November 16, 2020

Hurricane Iota, Latest Category Five On Record, Making Landfall In Pummeled Nicaragua

This has been one heck of a hurricane season and "it can always get worse" seems to be the rule at the moment. It's the middle of November. We're on our unprecedented 30th named storm. And Hurricane Iota, now a category five hurricane with 160 MPH sustained winds, is on track to make landfall in almost the exact same spot in Nicaragua where category four Hurricane Eta made landfall two weeks ago. Come on.

Iota rapidly intensified into a scale-topping hurricane on Monday morning as it encountered near-ideal conditions in the western Caribbean. The region features a deep reservoir of warm waters, light winds aloft, and ample moisture, all the necessary ingredients for a storm to thrive. The only limitation on the storm is that water temperatures—even a steamy 84°F—will only allow storms to intensify so far.

The latest forecast from the National Hurricane Center puts the storm into the Nicaraguan coast at full intensity. The only thing that could weaken the storm right now is either a hiccup in its internal structure that causes it to temporarily weaken, or the beginning of an eyewall replacement cycle that has the same effect. Time is running out for that to happen, though, and the storm is so strong that the catastrophic effects are essentially baked in at this point.

The National Hurricane Center's 10:00 AM EST discussion succinctly sums up the threat:
This is a catastrophic situation unfolding for northeastern Nicaragua with an extreme storm surge of 15-20 ft forecast along with destructive winds and potentially 30 inches of rainfall, and it is exacerbated by the fact that it should make landfall in almost the exact same location that category 4 Hurricane Eta did about two weeks ago.
Hurricane Eta killed more than 100 people in Central America after multiple feet of heavy rain triggered flash flooding and mudslides. It's always difficult to outline the true worst case scenario for any one region when a hurricane makes landfall, but Central American countries preparing for a category five hurricane just two weeks after the devastating winds and flooding of a category four hurricane has to sit pretty high up on the list. 

Adding insult to injury, there's a chance that another storm will form in the western Caribbean later this week. Indications point to the potential system not being quite so strong, but even a gentle shower over areas hit by these two hurricanes would make a horrible situation worse.

An infrared satellite image of Hurricane Iota on November 16, 2020. | Source: NOAA

The tropical Atlantic usually starts shutting down by the middle of November. The end of hurricane season isn't a hard deadline—it's based on climatology that shows waning tropical activity in the Atlantic as the cool, dry, and hostile winds of autumn start to call the shots in the northern hemisphere. While that's what usually happens, that isn't the case this month.

In addition to warmer-than-normal waters in the western Caribbean, Hurricane Iota likely managed to strengthen as a result of La Niña in the Pacific and a ridge of high pressure over eastern North America. 

La Niña, a period of cooler-than-average waters in the eastern Pacific, subdues thunderstorms over the eastern Pacific that could send strong wind shear eastward over the Caribbean. The ridge of high pressure over eastern North America, the one responsible for the relatively warm and calm weather we're experiencing today, further calmed the atmosphere over the Caribbean, fostering an environment where Iota could build itself up as much as possible.

It's also difficult to ignore the influence of climate change in a situation like this. We can't "pin" any one storm on climate change, but when you see rapid intensification in one storm after another, year after year, it becomes a worrying trend that could signal that we've crossed a threshold when it comes to warmer ocean waters and more favorable atmospheric conditions for rapid intensification.

Oh, and just in case you're keeping track...

Hurricane Iota is the 30th named storm of the season. The previous high water marks were 28 storms in 2005, 20 storms in 1933, and 18 storms in 1995.

We exhausted the list of 21 names back in September. Iota is the ninth letter of the Greek alphabet.

Hurricane Iota is the latest category five hurricane on record in the Atlantic Ocean.

This is the sixth major hurricane this season. 

This is the fourth storm to reach at least category four intensity this season.

This is now the fifth season in a row we've seen at least one category five hurricane in the Atlantic.

This is the eleventh storm this year to undergo rapid intensification, having jumped from 105 MPH to 160 MPH in just 12 hours. (Rapid intensification occurs when a storm strengthens about 35 MPH in one 24-hour period.)

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November 12, 2020

Why Tropical Storm Eta Followed Such An Odd, Zig-Zaggy Path Toward Florida

It's not a surprise that a strange storm formed during a strange year. We've been watching Tropical Storm Eta for almost two weeks now. The storm's followed a zig-zagging path from the Caribbean to the Gulf of Mexico, a winding journey that brought devastating flooding to Central America and more than a foot of rain on southern Florida. Here's a quick rundown of why the storm followed such an odd path.

