September 19, 2019

Texas Reels From Another Historic Flood After Imelda Drops Nearly Four Feet Of Rain



The remnants of Tropical Storm Imelda triggered yet another flash flood emergency in southeastern Texas, the fourth time this region has had to deal with historic, devastating floods in the last four years. Since Tuesday, the Beaumont area has seen bands of intense thunderstorms redevelop and sit over the same areas for hours at a time, producing nearly four feet of rain in some areas. The rain will slowly wane over the next day, but the damage is done.

A tropical wave moving across the northern Gulf of Mexico quickly strengthened into Tropical Storm Imelda on Tuesday as it made landfall. The disturbance organized into a tropical depression, strengthened into a tropical storm, and made landfall near Freeport, Texas, all within a two-hour window on Tuesday afternoon.

Imelda came ashore beneath a large ridge of high pressure over the eastern two-thirds of the United States; the storm's weak structure and the lack of steering currents meant that there was nothing to keep the storm moving north and away from the Houston/Beaumont areas. As a result, the system and its remnants have meandered over southeastern Texas for three full days. Ample tropical moisture and several sources of forcing allowed bands of thunderstorms—which produced 500,000 lightning strikes (!!!) in ten hours on Wednesday—to train over the same areas for hours at a time.


Some observing stations around Beaumont have seen more than three-and-a-half feet of rain since this all began on Tuesday. A foot of rain in one afternoon can trigger significant flash flooding just about anywhere; once you climb up two, three, four feet of rain, there's just no way to handle that even if you have the best infrastructure possible. The ground can't handle it. Natural waterways can't handle it. Man-made sewer systems can't handle it. Since it has nowhere else to go, the water just builds up and floods neighborhoods that have never experienced significant flooding before. This is why we hear "we've never flooded around here" after each of these events. Areas you don't think can flood really can flood if it rains hard enough for long enough.

Despite the system's rapid development, residents had plenty of warning that heavy rain would lead to flash flooding across southeastern Texas regardless of whether or not the disturbance became a named storm. Flash flood watches went into effect while the system was still over the Gulf. Local meteorologists went out of their way to make sure everybody knew the risks. However, there were few indications beforehand that rainfall totals would rival some of those seen in Hurricane Harvey just two years ago.

According to the National Weather Service office in Houston, the highest preliminary rainfall total from this event was 43.15" near Beaumont in Jefferson County, Texas. If that total verifies, the office said, it would make Tropical Storm Imelda the seventh-wettest tropical cyclone on record in the United States, and the fourth-wettest on record in Texas. This would also beat out Tropical Storm Allison's highest rainfall total of 40.68 inches; that storm in June 2001 served as the benchmark for tropical cyclone flooding for all subsequent storms until Harvey.

Tropical Storm Imelda is the fourth historic flood event in southern Texas in the last four years, following Memorial Day 2015, Tax Day 2016, and Hurricane Harvey in 2017. The Carolinas suffered tremendously in the flooding left behind by Hurricanes Matthew (2016) and Florence (2018). It's easily forgotten that Hurricane Barry, which made landfall (and produced two feet of rain) in Louisiana this past July, broke the all-time tropical cyclone rainfall record for the state of Arkansas after producing 16.17 inches of rain in the town of Dierks.

It's a common comment among meteorologists and weather enthusiasts during this event that there are few weather maps with a color scale large enough to cover the spread of rainfall totals. Topping-out the color scale on a rainfall map is a fairly arbitrary marker, but it demonstrates how unusual it is to see so many extreme rainfall events in such a relatively short period of time. We could go years without ever seeing another tropical system produce more than three feet of rain, or we could have another next month.

It's hard to link any one weather event directly to climate change, but it's also hard not to look at all these heavy rain events and ignore the influence climate change may play in current flood disasters and future storms. A warmer atmosphere is able to hold more moisture, which creates more opportunities for thunderstorms to produce heavier downpours. A changing climate will accentuate the extremes—dry spells will grow drier and flooding rains will grow even heavier.


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September 13, 2019

Tropical Storm Humberto Will Likely Develop And Approach Florida This Weekend

Tropical storm warnings are up in the northwestern Bahamas ahead of "Potential Tropical Cyclone Nine," a tropical disturbance that will likely develop into Tropical Storm Humberto over the next day or two. Its ultimate strength and track remains to be seen, but conditions are favorable for strengthening and the potential storm could bring foul weather to areas devastated by Hurricane Dorian last week.

Don't focus too much on the name of the storm right now. "Potential Tropical Cyclone" is a bureaucratic thing that lets forecasters issue watches and warnings before a disturbance becomes a tropical cyclone. The system is likely going to develop into a tropical depression on Friday and a tropical storm by this weekend.

A tropical storm warning is in effect for the northwestern Bahamas, including Great Abaco and Grand Bahama, the two islands devastated by category five Hurricane Dorian last week. Gusty winds and 2-4 inches of rain are possible in the northern Bahamas as the future tropical storm moves through the area. Tropical storm force winds (39+ MPH) are possible in the vulnerable northwestern Bahamas as early as Friday morning.



