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A tiny Tropical Storm Arlene swirls harmlessly in the central Atlantic Ocean on April 20, 2017.
Image Credit: NASA

6 Things to Know Now That Hurricane Season Has Started

Original image
A tiny Tropical Storm Arlene swirls harmlessly in the central Atlantic Ocean on April 20, 2017.
Image Credit: NASA

Tropical Storm Arlene formed in the middle of the Atlantic Ocean on April 20, 2017, briefly coming to life far away from land—where it was little more than an oddity to gawk at on satellite imagery. Even though the short-lived system wasn’t much of a threat (beyond aggravating some fish), the early start to the 2017 Atlantic hurricane season grabbed headlines.

But if you're a coastal resident anxious about the summer to come, fear not! It doesn't necessarily bode ill for the season. Now is as good a time as any to talk about what you can expect in this upcoming year, and to take a look at the innovative ways forecasters are improving how you can prepare for an approaching storm.

1. DON’T GET TRIPPED UP BY THE TERM SUBTROPICAL.

Tropical Storm Arlene first began its life as a subtropical cyclone. The word subtropical sounds intimidating, but it just describes the meteorological structure of the storm itself. Tropical cyclones are low-pressure systems that form over warm ocean waters and maintain their strength through thunderstorms raging near the center of the storm. They are tight, compact systems that are warm and muggy all the way from the surface to the top of the clouds.

The atmosphere is fluid, though, so not all storms perfectly fit that definition. That’s where subtropical cyclones enter the picture. A subtropical cyclone is one that resembles a tropical cyclone, but it’s not completely warm throughout the storm. It’s also not compact. Unlike a tropical cyclone, where the strongest winds are concentrated right near the center of the storm, the wind field in a subtropical cyclone can be far removed from the center and stretch hundreds of miles across. Sometimes these cyclones progress into tropical versions, sometimes they don't.

2. A STORM IN APRIL ISN’T AN OMEN FOR THE SEASON TO COME.

It’s not too unusual for a tropical or subtropical system to develop before the start of hurricane season. Hurricane season in the Atlantic runs from June 1 to November 30, but that’s just when they’re most likely to develop. The 2016 hurricane season started with Hurricane Alex in January—which was highly unusual—with the season’s second system, Tropical Storm Bonnie, forming in May. The last time we saw a storm in April was Tropical Storm Ana near Bermuda in April 2003.

Since 2007, we’ve seen eight tropical or subtropical cyclones develop before the official start of hurricane season. These early-season storms formed in years that were both quiet and active. In other words, storms that form before the start of hurricane season are usually case studies in their own right rather than a sign of things to come. Plus, no matter how many storms develop, it only takes one storm hitting land to cause major problems.

3. IT’S HARD TO TELL EXACTLY WHAT WILL HAPPEN THIS HURRICANE SEASON.

So much of what happens in the Atlantic Ocean’s hurricane season depends on what’s going on out in the eastern Pacific Ocean. El Niño and La Niña can have a major impact on how many storms are able to form. Years with El Niño conditions tend to see fewer storms in the Atlantic due to increased wind shear, which shreds potential storms apart before they can develop. Years featuring a La Niña can have the opposite effect, as cool waters in the Pacific help reduce destructive wind shear flowing out over the Atlantic—creating more opportunities for tropical systems to develop.

We’re in a “neutral” phase of the El Niño-La Niña cycle right now, which means that water temperatures in the eastern Pacific are right around where they should be. NOAA’s Climate Prediction Center is also calling for the chance for an El Niño toward the peak of hurricane season, though nothing is set in stone. If that happens as forecast, there’s a chance this season might come in a little quieter than average.

4. FORECASTS ARE A LITTLE BETTER THAN THEY WERE A FEW YEARS AGO.


A forecast map showing the cone of uncertainty for Hurricane Matthew on October 3, 2016.
Image Credit: Dennis Mersereau

When tropical storms and hurricanes fire up this summer, the most noticeable part of the coverage you’ll see online and on television is the cone of uncertainty, a shaded bubble that stretches along the length of the storm’s forecast track. This cone of uncertainty is the historical margin of error in hurricane track forecasts. Forecasts today are good enough that you can expect that the eye of a tropical cyclone will stay somewhere within that cone of uncertainty about two-thirds of the time.

