September 22, 2020

Big Teddy Will Bear Down On Atlantic Canada This Week With Strong Winds And Heavy Rain

Atlantic Canada will have a rough time of it over the next couple of days as Hurricane Teddy transitions into a powerful nor'easter-type storm and roars across the region. Intense winds, heavy rain, and coastal flooding could batter Nova Scotia, New Brunswick, Prince Edward Island, and eventually Newfoundland over the next couple of days.

Hurricane Teddy made an uncomfortably close pass to Bermuda on Monday, just a week after the eye of Hurricane Paulette made a direct hit on the tiny island in the western Atlantic. Teddy only brushed the island with gusty winds and heavy rain. The hurricane is picking up speed as it races toward Atlantic Canada, where it should make landfall in Nova Scotia on Wednesday.
Source: National Hurricane Center

Hurricane Teddy is undergoing a process known as "extratropical transition" as it approaches the region. I'll get more into that a little farther down in the post, but that has three practical effects for folks in the Maritimes:

➤ The storm is tremendously large now. The hurricane's wind field measures more than 1,500 kilometers (900+ miles) across now. This huge expansion in the storm's size will expose more communities to strong winds that could lead to widespread tree damage and power outages. The extent of the tree damage and power outages could take folks here off-guard since trees are still in full leaf and powerful windstorms don't typically strike this region until the winter.

➤ A dangerous storm surge is likely along the southeast coast of Nova Scotia, flooding from which will be exacerbated by waves that could grow as high as 10 meters (30 feet).

➤ The storm won't weaken as quickly as tropical cyclones normally would as they enter the colder waters of the northwestern Atlantic, prolonging the storm's duration and allowing it to affect a larger area at full strength.

If you live in Atlantic Canada, make sure you're prepared for at least a couple of days without power. Ready-to-eat foods (anything you don't have to cook) is a must. Bottles or jugs of water are handy if you have well water. Stay aware of tall trees or heavy limbs that might be near your home, avoiding those parts of the house during high winds if you can't take care of them before the storm starts.

Also remain mindful of flooded roads—it doesn't take much for a vehicle to become stranded in standing water, and it takes even less effort for moving water to lift a vehicle and sweep it off the road.

Extratropical Transition

Hurricane Teddy transitioning from a tropical cyclone to an extratropical cyclone between September 20 and September 22. Source: College of DuPage

Teddy has mostly completed its transition from a tropical cyclone to an extratropical cyclone. 

Tropical cyclones feature warm, muggy air across the whole storm. It's sticky, windy, and rainy on all sides of the storm. An extratropical cyclone is your common low-pressure system that feature frontal boundaries. Extratropical cyclones feature cool, dry air and warm, muggy air rotating around the storm, bringing a diverse array of weather as they pass through a region.

One of the biggest differences between the two types of low-pressure systems is how they derive their energy, and that's what makes this transition so important when a storm is closing in on landfall.
A history of Hurricane Teddy's wind field over the last couple of days.
A tropical cyclone is powered by strong, persistent thunderstorms around its center of circulation. The updrafts in these thunderstorms suck air away from the surface, leaving lower air pressure at the surface. This low-pressure center supports those persistent thunderstorms and creates a feedback cycle that allows the storm to strengthen. The storm's energy is condensed around the center of the storm, leading to a compact wind field that usually limits the extent of the strongest winds.

An extratropical cyclone, on the other hand, is powered by strong upper-level winds spreading out as they round troughs and jet streaks (pockets of stronger winds) within the jet stream. This divergence leaves a void in the upper-levels of the atmosphere that air from the surface has to rush upward to fill, creating low pressure at the surface. 

Since extratropical cyclones have a much larger and more diffuse source of energy, storms that undergo extratropical transition typically grow in size, affecting a much larger area with strong winds than they would have if they'd remained tropical cyclones. You can see the difference in the size of Teddy's wind field in the National Hurricane Center's wind analysis above. It's more than doubled in size since this weekend.

Tropical storms and hurricanes that survive their trek through the Atlantic Ocean often transition from tropical cyclones to extratropical cyclones as they race toward the northern latitudes. This is usually a run-of-the-mill process that happens far away from land, but it can be pretty dramatic if it's already a strong storm and the transition happens close to land.

The most famous (and probably the most extreme!) example of this process was 2012's Hurricane Sandy. The hurricane completed its extratropical transition right at landfall, which is why it had such an enormous and destructive footprint. Teddy isn't Sandy, but it's going to be a dangerous and memorable storm for Atlantic Canada.

[Satellite Image: NOAA]

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September 19, 2020

Tropical Storm Beta Could Pose A Major Flash Flood Threat For Texas & Louisiana Next Week

Tropical Storm Beta could bring copious amounts of rain to coastal communities in Texas and Louisiana through next week as it meanders toward the western Gulf of Mexico. The system is another slow-mover and its precise track will determine who sees the worst winds and rain. Folks along the coast from Corpus Christi to Lafayette should prepare for the potential for strong winds and flooding rains.

