Complex situation as model duel plays out

It has been an exceptional year in terms of how two of the world’s best global models have performed. I am speaking of the American generated GFS or Global Forecast System versus the European generated/supported ECMWF or European Centre for Medium-Range Weather Forecasting. Both models are highly sophisticated and provide a vast array of products for forecasters around the globe. However, both have had their share of issues over the years when it comes to forecasting tropical cyclone events.

Let’s take a look at TS Debby back in late June. The GFS was forecasting a turn to the northeast as a trough of low pressure dug in to the eastern portion of the U.S. On the other hand, the ECWMF was forecasting a ridge to build and push Debby back to the west. Here is a paragraph from the NHC’s discussion regarding Debby on June 24:

“THE TRACK FORECAST IS EVEN MORE COMPLEX. THE GFS INSISTS ON A TRACK TOWARD THE NORTHEAST AS DEBBY BECOMES EMBEDDED WITHIN A LARGE MID-LATITUDE TROUGH. HOWEVER…THE ECMWF AND THE HWRF BUILD A RIDGE TO THE NORTH OF DEBBY AND FORECAST A WESTWARD TRACK. GIVEN THE WESTWARD TURN INHERITED FROM THE PREVIOUS FORECAST…AS WELL AS THE HISTORICAL STRONG RECORD OF THE ECMWF…THE NEW OFFICIAL FORECAST MOVES DEBBY INITIALLY A LITTLE BIT TO THE NORTHEAST TO REFLECT CURRENT TRENDS BUT THEN TURNS THE CYCLONE BACK TOWARD THE WEST OR WEST-NORTHWEST IN 24 TO 36 HOURS. A MAJORITY OF THE GFS ENSEMBLE MEMBERS NOW ARE CONSISTENT WITH THE DETERMINISTIC RUN…WHICH WAS NOT THE CASE YESTERDAY…MAKING A STRONGER CASE FOR THE EASTWARD SOLUTION. WE MUST BE READY TO MAKE A CHANGE OF THE FORECAST TRACK AT ANY TIME.”

Note the reference to the ECMWF and how it has a “historical strong record”. Well, as it turned out, the ECWMF was wrong and Debby ended up turning north in to the Florida panhandle.

Forecast for Debby showing west track towards Louisiana

Forecast for Debby showing west track towards Louisiana

Later that day, the new forecast, which was the correct forecast, shows Debby headed north in to Florida panhandle

Later that day, the new forecast, which was the correct forecast, shows Debby headed north in to Florida panhandle

Now let’s fast-forward two months to Isaac in late August. Here again we had two significant differences between the GFS and the ECMWF. The GFS wanted to take Isaac north and in to a trough after entering the Gulf of Mexico, putting a substantial threat to the Florida panhandle and even the west coast.

Meanwhile, the ECMWF showed a much farther west track towards Louisiana. Here again is a quote from the NHC discussion on Isaac from August 22:

“HOWEVER…THE ECMWF CONTINUES TO SHOW A STRONGER RIDGE…AND THUS SHOWS A MORE WESTERLY MOTION THAN THE OTHER MODELS.”

As it turned out, the ECMWF was correct in a stronger ridge and Isaac ultimately made landfall in southeast Louisiana.

So what does this have to do with the current situation with Sandy? For the first few days of the forecast period, not much. Right now, the GFS and ECMWF are pretty close to each other since the pattern is fairly straight-forward right now. Sandy is forecast to move slowly northward and bend east of north and pass over or very close to Jamaica. Both models “agree” on this.

Then, both models have Sandy passing over eastern Cuba and in to the central Bahamas by around 72 hours. It’s after this time frame that the two models part ways and have two vastly different outcomes.

The GFS basically moves Sandy slowly to the northeast and out of the Bahamas. While the ECMWF takes Sandy more north by day four but also fairly slowly.

At day five, the GFS has Sandy roughly half-way between Florida and Bermuda while the ECMWF is quite a bit back to west, near 30N and 75W.

It seems that the GFS wants to hand off Sandy in to the Atlantic due to lower heights in the middle layers of the atmosphere because of a large ocean storm, partly the remnants of Rafael. This provides and escape route for Sandy to take, like a rock gradually rolling down a slope, not too steep, but just enough to build momentum and begin rolling. Sandy is the rock heading down the gentle slope.

The ECMWF does not allow Sandy to feel the slope, so to speak, and keeps it farther back to the west, much closer to the Southeast U.S. coast. Then, all “you know what” breaks loose with that model.