Eta is the 28th named storm of this hyperactive and historic Atlantic hurricane season. The storm, named after the seventh letter of the Greek alphabet, formed in the middle of the Caribbean Sea on October 31. This is exactly where you'd expect to see tropical development this late in the season. The Caribbean is really the only oasis left for tropical cyclones once you reach October and November.

Prevailing winds steered Eta west across the Caribbean Sea in the days following its formation. A ridge of high pressure over the western Atlantic intensified as the system approached Nicaragua, causing it to make a southward jog that steered it directly into the Nicaraguan coast.

The storm rapidly intensified as it approached landfall, growing into a powerful category four hurricane just about a hundred miles off the coast. Any tropical system in this region has the potential to generate catastrophic flash flooding and mudslides, but this storm's ferocity made a dangerous situation even worse. News reports indicate that more than a hundred people may have died in the region as a result of the storm's flooding.

Environmental winds beneath ridges of high pressure are usually pretty calm. The lack of steering currents forced Eta to putter over Central America for a couple of days, slowly weakening as it turned north over Honduras. After entering the western Caribbean two days after landfall, the system regenerated into a tropical storm and drifted north over Cuba as it approached Florida.

This is where the track got a little...creative.

A large ridge of high pressure over the eastern United States and western Atlantic effectively blocked Eta from continuing out into the Atlantic after it crossed over Cuba. This forced the storm to make a westward hook into Florida, making landfall at Lower Matecumbe Key on November 8.

As the ridge moved eastward, Eta slowed to a crawl over the southeastern Gulf of Mexico. The storm slowly drifted toward the tip of Cuba before an approaching trough forced Eta to start moving northeastward. The tropical storm briefly restrengthened into a hurricane as it moved parallel to the west coast of Florida—winds were strong enough in the Tampa area to generate coastal flooding from storm surge. 

Eta made its fourth landfall in Florida's Big Bend region on Thursday morning, and the system will accelerate out to sea and dissipate as it gets swept up by a cold front moving over the eastern United States.

This isn't the end of it. We're likely going to see our 30th named storm of the season form in the Caribbean by this weekend, possibly threatening the same stretch of Central America hit by Eta last week.

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November 9, 2020

Subtropical Storm Theta Makes 2020 Atlantic Hurricane Season The Most Active On Record

Of course it was going to come to this: Subtropical Storm Theta formed in the eastern Atlantic Ocean on Monday night, becoming the record 29th named storm of the 2020 Atlantic hurricane season. This is now the most active Atlantic hurricane season on record, beating the hyperactive 2005 hurricane season by one storm. Theta will slowly drift through the eastern Atlantic through the end of the week.

Theta formed far to the southwest of the Azores Islands from a cluster of thunderstorms along a frontal boundary. The cluster of storms became organized enough for the National Hurricane Center to declare the system a subtropical storm and begin issuing advisories.

A subtropical storm is a low-pressure system that exhibits both tropical and extratropical characteristics—it's a hybrid storm that looks and acts like a tropical cyclone, but it's not completely warm throughout and it derives some of its energy from upper-level winds.

The National Hurricane Center's current forecast shows Theta transitioning into a tropical storm as the thunderstorms near the core of the storm take over as the system's energy source. Theta will pose no threat to the United States, but it could bring hazardous conditions to Madeira this weekend or early next week.

Theta is the 29th named storm of this historic hurricane season. The previous record was 28 storms set back in 2005. The 2020 hurricane season beat 2005's record by starting early—Tropical Storm Arthur formed on May 16—and by racking up the storm count through several stretches of rapid-fire storm development.

Theta is the eighth letter of the Greek alphabet. The next letters in the Greek alphabet are Iota, Kappa, and Lambda. There's a decent chance we see at least one more storm this year. Hurricane season runs through November 30, and the final storm of the 2005 hurricane season developed on December 30.

[Satellite Image: NOAA]

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November 6, 2020

Tropical Storm Watches Up For South Florida As Eta Strengthens And Lingers

It's been...quite the news week...but something that shouldn't get lost in the chaos is that the atmosphere is still minting storms like they're state quarters. Eta, the 28th named storm of this historic hurricane season, is still plunking along in the western Caribbean Sea. Forecasters expect Eta to regain tropical storm strength as it heads toward Cuba and Florida through early next week.