It seems like we can't go more than two weeks this hurricane season without talking about another tropical system threatening to create a flash flood emergency. Beta comes just a week after Hurricane Sally itself stalled off the northern Gulf Coast before rapidly strengthening as it made a painfully slow approach into southern Alabama. Last week's hurricane produced more than two feet of rain over the western Florida Panhandle.
Source: NOAA

Beta is...not a looker. If you didn't know what you were looking for, it'd be hard to pick the storm out of a lineup based on this evening's infrared satellite imagery. Thunderstorms around the center of circulation aren't all that deep or powerful, lending the system an underwhelming appearance on infrared satellite, which measures the temperature of the cloud tops. Stronger thunderstorms push clouds higher into the atmosphere, so colder cloud tops reveal deeper thunderstorm activity.
Source: Tropical Tidbits

Nevertheless, Hurricane Hunter aircraft flying through the storm this evening found maximum sustained winds of 60 MPH—not too shabby for a tropical storm, especially a storm with an appearance only mother nature could love. The chart above shows this evening's recon data plotted out by Tropical Tidbits. This image makes it easy to see how the convection isn't quite linked up with the surface circulation—this is why the storm isn't strengthening like Laura and Sally did once they hit the hot waters of the Gulf.

The National Hurricane Center's latest advisory found a strong Tropical Storm Beta in the western Gulf of Mexico, packing sustained winds of 60 MPH and a tropical-storm-force wind field that measures almost 400 miles across. Forecasters expect Beta to slowly loop back toward the coast by early next week. There's a low chance that Beta will strengthen into a hurricane as it approaches the coast.

All hazards are possible with this tropical storm, including gusty winds that could lead to widespread power outages, a dangerous storm surge along the coast, tornadoes in the storm's outer bands, and flash flooding from heavy rain. Flash flooding is going to be the greatest threat from this system.

Here's the Weather Prediction Center's rainfall forecast for the next seven days:

A tremendous amount of rain could fall over the Gulf Coast over the next couple of days. Double-digit rainfall totals are possible from Port Lavaca to Houma, including the Houston metro area and southwestern Louisiana.

This kind of rainfall forecast is sensitive for folks in this region. The heavy rain will fall across areas devastated by Hurricane Harvey's flooding in 2017 and by Hurricane Laura just a couple of weeks ago. The best line of defense against a storm like this is to be prepared. Have a plan and supplies ready if you live in a flood-prone area, and keep plenty of alternate routes in mind if you travel across roads that easily flood during heavy rain.

Keep in mind the potential for power outages as a result of strong winds putting stress on trees and power lines on rain-soaked soil.

Tropical Storm Beta's precise track will determine how much rain falls and where the greatest threat lies. If the system dawdles farther offshore, that's much better news for coastal residents than if the center of circulation scrapes along the coastline like the NHC's forecast calls for right now. Tropical Storm Beta's future track is a little uncertain since the system is moving so slow and it's not particularly well organized.
SourceTropical Tidbits

Two different ridges of high pressure—a large ridge over the center of the country and another ridge over Florida and The Bahamas—will block Beta from simply following on Sally's heels or jetting east out into the open Atlantic. There's not much out there to steer the storm along, forcing the system to putter around in the western Gulf for a few days. It'll slowly creep around the outer periphery of that high pressure over the southeast, guiding it into the Texas coast. This kind of hesitating putter is why this system has the potential to produce so much rain. 

If you're wondering where this system came from...Tropical Storm Beta formed from a disturbance that's been lingering in the Gulf of Mexico since before Hurricane Sally entered the picture. The disturbance from which Beta formed first appeared in the eastern Gulf of Mexico more than a week ago. I mentioned the system in a post on September 11, since it was one of six areas of interest across the Atlantic Ocean that day. 

That disturbance slowly found its way into the western Gulf of Mexico and conditions eventually improved enough for the disturbance to strengthen into a tropical depression. The depression spent a few days getting itself together before it developed into Tropical Storm Beta on Friday afternoon.

Beta is the 23rd named storm of the 2020 Atlantic hurricane season. This is only the second year on record (after 2005) that we've exhausted the official list of 21 names and had to resort to Greek letters to name storms. Wilfred, Alpha, and Beta were all named within a few hours of each other on Friday, September 18th. Wilfred will quietly dissipate in the eastern Atlantic, while a subtropical storm making landfall in Portugal earned the distinction of becoming Subtropical Storm Alpha. 

After Beta, the next three storms will be called Gamma, Delta, and Epsilon. We still have eleven weeks left in hurricane season.

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September 16, 2020

Widespread Flash Flooding Likely As Tropical Storm Sally Crosses The Southeast

Hurricane Sally rapidly strengthened on its painfully slow approach to landfall last night, quickly becoming a strong category two hurricane with sustained winds of 105 MPH at landfall. The sudden and somewhat unexpected run-up in the hours before landfall exacerbated damage from wind and storm surge. The storm's winds will weaken as it pushes farther inland, but its prolific rains are far from over.