The official forecast from the National Hurricane Center brings future-Humberto into Florida as a tropical storm. The main impacts right now look to be gusty winds—some strong enough to down trees and power lines—and heavy rain, which could lead to flooding issues across areas that saw heavy rain from Dorian last week. Based on the current forecast track, the Weather Prediction Center expects a broad potential for 3-6 inches of rain across coastal parts of the southeast, with higher totals in some areas. Rainfall forecasts will likely change as forecasters get a better handle on the organization and ultimate track of the storm.

There's considerable uncertainty in forecast track for this potential storm. It's important to remember that this system isn't a fully-formed tropical cyclone. There's no center of circulation at the surface and the system hasn't developed the core that's necessary for a tropical cyclone to sustain itself and grow. The organization of a system heavily influences its future track; a weak and unstable system is more susceptible to sudden shifts, while a stronger and more well-rooted system can tap into deeper atmospheric steering currents.

We'll know much more about the future of this system once it actually develops. I know it seems like a million years ago, but we had a similar problem during the early days of Dorian. It wasn't a sure thing that the storm would survive beyond the Greater Antilles because of the young system's weak and fragile structure. Future-Humberto is a different system and it's rooted in a much different environment than the one that supported Dorian. That said, the ex-storm's first days in existence are a great example of how the internal structure of a storm can have a big influence on what it does in the future.

Now, about that name...

A "potential tropical cyclone" is a disturbance that's on the cusp of developing into a tropical depression or tropical storm, but it's close enough to land that watches and warnings are needed to give people adequate time to prepare for tropical storm conditions.

The old rules used to forbid the NHC from issuing watches or warnings until the system actually developed into a tropical depression or tropical storm. Sometimes it's too late to issue warnings by the time the storm actually develops.

One infamous example of this was Tropical Storm Bill back in 2015. Bill made landfall in Texas with 60 MPH winds just 12 hours after a tropical storm warning went into effect. If you went to bed early on June 15 and woke up late on June 16, you could have missed the entire warning ahead of the storm. That issue is remedied by the existence of "potential tropical cyclones."

Thankfully, the NHC usually doesn't have to use this designation for very long. These systems are so close to the line that they're typically upgraded to a depression or a storm within a couple of advisories, limiting the time that this newfangled term is thrown around in weather forecasts.


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September 11, 2019

Weather Forecasts Were Under Attack Well Before Trump. Fighting Back Is Long Overdue.



It’s been a heck of a couple of weeks for meteorologists. Expert forecasters had to juggle the precise path of a category five hurricane while the President of the United States led a bizarre campaign to undermine those very forecasts to avoid admitting he made a mistake on Twitter. The deep mistrust sowed in forecasts and forecasters in recent days will take years to undo, but don’t for a second think this eroding trust is a new phenomenon. It’s been stewing for years, and we’re all worse for it.

The National Hurricane Center accurately predicted the path of category five Hurricane Dorian as it came perilously close to Florida, nailing almost a week out that the storm's destructive core would curve within a hundred miles of the Florida coast. Dorian’s forecast path was one of the highest-stakes forecasts in recent years, and it’s a coup of both meteorology and human forecasting that they successfully predicted the path of a scale-topping hurricane.

A Mistake Becomes The Government Line

Not everyone appreciated the forecasting success. We’re all familiar with the flap about Hurricane Dorian “threatening” Alabama. The president tweeted on Sunday, September 1 that Alabama would “most likely be hit (much) harder than anticipated” by Hurricane Dorian, even after expert forecasters had ruled out impacts to Alabama.

The statement drew a mixture of confusion and anger from meteorologists, who correctly pointed out that the weekend forecast updates spared Alabama from any of the storm's hazards. 
The official forecast for Hurricane Dorian at the time of Donald Trump's first "Alabama" tweet on September 1, 2019. | NOAA/NHC


The president reportedly received hourly hurricane updates on the golf course over the weekend, which likely kept him aware of the forecast keeping Dorian east of Florida. The map above shows the forecast from Sunday morning when Trump sent his first "Alabama" tweet.

Trump, who would legally change his name to Donall if he spelled it wrong to avoid having to admit an error, didn’t take kindly to the corrections in the days that followed. The president kept doubling-down on the mistake with increasing intensity in order to save face.

During a public Oval Office briefing on Wednesday, September 4, the president displayed an outdated forecast from August 29 to justify his tweet from September 1. Trump had drawn on the map with a Sharpie to falsely extend the cone of uncertainty to include a portion of Alabama, a transparent attempt to justify his false tweet.

The falsely altered map drew even more intense criticism, and the president's one-off mistake turned into a full-blown Thing. Enraged by the added criticism of his falsified map, Trump tweeted an even older computer model image to justify his warning to Alabama, then commanded an adviser to release a statement that the president’s false claims weren’t false at all.

Again not satisfied with the intensifying criticism, the White House Chief of Staff reportedly ordered the Secretary of Commerce to threaten to fire top officials at NOAA if they didn’t issue a statement refuting a tweet from the National Weather Service office in Birmingham, Alabama, which accurately said their state would “NOT see any impacts from #Dorian."

