26 October 2020

Hurricane Zeta and déjà vu for Louisiana

On Monday afternoon, Zeta was upgraded to the season's 11th hurricane.  Looking back to 1851 when official records begin, only two previous seasons had 11+ hurricanes by this date: 2005 (13) and 1950 (11), so this is a truly remarkable level of activity. 

But, as if having 27 named storms and 11 hurricanes this season were not enough, Zeta looks like it will make landfall in roughly the same place where Tropical Storm Cristobal did in early June, Hurricane Laura in late August, Tropical Storm Marco in late August, Hurricane Sally in mid September, and Hurricane Delta in early October. It's only 340 miles between Sally's landfall point in eastern Alabama and Laura's landfall point in western Louisiana.

Zeta is forecast to clip the northern Yucatan peninsula on Monday night into Tuesday morning as a hurricane, then enter the Gulf of Mexico. While it should maintain hurricane intensity through its U.S. landfall on Wednesday, model guidance is consistently showing it weakening a bit as it approaches land, so it *could* be a tropical storm by that time. Regardless, heavy rain, strong wind, and storm surge will be hazards across a wide area. Keep in mind that a hurricane's impacts are far larger than a track line or the "cone of uncertainty".

Regarding track guidance, two of the global ensembles are packed pretty tightly now, with solutions ranging from western LA to the western tip of the FL panhandle, clustered most tightly around central-eastern LA.

The official hurricane season ends in 35 days, but nature does not have to stick to that artificial bound, so there's plenty of time for more storms this season. The next couple of names on the list are Eta and Theta. There's a slight hint among long-range models of another development in the western Caribbean in 10-14 days, but that is too far out to be reliable... think of it as the next potential time and region of favorable conditions.

25 October 2020

Zeta becomes 27th named storm, threatens northern Gulf coast

After a seemingly-endless wait, the disturbance in the western Caribbean was upgraded to Tropical Depression 28 on Saturday night, and then to Tropical Storm Zeta on Sunday morning.  This is the season's 27th named storm, and ties the record 2005 season, at least by that metric.

Zeta is expected to continue to organize and intensify, possibly hitting hurricane status by the time it reaches the northern Yucatan peninsula on Monday night.  Then, the environment is forecast to become increasingly hostile and Zeta should begin to deteriorate as it nears the U.S. coast.  However, that doesn't eliminate impacts from it, so stay tuned as we get closer to the middle of the week (landfall should be some time on Wednesday).

As if stuck in a rut, Zeta is also forecast to make landfall along the northern Gulf coast, just as Cristobal, Fay, Laura, Marco, Sally, Beta, and Delta did before it this season!

Rainfall, as usual, is a concern with this storm.  As of Sunday morning, the only part of the U.S. that will be impacted by it in the near future is extreme south Florida, where flood watches are in effect through Monday. But the Yucatan and western Cuba will also see heavy rain, and eventually, the north-central Gulf coast region will in a few days.

Catching up on the ACE (Accumulated Cyclone Energy) metric, 2020 is at about 145% of average for the date, but we can see where it lies in relation to historical mega-seasons. The top 5 through October 25th are 1933, 1926, 2004, 2017, and 1893. 2005 and 1995 just fall short of that list at 6th and 7th places. 

Elsewhere across the basin, things look quiet in the foreseeable future. But if and when the time comes, the next couple of names on the list are Eta and Theta.

23 October 2020

As Epsilon passes by Bermuda, Zeta could form in western Caribbean

Hurricane Epsilon is now a Category 1 hurricane with peak winds of 85 mph... it's centered about 200 miles east-northeast of Bermuda.  It should remain a strong tropical cyclone through the weekend, but will gradually transition to an extratropical cyclone as it passes east of Newfoundland on Sunday. Then, it could actually be a pretty powerful storm for the British Isles by the middle of next week.

The area of disturbed weather in the western Caribbean is now labeled Invest 95L.  Although still not a tropical depression, its organization has improved drastically in the past day, and NHC is giving it a 60% probability of formation.  It's presently centered near the Cayman Islands, but is broad and messy.  

Any activity in the western Caribbean in October is cause for concern; some very notorious hurricanes have explosively developed there.  In this map of ocean heat content, high values over the entire western Caribbean mean that there is a nearly endless supply of very warm water at its disposal.  If this develops, it would be Tropical Depression 28 and then Tropical Storm Zeta. You may recall that the record 2005 season finally ended with Zeta, which formed on December 30th.