The contiguous United States has seen four hurricanes make landfall this season—Hanna, Isaias, Laura, and Sally—and all four storms defied the odds to strengthen all the way until they made landfall. A slow-moving storm that suddenly intensifies as it approaches the coast is a scary scenario for folks in its path.

A few days ago, the National Hurricane Center's showed Sally approaching major hurricane strength as it neared landfall, but forecasters (and most models) backed off that scenario because the storm started to struggle with some wind shear and dry air disrupting its internal structure.

The storm's incredibly slow forward motion—just 2-3 MPH in the hours leading up to landfall—gave the system enough time to fight off the disruptions and fortify its eyewall, allowing the system to quickly strengthen as it approached Baldwin County, Alabama. 

Widespread damage and power outages resulted from the intensity and duration of the storm's winds. It'll take another day or so to get a full picture of the damage, which could be particularly severe in coastal areas that also experienced a destructive storm surge.

For all the damage and surge, Sally's legacy is still likely going to be the catastrophic flooding that resulted from more than two feet of rain. The map above shows the National Weather Service's precipitation analysis for the past 24 hours ending at 8:00 AM Eastern today. Pockets of Baldwin and Escambia Counties saw more than two feet of rain long before storm was over.

Drenching rains continued well after the end of this analysis, so tomorrow's analysis will give us a better view of the storm's total rainfall across the region.

Sally weakened to a tropical storm over the western Florida Panhandle this afternoon. The system will continue to slowly weaken as it chugs through Alabama into Georgia tonight. The storm is still producing quite strong winds—60 MPH sustained winds for a few hours is nothing to sneeze at—and it won't take much to blow over trees and power lines on wet soil.

Forecasters expect Tropical Storm Sally to lose its tropical characteristics on Thursday night as it enters the Carolinas. The precise track of the storm will determine which areas see the heaviest rain. Communities closer to the center of the storm will see higher rainfall totals, so any deviation from the NHC's forecast track will drag the heaviest rains in the same direction.

The Weather Prediction Center's latest rainfall forecast shows the potential for widespread flash flooding all the way through North Carolina as Sally and its remnants push toward the Atlantic Ocean. Many areas could see more than five inches of rain by the end of the storm on Friday afternoon. Flash flooding is likely near waterways and vulnerable roadways and urban areas where drainage systems can't keep up with the tropical rainfall rates.

It's worth noting that heavy rain is still falling across areas that were hard-hit by the storm last night. An additional inch or so of rain is possible across these areas before skies clear out behind the storm tonight. 

As if all the wind and the rain wasn't bad enough, there's a notable tornado threat to the south and east of the storm's track. Landfalling tropical cyclones are notorious for producing tornadoes as they push inland. There's enough spin in the atmosphere that thunderstorms in the outer rainbands can form into small supercells that can spawn dangerous tornadoes. Tropical tornadoes usually happen quickly and they often don't afford as much lead time as a "typical" tornado event. 

The greatest threat for tornadoes will exist across northern Florida and southern Georgia for the rest of the afternoon and evening on Wednesday, moving east into Georgia and the Carolinas during the day on Friday.

If you haven't already, turn on the wireless emergency alerts on your smartphone to make sure you're alerted to a tornado warning the moment one is issued for your location.

[Satellite Image: NOAA]

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September 15, 2020

Hurricane Sally Could Produce 'Historic Rain' As It Creeps Toward The Alabama Coast

A historic flash flood threat will follow Hurricane Sally inland as it makes landfall around Mobile Bay on Wednesday morning. Widespread rainfall totals of a foot or more could lead to significant flooding across southern Alabama and the Florida Panhandle as the hurricane (and its remnants) crawls across the region over the next couple of days.

The storm looked pretty scary there for a while on Monday. Sally strengthened from a 60 MPH tropical storm early Monday morning to a 90 MPH hurricane by noon, and the storm's winds kept ticking up through the afternoon until they plateaued around 100 MPH.
Source: NOAA/Gibson Ridge

Winds have since backed off a bit as the hurricane's struggled with its internal structure. A radar image from Tuesday afternoon (above) shows a well-defined eye with an eyewall that's lurking a few dozen miles south of Dauphin Island. It's good fortune that the storm wasn't able to continue intensifying through landfall like we saw with a few other hurricanes earlier this year. 

The NHC expects the hurricane to remain around its current strength through landfall.

The forecast has shifted east since Sunday and Monday. The weather shouldn't be too bad in southeastern Louisiana now, which is great news for folks in New Orleans bracing for a nasty storm based on earlier predictions. 

Hurricane Sally is poking around at a snail's pace today, lingering a few dozen miles offshore without any upper level winds to pick it up and move it along. The last advisory had it moving north at a whopping 2 MPH. An upper-level trough should allow Sally to begin to pick up some speed make landfall in southern Alabama on Wednesday morning. Winds will pick up on Tuesday evening as the eyewall creeps closer to land. 