NOAA's subsequent unsigned statement throwing their own forecasters under the bus to satisfy the president was widely derided, galvanizing support among meteorologists to call out the administration for warping the weather to suit the president's political needs.

It's Transparently Ridiculous

It’s all absolutely ridiculous, and what stings the most is that it’s so transparently ridiculous.
If the expert meteorologists at the National Weather Service can’t speak authoritatively on a major weather event because it might upset the fragile sensibilities of those in charge, then we’re longer lost as a functioning country than anyone cares to admit.

The weird defenses and justifications we’ve seen over the last week are just as concerning as the bad information itself. We all know what’s going on. We all know what happened. Contrary to every principle that's supposed to guide government officials in the United States, the president successfully mobilized the executive branch to lie about weather forecasts in order to defend a single incorrect tweet despite the fact that they all knew it was the wrong thing to do.

This is a protracted struggle to never admit a mistake. Saying “oops” is a weakness. If the facts don’t conform to what you said, just issue threats and make stuff up until people are too confused to tell the difference.

No amount of days-old backfilling can change the fact that there was no threat to Alabama by the time Trump tweeted on September 1, much less the state at risk of being “hit (much) harder than anticipated.”

Weather Has Been Under Attack For A While

We’re rapidly losing our ability to use basic reasoning to determine what’s real and what’s not.  Dorian was not a threat to Alabama on September 1. But after just one week of this partisan jackhammering, you could probably run a national poll and find a double-digit response who would all swear Alabama was in grave danger.

This didn’t start with Trump. This didn’t even start with Twitter. The nonsense we’re living through right now is why I’ve expended great effort trying to debunk conspiracy theories and blatantly fake weather forecasts put out by attention-seeking weenies.

Conspiracy theories, made-up weather forecasts, and the instinct to go full-hype on social media has primed people for the reality-adjacent bizarroworld we’re living in right now.

I’ve argued for years that conspiracy theories about the weather—kooky as they sound—will become extremely dangerous when enough people believe them for a long enough time. We seem to have reached that tipping point.

The wispy clouds behind cruising jetliners aren't weather- or mind-controlling chemicals. Antennas can't control the weather. Doppler radar dishes can’t control the weather. Meteorologists don't fake weather forecasts to scare people or drive up grocery sales. Meteorologists don’t rip their forecasts from a computer—oh, and they’re right a heck of a lot more than just half the time.

All that stuff is really easy to believe once you’ve lost trust in all things outside of your bubble. Once you’re convinced that the world around you is all an elaborate play and everything is controlled by just a couple of people, it doesn’t take much of a spark to flip you out. We’ve seen too many people, intoxicated by conspiracy theories, decide to take up arms and act on their twisted view of reality.

The vast majority of people who subscribe to those outlandish ideas believe it peacefully; or, as peaceful as you can be while screaming at nonbelievers via email. But words alone can cause serious damage.

If someone has lost so much trust in the world that they believe the government controls the weather, what are they telling their friends and family about the forecast for Hurricane Dorian? How many Facebook pages out there have hundreds of thousands of gullible fans lapping up the idea that an antenna array in Alaska can create storms on command? How often do you hear a cashier at the grocery store or a colleague at work brush off a weather forecast because “they’re always wrong” or “they don’t know what they’re talking about?” Yes, that banal small talk does damage after a while.

It’s not just the conspiracy theories we have to worry about. Fake and misrepresented weather forecasts are also a huge problem on social media. Have you ever seen a weather model image on Facebook that showed an enormous blizzard or hurricane racing toward a populated area in a week or two?

There’s a patchwork cottage industry of amateur weather enthusiasts and less-than-level meteorologists looking for clicks who all gleefully share horrifying and outlandish weather model runs on social media. Some folks even flat-out issue fake "forecasts" for clicks—this was such a big issue at one point that the NWS had to issue a statement in June 2011 calling out a single weather hoaxer by name to distance themselves from his faux-official products. And, no, it wasn’t Donald Trump.

We’ve been dealing with this trend of—apologies for the term—fake weather news for years. It’s not a new­ thing. It’s been a long struggle and it’s not one easily won in the social media era. You can’t stop Tri-County Weather Authority 3000 from screaming that the entire tri-county area is going to get buried in a blizzard that was never going to happen. You can’t stop Chief Meteorologist Chad Cheesebog from sharing a weather model showing a 934 mb hurricane hitting New York City in 15 days.

But we can call it out.

Speak Out

The one thing we can do to preserve the character and integrity of weather forecasting, the expert scientists who issue those forecasts, and the very foundation of the science of meteorology itself, is to speak up and fight back. This is no time for “stick to the weather” or “I don’t really like politics.” If you haven’t felt the pain or seen an attack on your little slice of life yet, trust me—it’s coming. I can only wonder how many proudly apolitical meteorologists never envisioned having to speak out against the president's statements before last week.

