October 9, 2020

Hurricane Delta On Track To Make Landfall In Already-Damaged Southwestern Louisiana


Hurricane Delta restrengthened into a major hurricane on Thursday as it steadily made its way toward the Louisiana coast. The hurricane will make landfall Friday afternoon in southwestern Louisiana, very close to where Hurricane Laura hit back in August. Destructive winds, a life-threatening storm surge, and flooding rains are likely along Delta's path into Louisiana. The effects of this hurricane will be exacerbated by lingering damage and structures weakened by the previous hurricane.

This has been a tenacious storm since the day it formed. Delta managed to strengthen into a powerful and tiny category four hurricane before crashing into Cancun on Wednesday morning. The storm weakened over land, but warm water and favorable environmental conditions over the southern Gulf of Mexico helped Delta recombobulate and begin to strengthen again. The hurricane even developed a clear eye for a little while on Wednesday evening.

Source: National Hurricane Center

The 10:00 PM CDT advisory from the National Hurricane Center bumped Delta's winds up to 120 MPH, making it a major hurricane again. The storm's winds will likely tick down a bit as it approaches landfall in southwestern Louisiana on Friday afternoon, but this is a powerful storm that'll do quite a bit of damage to an area still trying to recover from Hurricane Laura.

Communities around the point of landfall will experience the strongest winds and the greatest storm surge, but make no mistake—this is a large hurricane and it'll have wide-reaching impacts in the region.

As expected, Hurricane Delta's wind field is larger than it was Wednesday. The storm's growth will expose a larger region to damaging winds and a life-threatening storm surge that could measure as high as 11 feet above ground level near the point of landfall. The National Hurricane Center's latest advisory measured Delta's tropical storm force windfield at about 320 miles wide, with hurricane force winds stretching 80 miles across the eye.

Widespread power outages—numbering in the hundreds of thousands—are likely across Louisiana as Delta makes landfall and pushes inland. Trees weakened by Hurricane Laura will struggle to withstand Hurricane Delta, endangering homes that sit beneath large trees and tree limbs.

Source: Weather Prediction Center

Flash flooding is also a major threat along Delta's path inland. Communities from southern Louisiana to southern Arkansas could see more than five inches of rain through Saturday. This much rain falling this quickly will lead to flash flooding in vulnerable areas.

Even though I'm confident that you already know this if you're reading my blog (thank you, by the way!), it feels like a requirement to stick this in here, so here goes..

The leading cause of death during landfalling tropical cyclones in the U.S. is flash flooding from excessive rain. It only takes a small amount of water to lift up a vehicle and carry it downstream. It's impossible to tell how deep the water is before it's too late, and sometimes the floodwater can obscure that the road itself is washed away. It's not worth it. Find another route or stay put if you can.

[Satellite Image: NOAA]


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October 7, 2020

Hurricane Delta Will Likely Hit Louisiana On Friday As A Large And Dangerous Storm


Hurricane Delta will make landfall along the Louisiana coast on Friday. The latest forecast from the National Hurricane Center indicates Delta could reach land as a large and dangerous hurricane, bringing the threat for a life-threatening storm surge, destructive winds, and flash flooding from heavy rainfall. Any landfalling hurricane is bad enough, but this is a sensitive stretch of coastline and the area is still reeling from the damage left by Hurricane Laura back in August.

Delta isn't nearly as strong as it was this time yesterday. The hurricane strengthened into a (tiny!) category four storm with maximum winds of 145 MPH in the far western Caribbean on Tuesday. A combination of wind shear and changes in the storm's internal structure forced it to weaken before making landfall on the Yucatan Peninsula.

Source: NOAA
The system spent a couple of hours this morning over the Yucatan before emerging over the southern Gulf of Mexico. Delta has a pretty healthy appearance on satellite imagery this afternoon—the hurricane's well-build structure will allow the storm to take advantage of favorable conditions around it and begin restrengthening.

The National Hurricane Center's 4:00 PM CDT advisory placed Hurricane Delta's maximum sustained winds at 85 MPH, and the forecast calls for the storm to restrengthen into a major hurricane by Thursday afternoon. Unlike the previous four hurricanes that hit the U.S. this year, Delta should start to weaken a bit as it approaches land as a result of increased wind shear and cooler waters.

The system will still be a large and powerful hurricane by the time it makes landfall, so don't take much solace in the word "weaken" here. A larger storm will mean that the effects of storm surge and damaging winds will affect a larger area as the hurricane makes landfall and pushes inland.

Storm Surge

Source: NHC

Hurricane Delta's long-fetch approach into the northern Gulf Coast, combined with the storm's strong winds, will allow a life-threatening storm surge to build up along the coastline as it makes landfall.