Hurricane Eta made landfall in Nicaragua on Tuesday with maximum winds of 140 MPH. The system slowly wound down as it lingered over Nicaragua and Honduras these last couple of days, producing intense winds and several feet of rain over a region that's exceptionally vulnerable to flash flooding and mudslides.

The storm's core, while degraded, made it back over the Caribbean largely intact, giving the system a leg-up on reorganizing and strengthening as it moves over warm waters and encounters a favorable environment. Tropical storm conditions are likely across the Cayman Islands and much of Cuba over the next couple of days as Eta heads north.

Forecasters expect Eta's rain and wind to reach southern Florida by Sunday and linger for a couple of days as the tropical storm hesitates a bit. A ridge of high pressure to the north and east of Florida will prevent Eta from moving out to sea—without a clear exit, the storm is forced to meander into the Gulf of Mexico. What happens after that, though, is something we'll have to wait and watch.


If the current forecast pans out, Eta will arrive in southern Florida with sustained winds around 60 MPH with higher gusts. That's a pretty stiff sustained wind—they issue severe thunderstorm warnings for gusts that strong. It's enough to bring down trees and knock out power. Folks in southern Florida don't need to be told to prepare for power outages and whatnot, but it never hurts to take a look around to make sure you've got enough food and batteries to get through a day or two in the dark.


The rainfall here is a two-part story. We've got rainfall from Eta and rainfall influenced by Eta.

The greatest rainfall totals are likely across the southern tip of Florida as Eta passes through the area. Some communities could see up to half a foot of rain where the most persistent bands set up. Rainfall amounts are contingent upon the structure of the storm and its speed when it gets there. If it's better organized and meanders for a day or two as predicted, that leads to better odds of greater rainfall totals than if it's disorganized or moves faster than expected.

The rain farther north—from the Carolinas through the Northeast—is influenced by Eta. This is rainfall enhanced by the tropical moisture pushed north into the region. Several inches of rain are possible through the middle of next week. Heavy rain might cause some localized flooding issues—watch out for drains clogged with fallen leaves—but it'll likely just lead to a couple of dreary, rainy days.

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November 2, 2020

Hurricane Eta Rapidly Intensifies Into A High-End Category Four As It Approaches Nicaragua

Hurricane Eta rapidly intensified into a powerful category four hurricane in the western Caribbean Sea on Monday, packing maximum winds of 150 MPH as of Monday evening's advisory from the National Hurricane Center. This was...not anticipated until the strengthening trend had already begun, and now Eta is the strongest storm of the 2020 Atlantic hurricane season.

Satellite intensity estimates place Hurricane Eta in the upper echelon of storms. These automated intensity estimates use cloud patterns and temperatures (on the cloud tops and within the eye) to estimate the strength of a storm. It has a warm eye, a symmetrical and well-insulated core—an "angry wind bagel" as I used to tongue-in-cheekedly call it in a past blogging life—and the all-knowing algorithms consider it about as visually perfect as a hurricane can get.

Aircraft recon flying into the storm Monday night found winds pushing the upper bounds of category four intensity. The official NHC forecast brings the system up to category five intensity before it makes landfall in Nicaragua on Tuesday.

What else can you say? It's times like this when descriptors and pointing out broken records kinda loses its punch. Eta is the record-tying 28th named storm of the season. Eta is now one of the strongest Atlantic hurricanes ever observed in November. Its sudden and rapid period of intensification puts it up there with...well, pretty much every other hurricane we've seen this season, but this storm pushes the upper bounds for the fastest intensification seen in the Atlantic.

Here's the storm's wind history, taken from the NHC's updates every three hours since Saturday night. (All times Eastern.)

1100 PM SAT:    40 MPH / 1005 MB
100 AM SUN:    40 MPH / 1005 MB
400 AM SUN:    40 MPH / 1005 MB
700 AM SUN:    40 MPH / 1005 MB
1000 AM SUN:  50 MPH / 1000 MB
100  PM SUN:    50 MPH / 1000 MB
400 PM SUN:     65 MPH / 992 MB
700 PM SUN:     70 MPH / 989 MB
1000 PM SUN:   70 MPH / 989 MB
100 AM MON:   70 MPH / 989 MB
400 AM MON:   75 MPH / 987 MB
700 AM MON:   90 MPH / 974 MB
1000 AM MON  110 MPH / 962 MB
100 PM MON  : 120 MPH / 957 MB
400 PM MON:   130 MPH / 948 MB
700 PM MON:   150 MPH / 934 MB
1000 PM MON: 150 MPH / 927 MB

Meteorologists expected Eta to rapidly intensify given the warm sea surface temperatures and low wind shear surrounding the storm. However, rapid intensification is still very difficult to accurately predict, and it wasn't clear that this storm was going to explode the way it did until the process was already underway.