It’s on you to call out nonsense when you see it. Put people on the spot for peddling fake or inaccurate weather information. Call out inappropriate use of weather models on social media. Don’t politely nod when someone at the grocery store says “weathermen get paid to be wrong all the time.” Don’t stay out of the fray when the president draws on a hurricane forecast to make himself look right. If the president can successfully try to bully and bury official weather forecasts to fit his worldview, how can anyone ever trust a forecast again? 

Meteorologists have done a fantastic job of pushing back against the administration's political meddling since this whole ordeal began. A top scientist at NOAA denounced the statement issued by the agency's political leadership and vowed to launch an investigation. NWS Director Dr. Louis Uccellini strongly defended his agency's forecasters in a speech at this week's National Weather Association's annual meeting in—go figure—Alabama. Just about every meteorologist and weather enthusiast with an audience spoke out against the nonsense and held nothing back speaking to those who tried to defend it. 

That trend needs to continue. We need to make it loud and clear that you cannot mess with the integrity of weather forecasts, because once that trust is gone, it's gone for a generation. Lives are at stake when people start to believe that there are different versions of reality and the warnings and statements of expert meteorologists are issued under duress or with an ulterior motive. The only way the integrity of weather forecasting can withstand political spin and deep mistrust is if we stand up and speak out. Anything less is unacceptable.

[Top Image: Twitter/@WhiteHouse]


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September 6, 2019

Hurricane Warnings Issued For Nova Scotia As Hurricane Dorian Races Toward Canada

Nova Scotia will likely experience hurricane conditions on Saturday as Hurricane Dorian makes its final run as a named storm. Tropical storm conditions are likely in Prince Edward Island, eastern New Brunswick, and western Newfoundland before the hurricane races toward the Arctic and dissipates.

Hurricane Dorian made landfall on Cape Hatteras, North Carolina, early on Friday morning, bringing hurricane force winds and a major flooding to the state's Outer Banks. Some communities on the barrier islands recorded a significant storm surge, which was enough to inundate neighborhoods and cover roads in feet of sand and debris.

The hurricane continues to accelerate through the western Atlantic Ocean this evening as a trough over the northeastern U.S. scoops the storm toward higher latitudes. At 8:00 PM EDT, Hurricane Dorian still had formidable maximum sustained winds of 90 MPH with higher gusts.

A tropical storm warning is in effect for Cape Cod, Martha's Vineyard, and Nantucket as the storm passes off to the east. Heavy rain and wind gusts as high as 60 MPH are possible through Saturday morning as Dorian passes well to the east of the area.

Dorian will begin to affect Nova Scotia on Saturday morning, with conditions quickly deteriorating through the afternoon hours. A hurricane warning is in effect for central and northern Nova Scotia. A tropical storm warning and a hurricane watch are in effect for southern Nova Scotia and Prince Edward Island. Hurricane and tropical storm watches are in effect for western portions of Newfoundland.

The greatest risk for hurricane force winds (119+ km/h, or 74+ MPH) will occur around the center of the storm, likely bringing a period of dangerous conditions to central and northern Nova Scotia as well as eastern Prince Edward Island, including the cities of Halifax, NS, and Charlottetown, PEI. Widespread power outages and tree damage are possible in these areas. Soggy soil from heavy rain could make trees more susceptible to toppling in the strong winds.

Environment Canada warns of the potential for 50-100 mm [2-4 in.] of rain in Nova Scotia and Prince Edward Island, where some totals could reach as high as 150 mm [6 in.]. This much heavy rain in a short period of time could lead to flash flooding in low-lying areas. The National Weather Service's flood safety motto is "turn around, don't drown." It takes a surprisingly small amount of moving water for a vehicle to lose buoyancy and get washed downstream, and you can't reliably tell how much water actually covers the road ahead of you.

It's worth noting that the 5:00 PM forecast from the NHC keeps Hurricane Dorian a tropical cyclone as it crosses the Maritimes. Hurricane Dorian could soon undergo a process called "extratropical transition." After this occurs, the storm will be called "Post-Tropical Cyclone Dorian" in official forecasts and warnings. Don't let the new title throw you. It'll still be the same storm with the same hazards.

Extratropical transition has to do with the internal structure of the storm. Tropical cyclones are fueled by thunderstorms around the center of circulation. Tropical cyclones racing toward higher latitudes often lose that energy source and begin to derive their energy from the jet stream instead. This causes the tropical cyclone to become an extratropical cyclone, or the type of low-pressure system that develops cold and warm fronts. A storm's wind field grows larger as it undergoes extratropical transition. This would expose more of Atlantic Canada to damaging winds.

Dorian will remain a dangerous storm even after it experiences this structural change. As such, the National Hurricane Center will continue to issue forecasts, watches, and warnings as they are now, so long as the storm poses a threat to land.

[Satellite: NOAA]


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September 5, 2019

Dorian Producing Hurricane Conditions In North Carolina; Atlantic Canada Next In Line

Hurricane Dorian's eyewall will continue scraping along the North Carolina coast on Thursday night after bringing high winds and coastal flooding to South Carolina earlier in the day. Hurricane force winds and a life-threatening storm surge are possible tonight and through the first half of Friday as the hurricane makes its way up the North Carolina coast toward open waters. Atlantic Canada will likely see hurricane conditions on Saturday and Sunday as Dorian races toward higher latitudes.