Based on current forecasts, the worst surge will push into Vermillion Bay and the surrounding area. The flat, marshy terrain of Louisiana's coastline makes the region exceptionally vulnerable to a storm surge. A significant storm surge here could push many miles inland from the coastline.

The greatest push of water will occur in the right-front quadrant of the storm, which will be the eastern side of the eyewall. A slight westward or eastward nudge in the storm's track will cause the storm surge "bullseye" to follow in kind.

Since Delta's wind field is growing, a dangerous storm surge won't be confined to areas right around the point of landfall. Portions of southwestern Louisiana hard-hit by Laura's storm surge could see another surge deep enough to inundate the first floor of structures along the coast. A storm surge as much as 4 feet above ground level could occur as far east as Mobile Bay.

Winds

The growing size of the storm will expose a large area to damaging winds as Delta makes landfall and pushes inland. It's likely that hundreds of thousands of households across Louisiana and Mississippi will lose power at some point during the storm. The hardest-hit areas could be out for a week or longer depending on the extent of the damage.

Prepare for power outages even if you're hundreds of miles inland from the expected point of landfall. Make sure you have enough ready-to-eat food, water, batteries, and USB recharging packs to last at least a couple of days without power.

It's a good idea to spend Wednesday night and Thursday securing loose items outside—tables, chairs, grills—so they don't become projectiles in strong winds. Take care of any limbs or trees looming over your property. If you can't do that, avoid rooms where falling limbs or trees could crash through the roofs or walls. A significant number of injuries and deaths in recent storms were the result of trees crashing into homes.

Flooding


Delta and its remnants will produce widespread heavy rainfall across the southeastern United States through this weekend. The Weather Prediction Center's latest forecast, pictured above, shows the potential for 5+ inches of rain to follow the track of the system inland. This much rain in a short period of time will lead to flash flooding issues, especially in areas that are normally prone to flooding.

You probably know the deal by now—it takes a surprisingly small amount of water to lift up a vehicle and carry it downstream. It's impossible to tell how much water covers a roadway until it's too late. Sometimes floodwaters can completely obscure that the road is washed away. Make sure you've got alternate routes to get around if you have to go out during the heavy rain.


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October 6, 2020

Extremely Powerful Hurricane Delta Could Hit The Gulf Coast As A Major Hurricane On Friday


Hurricane Delta grew into an extremely powerful category four hurricane on Tuesday as it took full advantage of near-perfect conditions over the western Caribbean Sea. The system is on track to make a direct hit on Cancun, potentially devastating the resort town with storm surge, destructive winds, and flooding rain. Delta will continue into the Gulf of Mexico and threaten the northern Gulf Coast as a major hurricane by Friday.
Source: NOAA

Hurricane Delta's maximum sustained winds came in at an incredible 145 MPH as of the 7:00 PM CDT advisory, representing an enormous strengthening in just a short period of time.

Environmental conditions and sea surface temperatures will allow Delta to maintain this strength—or possibly grow a little stronger still—through Thursday as long as the system can maintain its composure. The hurricane has a healthy core with plenty of cloud-to-surface lightning detected by weather satellite, which is a sign of intense thunderstorm activity in the eyewall. 

Delta is a very small hurricane right now. The system has a pinhole eye about 5 miles wide, and the eye is obscured by cirrus clouds produced by the storm's outflow. The radius of hurricane force winds only extends about 30 miles from the center of the storm. 

Hurricane Delta's small size is also the reason it doesn't look all that imposing on satellite imagery right now. Don't let its compactness and non-traditional appearance fool you—this is one powerful hurricane. 

SourceNOAA/NESDIS

It appears that Delta experienced the fastest intensification of any storm ever recorded in the Atlantic Ocean, strengthening from a tropical depression to a category four hurricane in about 30 hours.

Small storms are highly volatile. Compact hurricanes can be both impervious and susceptible to the environments around them, allowing these tiny systems to ramp up in a hurry—as we saw here with Delta—and fall apart just as quickly when they encounter some resistance, as we saw with Hurricane Danny in 2015.

It's unlikely that Hurricane Delta will encounter much resistance over the next couple of days.


The only obstacle in Delta's path right now is the northeastern Yucatan Peninsula, where Cancun and its surrounding communities are bracing for one of their worst hurricanes in living memory. It doesn't look like the core of the storm will stay over land very long, which will allow a stronger storm to emerge into the southern Gulf of Mexico. Conditions here will allow the storm to make one last run-up in strength and organization before it makes its final approach to the northern Gulf Coast.

The system is likely going to grow in size over the next couple of days, which will make its hazards even more of a problem for the Gulf Coast when it arrives at the end of the week. Delta will inevitably undergo eyewall replacement cycles, which serve to temporarily weaken the storm's winds and redirect its energy into growing the storm's size.