By day six, a significant deep trough of low pressure digs in to the west of Sandy and causes the flow to turn more from the south out over the western Atlantic. Instead of pushing Sandy out like a broom sweeping across the floor, the trough instead scoops Sandy up and swings it back to the northwest and eventually in to New England as a powerful hybrid storm. Basically, the trough “captures” Sandy and pulls it in, not allowing it to turn east and out to sea like the GFS shows. The result is a remarkable storm for the mid-Atlantic and New England; the so-called “storm for the ages” that I alluded to yesterday.

Which solution will be right? I have no idea. I can see why both models show what they show but I also know that the GFS tends to have a bias in handing off tropical cyclones in to lower height fields more often than not. In other words, the GFS is taking the easy way out and sending Sandy in to the Atlantic. The ECMWF does not do this and instead keeps Sandy in the western Atlantic long enough for the big trough to dig in and capture it, creating a large ocean storm of epic size and strength.

Day seven of ECMWF showing powerful storm as Sandy gets drawn in to trough in the East

Day seven of ECMWF showing powerful storm as Sandy gets drawn in to trough in the East

There is a lot of talk about this situation in the weather blogosphere. Opinions about both scenarios abound and some folks simply refuse to believe such a wild scenario with the ECMWF. However, considering its track record in the long term, it has to be considered and thus, once Sandy is in the Bahamas, the story will begin to unfold as to what ultimately ends up being the true course that it will take.

In the end, one of these two powerhouse global models will end up being correct. Which one that is will have enormous implications on the weather for millions of people along the East Coast of the U.S. towards the very end of the month. Stay tuned, this has only just begun….

 

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Sandy likely to become a hurricane as it nears Jamaica

I have a feeling that Sandy is going to be a lot stronger than forecast. Why not? Intensity predictions are where there is the least amount of skill when it comes to tropical cyclones. Sandy is currently situated over some of the warmest, highest heat content water in the Atlantic Basin with an obvious building area of high pressure in the upper levels of the atmosphere. This should lead to a period of quick strengthening and people in Jamaica better be ready for the potential of hurricane conditions over the next couple of days.

Not much has changed today in the future track concerns for Sandy. It looks as though eastern Cuba and then the central Bahamas will take a direct hit from the storm (hurricane?) with plenty of heavy rain spreading across a good portion of the Greater Antilles.

What the models seem to all indicate is that Sandy will continue to strengthen once over the extreme southwest Atlantic Ocean in about three days. Here too water temps are very warm and undisturbed this hurricane season. As with Jamaica, I am concerned about portions of the Bahamas having to deal with an intensifying hurricane sitting on top of the area. Keep in mind too that Sandy is not forecast to move very fast, this will only prolong the effects in any given area.

Now, for the part where folks along the U.S. East Coast have to pay attention. The long range models are split in to two distinct camps. The GFS and its related modeling ejects Sandy out in to the Atlantic on a northeast track, easily staying away from the U.S. coastline.

On the other end of the spectrum, the two non-U.S. generated models, the ECMWF and the Environment Canada CMC models both show Sandy getting stuck in the pattern, trying to turn out but then hooking back northwest to north with a landfall along the Northeast coast. What is most concerning, but almost certainly overdone, is the absurd intensity that the models are suggesting. It is my sincere hope that there is just something not right with what the Euro and Canadian predict for the long range. If they are even close to being correct, Sandy could transition in to one heck of a hybrid mix the likes of which the region has not seen in almost a generation.

As I mentioned earlier today, even though there is a lot of interest in what happens a week from now, we need to be sure to stay focused on what may be a hurricane threat in and coming out of the Caribbean Sea. We’ll have loads of time to see how the steering pattern evolves once Sandy gets in to the Bahamas.

I would also like to mention that I believe we will see some strong winds, out of the east and northeast, for portions of the Florida east coast in the coming days. This will lead to an increase in rough surf and possible dangerous rip currents. And, if Sandy tracks closer to the coast than forecast, it is possible that tropical storm conditions could be felt in some areas of extreme SE Florida. This is a very complex situation and one that will end up affecting people across a large geographic swath.

I’ll have more here tomorrow morning including a new video blog posted to our iPhone app. I will also be watching closely to see how far west Sandy tracks and if it warrants a field mission to coastal Florida later in the week. I think the next 48 hours will tell a lot about the future for Sandy and what impacts the U.S. will feel.

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A storm for the ages? Perhaps. First, it is a Caribbean concern

99L about to become a tropical depression in the Caribbean Sea

99L about to become a tropical depression in the Caribbean Sea

There are very few instances when I have posted a headline like the one in this blog. Hype is not a tool I use to get the attention of my audience unless it is warranted and I feel it could help to save lives and property. What I am seeing in some of the global models is worthy of getting your attention and if it’s hype, then all the better in the long run.