Dorian's Holding Steady

Radar image of Hurricane Dorian at 9:10 PM EDT on September 5, 2019 | GREarth/AllisonHouse
We've still got a strong hurricane this evening. The 8:00 PM EDT update from the National Hurricane Center found maximum sustained winds of 100 MPH with higher gusts. Charleston, S.C., experienced sustained winds of 52 MPH and a wind gust of 69 MPH just before noon on Thursday. A station along the coast near Georgetown, S.C., reported sustained winds of 77 MPH with a gust to 85 MPH as the core of the storm approached the region around 4:00 PM. We're likely to see more reports of sustained hurricane force winds on the North Carolina coast tonight.

Current Forecast

Dorian is moving northeast right now, and its eye could make landfall somewhere along the North Carolina coast this evening. Regardless of whether a technical landfall occurs, hurricane force winds in the eyewall will continue to spread over land as the storm moves up the coast.

The hurricane's wind field continues to grow larger as it begins to feel the effects of the jet stream to its north. Tropical storm force winds extend 170 miles from the center of the storm—stretching as far inland as Fayetteville—with hurricane force winds stretching 70 miles from the center. This expansion will likely expose the Virginia Tidewater and the southern half of the Delmarva peninsula to tropical storm conditions on Friday morning.


According to PowerOutage.US, the storm has caused about 260,000 power outages across the Carolinas as of 9:20 PM EDT. This number will likely climb through Friday as strong winds move over populated areas.

Flooding

Radar rainfall estimate between 9:00 AM and 9:00 PM on Thursday. | GREarth/AllisonHouse
Multiple flash flood warnings are in effect across North Carolina as the storm wrings out every drop of tropical moisture in its rainbands. Radar estimates show widespread totals of 3-5 inches over the last 12 hours—with isolated totals as high as 7 inches—and plenty more heavy rain is on the way during the overnight hours. Remember, most flood-related fatalities are the result of motorists trying to drive across a water-covered roadway.

Tornadoes

Tornadoes are a threat with any landfalling tropical cyclone. There have been multiple confirmed tornadoes across North Carolina today, including in Carolina Shores and Emerald Isle on Thursday morning.

A tornado watch is in effect through the overnight hours in northeastern North Carolina and southeastern Virginia as thunderstorms in the outer bands tap into low-level wind shear and begin rotating. The tornado warning lead time on tropical tornadoes is lower than normal due to how quickly they form. Pay close attention to tornado warnings tonight and make sure the emergency alerts are activated on your cell phone.

Eastern Massachusetts

Once Hurricane Dorian clears the Mid-Atlantic on Friday afternoon, the next spot at risk is eastern Massachusetts.

A tropical storm warning is in effect for Cape Cod, Martha's Vineyard, and Nantucket as Hurricane Dorian races past the area on Friday night and Saturday morning. The center of the storm will pass well to the east of New England, but its wind field will grow so large by that point that a period of tropical storm conditions are possible in far-eastern Massachusetts.

NWS Boston warns of the threat for 30 to 40 MPH sustained winds—with wind gusts potentially as high as 60 MPH—across areas in the tropical storm warning. These areas could also see 2 to 4 inches of rain, which could lead to localized flooding issues.

Atlantic Canada

Hurricane Dorian will slowly lose its tropical characteristics as it approaches Atlantic Canada this weekend. Interaction with the jet stream will combine with cooler waters to force the hurricane to transition into an extratropical cyclone, or a "common" low-pressure system that derives its energy from the jet stream and features cold and warm fronts at the surface.

Despite the likely status change, ex-Dorian will still pack hurricane force winds, flooding rains, and the potential for a storm surge along the coast once it arrives in Nova Scotia on Saturday. Folks who live in Nova Scotia (especially around Halifax), eastern New Brunswick, and eastern Prince Edward Island should spend Friday preparing for a period of damaging winds on Saturday that could lead to widespread power outages, downed trees, and significant coastal flooding in vulnerable areas. The storm will move into Newfoundland on Sunday, bringing these hazardous conditions to communities on the western half of the island.


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September 4, 2019

Life-Threatening Storm Surge & Wind Damage Likely As Hurricane Dorian Hits Carolinas

The core of Hurricane Dorian will come perilously close to the South Carolina and North Carolina coasts over the next 48 hours, potentially generating a life-threatening storm surge, widespread power outages, wind damage, and flash flooding from heavy rain. These areas will likely experience significant impacts from the storm whether or not the eye makes landfall.