Model guidance is generally not aggressive with it (yet). We also need to interpret the guidance with caution, because models are not great with these broad and disorganized low pressure systems.  The overall consensus is for it to track toward the northwest, bringing it into the Gulf of Mexico early next week, perhaps as a tropical depression or tropical storm.  

But there are some notable outliers in both the global model ensembles and in regional hurricane models -- those outliers bring it north over Cuba and into south Florida or the western Bahamas on Monday-Tuesday. Those also happen to be the quicker and stronger solutions (this particular HMON run shown below ("HMNI") has a Category 1-2 hurricane just east of south Florida on Tuesday morning, for example). Given that this outcome would bring at least tropical storm conditions to urban southeast Florida starting Monday afternoon, it's worth keeping a very close eye on it.

With such a track spread, it's basically impossible to come up with a meaningful rainfall forecast. But Jamaica, Cuba, the Yucatan peninsula, the western Bahamas, and south Florida could easily see multiple days of heavy rain from today through Monday. Check https://www.nhc.noaa.gov/ for the latest forecasts.

22 October 2020

Epsilon becomes season's 4th major hurricane

Since my previous update on Monday, Tropical Depression 27 quickly strengthened into Tropical Storm Epsilon, the 26th named storm of the 2020 season.  Then it reached Category 1 hurricane intensity on Tuesday night (the 10th hurricane), and Category 3 hurricane intensity on Wednesday night (the 4th major hurricane). 

In this spectacular satellite image showing mid-level water vapor, Epsilon is the green thing in the middle in its envelope of moisture (blues) but is embedded within a huge trough flanked by dry air.  Not something you see every day, or year. Bermuda is the tiny red dot just west of Epsilon.

Fortunately for Bermuda, it is staying further east than originally predicted, so impacts will only be long-distance such as possibly getting periods of tropical storm force winds and large surf as the large and powerful hurricane passes by. Tropical storm force winds extend as much as 310 miles from the center.

Elsewhere in the basin, the pesky area of disturbed weather in the western Caribbean is still festering. 

NHC is giving it a 20% probability of development during the weekend as it drifts by south Florida and the Bahamas.  Regardless of development, it will bring elevated chances of heavy rain with it. Should it happen to reach tropical storm status, the next name on the list is Zeta. 

19 October 2020

New Depression could threaten Bermuda as Hurricane Epsilon

After a 1.5-week lull in activity, Tropical Depression 27 has just formed southeast of Bermuda. This area of interest first appeared on the National Hurricane Center's five-day outlook for potential formation five days ago... spot on!  Although not yet a named storm, it is fully expected to become a tropical storm later today and take the next name in the Greek alphabet: Epsilon. This would be the season's 26th named storm.

The current forecast from NHC brings the storm to a Category 1 hurricane by Thursday, and then maintaining that intensity into the weekend as it approaches Bermuda.

Looking at the model guidance, there is not much to suggest that it will be much stronger than that, but the models should improve once it matures a little more. This plot has forecasts from regional and global dynamical models (deterministic and ensemble means), statistical-dynamical models, and consensus. 

This has already been a rough year for the tiny island of Bermuda: Tropical Storm Edouard passed by on July 5, Hurricane Paulette passed directly over on September 14, and then Hurricane Teddy passed to the east on September 21.

Through October 19, this year's ACE (Accumulated Cyclone Energy) is at 142% of average for the date. That amount of ACE is half of what the 1933 season had accrued by this date and 54% of the 2005 season by this date.

Elsewhere across the basin, there is a slowly-evolving large-scale circulation in the western Caribbean -- this is rather typical for this time of year. If something should eventually form from it, it would head generally north toward Cuba and the Yucatan.  If and when the time comes, the name after Epsilon will be Zeta.

08 October 2020

Hurricane Delta following in Hurricane Laura's footsteps

In the 2+ weeks since my previous post (the first half of that was due to the Atlantic taking a break, and the second half was due to me taking a break), there was Tropical Storm Gamma and Hurricane Delta. Tropical Storm Gamma lasted for just under three days and was located near the Yucatan peninsula.  Then right behind it was Delta, the season's 25th named storm and 9th hurricane. Delta experienced a period of remarkable rapid intensification on October 6th, jumping from a tropical storm to a Category 4 hurricane in one day as it approached the northern Yucatan peninsula... reminiscent of Wilma in 2005.

