plane.

“It just so happens that [Air Force Hurricane Hunters] had an aircraft into the storm late yesterday,” Kottlowski said.

If you don’t have an aircraft, then you’re using satellite imagery to estimate the wind speeds and the pressure, which is less accurate.

“Patricia is the first hurricane where a reconnaissance aircraft has measured a wind speed of 200 miles per hour and pressure down to 880 millibars in the Eastern Pacific,” Kottlowski said

It’s conceivable that other storms in this region were underestimated. For example, a recon plane wasn’t available for Hurricane Linda in 1997. People estimated a pressure of 902 millibars, but that measurement was made with satellite estimates.


Conceptual animation illustrates the wind damage associated with increasing hurricane intensity, based on The Saffir-Simpson Hurricane Wind Scale. Video by Climate Central.

So as far as we know, Patricia has set a pressure record, topping Hurricane Wilma from 10 years ago. But why does it matter?

“Lower pressure gives a guesstimate of what the wind is going to be. The pressure doesn’t do any damage,” Kottlowski said. “It just gives a measure of how intense the storm is. The lower the pressure, potentially the stronger the winds.

Wait, is Patricia a hurricane, a cyclone or a typhoon?

All of the above. From a meteorological view, hurricanes, cyclones and typhoons are one in the same. They’re all storms born in tropical waters., Hurricanes, cyclones, typhoons, tropical depressions and tropical storms are all technically known as tropical cyclones.

When did people start using these different terms?

According to an article published in 1880 by the Royal Geographical Society of London, the word “typhoon” was first mentioned in print in 1560 by Portuguese explorer Fernão Mendes Pinto. From the article:

“The history of this word which, at the present day, may be considered the common property of about all European languages, is buried in the first reports of Western travellers on their adventures in Chinese waters.

The earliest print making mention of a typhoon seems to be “Pinto’s Journey,” first published in 1560. Here the word appears in its Portugese form at tufaõ, and Pinto himself says that this storm, which he encounterd on two occasions, is so called by the Chinese…The present spelling, typhoon, may be traced to the end of the 17th century; Lecomte, whose Memoirs first appeared in 1693, describing a Typhon, thus spelt.

This account speaks to the regional legacies of describing these storms. The word hurricane derives from the Spanish word “huracan”. Its roots sprouted among Spaniard colonists, who borrowed it from Hunrakan, the Mayan storm god, and Hurakan, a Taino and Carib god, according to The Weather Channel. Cyclone comes from the Greek word for circle, kuklos, but British merchant Henry Piddington is credited for applying the term toward an Indian Ocean storm in 1845.

How are these storms classified today?

The local derivatives stuck, Kottlowski said.

Hurricane is used for storms in the western Atlantic, Caribbean and eastern Pacific.

In the Northwest Pacific, people use the word “ typhoon”, though when the storms reach Category 4 or above 150 miles per hour, they’re called “super typhoons.”

Around Australia, India and throughout the Indian Ocean, these storms are called cyclones. Cyclon is also used for the rare occasions when a tropical storms hits the Mediterranean Sea, which has only happened five times since 1947.

Forecasters have been naming tropical cyclones since the late 19th century, but the habit didn’t become an official practice until 1945, when U.S. armed servicemen in the Western Pacific started naming the storms after their wives. This naming system became alphabetized two years later, according to the National Oceanic and Atmospheric Administration’s Hurricane Research Division:

“Starting in 1947, the Air Force Hurricane Office in Miami began designating tropical cyclones of the North Atlantic Ocean using the Army/Navy phonetic alphabet (Able-Baker-Charlie-etc.) in internal communications. During the busy 1950 hurricane season there were three hurricanes occurring simultaneously in the Atlantic basin, causing considerable confusion. Grady Norton then decided to use the Air Force’s naming system in public bulletins and in his year-end summary. By the next year, these names began appearing in newspaper articles.”

The Interdepartmental Hurricane Conference and the U.S. Weather Bureau officially adopted the practice of using female names for hurricanes in 1953, which caused an uproar, according to The Weather Channel. Equal rights activists fought for nearly 30 years to change the practice. Male names were finally adopted in 1979.

In 2014, a study in PNAS claimed hurricanes with female names caused more damage because they spur less fear in the general public; however, as Ed Yong highlighted for National Geographic, experts question the statistical methods used in the research.

The reckoning.

Kottlowski expects that Patricia will do serious damage this weekend. The storm is expected to make landfall just to the west of Manzanillo, Mexico and hit the Sierra Madre mountains..

“The low level part of the storm will fall apart, but the upper level structure of the storm will continue to transport deep tropical moisture through central mexico and into the US,” he said.

The storm will drop up to 6-12 inches, though higher terrain could see rainfall totals of up to 2 feet.

Extreme storm surge is expected to hit the coast. Early estimates predict a surge of 10 feet, though Kottlowski said that it could be much worse.

This satellite image from the National Oceanic and Atmospheric Administration shows Hurricane Patricia in the Pacific Ocean headed toward the Mexican coast.

Hurricane Patricia should make landfall in Mexico Friday evening. Image by the National Oceanic and Atmospheric Administration.

“When we look at surges with some of the bigger storms that hit the U.S., such as Hurricane Katrina, we see a storm surge of 25 to 26 feet. It’s conceivable that [Patricia] could create a storm surge that high.”

Once Patricia moves into the mountains, rain will be the biggest threat. Kottlowski said places like Puerto Vallarta, Guadalajara, and Manzanillo, Mexico are going to see a lot of rainfall, flooding and mudslides — all will be life threatening.

The storm will track eastward into the U.S. and develop into big rainstorm near the Texas coast, dumping heavy rain tomorrow, Sunday and perhaps into Monday over Southeast Texas.

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