The storm will continue crawling inland over the next few days as it begins to lose its tropical characteristics, but the heavy rain will persist until the system moves out over the Atlantic this weekend.

Flooding Rain

The northern Gulf Coast is no stranger to heavy rain. I went to school in Mobile. It rains quite a bit down there. This is no ordinary rainstorm. The potential rainfall from this hurricane is a high-end ordeal even by this region's standards. There are tons of flood-prone areas around here, ranging from roads with poor drainage (shout out to University & Old Shell!) to the abundance of tiny streams and creeks and swampy areas that can fill up and overflow in a flash.

The slow forward motion of the storm will allow rainfall totals to push or exceed 20" near and east of the point of landfall, which right now looks like it'll be Mobile Bay eastward through Pensacola. NWS Mobile is characterizing this as a "historic" rainfall event for the region, a testament to how much rain is expected as the storm moves inland. 

Flooding rains won't stop at the coast. The hurricane and its remnants will slowly push into the southeastern states through the end of the week. Flash flooding is a threat all the way through parts of North Carolina. A swath of 5"+ of rain is possible along the storm's track through Alabama, Georgia, and South Carolina. This could lead to significant flash flooding hundreds of miles inland from the point of landfall.

The standard warning applies: most deaths in landfalling tropical cyclones in this country occur when motorists try to drive across a flooded roadway. It only takes a few inches of water for a car to lose contact with the road and get washed downstream. Sometimes the road gets washed out by a flood and the water obscures the fact that there's no road there anymore.


Don't let the storm's strength lull you into a false sense of security. (Oh please. I know how it goes. iT's JuSt A cAtEgOrY oNe my foot.). Severe thunderstorms are warned for wind gusts of 58 MPH or stronger. This hurricane has sustained winds of 80 MPH. Sustained winds that strong—with higher gusts—will do a number on trees, power lines, roofing, siding, and loose items that can get tossed around.

It's not just that these winds can do damage on their own. It's the duration of the storm that's going to stress otherwise-resilient trees and power lines. Strong winds are already causing damage near the coast in Alabama and Florida and the core of the storm won't be fully over land for another 18 hours or so. The extended duration of the strong winds will lead to more damage and power outages than the region would've seen if the storm had moved along at a steady pace.

Storm Surge

Source: NHC

Any hurricane approaching the coast is bad enough for coastal residents, but a slow-moving hurricane will allow ample time for a damaging storm surge to build along portions of the coast expecting the strongest of Hurricane Sally's winds.

Based on the storm's current intensity and predicted path, the National Hurricane Center expects a maximum potential storm surge of 4 to 6 feet above ground level to occur on Dauphin Island and in Mobile Bay, with lower values possible in portions of Louisiana, Mississippi, and Florida.

It's worth noting that the extensive rainfall could exacerbate the effects of a storm surge right along the coast in places like Mobile Bay, where the excess runoff from flooding rains in the Mobile, Tensaw, and Dog Rivers will jam up against the surge flowing into Mobile Bay.


Tornadoes are possible around and to the east of the point of landfall. The threat for tornadoes will shift east on Wednesday as the hurricane moves farther inland. The SPC says there's also a tornado risk in the southeast on Thursday, but uncertainties in the track and strength of the storm (or its remnants) means it's too soon for details on exactly where.

Tropical tornadoes occur quickly and often come with reduced tornado warning lead time. Make sure you've got a way to quickly receive tornado warnings if you're in the path of the storm over the next couple of days, especially at night when you're asleep. The wireless emergency alert feature on your phone is great because the screeching tone can wake you up from even the soundest sleep.

[Top Image: A "sandwich" satellite image that overlays infrared imagery on top of visible imagery, via NOAA]

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September 13, 2020

Significant Flash Flooding, Intense Winds Likely As Sally Heads Toward Northern Gulf Coast

Tropical Storm Sally will likely strengthen into a hurricane as it crawls toward the northern Gulf Coast over the next 36 hours. Forecasters expect a slow-moving hurricane to approach land Monday night. Strong winds and heavy rain will overspread Louisiana, Mississippi, and Alabama overnight Monday and through the day on Tuesday as the center of the storm approaches landfall.

Intense winds could knock out power for hundreds of thousands of people. A life-threatening storm surge at the coast and prolific rainfall along the storm's track will make flooding this storm's most dangerous hazard.

The Setup

Sally formed from a disturbance over The Bahamas late last week. The system moved over southern Florida on Friday and brought prolific rainfall to the Florida Keys. Key West measured 9.37" of rain on Friday alone, marking the city's third-highest one-day rainfall total in records dating back to 1948.

This tropical storm is moving over the steamy waters of the Gulf of Mexico at the climatological peak of hurricane season—it's not much of a surprise that the system is expected to attain hurricane strength by the time it makes landfall.