The latest forecast from the National Hurricane Center, which was not drawn with a sharpie, shows the center of the storm tracking along the southeast coast through Friday afternoon. The storm will race toward Atlantic Canada this weekend, where several provinces could experience hurricane conditions.
Visible satellite imagery of Hurricane Dorian on September 4, 2019. | College of DuPage
Hurricane Dorian remains a strong hurricane this evening, packing maximum sustained winds of 110 MPH with higher gusts. This is a healthy hurricane and it managed to strengthen a bit this afternoon, and there's a chance it could strengthen into a major hurricane again as it passes over the Gulf Stream. Don't pay too much attention to fluctuations in maximum sustained winds over the next couple of days. Hurricane Dorian is a dangerous storm with wide-ranging effects for folks along the coast and for several counties inland.

Storm Surge

NHC's surge forecast on September 4, 2019. | Twitter/@NHC_Atlantic
The most pressing concern right now is a life-threatening storm surge along the coast between northeastern Florida and the southern Virginia Tidewater. This is a long stretch of coast that could experience a significant storm surge between now and Friday.

A storm surge of 5 to 8 feet above normal tide levels is possible on the central South Carolina coast, including the Charleston and Myrtle Beach areas. That type of storm surge is deep enough to inundate the first floor of buildings along the coast, posing a serious threat to the lives of those who couldn't or wouldn't evacuate.

There are so many different surge forecasts for the coast that it's a bit daunting in text form, so the National Hurricane Center tweeted out a handy map of possible surge heights this morning. It's critical to heed evacuation orders in these areas.

Flooding Rains

Hurricane Dorian could produce rainfall totals of 5-10+ inches of rain across eastern parts of South Carolina and North Carolina through Friday. This much rain in a short period of time will likely lead to widespread flash flooding. The Weather Prediction Center shows the possibility of double-digit rainfall totals near the coast, including Charleston and Wilmington.

The vast majority of fatalities in landfalling tropical cyclones in recent years were the result of freshwater flooding. It's nearly impossible to judge water depth on a flooded roadway until it's too late. Find an alternate route if you know the roads ahead of you are susceptible to flooding.

Winds

The storm's wind field has grown since yesterday. Dorian's hurricane force winds now extend 70 miles from the center of the storm, with tropical storm force winds possible 175 miles from the center of the storm. A larger wind field will expose more communities to the storm's hazards, including the risk for widespread power outages and downed trees.

Hurricane warnings are in effect for all coastal counties in South Carolina and North Carolina. Areas under a hurricane warning could see sustained hurricane force winds over the next two days, as well as a significant storm surge along the coast and flash flooding from heavy rain.

Tropical storm warnings are in effect for northeastern Florida and counties in eastern Georgia on the south side of the storm, and for southeastern Virginia on the north side of the track. Tropical storm warnings extend quite a distance inland in the Carolinas, including Florence SC, Fayetteville NC, and Raleigh, NC, as the storm's large wind field could lead to damaging winds and wind gusts well away from the coast.

The greatest wind-related threat from Hurricane Dorian is widespread and potentially lengthy power outages, especially in areas that experience hurricane or near-hurricane force winds. You don't realize how disruptive a power outage is until the lights go out. It's important to have a stock of non-perishable food, drinking water, batteries, battery-operated flashlights, medicine, personal hygiene supplies, and a little bit of cash (if you can afford it) to get you through a days-long blackout.

Downed trees and tree limbs are also a significant hazard, especially for homes with tall trees looming nearby or motorists driving under unstable trees and limbs. Be mindful of where you go in your home if there are large trees or limbs that could fall and crash through the roof during strong winds.

Heads Up, Atlantic Canada

As I mentioned last night, Prince Edward Island, Nova Scotia, and Newfoundland need to prepare for a direct strike from a fast-moving hurricane this weekend. It doesn't matter whether or not Dorian is still a hurricane or if it's transitioned to a "post-tropical cyclone" by that point. Labels are irrelevant when you're dealing with the potential for hurricane force winds, storm surge, and flooding rains.

If you live in Nova Scotia—especially around Halifax—or on the eastern half of Prince Edward Island, you need to spend Thursday and Friday preparing for a potential direct strike from Hurricane Dorian on Saturday. It's likely we'll see hurricane watches and warnings go up for some of these areas in the next couple of days. Make sure you're preparing the same hazards as folks in the Carolinas, stocking up on non-perishable food, containers of drinking water, batteries and flashlights, as well as incidental items you might not be able to buy if there's no electricity.


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September 3, 2019

Hurricane Conditions Possible In The Carolinas As Dorian Scrapes The Coast On Thursday



Hurricane conditions are possible between Savannah and Cape Hatteras on Thursday and Friday as Hurricane Dorian begins its long-anticipated track toward the north. Over the next couple of days, the hurricane could produce a life-threatening storm surge along the coast, as well as damaging winds and the potential for flash flooding from torrential rainfall.

Squally Night In Florida

Weather radar for central Florida at 9:22 PM EDT on September 3, 2019. | GREarth/AllisonHouse
While all the focus is on the Carolinas at the moment, we can't forget about poor Florida. The storm-stressed state is feeling the effects of the storm they prepared for a week ago. Thankfully, it's nowhere near as bad as it could have been, but strong winds and coastal flooding are still a serious deal if you're caught in the wrong place.