At the end of each hurricane season, meteorologists at the National Hurricane Center (NHC) calculate the error in their previous forecasts and determine how far off their track forecasts were, on average. The NHC takes this average error at each time step and uses the resulting distance to draw a circle around their forecast points, connecting each circle to make the cone we’re all familiar with. The cone of uncertainty has steadily shrunk over the years—and the cone will grow a little narrower once again this year.

5. GET READY FOR STORM SURGE WARNINGS.

The deadliest part of a landfalling tropical storm or hurricane is flooding from storm surge, or the sea water that’s pushed inland by strong, persistent winds. Most storm surges are small; however, the surge in a large or intense storm can completely submerge a one-story home and push water several miles inland.

Since the threat for storm surge flooding can get lost in the focus on how strong the wind is blowing, the NHC will start officially issuing storm surge watches and warnings this year. Communities placed under one of these new storm surge warnings can expect life-threatening coastal flooding within 36 hours. This new focus on flooding might help convince people who would otherwise attempt to ride out the storm that it’s a better idea to leave for a few days than risk their lives.

6. YOU’LL HAVE A BETTER IDEA OF WHEN THINGS WILL GET UGLY.


A map showing the forecast arrival time for tropical storm force winds in Hurricane Matthew on October 3, 2016.
Image Credit: NOAA/NHC

Another new product being introduced this year by the National Hurricane Center is an arrival time map [PDF]. This forecast will show you when you can reasonably expect the damaging winds of a tropical storm or a hurricane to reach a certain point based on the storm’s current forecast track. This will help people and agencies gauge just how long they have to prepare for a storm before conditions deteriorate and venturing outside is too dangerous. However, these times are estimates—if the storm changes direction, speeds up, or slows down, the arrival times will change accordingly. Generally with storm systems, you can never be too prepared.

Original image
A tiny Tropical Storm Arlene swirls harmlessly in the central Atlantic Ocean on April 20, 2017.
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Weather Watch
3 Ways We Can (Kind of) Control the Weather, and 5 Ways We Can't

Humans have the incredible ability to control the world around us. We can move mountains and land robots on other planets. We can keep each other alive longer than ever before and even bring entire species back from the brink of extinction. But despite all of our leaps forward, we're still unable to control the weather, a tremendous force that affects every human being on this planet. Still, humans have come up with some pretty crafty ways of influencing the weather—in small doses.

1. WE CAN MAKE IT RAIN … SOMEWHAT.

The desire to control weather has been a mainstay of imagination since, well, the beginning of imagination. The fortunes of entire societies can hinge on flood or drought. We have strong motivation to want to create a rainstorm in one spot or moderate snowfall in another. But the greatest success we've ever had is a technique that can (maybe) encourage a tiny bit of rain to form over a tiny area.

Cloud seeding is a process through which fine particles like silver iodide are released into a cloud in order to encourage the formation of rain or snow. These particulates serve as a nucleus around which water vapor can condense and turn into a raindrop or a snowflake. This is most commonly done with small airplanes, but it can also be accomplished by launching tiny rockets or flares from the ground.

In theory, the practice of cloud seeding could have innumerable uses around the world, including crop maintenance, providing drinking water, and even possibly weakening severe thunderstorms or hurricanes. There's only one problem: It doesn't work all that well.

The effectiveness of cloud seeding is a hot topic of debate among scientists, but most studies have either found negligible impacts on precipitation, or the researchers were unable to determine the exact impact of cloud seeding. Cloud seeding is a great concept if you want to help one cloud produce a little extra rain or snow just to say you can do it, but it's not the way to go if you're desperate and want to trigger a deluge. This process requires the pre-existing presence of clouds, so even if the technology improves in the future, it's not a viable solution for drought-stricken areas that haven't seen meaningful clouds in weeks.

