August 30, 2019

Hurricane Dorian, Now A Category Four, Poses A Major Threat To Southeast Next Week

Hurricane Dorian rapidly strengthened into a category four storm on Friday evening, packing winds of 140 MPH by the 11:00 PM EDT advisory. We've known for a few days now that the storm would enter an extremely favorable environment for strengthening by the time it got to this point. The storm's track is still highly uncertain right now, with the probability of the coast-hugging scenario I mentioned yesterday ticking upward.
Hurricane Dorian at 11:50 PM EDT on August 30, 2019. | College of DuPage
It's impressive to watch satellite loops of Dorian organize into a near-perfect hurricane through the day on Friday, and that organization is evident in advisory updates through the evening. Here's how quickly the storm strengthened in just six hours this evening:

5:00 PM EDT  —  115 MPH, 970 mb
8:00 PM EDT  —  125 MPH, 950 mb
8:30 PM EDT  —  130 MPH, 950 mb
11:00 PM EDT — 140 MPH, 948 mb

It could remain a major hurricane as it approaches Florida next week.

The National Hurricane Center's latest track forecast shows Dorian approaching Florida on Monday and Tuesday as a major hurricane. The official forecast follows model guidance showing an earlier turn near the coast, a scenario that would cause the storm to "hug" the coast in a very similar manner to Hurricane Matthew back in 2016. This path could expose coastal sections of Georgia, South Carolina, and North Carolina to hurricane conditions by the middle of next week.

There's still quite a bit of uncertainty in that forecast. We're still three to four days from the core of the storm approaching land. When it comes to an uncertain track like this, a shift of a few dozen miles either way can mean the difference between tragedy and a near miss most people will forget in a year.

A ridge of high pressure to the north of Dorian is responsible for the uncertainty. The ridge is acting like a buffer that keeps Dorian from simply racing north and out to sea. As soon as the ridge weakens or moves, though, Dorian is going to make that northward curve. Models disagree when the ridge will weaken enough for the hurricane to make that turn. Some say the ridge will stay stronger longer, while others weaken it much faster. That relatively small difference is the source of all the consternation.

Aircraft reconnaissance will fly through, above, and around the storm through next week to feed forecasters a constant feed of data to help them understand Dorian's structure and the environment around it. Weather balloon launch sites across North America will release balloons four times a day—as opposed to twice a day—to collect upper-air data to aid in the forecast process. All of this extra data gets fed into weather models to give them a better starting view of the atmosphere, helping them to create more accurate guidance.

Potential Impacts

The forecast for the northwestern Bahamas is downright terrifying to read. In addition to (and as a result of) the potential for category four winds, some islands that experience the core of the storm could see a 10- to 15-foot storm surge. This would likely inundate much of the city of Freeport on Grand Bahama. Flash flooding is also likely due to rainfall totals exceeding one foot along the path of the storm.

Unfortunately, it's still too early to talk about specific impacts in the United States until forecasters are more certain about the track of the storm. Anyone along Florida's east coast is at risk for a period of intense winds, significant storm surge, and widespread flash flooding from heavy rainfall if the storm follows its predicted track. Hurricane Dorian will be a slow-moving storm when it approaches Florida. This slowness would exacerbate the effects of strong winds, storm surge, and heavy rainfall.

A near-shore curve could bring high winds, storm surge flooding, and flooding from heavy rains to Georgia and the Carolinas. However, since these effects are more than five days out—geez, it feels like we're going to deal with this storm forever—they're not included in official forecasts.

A Note About Weather Models

I wrote a post about using weather models over at my Forbes blog. Be careful looking at weather models. Meteorologists and enthusiasts share them openly on Facebook and Twitter, and it's easy to mistake these guidance products as official forecasts.
Using a weather model without proper training is like arguing with a medical diagnosis by waving a printout from Google in your doctor’s face. Contrary to popular wisecracking, meteorologists don’t just rip their forecasts from the models. Weather models are guidance. It takes a trained eye to analyze weather model output and use that information to craft their forecast.
Always rely on the National Hurricane Center's forecasts to make decisions.

