ACE score tells the true story of the hurricane season

Tropical storm Henri gives us a total of eight named storms thus far in the Atlantic hurricane season. This is getting us close to the 100+ year average of about 10 named storms. We’ve only had two hurricanes form from those eight named storms – one of which became a “major” hurricane with 115 mph winds, Danny. Seems like the season is a little busy? Yes and no.

Let’s take a closer look at the real measure of the hurricane season from an energy output perspective. We call this ACE or Accumulated Cyclone Energy. It’s a score, like a college basketball team achieves in a single game. Each player is like a named storm. Some will score big and lead the way while others may get a lot of playing time but only add a few points to the overall total. In the end, you may have 7 or 8 players who rotated in and out for the night but only a few truly had an impact on the final score. This is how the hurricane season works, in a general sense anyway.

ACE is simply a way to measure how long each storm lived and how much wind energy it generated. It has nothing to do with landfall, dollars cost or lives lost. It’s all math and is totally objective. In short, it is a great way to sum up the quality of a particular hurricane season, not just the numbers of named storms.

A typical Atlantic hurricane season will yield a final ACE score of around 100 points (give or take a few). Some have been hyper-active with 20o+ points in a single season (2004 and 2005 come to mind).

For this season, Colorado State University’s hurricane seasonal forecast predicts a final ACE score of around 35 points, well below the average. Right now, the score is roughly 25.

Why does this matter? For one, it helps to better define how a particular hurricane season behaved. We could have 12 to 15 named storms but if most are weak and short lived, then the energy output is relatively low and thus you can have a seemingly busy season with a fairly low ACE score.

Conversely, a season like 1961 which featured “only” 11 named storms racked up an ACE score of 211. This is because there were seven, yes seven, MAJOR hurricanes that season. The stronger the hurricane, the faster the ACE accumulates over time.

The largest single ACE event for the Atlantic was for a hurricane in 1899 which scored 73 points of ACE – all by itself. This is higher than many entire hurricane seasons from just ONE hurricane!

Then you have a season like 2015. So far, eight named storms and things have seemed pretty busy since about the end of August. In fact, we’ve had something to talk about or track every day since about August 20. Might seem like an active season to some. The ACE argues otherwise. Only Danny really amounted to creating any significant ACE points (around 9) but it was fairly short-lived as shear coming out of the Caribbean put a quick end to Danny’s run.

Had Erika lived up to the various computer models’ forecasts of being an intense hurricane, it would have certainly piled on perhaps 20 ACE points, maybe more. Instead, Erika died out and scored very low: 3 total ACE points.

This tells us a lot about how the season is behaving. The low quality of the storms and the short-duration hurricanes can be looked at as the reason why the ACE points are so low even though we’ve had plenty to track.

In the end, ACE says nothing for impact and we need only look to Dominica for that fact. Heavy rain took a devastating toll as Erika moved through and it is likely, in my opinion, that it will be retired from the list of names due to the damage and loss of life it caused, despite it’s poor ACE showing.

I bring all of this up as we are now at the climatological peak of the Atlantic hurricane season. Henri is churning out over the open water well away from Bermuda. It will score only a few ACE points since it is not likely to become a hurricane. We’ll probably see two or three more named storms before all is said and done which will be above what most experts predicted for the season as a whole. However, unless there is a particularly intense hurricane at some point, lasting for a few days, it is doubtful that the season will be memorable from an ACE perspective, at least not from the high end of things. You never know, all it takes is for a hurricane to form and just roam around the Atlantic for a week and we could end up with an ACE score closer to the long-term average.

As far as the tropics go, Henri is a non-issue except for shipping lane interests in the North Atlantic. Elsewhere, there continues to be talk of a possible western Gulf of Mexico storm or hurricane next week. Right now, it’s just that, talk and speculation. The global models have not been much help this season with predicting genesis of storms and then their subsequent intensity. So let’s just wait and see after this cold front comes down and quickly lifts out what happens. It’s peak time of the hurricane season, everyone should be paying attention anyway – if something develops, we’ll deal with it then.

I’ll have more tomorrow morning.

M. Sudduth 11:20 AM Sept 10


Erika gone, new tropical storm developing near Africa, Pacific as busy as can possibly be

NHC map showing remnants of Erika (orange) and invest area 99L (red)

NHC map showing remnants of Erika (orange) and invest area 99L (red)

There is a lot to talk about today. I do realize it is also the 10th anniversary of Katrina’s historic landfall but instead of piling on more about that right now, let’s save it for another time, another in-depth blog post perhaps. For now, let’s focus on the current goings on.

Erika caused quite an uproar this past week with model mayhem galore. One day it looked like Florida would see an end to the hurricane drought. The next day, look out Carolinas! It just went on and on and yet Erika completely failed to behave as the models suggested – most of them anyway.