As of Thursday afternoon, Delta is a powerful Category 3 hurricane and is headed north toward Louisiana. A clear eye is becoming evident, signaling some additional strengthening. As the title of the post mentions, Delta's landfall location will be almost identical to Laura's back in late August.  Much of that area has still not cleaned up or started to recover before Delta's arrival. The last time two hurricanes impacted western Louisiana in the same year was 1886.

As it tracks north, it will encounter slightly cooler water temperatures, lower ocean heat content, and somewhat drier air; these factors should limit significant intensification prior to landfall (meaning a Category 4 or 5 is very unlikely).

Landfall is expected in western Louisiana on Friday evening, though conditions are already going downhill with rising water levels and outer rainbands scraping the coast. Tropical storm force winds should begin in coastal areas of eastern Texas and Louisiana by Friday morning.

No major changes in intensity are expected, so it should make landfall as a Category 2-3 hurricane, and produce a 7-11-foot storm surge to the right of its center. Rainfall totals could reach one foot in parts of western Louisiana.

The Accumulated Cyclone Energy (ACE) for the season is about 138% of the average value through October 8. Other years that had higher values by this date were 2019, 2017, 2010, 2008, etc -- in other words, this season is not that notable by this metric. Sure, we have cruised through named storms at a record pace, but 14 of the 25 named storms were around for three days or less!

Elsewhere across the basin, no new activity is expected in the coming week. But if and when the time comes, the next couple of names on the list are Epsilon and Zeta.

22 September 2020

Beta makes landfall, Teddy heads for Canada, Paulette is back

Tropical Storm Beta made landfall in Port O'Connor, Texas on Monday night and as anticipated, the wind and the storm surge were not a big deal, but the rain was, and still is. Here is a three-day rainfall accumulation estimate (there's also a regional radar loop going back to the 19th at bmcnoldy.rsmas.miami.edu/tropics/radar/) showing the not-too-impressive-looking storm and its stagnant sprawling rain. Beta is already the NINTH named storm to hit the continental U.S. this year... tied with 1916 for the most in an entire season.

Beta is forecast to continue to sit in roughly the same area for another day or so before getting kicked off toward the northeast. This will result in more rain over the same general areas, so flash flooding is of course a significant hazard.

Hurricane Teddy passed east of Bermuda on Monday (exactly a week after Hurricane Paulette passed directly over the island) and is making the transition to an extratropical cyclone... but it's still technically a Category 2 hurricane and is rapidly headed for Nova Scotia at 30 mph. The wind field is large, with tropical storm force winds extending up to 350 miles from the center, and hurricane-force winds as much as 105 miles from the center. This will be a very impactful storm there and in Newfoundland, both in terms of wind and storm surge. The last few hurricanes to make landfall in Nova Scotia were Dorian (2019), Earl (2010), Kyle (2008), and Juan (2003).

Fifteen days after it first formed, eight days after passing over Bermuda, and six days after it was declared to be extratropical, Paulette is back as a tropical cyclone. Located between the Azores and the Canaries, Tropical Storm Paulette is now stuck in an area with very weak steering currents, so it should be around for a few more days, basically in the same spot.  It is not expected to strengthen much, but it's enough of an oddity to fit in well with the rest of the odd season.

Finally, there's a small disorganized disturbance that formed along a frontal boundary over the weekend... it's centered over western Cuba and south Florida, and is not forecast to move much. Development is very unlikely, but it will make for some breezy and rainy conditions in the region for a day or two. In the infrared satellite image at the top of the post, it's hard to distinguish it amidst the rest of the active front draping down from Teddy.

With the surge of activity lately, the ACE (Accumulated Cyclone Energy) has jumped up to about 147% of average for the date. But it still doesn't touch the values from some of the mega-seasons of the past through September 21 -- the top five through this date are 1933, 2004, 1995, 1926, and 2017.

Elsewhere across the basin, things look quiet for the foreseeable future. But when the time comes, the next names on the list are Gamma and Delta.

19 September 2020

Now two names into the Greek list, and watching five storms

For the first time since 1893, THREE named storms formed in one day: Wilfred, Alpha, and Beta. When I started writing yesterday's blog post, Wilfred had just formed. Shortly after publishing it, Alpha formed, and a few hours later, Beta formed. I certainly can't recall anything like this happening in my 25 years of writing these posts! And to keep it even more interesting, Teddy's still a Category 4 hurricane and ex-Paulette is still out there and has a decent chance of re-developing.

