August 21, 2019

Tropical Storm Chantal Forms Out In The Middle Of Nowhere

A disturbance in the northern Atlantic Ocean developed into Tropical Storm Chantal on Tuesday evening, becoming the third named storm of the unusually quiet-to-this-point Atlantic hurricane season. Forecasters expect the storm to remain far out in the north-central Atlantic, posing a threat to no one but some ships and maybe a floating beach ball or whatever.
An infrared satellite loop of Tropical Storm Chantal on the evening of August 20, 2019 | Tropical Tidbits

The National Hurricane Center began mentioning this disturbance in its tropical weather outlooks last Friday, and it remained at a 10 percent chance of development until the system began to get its act together on Tuesday morning. Hey—a 10 percent chance is still a chance.

The system became Tropical Storm Chantal after developing a sustained patch of thunderstorms this morning, which in turn induced the development of a closed circulation at the surface. Westerly wind shear is keeping the system from looking its best tonight. The storm is moving east at a decent clip and its thunderstorms are all confined to the east of the center of circulation.

This tropical storm is what you stare at when you're a bored weather enthusiast aimlessly wandering around the internet looking for something to do on a late summer weeknight. It's underwhelming, but it's better than watching a King of Queens rerun on TV Land for the 87th time.

Tropical Storm Chantal should remain far out in the central Atlantic Ocean; the 11:00 PM EDT forecast shows the system barely clinging to tropical storm status as it wanders somewhere between Bermuda and The Azores. A cone of uncertainty forms a haphazard blob over the central Atlantic as a result of the storm's expected curly track toward the end of its life cycle—if it survives that long, of course.

Chantal is the first storm we've seen in the Atlantic since Hurricane Barry made landfall on the northern Gulf Coast in the middle of July. That's the longest mid-summer quiet stretch since at least the early 80s. We're approaching peak season and it doesn't take much for one storm to turn into a serious threat if it approaches land. Even though it's quiet and we're talking about one thunderstorm over a semi-naked wind swirl right now, it's wise to make visiting the National Hurricane Center a part of your daily routine for the next month or two. Things can change in a hurry.

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August 15, 2019

GOES-17, The Little Weather Satellite That Could, Survived Another Hiccup Last Night

The United States' newest weather satellite survives to sense another day. GOES-17, known in service as GOES-West, suffered a 10.5-hour outage this morning after a reported software glitch caused the satellite to stop transmitting products and imagery. Engineers were able to fix the problem and the satellite began scanning the skies again this afternoon.

Meteorologists and amateur weather enthusiasts collectively held their breath this morning when NOAA said engineers were looking into a "spacecraft anomaly" that caused an outage of all visible and infrared imagery from the satellite.

The term "spacecraft anomaly" can be one of those coy euphemisms used to describe a particularly bad incident in a way that doesn't sound so upsetting. It's not unlike a chipper flight attendant casually describing what to do in a "water landing," which sounds much more agreeable than "crashing into a lake."

However, and thankfully!, things aren't always as bad as they first seem when an "anomaly" is first spotted. This issue was reportedly a software glitch that engineers solved with a restart of the Advanced Baseline Imager (ABI), the instrument that provides us with visible, infrared, and water vapor imagery.

The satellite is back online and working fine now. The image at the top of this post is a view from the satellite this afternoon. (Ohh. Ahh. Pretty.)

GOES-17 Is No Stranger To Struggle

This isn't the first time the newest GOES satellite acted up. The satellite's ABI encountered a significant failure of its cooling system when engineers booted up the satellite for testing in the spring of 2018. NOAA concluded just two weeks ago that a clogged pipe prevented the ABI's coolant system from working properly.
An example of interference in infrared satellite imagery caused by excess heat given off by the ABI. | NOAA

The problem seemed pretty bad at first—so bad, in fact, that it looked like the satellite would have limited functionality that could hamper its effectiveness.

A geostationary satellite like GOES-17 orbits at the same speed Earth rotates, fixing the satellite over one point on the equator. This fixed position affords the satellite the exact same view of Earth for its entire service life. The altitude required to achieve geostationary orbit also exposes the ABI instrument, which faces Earth, to direct sunshine for several hours a day around the winter and spring equinoxes.

The above picture shows why that's a problem when the cooling system doesn't work properly. The ABI works by sensing 16 different spectral wavelengths (known as "bands") to provide us with the visible, water vapor, and infrared imagery we see in weather reports every day. When the ABI's cooling system fails and it overheats, the heat of the instrument itself begins giving off longwave radiation that matches the wavelengths used to create water vapor and infrared imagery. 

The interference from the overheating instrument leads to noisy, useless satellite imagery across the affected wavelengths for those couple of hours of direct sunshine. Engineers were able to implement fixes and workarounds that brought the satellite up to 97 percent functionality, which is pretty darn good given the bleak outlook just a few months earlier.

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August 9, 2019

The Eye Of A Powerful Typhoon Abruptly Swerved Around This Japanese Island

The eye of Typhoon Lekima made an unusual and impressive curve around Japan's Tarama Island on Thursday evening, preventing the center of the storm from making a direct landfall on the tiny island. The unexpected wobble in the storm's track—which only amounted to a couple of miles—is a testament to how minuscule changes in the track of a storm can have dramatic consequences.