A Note To Vacationers

A ruined vacation sucks. I know it. A hurricane threatening land on Labor Day weekend isn't exactly an unexpected event. There's literally a historic hurricane called the "Labor Day Hurricane." Any trip to the southeastern United States this close to the peak of hurricane season comes with the inherent risk of not happening due to the weather.

Every year, we hear about visitors who dig-in and insist that they're not leaving because of a storm.

If and when the authorities say to leave, that's the end of your vacation. Better luck next year. You are a guest in whatever town you're visiting. If you put yourself in harm's way for the sake of getting your money's worth or the thrill of experiencing a hurricane, you are selfishly taking from the people who actually live there and may not have the money or means to evacuate. An emergency crew assisting you is an emergency crew not assisting somebody who actually belongs there.

A Note to Meteorologists

Hi. Thanks for all your hard work. As I mention every couple of months when a big weather event happens, keep in mind that those of us tuned into the weather 24/7 follow no fewer than 500 other weather folks on Twitter. You're going to see the same information about Dorian over and over and over again. Please don't shame folks out of sharing the same basic forecasts and satellite images because you're seeing it so often. Their followers may only see that information cross their feed once or twice and there's always a chance it could help a few of them. That's all that matters.

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Hurricane Dorian Poised To Threaten Florida As A Major Hurricane Early Next Week

Hurricane Dorian grew stronger in the southwestern Atlantic Ocean on Thursday, steadily moving toward the northwest as it pulls away from the Greater Antilles. Great uncertainty remains in the storm's eventual track and where—even if—the storm will make landfall in Florida or the southeastern United States early next week.

The National Hurricane Center's official forecast at 11:00 PM EDT on Thursday looks similar to forecasts from the last couple of days, with a couple of notable changes. The forecast makes the hurricane stronger, slows it down as it approaches land, and pushes the track farther south. Landfall next week is now expected to occur on Monday night or Tuesday, but that can (and likely will) change as we get closer to the weekend.

Dorian Is Strengthening

Aircraft reconnaissance found Hurricane Dorian strengthening rapidly on Thursday night, with its minimum pressure dropping from 986 mb to 977 mb between the 5:00 PM and 11:00 PM advisories. The storm now has maximum sustained winds of 105 MPH, which makes it a category two on the Saffir-Simpson Hurricane Wind Scale.

As you'd expect given its intensification, the hurricane looks better on satellite tonight than it did last night. Dorian lost the "blob" of convection on its east side and it looks more tightly wound than it did yesterday (don't we all). The hurricane is also more symmetric than it was this morning, with hurricane force winds now completely surrounding the storm's eyewall rather than occurring all on one side of a storm.

Hurricane Dorian spent Thursday getting itself better organized, and given the favorable environment it'll encounter north of The Bahamas, all indications point toward continued strengthening through the weekend. Strong hurricanes tend to fluctuate in intensity, so don't be surprised if its wind speeds go up and down as the storm grows in size and it undergoes eyewall replacement cycles.

The Cone Is All That Matters Right Now

It's important not to focus on specific landfall locations. Anyone in and around the cone of uncertainty is at risk for effects from this storm. The NHC's average margin of error five days out is 228 miles, and it's even greater than that about a third of the time. The cone of uncertainty doesn't account for all of the uncertainty in the forecast, and there are a wide range of scenarios that depend on small changes in the environment around Hurricane Dorian.

Four Scenarios Are Possible

Hurricane Dorian is still far enough away that every little jut and jog and gyration in the storm's structure and path will have an effect on where it goes in a couple of days. A move to the north or south, or the storm moving slower or faster than anticipated, can have big implications on its ultimate track.

Much of the nervousness right now is centered around the strength of ridges of high pressure over the United States and central Atlantic Ocean. Each weather model is resolving these features a little different, leading to disagreement between the models on exactly when the hurricane will begin its curve toward the north.