Source: NOAA

Tropical Storm Sally's structure struggled today as it fought against some northwesterly wind shear. The center of circulation spent most of Sunday exposed or nearly exposed, with the heaviest thunderstorm activity sheared off toward the eastern side of the cyclone. The storm is starting to consolidate around its center of circulation, the first step toward strengthening. Forecasters expect the system to reach land as a hurricane on Monday and Tuesday.

Sally is moving into an environment without strong winds to steer it along in a hurry. Much of the United States is covered by an upper-level ridge, resulting in light winds throughout the atmosphere across the southern half of the United States. The thunderstorms around the center of a tropical cyclone act like a sail that catches atmospheric winds and steers the storm along. Storms can crawl along or even stall out without sufficient winds to move them poleward.

As a result, Sally will spend the next 36-48 hours just kind of puttering along until it makes landfall along the northern Gulf Coast. After that, the upper-level environment should allow Sally (or its remnants) to start moving across the southeastern states toward the Atlantic by the end of the week. There's a chance that this system lingers in the southeast through the end of the week, which could exacerbate flash flooding issues.

A slow-moving hurricane moving into a sensitive stretch of coastline is enough to cause anyone in the region some heartburn. Here's what to expect as Sally approaches over the next few days.


Forecasters expect Sally to make landfall as a hurricane. Strong winds will knock down trees, create long-lasting power outages, and damage buildings. Flying debris, shattering windows, and failing roofs could be serious threats to folks in the path of the storm.

Strong, damaging winds could last for an extended period of time given the expected slow forward motion of the storm. A long-duration wind event will add even more stress to trees, buildings, and power lines.

Falling trees and tree limbs are a serious threat to motorists and folks at home. If you live near tall trees or tree limbs that could fall into the house/apartment/wherever, it'd be a good idea to sleep or stay in another room during the strongest winds. Lots of people are injured and killed during high wind events as a result of trees falling into homes. 

Widespread power outages will result from sustained hurricane force winds. It's likely that power outages will last a week or longer in the hardest-hit areas. If you live in the region, the latest you can prepare for power outages is Monday morning. Make sure you've got enough ready-to-eat food, drinks, and batteries to last an extended power outage. 

Storm Surge

Source: NHC

A life-threatening storm surge is a risk in any landfalling hurricane, especially one that's hitting such a sensitive stretch of coastline. The National Hurricane Center's latest forecast calls for a maximum potential storm surge of 7 to 11 feet along portions of Louisiana and Mississippi expected to be under or near the center of the storm. A surge of 4 to 6 feet is possible in Lake Pontchartrain, and several feet of storm surge is possible along the coasts in Mississippi and Alabama. 

The map above from the NHC shows a generalized version of their maximum potential storm surge forecast. These values will change as forecasters refine Sally's track and intensity. 

Much of New Orleans sits below sea level. The city is protected by a large system of levees, floodwalls, gates to keep water out. The system is designed to protect against a "1-in-100 year" storm surge, which is about 15 feet, according to Dr. Jeff Masters in a blog post last year.

The city's system of rainwater drainage pumps might face a bigger challenge. 


The biggest threat from this storm will be flash flooding from heavy rain. This storm's ample moisture—combined with its painfully slow forward motion—could lead to a significant flash flooding event across the northern Gulf Coast.

The Weather Prediction Center issued a high risk for flash flooding as the core of the storm moves inland. The agency doesn't do that lightly—they've only issued a high flash flood risk three days in advance during Hurricane Harvey and Hurricane Florence. That should drive home the flash flood potential posed by this storm.

The WPC's forecast calls for more than 10" of rain in parts of southeastern Louisiana, southern Mississippi, and southern Alabama, including New Orleans, Gulfport, Biloxi, and Mobile. Some areas could wind up seeing more than 20 inches of rain if an exceptionally nasty rain band gets stuck training over the same areas.

Adjustments in the storm's track will affect these rainfall forecasts—if the storm tracks to the east of current forecasts, the heaviest rainfall totals will follow.

Flash flooding is responsible for most of the deaths that result from landfalling tropical cyclones, and many of those deaths are the result of motorists attempting to drive across flooded roadways. It takes as little as six inches of water moving across a roadway to lift a vehicle and carry it away. And there's no guarantee that the road is there at all. Roads can wash out during a flood, and the water can obscure the fact that the road is gone.


As always—and I feel like a broken record here, putting this same blurb in almost every post for the last few months—tornadoes are a hazard during any landfalling tropical cyclone. The greatest threat for tornadoes will exist along and to the right of the storm's forward motion. This would put southern Mississippi, southern Alabama, and the western portion of the Florida Panhandle under risk for tornadoes for several days beginning on Monday and lasting until...well, until the storm pulls away.

Tropical tornadoes can occur quickly. Make sure you've got a way to receive warnings—check that the wireless emergency alerts on your phone are activated—and take quick action if your location goes under a tornado warning.