2. WE CAN DEFINITELY ATTRACT LIGHTNING USING ROCKETS.

Lightning safety is one of the things you learn from a very young age. "When thunder roars, go indoors," as the motto goes. We learn to stay away from open areas and water during thunderstorms. But what if you wanted to attract lightning? It's surprisingly easy to do if you have the right equipment and really, really want to encounter some of nature's fury.

Scientists who want to study lightning can bring it right to their doorstep by using specially designed rockets attached to conductive wires that lead to the ground below. When a thunderstorm blows over the observation station, operators can launch these rockets up into the clouds to trigger a lightning strike that follows the wire right down to the ground where the rocket was launched. Voila, instant lightning. Just add rocket fuel.

3. WE CAN CREATE CLOUDS AND HEAT—EVEN WHEN WE DON'T MEAN TO.

Most of the ways in which we control—or, more accurately, influence—the weather is through indirect human actions—often unintentional. "Whoops, the nuclear power plant just caused a snowstorm" isn't as crazy as it sounds. Steam stacks can and do produce clouds and updrafts with enough intensity to create rain or snow immediately downwind. The very presence of cities can generate microclimates with warmer temperatures and heavier rain. And there's also climate change, the process in which our accumulated actions over a long period of time are influencing the very climate itself.

BUT WE CAN'T DO THE FIVE FOLLOWING THINGS.

Despite our limited ability to influence a few aspects of weather over small areas, there are some rather colorful conspiracy theories about whether or not governments and organizations are telling the whole truth about how much we can accomplish with today's technology. There are folks who insist that the trails of condensed water vapor, or "contrails," left behind jet aircraft are really chemicals being sprayed for sinister purposes. (They're not.) There are theories that a high-frequency, high-power array of antennas deep in the Alaskan wilderness can control every weather disaster in the world. (It doesn't.) There are even folks who insist that Doppler weather radar carries enough energy to "zap" storms into existence on demand. (Dr. Evil wishes.)

There are also some bizarre and unworkable theories that are offered in good faith. A meteorologist a few years ago opined on whether building an excessively tall wall across middle America could disrupt weather patterns that could lead to tornado activity. And every year the National Hurricane Center is peppered with questions about whether or not detonating nuclear bombs in a hurricane would disrupt the storm's structure. Unfortunately, while pseudoscience offers up great theories to test in the movies, when it comes to weather, we're still not in control.

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A tiny Tropical Storm Arlene swirls harmlessly in the central Atlantic Ocean on April 20, 2017.
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Weather Watch
NASA Figures Out Why When It Rains, It (Sometimes) Drizzles
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What’s the difference between drizzle and rain? It has to do with updrafts, according to new research by NASA scientists into the previously unexplained phenomenon of why drizzle occurs where it does.

The answer, published in the Quarterly Journal of the Royal Meteorological Society, could help improve how weather and climate models treat rainfall, making predictions more accurate.

Previously, climate researchers thought that drizzle could be explained by the presence of aerosols in the atmosphere. The microscopic particles are present in greater quantities over land than over the ocean, and by that logic, there should be more drizzle over land than over the ocean. But that's not the case, as Hanii Takahashi and her colleagues at the Jet Propulsion Laboratory found. Instead, whether or not rain becomes full droplets or stays as a fine drizzle depends on updrafts—a warm current of air that rises from the ground.

Stronger updrafts keep drizzle droplets (which are four times smaller than a raindrop) floating inside a cloud longer, allowing them to grow into full-sized rain drops that fall to the ground in the splatters we all know and love. In weaker updrafts, though, the precipitation falls before the drops form, as that light drizzle. That explains why it drizzles more over the ocean than over land—because updrafts are weaker over the ocean. A low-lying cloud over the ocean is more likely to produce drizzle than a low-lying cloud over land, which will probably produce rain.

This could have an impact on climate modeling as well as short-term weather forecasts. Current models make it difficult to model future surface temperatures of the Earth while still maintaining accurate projections about the amount of precipitation. Right now, most models that project realistic surface temperatures predict an unrealistic amount of drizzle in the future, according to a NASA statement. This finding could bring those predictions back down to a more realistic level.

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