Rather than discussing these in alphabetical order, I'll start west and go east. Tropical Depression 22, which had been festering for a long time in the western Gulf of Mexico, was upgraded to Tropical Storm Beta on Friday afternoon.  It is forecast to intensify to the season's ninth hurricane shortly as it drifts northwest toward Texas. The map below shows the NHC forecast track, the various tropical storm/hurricane watches and warnings, and the probability of tropical storm force winds.

But the hurricane part isn't the problem... it's the drifting. Models have been indicating that Beta will stall near the Texas coast and produce tremendous amounts of rainfall in the coming days.  It's essentially a toned-down version of Harvey in 2017 (that was a Category 4 hurricane at landfall and then stalled further north for several days). There's still uncertainty in the track of course, so the exact placement of rainfall maxima is impossible to know this far out, but a large swath of eastern Texas and Louisiana should be preparing for significant flooding.

On to Teddy... tropical storm warnings have been issued for Bermuda as the Category 4 hurricane approaches.  Teddy will pass east of the island and spare it from a second major impact in one week, but tropical storm conditions are possible as it zips by on Monday. But then, there's strong agreement among models that it will slam into Nova Scotia on Tuesday, possibly still with hurricane-force winds (even if it's technically not a hurricane anymore).

As expected, Tropical Storm Wilfred is battling a hostile environment and will likely not be around much longer. It's very disorganized and should dissipate by Sunday or Monday. This is something that might seem strange: a dissipating tropical storm in the heart of the deep tropics in mid-September. This fits in with what I'll discuss at the end of the post: lots of storms but they don't last long.

Moving on to Subtropical Storm Alpha, which made landfall on Portugal's coast on Friday night and has since weakened. This formed from an extratropical low pressure system that NHC began watching for development last Monday night, so it certainly didn't come out of nowhere, but the uncertainty was around whether or not it would acquire subtropical or tropical cyclone characteristics before reaching land -- it did, briefly. As a result, it got named, and Portugal got to usher in the use of the Greek alphabet for Atlantic storms this year.

And finally, we're still keeping an eye on what was Hurricane Paulette.  This isn't too surprising though, as many models had been suggesting that it would make a sharp turn to the south and return to warmer waters and possibly regain tropical cyclone characteristics. The turn happened, but the tropical transition has not happened yet. It's presently near the Azores, and has tropical storm-force winds. It also has a lot of smoke from the California wildfires wrapping into the circulation, which shows up here as the milky colors.

Don't believe me?  Using NOAA's HYSPLIT model, here's a backward trajectory that I calculated starting at Paulette's present location and going back eight days... the smoky air wrapping into Paulette came directly from southern California.

Wilfred, Alpha, and Beta are the season's 21st, 22nd, and 23rd named storms, which puts this season an incredible 33 days ahead of 2005's record pace. But, 12 of the 23 named storms this year were around for three days or less, and only 2 of the 23 were major hurricanes (Laura and Teddy).

So in terms of ACE (Accumulated Cyclone Energy), the average ACE per storm through today in 2020 is 3.8, while at this point in 2005, it was 8.7.  And at this point in 1933, the average ACE/storm was 15.2!

In fact, 2005 isn't even in the top five ACE producing years as of today... the top five are 1933, 1995, 2004, 1926, and 1950. But as of September 19, the ACE is 136% of average for the date -- a big spike after being near-average just a week ago. As you can see below, it's really comparable to 2018 and 2019 as of today.

18 September 2020

Wilfred and Alpha form in eastern Atlantic

For only the second time in history, the list of Atlantic tropical cyclone names has been exhausted. The wave in the eastern Atlantic was upgraded to Tropical Storm Wilfred on Friday morning.  This is the 21st named storm of the season, and is now three *weeks* ahead of 2005's record pace.

In the near term, Wilfred is expected to strengthen just a bit more, but then environmental conditions should become rather hostile by Monday, and the official forecast actually shows it dissipating in the deep tropics over the central Atlantic early next week.

Teddy has continued to intensify and is now a powerful Category 4 hurricane.  It's headed in the general direction of Bermuda, and should pass just east of the island on Sunday night.

Beyond the Bermuda encounter, it appears very likely that it will impact Nova Scotia as a strong hurricane (or extratropical cyclone with hurricane-force winds) on Tuesday.  The last few hurricanes to hit Nova Scotia were Dorian (2019), Earl (2010), Kyle (2008), and Juan (2003). 