The hurricane will continue moving northwestward until it reaches the southern Gulf. A trough over the central United States will weaken a ridge of high pressure over the southeastern United States, causing the storm to turn northeast and begin tracking into the Gulf Coast. Cooler water and increased wind shear should force the storm to start weakening on Friday, but it'll be a race against time to see how much it can weaken before it runs into the coast.

Right now, forecasters expect the storm to make landfall as a major hurricane in central Louisiana at some point on Friday evening. However, a small change in the storm's track could lead to big changes in where the system will make landfall—the cone of uncertainty, the historical margin of error in previous track forecasts, stretches from Galveston to Biloxi.

That's a sensitive and scary path for a major hurricane to take for any number of reasons. 

Southwestern Louisiana is still reeling from Hurricane Laura back at the end of August. Laura was the strongest hurricane on record to strike this stretch of coastline. The storm heavily damaged or destroyed thousands of homes and businesses in the area and left remaining residents in the dark for up to a month. A storm surge nearly 20 feet deep devastated coastal communities just south and east of Lake Charles. 

The heart of Acadiana—south-central Louisiana, centered around Lafayette—is just as vulnerable to a significant storm surge as southwestern Louisiana. Calling the coastline here a "coastline" is just a formality. The whole stretch of coast from Lake Charles to the mouth of the Mississippi River is miles and miles of swamps and bayous. When a storm surge rolls over this marshy land, there's not really any actual land there to stop the surge. This can allow a major storm surge to push dozens of miles inland, affecting communities far away from the shoreline. 

Hurricane Delta will also make a much more direct approach to the coast than Hurricane Laura did. Hurricanes that approach the coast on a straight path can produce a more significant storm surge than those that hit at an angle or make landfall after a sharp turn. Delta will spend about 24 hours moving along a straight path toward the coast, giving the storm time to build up a long fetch that could exacerbate the threat of a storm surge in communities along its path. 

There's also the threat to New Orleans, which is within Hurricane Delta's cone of uncertainty. The city is infamously vulnerable to storm surge from approaching hurricanes. Even a storm that misses a direct landfall here could produce major flooding in and around the city. 

Folks on the northern Gulf Coast are running out of time to get ready for this system. Anyone along the potential path of this system—from the coast on hundreds of miles inland—needs to prepare for widespread, lengthy power outages and significant flash flooding.

If the storm makes landfall as a major hurricane, power outages will stretch very far inland and catch many folks off-guard. Go to the store on Wednesday and make sure you've got enough ready-to-eat food and water to get you through at least a week without power, along with the batteries and cell phone recharging packs to last the same amount of time.

We'll have a clearer idea of its track and resulting impacts on Wednesday.

[Satellite: NOAA]


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October 5, 2020

Tropical Storm Delta Could Hit The Gulf Coast As A Hurricane Late This Week


It's the season that keeps going and going. We're watching a new tropical storm in the Caribbean that could become a big problem for folks on the Gulf Coast by the end of the week. The National Hurricane Center expects Tropical Storm Delta to approach the northern Gulf Coast as a hurricane on Friday. It's still early, so folks from Texas to Florida need to make sure they're prepared and follow the system's development.

Tropical Storm Delta formed from a disturbance that didn't follow far behind Tropical Storm Gamma, which made landfall on the Yucatan Peninsula last Friday. Gamma is still hanging out in the Gulf...well, sort of. The system is basically just a naked swirl out for a skinny-dip off the northern tip of the Yucatan. Gamma (or its remnant circulation) could play a role in Delta's future track and intensity, which makes the ailing system a wildcard in what happens over the next couple of days.


Hurricane Hunters began investigating Tropical Storm Delta this afternoon and found that the system rapidly strengthened and was nearly a hurricane by early evening. One look at satellite and it's not hard to figure out why the system is quickly strengthening. The storm looks very healthy today. Delta isn't lopsided or struggling with dry air, so that'll help its inner-structure continue to organize and allow the storm to steadily gain strength over the next couple of days.

The environment ahead of Delta is quite favorable for development, with calm wind, ample moisture, and warm sea surface temperatures in the western Caribbean and southern Gulf. Forecasters expect Delta to rapidly strengthen into a hurricane by the time it reaches the Gulf of Mexico, possibly reaching major hurricane status by the time it passes the Yucatan Peninsula.

Sea surface temperatures are chillier once you get to the central and northern Gulf, though, as a result of recent storms and recent cold fronts sweeping across the region. These colder water temperatures should stop Delta's strengthening and allow the storm to slowly weaken on approach to the U.S.. That's a welcome change from the previous four hurricanes to hit the United States—Hanna, Isaias, Laura, and Sally all rapidly strengthened as they made landfall.