Typhoon Lekima approached Japan's Ryukyu Islands with maximum sustained winds of 130 MPH, making it the equivalent of a category four on the Saffir-Simpson Hurricane Wind Scale. The Ryukyus are the archipelago of tiny islands of between the southern Japanese island of Kyushu and the northern tip of Taiwan.
Infrared satellite view of Typhoon Lekima wobbling around Tarama Island on August 8, 2019. | CIMSS, University of Wisconsin
It looked like the eye of powerful Typhoon Lekima would make landfall when it crossed the archipelago on Thursday night. But just as the typhoon's strongest winds approached Tarama Island, the eye of the storm suddenly changed course.

Over the course of a couple of hours, the typhoon's eye performed a sudden curve around the island and missed landfall altogether. This wobble exposed the island of 1,250 people to the eyewall's intense winds for several hours. While the halting loop of Lekima's eye is unusual compared to other storms, wobbles are common in strong cyclones and these minor track deviations it can make all the difference for those in a storm's path.

Typhoon Lekima's abrupt wobble around Tarama Island is a fantastic example of trochoidal motion within a tropical cyclone. The center of a tropical cyclone doesn't move in a straight line. The paths we see on weather maps are smoothed out over a period of several hours. If you tracked the center of a strong hurricane using each update of a weather radar, you'd get a wiggly line—or a trochoid, hence the name—rather than a pleasantly smooth, computerized line.

Trochoidal motion can occur in the track of a storm's eye for a variety of reasons; in Typhoon Lekima's case, this likely included an eyewall replacement cycle and an uneven distribution of strong thunderstorms within the eyewall itself. Eyewall replacement cycles are common in intense storms as a new eyewall forms around the old eyewall, eventually choking off the old core of the storm and taking over as the storm's dominant feature. The center of the storm can wobble a great deal during this process.

Uneven thunderstorms in the eyewall can also cause a storm's eye to wobble. Strong thunderstorms forming in one part of the eyewall can destabilize the eye of the storm, as these new thunderstorms tug the center of the storm toward them. A fast-changing eyewall can push and pull the center of the storm over a couple of miles in a short period of time, causing wild gyrations like we saw when Lekima approached Tarama Island.

Despite the extended blow from the storm, news reports seem relatively positive despite the storm's size and strength. NHK World reported Friday that the storm caused four minor injuries and power outages to the islands affected by the core of the storm.
Super Typhoon Meranti making landfall on Itbayat Island, Philippines, in September 2016. | CIMSS, University of Wisconsin
Wobbling typhoons can pose a grave threat to the vast expanse of tiny, populated islands of the western Pacific Ocean. These storms are so common—and islands so plentiful—that a handful of these isolated communities take a direct or near-direct hit every year.

Super Typhoon Meranti made landfall on Itbayat Island in the far northern Philippines in September 2016, wobbling just right that the entire island wound up in the eye of the storm for a period of time. Itbayat and nearby islands saw heavy damage from the 2016 super typhoon, but suffered no fatalities as a result of the high construction quality of the buildings there.

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August 1, 2019

A Tropical Depression Is Likely In The Atlantic By Early Next Week

We could see our third named storm of the 2019 Atlantic hurricane season by this time next week. The suspect is a tropical disturbance that's currently about halfway between the Caribbean and Africa. The National Hurricane Center gives the system a high chance of developing into a tropical cyclone as it approaches the Lower Antilles early next week.

The first week of August is when tropical activity in the Atlantic Ocean typically begins to pick up steam. Right on cue, a tropical wave that moved off the western coast of Africa last week is the likely candidate for our next tropical system. The disturbance, currently called Invest 96L for tracking purposes, is rather healthy looking at the moment as far as tropical waves go. The system has plenty of thunderstorm activity and a defined, broad "swirl" in satellite imagery.
Invest 96L on satellite imagery around midnight on August 1, 2019. | Source: GREarth/AllisonHouse
A favorable environment will greet Invest 96L once it moves northeast of the Lesser Antilles next week; as a result, the National Hurricane Center gives the system a 70 percent chance of developing into a tropical depression by early next week.

It's far too early to talk about strength. But the overall pattern in the Atlantic right now does give us an idea of the general track a potential named storm would take. The paths of most tropical cyclones that develop in this part of the Atlantic are driven by the Bermuda High, or the big dome of high pressure that dominates the middle of the Atlantic Ocean in the summer months.

A stronger high tends to push tropical cyclones closer to land, shunting them into the Caribbean or threatening The Bahamas or the U.S. East Coast. A weaker high allows the storm to begin its curve out to sea sooner, posing only a threat to Bermuda and shipping lanes in the northern Atlantic. The strength of this high—as well as a trough that's likely to approach the East Coast late next week—will determine the path of the system (should it develop, of course).

What can you do right now? I'd say "don't worry about it," but I'm a weather-worrier myself. I know how it is, even something like 10 days out. Consider this a great time to make sure all of your preparations are in order even if you're hundreds of miles inland. Take the time to inventory and gather up your supplies, documents, plans—all the stuff we should take care of at the beginning of hurricane season to begin with. If the storm forms and threatens, you're ready. If not, you're ready for the next one.

The National Hurricane Center issues tropical weather outlooks four times a day at 2:00 and 8:00 AM/PM Eastern. The agency won't begin issuing official wind/track forecasts unless the storm actually develops into a tropical depression, which likely wouldn't happen until Sunday at the earliest.

There is another disturbance the NHC has painted on its Wednesday night outlook. The system has a 10 percent chance of developing into a tropical cyclone off the southeastern coast late this weekend or early next week. I left it off of this map because it has such a low chance of developing and the fact that a big highlighted area right next to the U.S. is distracting when we're talking about a different system thousands of miles away.

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