The core of Hurricane Dorian isn't far off of Cape Canaveral this evening. We've seen multiple reports of sustained tropical storm force winds on Florida's east coast today, and conditions will continue to deteriorate farther up the coast through Georgia (and improve farther down the coast in FLorida) as the storm continues lifting north on Wednesday.

Current Forecast

Dorian remains a strong hurricane on Tuesday evening with maximum sustained winds of 110 MPH. Don't focus on the fact that the maximum winds have come down since the storm's peak the other day. This hurricane has a large wind field and wind gusts of just 60 MPH are enough to bring down trees, create flying debris, and lead to widespread power outages. (Why is it that people will panic over a severe thunderstorm with 60 MPH wind gusts, but then shrug their shoulders at tropical cyclones with sustained winds much stronger?)

The National Hurricane Center's forecast track hasn't changed much over the last day or so. The core of hurricane force winds will come very close to the South Carolina and North Carolina coasts throughout the day on Thursday, with the center of the storm potentially making landfall in northeastern SC or eastern NC on Thursday afternoon or evening. These areas stand the greatest risk of seeing a life-threatening storm surge, wind damage, power outages, and the heaviest rainfall totals.

The hurricane will finally clear land on Friday and head toward Atlantic Canada this weekend. Folks in Nova Scotia and Newfoundland need to keep a close watch on the hurricane and its remnants on Saturday (NS) and Sunday (NL). Even though the storm will likely lose its tropical characteristics as it races through the northwestern Atlantic, the storm's wind field will grow larger and many populated areas in Nova Scotia and Newfoundland could see a period of damaging winds, flooding rain, and coastal flooding this weekend.

Impacts



FLOODING RAINS: Flash flooding from heavy rain is possible as Dorian swings through the region over the next couple of days. After Hurricane Matthew in 2016 and Hurricane Florence last year, you don't really have to warn folks in this part of the country about the danger of flash flooding from tropical cyclones.

A swath of 5-7 inches of rain is possible along the South Carolina coast and eastern parts of North Carolina, with lower—but not insignificant—totals possible inland. Heavy, persistent rain could lead to flash flooding in vulnerable areas. I know "turn around, don't drown" sounds kinda hokey, but most fatalities in tropical cyclones are the result of drowning in freshwater flooding and it's very easy for a driver to misjudge water depth and get swept away by a small amount of moving water.



DAMAGING WINDS: Strong winds could lead to downed trees and power outages along and near the coast. The stretch of coastline between Charleston, South Carolina, and the NC/VA state line faces the greatest risk for damaging winds from this storm. Some areas could experience a period of sustained hurricane force winds if the core of the storm comes close to land or makes landfall.

The above map shows where tropical storm and hurricane watches and warnings are in effect. These alerts don't stop at the coast—in some cases, like in eastern North Carolina, they can extend far inland. Areas in a hurricane warning could see hurricane force winds as the storm passes by.

LIFE-THREATENING STORM SURGE: Those damaging winds could generate a storm surge along the coast. The deepest surge is possible where strong, persistent winds press against shallow waters along a curved or marshy coastline.

A storm surge of 4 to 7 feet above normal tide levels is possible between the Savannah River in Georgia and Cape Lookout, North Carolina. That would be a life-threatening surge of seawater flooding for homes, businesses, and roadways along the coast. Slightly lower surge levels are possible to the north and south of these areas, but any storm surge is dangerous if you're caught in a flooded building or if you drive into a flooded roadway.

TORNADOES: The Storm Prediction Center has a marginal risk for severe weather for counties near the southeast coast on Wednesday and Thursday. There's a small risk for tornadoes in some of Dorian's outer bands. Tropical tornadoes can happen quickly and radar can miss them. Keep an eye out and act quickly if you find yourself in a tornado warning.

Conditions Improving In The Bahamas

A visible satellite loop of Hurricane Dorian on September 3, 2019. | College of DuPage


Hurricane Dorian finally pulled away from Grand Bahama on Tuesday morning after producing hurricane force winds over the island for 36 hours, likely one of the most intense single weather events in recorded history. Aerial footage from Marsh Harbour on neighboring Great Abaco, the first island hit by Dorian's category five winds, showed a devastating storm surge in low-lying areas and catastrophic damage in poor communities where homes weren't build to withstand such intense forces. We'll likely see similar heartbreaking images from parts of Grand Bahama once the weather clears enough for search and rescue teams to reach the island.


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September 2, 2019

Hurricane Dorian Remains A Powerful Storm As It Prepares To Curve Up Southeast Coast



Dorian remains a powerful hurricane Monday night as it sits stationary just two-dozen miles north of Grand Bahama. The hurricane's intense winds continue to roar across the Bahamian island after more than a day, an event of unprecedented intensity and duration. The storm will come dangerously close to the southeastern United States over the next three days, potentially bringing hazardous conditions to the entire coast from West Palm Beach, Florida, to Cape Hatteras, North Carolina.