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September 11, 2020

Tropical Storm To Develop In Gulf On Saturday—One Of Six Atlantic Systems To Watch

The National Hurricane Center's tropical outlook map is lit up like the dashboard on a rickety old car. Forecasters are tracking six different features in the Atlantic Ocean: two named storms, a soon-to-be named storm, and three disturbances that could develop soon. The greatest risks to land right now are a tropical depression over The Bahamas and Tropical Storm Paulette, which could hit Bermuda as a hurricane early next week.

This week marks the climatological peak of hurricane season. This is the point when atmospheric conditions and sea surface temperatures are usually most favorable for tropical activity in the Atlantic Ocean, and it's certainly proving true this year.

Tropical Depression Nineteen

A disturbance we've been watching for a few days organized into Tropical Depression Nineteen over The Bahamas on Friday afternoon. The system will likely strengthen into Tropical Storm Sally within the next day or so as it moves across southern Florida and heads into the eastern Gulf of Mexico.

A tropical storm watch is in effect for southeastern Florida ahead of the depression's landfall tonight, and it's likely that more watches and warnings will be needed for the Gulf Coast later this weekend.

The Gulf is plenty warm enough to sustain a storm. It's been a few weeks since Marco and Laura and those storms didn't do much to cool down the water anyway. Atmospheric conditions should be favorable for further development if the depression can root itself in the environment and organize as it heads toward land.

The NHC's forecast shows the system nearing hurricane strength when it reaches the northern Gulf Coast on Monday and Tuesday.

Regardless of its strength, the system looks like it'll bring some heavy rain to the Gulf Coast. The Weather Prediction Center's precipitation forecast issued on Friday afternoon shows the potential for 5"+ of rain along the northern Gulf Coast, with higher totals likely if the storm organizes and strengthens.

Folks from New Orleans to Tampa need to watch this system closely and get ready to take action early next week as it closes in on the area. Make sure you've got a plan if you live in a flood-prone area. Check your supplies and make sure you've got enough food, water, and batteries to make it through a couple of days without power. 

Tropical Storm Paulette

Paulette's still out there. The storm formed way out in the eastern Atlantic last Sunday and it's spent the week chugging along a west-northwestward track across the Atlantic Ocean. 

The NHC's latest advisory calls for Paulette to strengthen into a hurricane as it heads toward Bermuda this weekend. A cold front sweeping off the U.S. East Coast will meet the hurricane in the western Atlantic on Monday, forcing the storm to stop in its track and abruptly curve northeast.

The timing of when the hurricane meets the cold front will make all the difference for Bermuda. There's a chance that the storm pivots and makes a direct landfall in Bermuda, which would expose the island to a period of intense winds and storm surge. If the turn happens sooner or later, the island would feel fewer impacts from the storm.

Tropical Storm Rene

Rene formed just a little while after Paulette. The system moved through the Cabo Verde Islands as a tropical storm earlier this week, bringing bad weather to an island chain that usually escapes the direct impacts of a strengthening storm. (Systems that originate in Africa usually don't organize until they're well west of the Cabo Verde Islands.)

The tropical storm has been clinging to existence since it developed, and it'll continue maintaining itself through the weekend. It's not much bigger than your average thunderstorm over land. The size comparison above shows Paulette (top-left) and Rene (bottom-right).

Rene will stay out in the middle of the Atlantic and it shouldn't pose any threat to land.

Invest 95L

Source: NHC
The next best chance of a named storm out in the Atlantic Ocean is a disturbance that rolled off the western coast of Africa a couple of days ago. Invest 95L, as it's dubbed for tracking purposes, is a broad area of disorganized showers and thunderstorms that's far out in the eastern Atlantic. Conditions are favorable for the system to coalesce and develop into a tropical depression or a tropical storm this weekend.

The system is far enough south that it's something we need to watch for potential issues in the Caribbean next week. It's far too early to talk about what it could mean for the United States—it's still more than a week and a half away from the U.S., which is plenty of time to watch and wait.

African Disturbance

Source: NHC
Another disturbance coming off the western coast of Africa had a 40 percent chance of development in the NHC's latest outlook. This system will bring some foul weather to the Cabo Verde Islands as it moves west-northwest this weekend. It's on a path that'll probably take it into the central Atlantic and away from land. 

Gulf Disturbance 

There's a disorganized cluster of thunderstorms south of Mobile that the NHC has pegged for a 30 percent of development as it moves west through the Gulf of Mexico.

The system only has a low chance of development right now, but with warm waters, low shear, and plenty of moisture to work with, there's always the chance that it could get its act together as it moves into the western Gulf. The disturbance could bring an inch or two of rain to coastal Texas regardless of its development.

Greek Watch '20

The countdown to running out of names in the Atlantic forges ahead. We've already had 17 named storms this year and there are just four names left on this season's list of names: Sally, Teddy, Vicky, and Wilfred.