Now, to be clear, Erika had major consequences for some locations in the Caribbean Sea. Dominica has had terrible loss of life and an overwhelming loss of infrastructure. All of this due to one seemingly benign effect: rain. Over the centuries, I bet freshwater flooding has led to more misery than any other hazard from tropical cyclones. Storm surge poses the greatest risk in any one vulnerable location but flooding from too much rain seems to rear its ugly head one time too many as of late.

Erika is now just a remnant low moving across the southern portion of the Florida Straits. I do not see anything that leads me to believe that it has a chance of any significant comeback. While we need to certainly monitor its progress in case of any surprise endings, I wouldn’t worry too much about the left-overs becoming more than a nuisance – though it might bring heavy rain which of course has its own potential for causing issues.

Invest area 99L just off the coast of Africa

Invest area 99L just off the coast of Africa

Meanwhile, another strong tropical wave and associated low pressure system just off the coast of Africa is likely to be our next named storm: Fred. However, it won’t last very long. The favorable environment that it is currently a part of will be short-lived. It will be interesting to see the effects on the Cape Verde Islands as it looks like the system will pass over that location while intensifying some. I fully expect it to die out over the open eastern Atlantic some time next week.

One thing to note – if this system (99L) does in fact become a tropical storm or even a hurricane, it will be the third in a row to come from the so-called MDR or Main Development Region. I bring this up because this alley-way was supposed to be almost completely dead this year due to hostile conditions. I believe the warmer than normal water that has developed across much of the MDR has changed things somewhat. But, the upper level winds are still just too strong and as we saw with Danny and Erika, we may have MDR development but it will be tough for it to survive or thrive very long.

In the Pacific, we have three incredible hurricanes going on at once: Kilo, Ignacio and Jimena. None pose a substantial threat to land but all three are a testament to the remarkably warm water of the northern Pacific Ocean. This really has little to do with the El Nino itself, just a much warmer Pacific, away from the Equator, than we are used to seeing.

Hurricane Ignacio forecast track map from the CPHC

Hurricane Ignacio forecast track map from the CPHC

Hurricane Ignacio could bring tropical storm conditions to parts of Hawaii and as such, the Central Pacific Hurricane Center has posted a tropical storm watch for the Big Island. As long as Ignacio remains on track, the overall impact will be minimal to the area.

It has been a busy couple of weeks and it looks to remain that way going forward. So far, the United States has had little to deal with from the tropics. As we saw 10 years ago, that can change and have long-lasting effects that linger for generations. As August draws to a close, we know that September is traditionally the peak month for hurricane activity. We’ve been fortunate so far in 2015 (except for Dominica) and we can hope to have a quiet second half ahead of us. Only time will tell.

I’ll have more here tomorrow.

M. Sudduth 5:10 PM ET August 29

End of the road coming up for Erika? More like hitting a brick wall…

It has been a tough few days for hurricane forecasters and not because of something like Katrina 10 years ago. This time, it has been because the storm in question, Erika, has been such a pain in the neck to forecast. Fortunately, any deviations from the ideas set out by the National Hurricane Center, then echoed by others (including me), have been positives in terms of overall impact. In other words, Erika has not lived up to expectations and that is a good thing.

Before I get in to the (likely short) future of Erika, let’s not forget what happened around this time yesterday. Copious amounts of rain fell as deep convection developed right over Dominica in the eastern Caribbean Sea. This led to the unfortunate loss of life and terrifying flash flooding in the mountainous terrain of the island. Please let this be a reminder that even a tropical storm can be lethal. So much emphasis is placed on wind speed and pressure and category that the general public loses sight of the overall idea that we are talking about a destructive weather phenomenon. Rain is absolutely an impact from tropical cyclones as the people of Dominica were painfully reminded of yesterday.

So what does the future hold for Erika and any potential impacts to the United States? The answer to that question is rooted within what happens during the next 24 hours or so.

Satellite photo showing the poorly organized structure of TS Erika as it approaches Hispaniola

Satellite photo showing the poorly organized structure of TS Erika as it approaches Hispaniola

Erika is poorly organized but does have a fairly large envelope of energy. Tropical storm conditions are mainly being felt to the east of the center of circulation which itself is located just to the southeast of the Dominican Republic. In fact, you can see in the satellite photo that a burst of convection has popped up right near that center, giving Erika a little longer before the brick wall.

The United States and even Cuba for that matter owes a great deal of its hurricane protection to the island of Hispaniola. It’s all a matter of luck and geography but the fact remains that without Hispaniola in the way, many more powerful hurricanes would have lashed Florida, Cuba and eventually other locations along the western Atlantic Basin. This comes with a price though. The high terrain of the island literally wrings out the moisture from passing tropical storms and hurricanes. The resultant flash floods and mudslides can produce appalling loss of life and mind-boggling damage. Erika is headed right for the island and will slam in to it – likely bringing very heavy rain to the region.