This is a terrible development for folks in the path of the storm. 

Yesterday—yes, yesterday—the storm looked like it would creep up to hurricane status and become a major flood threat for Nicaragua, Honduras, and El Salvador. That's a pretty bad situation on its own. The region is poor, geographically primed for major flash flooding and mudslides, and also stricken by the same pandemic as the rest of the world. The potential for flooding alone could have produced a humanitarian catastrophe.

Now this is a different situation altogether. A major, potentially historic storm is knocking on the region's door. The winds of a high-end category four hurricane will devastate communities with destructive winds and a catastrophic storm surge that could easily inundate one-story buildings near the coastline. And that's on top of flash flooding and mudslides from several feet of heavy rain.

As I mentioned last night, landfall isn't the end of this system. We have to watch what it does by the end of the week. Eta could regenerate into a tropical storm in the western Caribbean. Don't let your guard down if you live along the U.S. coast. Hurricane season isn't over yet.

[Satellite imagery from NOAA. Top image is infrared and the bottom image is water vapor.]

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November 1, 2020

Tropical Storm Eta, Historic 28th Named Storm Of 2020, Threatens Central America This Week

Tropical Storm Eta could strengthen into a hurricane before making landfall in Central America later this week, bringing damaging winds and flooding rain to parts of Nicaragua, Honduras, and El Salvador. The storm's slow movement will lead to widespread flash flooding across a mountainous region that's exceptionally vulnerable to flash flooding and mudslides.

Models have signaled for a while that the Caribbean would be favorable for tropical development around the beginning of November. Just like Zeta last week and Delta before it, Eta formed right about where you'd expect to see tropical systems develop this time of year. The Caribbean is home to the warmest waters and the most favorable atmospheric conditions to support tropical development this late into the season.

Eta will slowly move west toward Central America over the next couple of days. Hurricane conditions are likely in eastern Nicaragua and eastern Honduras on Wednesday as Eta makes landfall. While the wind will damage weaker structures and the electrical grid, the big story from this storm is rain.

Any tropical cyclone making landfall in Central America is a scary prospect because of the region's heavily mountainous terrain.

The National Hurricane Center's latest forecast notes the potential for 15-25 inches of rain in parts of Nicaragua and Honduras, with upwards of three feet (really!) of rain possible in higher elevations. Tropical cyclones are terrible in mountainous regions because the moist winds of a hurricane roaring up the side of a mountain is the atmospheric equivalent of wringing out your washcloth in the shower.

There's some nervous hesitation about what happens after Eta makes landfall. The most likely scenario, the one depicted by the NHC's forecast, is that Eta will slowly degenerate over land as the rough terrain takes its toll on the storm's structure.

There's a chance that either 1) the storm reemerges into the Caribbean later in the week, or 2) a different storm forms in the same area. It's a little too far off to say anything for sure, but it's something to file in the back of your mind so it doesn't come as a galloping shock in our post-election daze. 

Speaking of the potential for one more storm...

Some (More) Record-Keeping

Eta is the 28th named storm of the 2020 Atlantic hurricane season, tying the all-time record of 28 storms seen back in 2005.

Matching 2005's record is a remarkable feat for a remarkable year. It's tremendously difficult for the Atlantic basin to produce this many storms in one season. The previous all-time high was 20 storms back in 1933. Even hurricane seasons held in infamous regard like 1995 and the 2010-2012 stretch were only able to produce 19 storms each.

While 2005 stands alone for the sheer strength of the storms that formed that year—Dennis, Emily, Katrina, Rita, Wilma— this year saw its 28th storm nearly two full months before that historic season. The 28th named storm formed on December 30, 2005, so there's a decent chance this year could break the record before it's over.

The next three names on the list are the Greek letters Theta, Iota, and Kappa.

This is also the first time we've ever used the seventh Greek letter—Eta—to name a storm in the Atlantic.

The "missing" storm from the 2005 season was an unnamed subtropical storm that forecasters didn't catch until they conducted their routine post-season analysis the following spring. If forecasters had caught the unnamed storm contemporaneously, it would've been called "Subtropical Storm Tammy" and every subsequent storm that formed after October 4, 2005, would've been pushed back one letter, making the final storm Eta instead of Zeta.

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