Current Forecast

Hurricane Dorian stalled over Grand Bahama on Sunday night and hasn't moved but a few dozen miles since then, raking the island with hurricane force winds for more than an entire day. The hurricane remained stationary on Monday evening, but it should start to lift northwest on Tuesday and pick up speed through the rest of the week.

The latest forecast from the NHC shows Dorian passing Florida's east coast with maximum sustained winds in excess of 120 MPH. The core of the storm will come close enough to the Florida coast that tropical storm force winds could extend as far inland as Orlando. Hurricane force winds are possible for a time near the coast as the storm passes by. Folks in Florida under watches or warnings should be prepared for downed trees, flooded roads, and the possibility of a few days without power.

Keep in mind that it wouldn't take much of a westward nudge in Dorian's track to bring dangerously high winds and storm surge closer to the coast.

Forecasters expect the hurricane to begin its curve northeast on Wednesday night or Thursday morning, roughly paralleling the southeast coast until it passes the Outer Banks on Friday. Hurricane watches are up from the Florida/Georgia line north through the Charleston area. Expect these watches to be upgraded to tropical storm or hurricane warnings by Tuesday morning, with more watches and warnings following the track of the storm up the coast through Thursday.

Hurricane Dorian will lose its tropical characteristics as speeds northeast through the western Atlantic Ocean by the end of the week. Nova Scotia could see a period of hurricane force winds from this storm as it races through the region next weekend. Folks in Atlantic Canada should closely monitor this storm and start preparing now for the possibility of hurricane force winds, power outages, coastal flooding, and flooding from heavy rain.

Expanding Wind Field

Hurricane Dorian finally experienced an eyewall replacement cycle early Monday morning. Dorian managed to maintain its category five intensity for so long in part because it never underwent an eyewall replacement. It's likely that upwelling of cooler waters and the friction of sitting over land finally destabilized the hurricane's inner structure enough that the storm went through the process of generating a new eyewall.

As I pointed out in last night's update, the process of shedding and generating new eyewalls weakens a storm while causing the storm's overall wind field to expand outward. Tropical storm force winds (38+ MPH) extend 150 miles from the center of the storm, while hurricane force winds (74+ MPH) extend 45 miles from the center of the storm.

Impacts


Every state between Florida and Virginia has declared a state of emergency for areas expecting to deal with hazardous conditions this week. These emergency declarations sound ominous, but it's just an order that activates different parts of state and local government to respond to a storm. A state of emergency allows officials to do things like order evacuations and call up the National Guard to help with preparedness and response. These orders are also a prerequisite for states to receive emergency funds from federal agencies like FEMA.

Here's what you can expect along and near the southeast coast as Hurricane Dorian starts pulling through the region over the next three days.

WIND: Hurricane force winds are possible along the coast where hurricane warnings are in effect. Winds in excess of 74 MPH could lead to power outages, downed trees, flying debris, and structural damage. Tropical storm force winds are possible even farther inland, which could also lead to downed trees and power lines. The threat for damaging winds will go up if the storm tracks closer to land.

STORM SURGE: A 4-7 foot storm surge is possible at high tide along the coast where hurricane watches and warnings are currently in effect. Wind direction, wind speed, and coast shape will determine surge depths in each individual spot along the coast. Some areas could see no surge, while others could see a life-threatening inundation. The probability of a storm surge increases with stronger onshore winds.

FLOODING: Heavy rains near the coast could lead to flash flooding. The Weather Prediction Center expects 4-8 inches of rain along and near the southeastern coast, with higher amounts where rain bands begin training or if the storm makes landfall. The highest rainfall totals are likely in the eastern Carolinas where the center of the storm could make (or come close to making) landfall.

TORNADOES: The threat for tornadoes is low since the right-front quadrant of the storm is forecast to remain offshore.

Unprecedented Conditions In The Bahamas

An infrared satellite loop of Hurricane Dorian between 8:01 AM EDT September 1, 2019, and 9:01 PM EDT September 2, 2019. | College of DuPage


Folks on Grand Bahama continue to experience what is likely one of the most extreme weather events ever experienced by humans outside of mountaintops or polar shipping lanes. We use "extreme" and "catastrophic" and "worst-ever" so often that it can lose its punch. This is one of those rare instances where you can't exaggerate reality because it's so deeply unprecedented.

Most scale-topping hurricanes keep moving and quickly lose steam once they touch land. This storm didn't do that. Hurricane Dorian found an extremely favorable environment over the northwestern Bahamas for strengthening and maintaining that strength. Calm winds throughout the atmosphere around the storm have allowed the hurricane to sit and spin over the same spot for hours at a time. The terrain of Grand Bahama is low and flat enough that it hasn't had a destructive impact on the storm's internal structure.

This sequence of events left much of Grand Bahama firmly wedged in the eyewall of a category five/category four hurricane for 24+ hours with almost no break except for where the eye passed overhead. There have only been a handful of hurricanes this intense in recorded history, and none of them slowed to a crawl over an island and maintained their intensity for almost an entire day.

This will be a historic storm for many reasons, but not the least of which is the level of destruction we're likely to see on Grand Bahama once rescue crews are able to make their way to Freeport and surrounding areas.


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