As the storm traverses the rugged terrain, the low level center will almost certainly dissipate and we will be left with a trough of low pressure that was formerly Erika. Now, there’s a chance that the tenacious storm will just dance across and emerge in to the Florida Straits ready to go. I wouldn’t bet on that happening but you never, ever turn your back on a tropical anything coming through water that is near 90 degrees F! The next day or so is the key. If there is anything left of Erika once it passes over Hispaniola, then Florida might have to deal with a tropical storm and maybe, just maybe, a hurricane. So much will depend on how much warm water it has to work with and what the upper level winds are like. For now, Erika is headed for the Caribbean Road Block otherwise known as Hispaniola. What happens after that is beyond my ability to figure out – it’s a wait and see deal, nothing more.

Meanwhile, in the Pacific, hurricane Ignacio continues to track northwest in the general direction of Hawaii. The five day forecast keeps the center north of the island chain but we know how that can go. Obviously, interest out that way should keep watching and be ready to act should the track shift south even by a little bit. Water temperatures in the east Pacific, especially the northern Pacific, are quite a bit warmer than normal. So far, Hawaii has escaped major calamity this season – we’ll see if that luck holds.

I’ll have a video discussion on Erika and other happenings in the tropics, including a look back at Katrina 10 years ago today, posted later this afternoon.

M. Sudduth 8:55 AM ET August 28

One last hurdle for Erika, if it makes it, Southeast coast beware

There’s a lot going on this morning, not only with Erika but also with another storm – in the Pacific – that could impact Hawaii next week.

Actually, my thoughts on Erika will be fairly short and to the point.

Radar image from San Juan, PR showing a few outer bands of Erika moving through. The rain will increase in coverage and intensity as the day wears on

Radar image from San Juan, PR showing a few outer bands of Erika moving through. The rain will increase in coverage and intensity as the day wears on

Right now, the storm is moving through the northeast Caribbean where the rain it is bringing is badly needed. Take a look at the radar from San Juan, PR. Not much rain yet but the bands from Erika will begin to move through as the day progresses. A few inches could fall and in fairly short order, thus flooding could be a concern, especially in higher terrain areas.

I think it all comes down to the next 48 hours, maybe less. Right now, Erika is doing well for itself despite moderate shearing winds that are continuing to displace the convection away from the low level center. The pressure has been up and down a few millibars overnight with a slight uptick in wind speed.

Wind shear map from the University of Wisconsin CIMSS site. I have added some annotation to help define the track that Erika needs to live through before it can strengthen significantly

Wind shear map from the University of Wisconsin CIMSS site. I have added some annotation to help define the track that Erika needs to live through before it can strengthen significantly

Before we even begin to think about where Erika might end up, we need to see what happens over the next two days. I believe that if Erika can get through the strong band of upper level winds that appears to be waiting just to its west, that we will in fact have quite a hurricane to deal with somewhere along the Southeast coast. Keep in mind, it’s all about the impact – not just where the eye goes. Erika is likely to kick up some serious surf and cause a great deal of anxiety for people from Florida up through the Carolinas. That’s assuming the storm survives this one last gauntlet of strong upper level winds.

Looking at the graphic, you can clearly see where Erika is in relation to the stronger upper level winds that are blowing across the tropical storm. I have highlighted in red the area that I think Erika has to navigate and if it does so intact, it’s open for as much intensification as the environment will allow. The models generally see this, though some waffle back and forth from run to run. The end result is that a majority of the intensity guidance suggests that Erika will survive the shear and come out the other side ready to strengthen and do so quickly as it approaches the Southeast coast.

So let’s see what happens over the next 36 to 48 hours and go from there. I’ll certainly post updates between now and then but there’s no use worrying about where Erika will end up until we have a sure thing that there will be much of an Erika at all. If the shear kills off the storm, then the rest of the story is moot. The clock is ticking, we’ll see what happens over the next day or two.

TS Ignacio track map in the east Pacific showing a course towards Hawaii early next week

TS Ignacio track map in the east Pacific showing a course towards Hawaii early next week

Meanwhile, newly upgraded hurricane Ignacio could impact Hawaii next week. It is tracking WNW right now. The forecast calls for it to become a major hurricane over the warmer-than-usual waters of the northern east Pacific. Hawaii has had a few darts thrown their way this season, so to speak, with everything missing for the most part. Will Ignacio follow suit or break the streak and bring hurricane conditions to the islands? As usual, it’s too soon to know for sure.

Most of the model guidance suggests, at least at this point, that the hurricane will track just to the north of Hawaii. This will be something to watch closely and interests in the region should be doing so.

I will have another blog post here this evening but before that, I will post a video discussion early this afternoon concerning Erika and Ignacio. There will be a lot to cover, that is for sure. The tropics are busy, even in a year when the Atlantic was supposed to be “quiet”. Right now, it is anything but.