A ridge of high pressure to the north of a hurricane acts like a buffer that prevents the storm from moving north, guiding the storm around the edges of the ridge until the storm finds opening or the ridge itself weakens.

Most Likely Scenario: Landfall In Florida, Southeast Soaking

This is the scenario covered by the National Hurricane Center's current forecast. The most likely outcome right now, according to experts analyzing current data, is that Hurricane Dorian will slow down as it approaches Florida next week, making landfall somewhere along the state's east coast during the day on Monday.

After landfall, the storm is likely to begin a very slow turn toward the north in the following days. This turn, and any movement after that, is too far out to show up in the National Hurricane Center's forecasts.

The slow forward motion of the storm would lead to an extended period of heavy rain and strong winds over Florida, as well as any other state that ends up in the storm's path next week.

Other Possible Scenarios

The cone of uncertainty exists to remind us that hurricane track forecasting is still an inexact science. It's a heck of a lot better than it was a decade or two ago, but meteorologists today still don't know all the answers. That's especially true with a storm like Hurricane Dorian, where small changes in the surrounding environment can have huge ramifications a few days down the line.

I like this "extended" cone of uncertainty graphic by Tim Buckley, chief meteorologists of WFMY-TV here in Greensboro, NC. It shows the range of possibilities for the storm beyond the NHC's five-day cone.

Here are some more scenarios that could play out over the next couple of days. Again, these aren't reflected in the current NHC forecast, but each scenario isn't out of the realm of possibilities given the environmental setup and uncertainty.

Slightly Weaker Ridge: Scrapes Florida, Hits Georgia Or The Carolinas

This outcome, which is reminiscent of Hurricane Matthew in 2016, isn't too terribly far-fetched. A slightly weaker ridge would allow the storm to make its northward turn earlier than currently predicted, allowing the hurricane to scrape the Florida coast and make its way toward Georgia or one of the Carolinas. This would subject a long swath of coastline to intense winds and storm surge flooding, not to mention the threat of heavy rain from a slow-moving system.

Much Weaker Ridge: Turns Shy Of The Coast

One possibility is that the ridge to Dorian's north breaks earlier than anticipated, allowing the storm to turn shy of the coast and recurve rather than hitting Florida. It was a hot topic of discussion for much of the day on Thursday after a run of the European model hit social media. It could happen

Slightly Stronger Ridge: Landfall In Florida, Enters The Gulf

If the ridge stays stronger than predicted, there's a chance the storm could traverse the Florida Peninsula and emerge in the Gulf of Mexico by the middle of next week. If this scenario were to play out, it would put the northern Gulf Coast in contention for impacts from this storm. That said, the odds of this outcome seem to have waned a bit over the last day or so, but it's a possibility nonetheless.

Hard As It Is, We've Got To Wait On Specifics

It's maddening not to get specific information when so much is at stake. I know it. We're too far away from any potential landfall to tell you wind speeds, rainfall amounts, storm surge heights, or tornado potential for any one point on land. That's information we'll get in a couple of days when models and forecasters have a better handle on the track the storm will take.

The best thing to do right now is pay attention to each advisory from the National Hurricane Center and make sure you're prepared for extended power outages and, if you live in a flood zone, plans for what to do if you're ordered to evacuate.

This is going to be a slow-moving and prolonged storm. We've got a ways to go before it reaches land. Watch and wait, but don't hyperventilate. (And I promise I didn't mean for that to rhyme.)

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August 29, 2019

Hurricane Dorian Quickly Organizing In The Southwestern Atlantic Ocean

Dorian strengthened into a hurricane over the U.S. Virgin Islands on Wednesday afternoon, passing into the southwestern Atlantic Ocean where it will spend the next four days in a prime environment for strengthening. The National Hurricane Center expects the storm to make landfall in Florida on Sunday, but the storm's specific track—and what happens beyond landfall—is still an open question.