There is a storm brewing in the Caribbean that will soon get a name: Sandy. Right now we know it as 99L, an area of investigation with potential to develop. Within the next 10 days, we may remember it as one of the great ocean storms of recent memory. Before all of that, it will be a problem for the Caribbean and that much is certain.

So far, development of 99L has been slow. It now looks as though things are coming together in the western Caribbean, a few hundred miles south of Jamaica. Water temps are as warm as could be and upper level winds are becoming more and more favorable. The NHC gives the area an 90% chance of becoming a tropical cyclone within 48 hours. I think it’s as good as done at this point and we’ll soon have TS Sandy to track.

72 hour ECMWF showing "Sandy" over Jamaica

72 hour ECMWF showing "Sandy" over Jamaica

People with interests in Jamaica need to be watching this system closely. It will bring periods of heavy rain and an increase in wind as it moves slowly towards the northeast with time. This slow forward motion is going to be a problem as the tropical rains will have a lot of time to fall over the same area for a couple of days or more. I would also not be surprised to see this become a hurricane before it reaches Jamaica. Intensity prediction is very poor even in this day of high-end computer models. Hopefully we’re only talking about a weak tropical storm in a few days but remember that hope is not a good planning tool. Being prepared is far better.

After Jamaica, the threat shifts to Cuba, Hispaniola and the Bahamas. Here too, the main issue will be excessive rain from what is surely to be “Sandy” by mid to late week. How strong it is depends on how quickly it can develop a solid inner core. Interests in the region should be paying close attention to what happens as this feature grows. We are not talking about an “in and out” system that gets kicked in to the Atlantic in a day or so. I think the big story will be the heavy rain even if this does become a hurricane in the Caribbean.

It’s what happens after the Caribbean that has the potential to make this storm one that people talk about for a long, long time.

Day five of the ECMWF showing "Sandy" after moving through the Bahamas

Day five of the ECMWF showing "Sandy" after moving through the Bahamas

To put it in simple terms, some of the global models are indicating that this storm will get caught in the southwest Atlantic and grow in to a hybrid mix of a hurricane and a Nor’easter the likes we have not seen since as far back as 1991 with the “Perfect Storm”. The closest event I can recall is “Nor-Ida” in 2009 which took the tropical leftovers of hurricane Ida from the Gulf of Mexico and transitioned it in to an epic ocean storm that blasted the North Carolina coast and points north. I was in that one and will never forget it. This storm could make that one look like a day in the park.

It all seems to have begun yesterday when some of the global models began to change their track for 99L from an out to sea event to one that may affect people from Florida to Maine. The Canadian was one of the first to show it. Then the American based GFS and finally, the very reliable ECMWF or Euro. People began talking about it within the weather blogs as if sniffing out something that movies are made out. It was incredible to read what people were saying could happen if this came to pass. Surely it was a one time fluke in the models and things would return to normal a mere 12 hours later. Not so much.

The overnight run of the Canadian global model shows pretty much the same scenario as yesterday. It takes what would be Sandy and turns it in to this enormous ocean storm that would cause coastal flooding, high winds and heavy rains for a large portion of the U.S. East Coast.

Day 8 of the ECMWF which shows a powerful coastal storm impacting the Mid-Atlantic region

Day 8 of the ECMWF which shows a powerful coastal storm impacting the Mid-Atlantic region

Looking at the latest Euro run, it too continues its forecast of developing a very large and powerful storm as the tropical energy from what would be Sandy gets pulled in to a deep trough digging in. This entrainment and phasing is rare but when it happens, it can lead to very powerful hybrid storms that have both tropical and non-tropical characteristics. The Perfect Storm in 1991 was just such an example. The overnight run of the Euro is jaw-dropping, there is no other way to describe it.

On the other hand, the GFS has all but abandoned this idea and simply sheds off the energy from the tropics in to a separate ocean storm way out in the open Atlantic. The result is….nothing. No big storm once 99L/Sandy leaves the Caribbean. It is remarkable to see such vast differences in the models and goes to show how complex the situation is. We are talking about an event that is forecast by some of the models to take place more than a week away. I debated whether or not I should even discuss it since it’s so far out in time. But I figured that rational people who read my blog would understand and appreciate the heads up if this in fact comes to pass….the bad storm that is. Maybe it’s all just a fantasy by the models that show it and the only concern, albeit a very legitimate one, will be for the Caribbean and the Bahamas. If not, and this storm happens the way the Euro shows it and the GFS showed it yesterday for a time, then we will be talking about this well past the hurricane season.

For now, we wait and go with the short term which is that we see what is a developing tropical depression in the western Caribbean. The first impacts will be felt in Jamaica and eastern Cuba. From there, we will just have to see how things turn out. The next several days could be very interesting if not very important in shaping how the hurricane season comes to an end.