M. Sudduth 9AM ET August 27

Is Florida’s nearly ten-year hurricane drought about to end?

Latest tracking map with cone of uncertainty showing the potential for Erika to impact Florida in the coming days

Latest tracking map with cone of uncertainty showing the potential for Erika to impact Florida in the coming days

Wilma was the last in many ways. It was the last of the 21 names on the 2005 list of names for the North Atlantic hurricane season (after Wilma, the Greek Alphabet was used). It was the last major hurricane (cat-3 or higher) to make landfall in the United States and it was the last hurricane to make landfall in Florida.

Not a single hurricane since for the Sunshine State- though there have been a couple of close calls.

Is this long-standing hurricane-free drought about to come to an end? It is possible though not officially forecast just yet. Here’s what we know…

Of course, I am talking about tropical storm Erika which is still well east of the Lesser Antilles this morning. Overnight, the storm has made a bit of a comeback with deep convection returning and the pressure dropping just a little bit.

The latest discussion from the National Hurricane Center is still full of uncertainties. How can this be in this day and age? That’s an easy question to answer: tropical storms and hurricanes will likely always be tricky – not of all of them, but most. It’s just not cut and dry that this will happen or that will happen. In a season like this with so many road blocks in front of systems like Danny or Erika, it’s hard to put stock in model forecasts. So much can change and people are left either scratching their heads as to what the heck is going on (hype) or left unprepared because something happened that was not expected. Neither scenario is acceptable and so the challenge for the people at the NHC is to get the forecast right, even if that means forecasting a hurricane in to Florida in a few days. It’s darn close right now.

Erika is moving over warmer and warmer water as it moves west. This is an obvious plus for development. However, upper level winds are not very favorable and are tending to blow across the storm and this has acted to push the convection or thunderstorm activity away from the low level center. Without this machine running at full speed, the storm cannot intensify – at least not quickly.

I think the issue of dry air will be moot once Erika gets past around 65 degrees west longitude. The tropical Atlantic has become more favorable in recent weeks from a moisture standpoint. Another plus for Erika to eventually strengthen.

Then we have the models. This has been a real interesting phenomenon to watch over the past few days. You have some computer guidance indicating a very strong hurricane while, on the other hand, some of the best global models (not developed to predict hurricanes per se) simply get rid of Erika almost entirely. That would solve the problem, wouldn’t it?

Added to the madness are situations like the ECMWF which is widely regarded as the best overall global model on Earth. It has been going back and forth from run to run showing an intense hurricane followed 12 hours later on a subsequent run, a much weaker one at best. This happened night before last and the Internet hurricane world blew up with talk of a major hurricane lurking off the Southeast coast next week. Then, just like that, it was gone. Crickets….

Just wait 12 hours and a new version of “look out!” is cooking up with the ECMWF now showing a hurricane threat for Florida in less than a week. What is one to do? Well, I have the answer for that as well.

I have been doing this long enough to know that none of the models matter this far out. Seeing the ECMWF or the HWRF or whatever model you wish to follow show one thing after one run and something else later on will not change the outcome. What ever is going to happen will happen with or without computer guidance. To put it in simpler terms – people in the path of Erika or any future hurricane will likely have ample time to prepare and evacuate if need be. Relax. Spend less time fretting over the latest amazing model output map (there are some talented map makers out there – that is for sure!) and more time planning on what YOU will do if Erika heads your way. We have a five day forecast now from some of the best in the world. Trust that, not something affectionately called a “spaghetti plot”.

So as we watch Erika in the coming days, it will be prudent to remind people, as the NHC mentioned this morning in their latest discussion, that track errors at days four and five can be significant. A good deal of the Florida peninsula is now in the cone of uncertainty. In this case, Erika is providing plenty of uncertainty but as time goes by, things will settle down, leaving anyone within the path of the (potential) hurricane with time to take action.

It’s been a while for Florida since a hurricane threatened landfall. Erika may be the one to end the drought and if it is, I challenge people in Florida to be ready and not let all the fuss get to your heads. If you’re new, ask a hurricane veteran what it’s all about. Avoid stressing over social media posts of doom and gloom. If the time comes and Erika prompts a hurricane watch or warning, listen to your LOCAL TV and radio sources, check Twitter and Facebook for LOCAL information from emergency management. Above all else, do not give the hurricane trolls the time of day. They will be lining up to post ominous no-context maps just to gain “likes” or “clicks”. That’s feeding their ill-found egos. Look for local, trusted sources and of course, the National Hurricane Center and your local National Weather Service office. Do that and you’ll be fine. Act like you’ve been there Florida – even though it’s been nearly ten years, you all know hurricanes probably better than most.

I’ll have more here late this afternoon.

M. Sudduth 5:30 AM ET August 26