The NHC starts naming storms using the Greek alphabet if a season exhausts its official list of 21 names. It's worth pointing out that 11 of the 18 named storms that formed last year formed on or after September 12.

Barring some freakish and unforeseen shutdown of the atmosphere over the Atlantic Ocean, it's almost certain that we'll dive into Greek letters this year for just the second time on record. The only season to exhaust its list of names was 2005, which required the use of six Greek letters to name the season's final handful of storms.

Any named storms after Wilfred that will come from the Greek alphabet. The Greek alphabet goes: Alpha, Beta, Gamma, Delta, Epsilon, Zeta, Eta, Theta, Iota, Kappa, Lambda, Mu, Nu, Xi, Omicron, Pi, Rho, Sigma, Tau, Upsilon, Phi, Chi, Psi, and Omega. We made it up to Zeta by the end of December 2005.

[Satellite Images: NOAA]

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September 9, 2020

The Weather Is Not Good

Fires, drought, heat, humidity, hurricanes, a deadly pandemic virus, rising inequality, a rapidly changing climate. Things are bad right now. The weather is bad right now. We can deal with bad things and bad weather as they come, but the convergence of multiple catastrophes at once is a societal strain we haven't experienced in generations. 

California just came through an intense heat wave. A high of 121°F was the hottest temperature on record in Woodland Hills, which was also the hottest temperature ever recorded in Los Angeles County. The high on Monday hit 117°F in Paso Robles, breaking their all-time high record, and Burbank tied its hottest-ever measurement with a high of 114°F. Many other stations around the state recorded highs in the 100s.

As a result of this summer's extended warmth and a worsening drought, California is now in the middle of its most intense wildfire season on record. This year has seen the second-, third-, and fourth-largest fires ever recorded in California, and the uncontained Creek Fire seems on track to crack the top-ten as well. The 'peak' of a traditional wildfire season doesn't occur until later in the fall. 

This weekend's Creek Fire in central California required the air evacuation of hundreds of people stranded at Mammoth Pool when the fast-spreading fire cut off all roads out. A fire in southern Oregon—one of many burning across the state—encroached on Medford on Tuesday evening, forcing the evacuation of tens of thousands of people. The state's governor called the scope of the current fires and the losses therein "unprecedented" in the state's history.

The sheer intensity and widespread nature of the fires pumped immense amounts of smoke into the sky across Oregon and California, resulting in scenes that looked like high noon on Mars rather than any earthly location.

And here's what that looked like from space:
Source: NOAA
Dense smoke filtered the sunlight and only allowed longer orange and red wavelengths to reach the surface, turning the sky a deep shade of grim. Temperatures across the region were also lower than predicted as a result of the dense smoke reflecting solar radiation back out to space.

It's no wonder that we've seen one horrible fire after another this summer. This summer was so hot and dry that we've seen the largest extent of drought conditions in the United States in more than two years. A solid two-thirds of the western half of the country was in some level of drought last week, and it'll likely grow in this week's update as a result of the past week's extreme heat. 

The Central Plains and Front Range sweltered this weekend in temperatures around 100°F. High heat and low humidity allowed several wildfires to spark in Colorado and Wyoming. Dense smoke also filled the skies around Denver on Sunday afternoon, making a hot afternoon even worse.

A significant cold front swept across the Plains on Monday, sending temperatures from 100°F to below freezing by Tuesday morning. The Denver area experienced one of its most extreme temperature swings on record. The city set numerous notable temperature records over the last couple of days, including the warmest temperature recorded the day before measurable snow.  

It's not just the west. This was one of the hottest summers on record in the United States, and the hottest for some cities back east. 2020 is already on track as one of the hottest years on record, joining 2019, 2018, 2017, 2016, 2015, 2014, and 2013 among the top-ten hottest years ever recorded.

The northeast (and eastern Canada!) experienced some of their most intense heat waves on record earlier this year. Montreal recorded one of its hottest temperatures in the books with a 98°F high on May 27.

While the heat was bad, the mugginess is what makes it unbearable. Greensboro recorded more than 1,000 hours of dew points at or above 70°F in June, July, and August. Washington, D.C., saw more than 1,500 hours of dew point at or above 65°F this summer, with nearly 800 hours of that kind of swampy moisture recorded in Boston—even as the region slipped into a drought! (You can compile dew point statistics at the Iowa Environmental Mesonet's site.)

Low temperatures typically come in warmer than normal when it's muggy, increasing the misery and accounting for much of the above-normal temperatures we've seen in recent years.

Climate change will exacerbate droughts, increasing the potential for more common and more intense wildfires. Climate change doesn't only increase overall temperatures, but it increases nighttime lows and increases mugginess.

And that's not all we've got to deal with!
Source: NHC

This week marks the climatological peak of hurricane season.