Even with the colder water, forecasters expect the storm will move at a decent-enough clip that any weakening before landfall would be slow to occur. Accordingly, their latest forecast calls for a hurricane to make landfall somewhere along the northern Gulf Coast at the end of this week.

This is a serious storm that could have wide-reaching effects for folks on the northern Gulf Coast and interior parts of the southeastern states. Heavy rain and wind doesn't stop at the coast. Flash flooding, wind damage, and a threat for tornadoes would be possible well inland along the storm's path.

If you live along the coast—or even a few hundred miles inland—it's a good idea to spend the next day or two making sure you're prepared for the power outages and flooding. Keep enough ready-to-eat food and water to get you through a couple of days in the dark, enough batteries to power flashlights and radios, and charging packs to give your cell phone a few extra charges.

The storm's name, Delta, is the fourth letter of the Greek alphabet. We've seen 25 named storms so far this year. If Delta makes landfall in the United States, it'll be the tenth named storm to make landfall in the country this year, which would be an all-time record for U.S. landfalls in one season.

[Satellite: NOAA]


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October 3, 2020

Tropical Storm Gamma Hits Mexico, Another Storm Might Move Into The Gulf Next Week


We enjoyed a brief lull in tropical activity across the Atlantic Ocean before things started to pick up again. A tropical storm made landfall on the Yucatan Peninsula this afternoon and it'll continue producing heavy rain over parts of Mexico through the middle of the week. Another disturbance in the Caribbean could develop into a depression or storm as it enters the Gulf, and there are a few other disturbances out in the Atlantic that might help beef up this year's already-beefy storm count.

We're a few weeks past the peak of hurricane season but the threat isn't over yet. I wrote a post a few days ago explaining that tropical activity in October and November typically forms in the Gulf of Mexico and Caribbean—we're creeping back into the period when we won't have the luxury of watching disturbances roll off Africa nearly two weeks before they become an issue for the U.S.

Tropical Storm Gamma


Gamma formed on Friday from a vibrant disturbance in the western Caribbean. The system rapidly strengthened into a 70 MPH storm before making landfall on the Yucatan Peninsula early Saturday afternoon.

The tropical storm will weaken a bit before it emerges over the southern Gulf of Mexico on Sunday and turns back toward Mexico. A cold front draped across the Gulf of Mexico will prevent the storm from continuing north into the United States.

The greatest threat from this system is flooding rains in Mexico. The storm could produce up to a foot of rain in higher elevations, which could lead to widespread flash flooding and mudslides in vulnerable areas.

A Trio Of Disturbances


➤ System #1

Hot on the heels of Tropical Storm Gamma is a disturbance that has a high (70 percent) chance of developing into a tropical depression by early next week. If it develops into a tropical storm, its name would be Delta.

The cold front that blocked Gamma from moving toward the United States will dissipate by early next week, allowing this new disturbance to move through the Yucatan Channel into the Gulf of Mexico.

If the system manages to develop, there's a decent chance that we'll have a tropical system moving toward some stretch of the Gulf Coast by late next week. The environment should be conducive to some strengthening and sea surface temperatures in the western Caribbean and southern Gulf are still in the mid- to upper 80s. 

It's too early for many specifics on the system beyond . It's something to keep an eye on this weekend and a reminder that the season isn't over yet. These next couple of days are a great time to make sure you've got the supplies needed—ready-to-eat food, water, batteries—to make it through a power outage, and plans in place in case of flooding or evacuations.

➤ System #2

Remember Hurricane Paulette from early last month? The remnants of that thing are still hanging around in the Atlantic Ocean. Paulette formed on September 11th and became a large hurricane that made a direct hit on Bermuda on September 14th.

The system raced off to the northern Atlantic and became an extratropical cyclone, but it slowed down, turned, and regenerated into a tropical storm near the Azores on September 22nd before weakening into a remnant low the following day.

Well...that remnant low is still hanging around in the central Atlantic after three weeks. The National Hurricane Center gives it a 10 percent chance of becoming a tropical cyclone for a third time, but it's running out of time before it's sheared apart.

➤ System #3

A tropical wave that moved off of Africa—probably one of the last African waves we'll see this year—has a 20 percent chance of developing into a tropical depression before it encounters destructive wind shear east of the Lesser Antilles.

Greek School


We're three letters deep into the Greek alphabet now. The next name on the list is Delta, followed by Epsilon and Zeta. We only got as far as Zeta during the record-setting 2005 hurricane season. It's possible that we'll manage to get beyond the sixth Greek letter, but we'll be cutting it close. The 2005 hurricane season didn't reach Delta and Epsilon until Thanksgiving weekend, and Zeta formed on December 30th that year.

[Satellite Images: NOAA]


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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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