Surprisingly, a low pressure system off the coast of Portugal developed today too, and is now Subtropical Storm Alpha.  This is the 22nd named storm of the season, and thus the first one to use the Greek alphabet! This won't around very long, but it certainly is interesting... the last subtropical storm to hit Portugal was Leslie in 2018.

We are also really close to having Tropical Storm Beta in the western Gulf of Mexico.  It's currently Tropical Depression 22, and models have been trending stronger.  The NHC forecast brings it up to hurricane intensity on Sunday and Monday as it drifts north, but then *possibly* weakening back to a tropical storm on Tuesday as it nears the Texas coast and slows to a crawl.

Unfortunately, regardless of just how intense it gets in the coming week, the rainfall will be very significant: this map below shows the rainfall forecast through next Friday. The sluggish motion will allow it to rain over the same locations for days.

Elsewhere, there is not much worth monitoring at this time.

16 September 2020

Sally makes landfall, Teddy upgraded to hurricane, Vicky weakens

For a few hours on Wednesday morning, the Atlantic basin was buzzing with three Category 2 hurricanes (Paulette, Sally, Teddy) and one tropical storm (Vicky).  Since my previous post on Monday afternoon, Sally weakened a bit on Tuesday but then intensified to a Category 2 hurricane as it made landfall on Gulf Shores, AL in the early morning hours on Wednesday. This is the *8th* named storm to make landfall on the mainland United States this season already... a new record.

The storm's slow forward motion continued through landfall (literally moving slower than a walking pace), creating tremendous flooding in parts of Alabama and the Florida peninsula.  I have long radar loops available at http://bmcnoldy.rsmas.miami.edu/tropics/radar/. Sally will continue to produce heavy rain along its track for the next several days, so the inland portion of its journey is just beginning.

Sally also generated something we tend to gloss over when it comes to hurricane impacts: the "anti-surge".  Storm surge is when strong onshore winds essentially and relentlessly bulldoze water onto land, often resulting in very destructive flooding.  But what about when the offshore part of the eyewall passes over a body of water? Well, Sally's western eyewall did just that: it passed over Mobile Bay and pushed a LOT of water out of the bay. At this tide gauge near Mobile, the water level fell 8 FEET as Sally made landfall, and then the water was eventually allowed to rapidly flow back into the bay. Of course, areas that experienced the eastern eyewall got the opposite effect.

Paulette was a hurricane up until midday Wednesday when it was officially transitioned from a tropical cyclone to an extratropical cyclone, at which point, NHC ceases advisories (though it's still a powerful low pressure system with hurricane-force winds!).

Vicky has remained a low-to-mid grade tropical storm, but is now weakening in the face of increasing wind shear (generated by Hurricane Teddy's outflow), and is expected to dissipate by the weekend.

Teddy has rapidly intensified to a Category 2 hurricane and is forecast to strengthen even more this week.  It's presently located about 750 miles east of the Windward Islands, 1350 miles southeast of Bermuda, and is moving toward the northwest at 12 mph. Models are in excellent agreement on a track toward the northwest, which unfortunately brings it to Bermuda on Monday -- they just got a direct hit from Category 2 Hurricane Paulette this past Monday!  Bermuda is the tiny cyan speck in the upper left corner of the satellite image below (can you find it?).

Then there are a couple areas of interest to monitor in the coming days. One is an easterly wave just south of Cabo Verde (Invest 98L). It's worth watching, but as of now, it faces a grim future according to long-range models.  While it's fairly likely to become at least a tropical depression in the coming days, the outlook as we head into early next head appears to include a more hostile environment for it. It's marginal though, with a few models showing continued development -- not an urgent threat to anyone.

The other is a disturbance in the western Gulf of Mexico (Invest 90L). It is in an area of virtually no steering flow, so it should just sit in place and gradually get organized.  What does the future hold for it? No model has a useful or consistent forecast, so for now, we wait and see what it does.

Only one name remains in the regular list: Wilfred.  After that, we start using names from the Greek alphabet: Alpha, Beta, Gamma, Delta, etc.  You may recall that the hyperactive 2005 season went into the Greek alphabet too, but not until October 22.  In terms of ACE (Accumulated Cyclone Energy), this recent burst of action has taken the season from near-normal a few days ago to about 125% of normal for this date.

As mentioned before, while the 2020 season is blasting its way through names, it's far from competing with previous hyperactive seasons in terms of ACE. The top five historical seasons as measured by ACE through September 16 are: 1933, 1995, 2004, 1950, and 2005.