Tropical Storm Paulette and Tropical Storm Rene formed this weekend. They're the earliest sixteenth and seventeenth named storms on record, beating the record pace set by the hyperactive 2005 season and setting us on track to exhaust the official list of names and dive into Greek letters to name the remaining storms later this season. There are several more disturbances out there that could develop into tropical systems over the next week or so.

Even though we're on pace to see a near-record number of storms this year, the overall strength and duration of the storms is about on par for the second week of September.

The fact that this year's plentiful storms have been relatively weak isn't much consolation to the hundreds of thousands of people in southwestern Louisiana who've been forced to live a 19th century lifestyle after a 21st century storm.

Hurricane Laura made landfall near Lake Charles with 150 MPH winds, damaging or destroying thousands of homes and plunging the entire region into a weeks-long power outage. Most power won't be restored until later this month, forcing the people here to live in the dark with no air conditioning, no refrigeration, little water—all during a raging pandemic that's claimed 200,000 people in the United States over the last seven months and an average of about 1,000 people a day for the foreseeable future.

Things aren't good. I try to end even the most dismal posts on a positive note even if one is tough to find. Help each other and yourself. Care for each other and yourself. Be kind to others and yourself. Vote for good—please vote. Donate for good. Strive for good. And keep tabs on the weather. We can't always control bad weather, but we sure can see it coming and that ain't nothing.

[Top Picture: A smoke-filled orange sky looms over San Mateo, CA, on Wednesday afternoon. Photo by Cody Robertson]

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September 4, 2020

California Will Roast This Weekend While Fall's First Freeze Slides Down The Rockies

The big weather story this Labor Day weekend, for the first time in years!, doesn't involve hurricanes or severe weather. This weekend will see wild temperature extremes across the western half of the United States, roasting California in blistering heat while the Rockies and Plains have to deal with a powerful cold front that generates a 60°F temperature swing between Sunday afternoon's high and Tuesday morning's low.

California Heat

A model image of the intense upper-level ridge over the West Coast this weekend. | Source: Tropical Tidbits

A record-smashing heat wave in California will make a bad summer even worse. Temperatures on Sunday and Monday could threaten to break all-time high temperature records in some communities.

The heat is the result of a really strong ridge of high pressure building over the West Coast, pictured in the model image above. Air sinks beneath an upper-level ridge, drying and warming as it descends toward the surface. Stronger ridges can foster stronger heat waves.

Here's the National Weather Service's high temperature forecast for Sunday...

...and the same for Monday:

These temperatures will push daily, monthly, and even all-time record high temperatures in communities across California. A high of 111°F on Sunday would be the third-hottest temperature ever recorded in downtown Los Angeles. A high of 111°F on Sunday in Sacramento would be the city's hottest day since July 2006 and also one of the top-ten hottest days on record there. And so on down the list for communities across southern California and the Central Valley.

It'll be hot enough that folks won't have to spend too much time in the heat to incur heat-related illnesses. Even otherwise-healthy folks could succumb to the heat if they're exercising or working too hard in the heat without frequent breaks and access to air conditioning. This kind of heat will affect elderly folks and those who are battling illnesses (like COVID-19!) especially hard.

It's not just the heat itself. The intense heat and low humidity will create favorable fire weather conditions for the duration of the event. California's already been hit hard by wildfires this year. Three of the ten-largest wildfires on record started last month in California and they're still burning today. Conditions this weekend will allow fires to spark and spread with little effort, putting pressure on already-strained resources across the state.

Heatwave Breaks In A Cold Snap On The Plains

An upper-level trough riding around the outer edge of the western ridge will dive south along the Rockies by the end of the weekend. The trough will drag south with it a tremendous surge of frigid air from Canada. This will be the first big blast of fall for the center of the country.

This event isn't quite a blue norther—a cold front that rides along the eastern edge of the Rockies and brings dramatic temperature changes—because those events are characterized by temperatures plummeting dozens of degrees in just an hour or two. This cold front will hit and steadily erode the temperature for hours and hours until you bottom out around freezing.

Here's the NWS's high temperature forecast for Sunday:

And then the low temperature on Tuesday morning:

Big difference!

The Denver area will see a highs in the upper 90s on Sunday and another high in the upper 80s during the day on Monday. The cold front will enter Colorado on Monday night, allowing temperatures to steadily drop to freezing by Tuesday morning. It's going to be one of those days where most people in this region will see their high temperature at 12:00 AM one day. 

Rain and snow are likely behind the cold front. It's still too early to talk about accumulation potential, but the snow could get heavy in some areas—especially at higher elevations. Snow this early in the season can be dangerous since trees are still in full leaf and the weight of the snow in addition to the weight of the leaves can stress trees and tree limbs to their breaking point. Areas that see several inches of heavy, wet snow accumulation could see widespread tree damage and power outages as a result.

The animation at the top of this post shows high temperatures through next Wednesday. Comfortable temperatures and lower humidity will stretch all the way down into Texas. It's not here to stay, but next week will be a nice reprieve from a long, awful summer.

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