The 11:00 PM EDT advisory from the National Hurricane Center shows Dorian making landfall on Florida's east coast as a major hurricane on Sunday or Monday. The cone of uncertainty stretches from the Everglades to the central Georgia coast, though, so don't get too hung up on exact landfall locations this far in advance. Everyone in Florida and along the southeastern and Gulf coasts should carefully follow the storm's progress.

Hurricane Dorian ramped up in a hurry on Wednesday. The storm was a disheveled mess on Tuesday, struggling to maintain itself in the eastern Caribbean Sea and constantly reforming its center of circulation to the northeast. At the time, it wasn't entirely clear if the storm would survive its encounter with the Greater Antilles, given its disorganized state and the mountainous terrain of Puerto Rico.

Those northeasterly jogs kept the bulk of the storm east of Puerto Rico, bringing hurricane conditions to the U.S. Virgin Islands and keeping the center of circulation mostly over water. This allowed Dorian to organize its structure and strengthen into a hurricane on Wednesday afternoon.
Tropical Tidbits
Dorian is now moving away from the Greater Antilles and into the open waters of the southwestern Atlantic Ocean. At 11:00 PM EDT, aircraft investigating the storm found maximum winds around 85 MPH with a central minimum pressure of 986 mb. The storm is struggling a bit due to intrusions of dry air. You can see the structure of the storm really well on the radar out of San Juan:
Gibson Ridge
The hurricane is lopsided at the moment, with a core and heavy bands off to the east. This band shows up as that "blob" on the satellite imagery above, which could be the result of easterly winds causing convergence on the east side of the system. Fluctuations in organization and intensity are common in storms, especially as they start to get their act together, but the overall environment is favorable for Dorian to use the next four or five days to grow into a major hurricane as it heads toward Florida.

The NHC issues official forecasts every six hours—at 11:00 and 5:00 AM/PM—with intermediate strength and position updates every three hours in between. If you live in the southeastern United States, even if you're dozens of miles inland, make sure you have enough food, water, and batteries to get through several days without power. Make plans to go somewhere if you have to evacuate from storm surge or inland flooding due to heavy rain.

I'll have a longer and more detailed post here at DAMWeather during the day on Thursday.

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August 26, 2019

The Tropical Atlantic Grows Active Again After An Unusually Long Midsummer Silence

It's been an unusually quiet summer so far in the Atlantic Ocean. We didn't see a named storm between Hurricane Barry making landfall on July 17 until weak ol' Tropical Storm Chantal formed in the oceanic boondocks early last week. That quiet trend is coming to an end, right on time for the peak of hurricane season.

Tropical Storm Dorian Approaching The Caribbean

A tropical wave managed to survive the persistently dry and dusty air puffing off of the western African coast, developing into Tropical Storm Dorian on Saturday afternoon out in the tropical Atlantic.

I wrote a detailed post about the storm over at my Forbes blog on Saturday night. This is the first storm we've seen so far this season that's actually developed in the tropics. The NHC expects the storm to enter a window of favorable conditions for strengthening, so their forecast shows Dorian reaching hurricane strength by the time it enters the Caribbean on Tuesday. There's a chance that the storm could undergo rapid intensification at some point over the next couple of days, so a storm like this can quickly grow serious sooner than expected.

It's scary to see Puerto Rico in the cone of uncertainty. Puerto Rico—which, by the way, is a territory of the United States and whose residents are American citizens—is still struggling to recover from Hurricane Maria in September 2017. Maria made a direct strike on the island as a major hurricane; thousands of people died during the storm and in the prolonged suffering that followed. Many parts of the island weren't reconnected to the power grid for months after the storm.

The island territory's situation at the moment is precarious at best—a faltering economy, survivors trying to get back on their feet after the first storm, a local government in chaos, and a federal government run by individuals who couldn't seem to care less about the continued suffering of several million American citizens on American soil—so even a glancing blow by a storm of any strength comes with a heightened potential for harm.

Watching Invest 98L

Invest 98L off the southeastern coast on August 26, 2019. || College of DuPage

The other disturbance out in the Atlantic right now is Invest 98L, a slow-moving system that's been meandering off the Florida coast since last week.

Models look a lot less favorably on this system than they did a few days ago. Nevertheless, the NHC gives this system a high chance of developing into tropical cyclone as it slowly moves away from the East Coast through midweek. It doesn't look like there's an immediate threat to the East Coast as a cold front approaches from the west, but it's good to stay vigilant every day through the end of hurricane season—when you're keeping tabs on everything, very few things have the chance to surprise you.

It's Been A Quiet Summer. (That's A Good Thing!)

It's uncommon to see such a long stretch in the middle of summer without a named storm anywhere in the Atlantic. We didn't see one named storm in the Atlantic Basin between July 13, when Hurricane Barry made landfall on Louisiana, and when Tropical Storm Chantal developed this past Monday. We had one tropical depression near Florida about a week after Barry made landfall, but it only managed to last for 18 hours. (Really!)

Such a long period of silence between mid-July and mid-August is one of the longest midsummer stormless stretches we've seen in the satellite era, rivaled only by a couple of slow hurricane seasons in recent decades. A quiet start to hurricane season is good news for folks who live near the coasts for obvious reasons, but this silence also gives people plenty of time to prepare for when tropical activity inevitably starts to pick up in a couple of weeks as we approach the peak of hurricane season.

El Niño Is Gone

Forecasters continue to predict a near- or above-average Atlantic hurricane season this year due to a waning El Niño in the eastern Pacific Ocean. This forecast accounts for the number of tropical storms and hurricanes we'll see in a given year—an average year sees 12 named storms, 6 hurricanes, and 3 major hurricanes. We've already seen three tropical storms and one hurricane this year.

One large-scale factor that plays an indirect role in the Atlantic Ocean's tropical activity is El Niño, which occurs when water around the equator in the eastern Pacific Ocean grows abnormally warm for many months at a time. This warming can generate excess thunderstorm activity in the eastern Pacific, which in turn creates wind shear that can suffocate any disturbances trying to develop over in the Atlantic.

The National Weather Service reported on August 8 that the El Niño that began last fall has finally subsided. The agency predicts that we'll remain in a neutral state—no El Niño or La Niña—through the balance of hurricane season, which could lessen that destructive wind shear and make conditions a little more favorable for tropical development in the coming months.

Another major factor in this year's oceanic snoozefest is dry, dusty air blowing off the western coast of Africa. These pulses of arid desert air choke off any convection that tries to form in areas we would typically watch for tropical development. A tropical cyclone can't form out of thin air—it has to form from an existing complex of thunderstorms, and those can't exist if dry air keeps chomping away at them.

It's not good to seek security in the raw number of named storms. Some of our most destructive hurricanes formed in "slow" hurricane seasons, and rain is often the greatest threat of any landfalling system—even unnamed tropical disturbances.

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August 25, 2019

President Trump (Allegedly) Wants To Know If We Can Stop A Hurricane With Nuclear Bombs

Axios reported Sunday evening that Donald Trump, former host of The Apprentice and current President of the United States, reportedly asked Homeland Security officials on multiple occasions if we could "nuke" or simply bomb a hurricane to disrupt the storm and prevent it from posing a serious threat to land.


[sharp breath]

Those who follow me on Twitter know that I am not inclined to give our forty-fifth president the benefit of the doubt. However, I am a benevolent partisan with the greatly stressed and likely clogged heart of an educator ready for summer vacation, so I'm willing to cede two points:

1) The desire to stop a hurricane before it hits land is a virtuous impulse, very good; and

2) Facetiously or not, lots of people ask this question! In fact, this is probably one of the most common weather-related questions I hear when a major hurricane is in the news.

Now, the latter of those two points is important. This is a question I enjoy hearing from an inquisitive reader. They're curious about the mechanics of a big storm and it's natural to wonder if the most powerful and destructive force ever created by humankind could take it down. I respect that.

That being said, I expect the President of the United States, the person who singularly controls no fewer than 6,000 nuclear weapons, to know why you can't detonate a nuclear bomb in the middle of a hurricane. But we've long since established that Donald Trump possesses unique knowledge of many things, so I'm not surprised this came up. (Though, to be fair, I expected it much sooner.)

Here's why you can't detonate a nuclear weapon in the middle of a hurricane.

A Nuclear Bomb Won't Stop A Hurricane

Hurricane Michael making landfall near Panama City, Florida, on October 10, 2018. || Gibson Ridge
Understanding why a nuclear bomb won't come close to stopping a hurricane requires a quick and admittedly simplified explanation of how tropical cyclones gather their strength.

Tropical cyclones—the term for the low-pressure systems we call tropical depressions, tropical storms, and hurricanes—are powered by thunderstorms packed in an eyewall that surrounds the center of the cyclone. A thunderstorm's updraft draws air away from the surface, leaving behind lower air pressure in its wake.

Stronger thunderstorms can draw vast amounts of air away from the surface and vent it into the upper atmosphere. This mass evacuation of air from the surface lowers the air pressure at the center of the storm, causing the cyclone to grow stronger. A stronger tropical cyclone can maintain stronger thunderstorms around the center, triggering a feedback process that results in a strengthening storm.

A tropical cyclone can continue this feedback process for as long as it remains in favorable conditions for development—warm water, ample moisture, and low wind shear. That's why tropical cyclones can fall apart in spectacular fashion once thunderstorms are disrupted by dry air or wind shear, or if the storm moves over land or cooler waters and thunderstorms lose their fuel source.

Detonating a nuclear bomb in or near a hurricane won't do anything to disrupt the energy sources that hurricanes need to survive. The force of a nuclear explosion—even many nuclear explosions—would pass right through the thunderstorms in the eyewall. You couldn't generate enough heat or shockwaves to rip the storm apart. Hurricanes are simply too big, and nuclear explosions too comparatively tiny, for such a mission to come close to success.

Let's say you went another route: what if, instead of trying to destroy the storm from within, you tried to alter the environment around it instead?

Water Temperature: It's not feasible to detonate enough bombs beneath the ocean surface to induce the type of upwelling needed to cool sea surface temperatures and rob a storm of the instability it needs to survive. Again...tiny bombs, big storm.

Atmospheric Moisture: Using nuclear bombs to lower the humidity around a hurricane wouldn't work, either. Like a truck driving through a puddle, the size of the hurricane would easily overcome any localized effects on humidity levels.

Wind Shear: The wind created by the explosion of a nuclear bomb is localized to the area right around ground zero. Even the well-timed atmospheric detonation of many bombs could never create the sustained wind shear necessary to disrupt the thunderstorms that power the storm.

It Would, However, Succeed In Spreading Radiation Everywhere

A nuclear bomb wouldn't stop a hurricane, but it would turn the hurricane's path into one long superfund site. The detonation of one or more nuclear bombs in the center of a storm would spread radiation everywhere. Getting hit by a hurricane is bad enough without worrying about radiation poisoning and cancer clusters for decades after the storm.

Radioactive fallout would contaminate the ocean beneath the storm. The winds within the storm would spread the fallout across a wide area along the track of the storm. Winds above the storm would vent radioactive fallout hundreds of miles outside the storm. Multiple nuclear detonations would generate even more fallout, making matters worse and increasing the odds of a mammoth, historic radioactive contamination event that would render vast swaths of the Atlantic basin uninhabitable.

We generally understand nuclear explosions to be a bad thing. Radiation is bad. No good comes from the detonation of a nuclear weapon, even when it's high in the sky and far away from land. This universally accepted fact is why humankind the world over has worked so hard (and so successfully!) to eliminate nuclear weapons testing.

I never expected to have to write these words together and in this order, but good golly, here we are: you can't stop a hurricane with a nuclear bomb, Mr. President, so please don't try.

(Top Photo: "Redwing" nuclear bomb test, Enewetak Atoll, July 8, 1956 || Dept. of Energy)

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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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