I’ll post another short update this evening to go over the latest on the situation in the Caribbean. I’ll also have the video blog posted to our iPhone app by early this afternoon and it will incorporate the overnight model runs as well as the early morning or 12Z model runs to compare. If you don’t have our app, you’re missing out on a great tool in the daily video blog. It brings this discussion to life with numerous graphics, satellite shots and an in-depth explanation of what’s going on in the tropics now and what’s forecast several days out.

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Major changes with models for 99L that could lead to significant impacts for East Coast

GFS depiction of tropical cyclone over eastern Cuba in 96 hours

GFS depiction of tropical cyclone over eastern Cuba in 96 hours

There is a lot to discuss regarding the future track and intensity of 99L as it could affect literally millions of people from the Caribbean to the U.S. East Coast.

First, the current situation. Right now, 99L is rather disorganized over the Caribbean Sea but is forecast by all of the global computer models to gradually organize and become a tropical cyclone within the next two or three days. It looks like Jamaica, eastern Cuba and Hispaniola could be in line for quite a bit of rain and wind by the middle of next week.

By Thursday, the GFS places a strengthening tropical cyclone over eastern Cuba with heavy rains spreading across the southeast Bahamas. Water temps in this region are still very warm and it is possible that we could be looking at a rather strong tropical storm by this point as most of the guidance suggests steady strengthening.

By late next week, most of the reliable model output suggests a track in to the northern Bahamas, not too far off the Florida east coast. This is important because there is likely to be an indirect impact to Florida because of the presence of this system and a high pressure area to its north. It appears that a fairly strong surface high will move off the Northeast coast late next week and it could do two things. First, the high pressure north, coupled with the deepening low pressure off of Florida, will create quite a strong pressure gradient. This means the winds will be quite stiff out of the northeast for a good deal of the east side of Florida. So at the very least, rough surf and rip currents are a good bet towards the end of the week for Florida.

Sea surface temps along East Coast running at least 2 degrees above normal

Sea surface temps along East Coast running at least 2 degrees above normal

The other issue is that this high could act to block what would presumably be “Sandy” from turning out to sea. In fact, both the GFS and the ECMWF show this scenario and take what looks strong enough to be a hurricane right in to the East Coast of the U.S. somewhere north of Cape Hatteras. Sea surface temperatures in this region are running a couple of degrees above normal for this time of year and have not been disturbed by a previous hurricane earlier in the season. We are going to have to watch the evolution of this pattern very carefully over the next few days. What looked like a sure bet to send “Sandy” out to sea is no longer such a home run, so to speak. This could mean that people from the Caribbean Sea to Florida and eventually the East Coast have to deal with some degree of a tropical system over the next week or so. Interests in Jamaica, Cuba, Hispaniola and the Bahamas need to watch this system closely. We’ll see how things progress and can focus more on potential U.S. impacts as we get in to next week. For now, it looks like a slow process for 99L to develop but once it does, there is potential for it to impact a lot of people over a wide geographic swath.

I’ll post more here about 99L tomorrow morning. I also will be posting regular video blogs to our iPhone app which is a great way to visually understand what I discuss here in the blog posts. If you don’t have the app, there is no better time to get it. We’ve recently added our own tracking maps and of course have the exclusive in-field weather data, live web cams and video blogs should a landfall take place.

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Tropical depression and eventually a hurricane could form from 99L in the Caribbean

A look at invest 99L in the Caribbean Sea

A look at invest 99L in the Caribbean Sea

The MJO and climatology are working together to bring about what I have been alluding to for the past couple of weeks. It seemed almost inevitable that at least one more named storm would develop in the Caribbean Sea and the way things look now, it’s only a matter of time.

We have 99L moving through the central Caribbean this afternoon. The NHC gives it a high chance of becoming a tropical depression within the next couple of days. Water temps and ocean heat content in the region are high while upper level winds continue to become more favorable. Most of the reliable intensity models indicate that 99L will become a tropical storm and eventually a hurricane. Before any of that happens, it will be a persistent rain maker for the region. This will have its own set of problems as areas like Jamaica, Hispaniola, eastern Cuba and eventually the southeast Bahamas could see a lot of rain over the next several days.

The problem is that steering currents are relatively week. This is not a system that will develop and scoot out rapidly to the northeast. It’s going to take some time, perhaps nearly a week, for it to clear the Caribbean entirely. This will lead to excessive rain fall totals for some of the islands in the area and this needs to be taken very seriously. Tropical cyclones and even those in the genesis stage can dump 10 to 20 inches of rain in short order. The longevity of this event for the Caribbean is going to be serious.

For now, the track of the low pressure area will be west and south of west for a couple of days. This will place the low in the western Caribbean first as it awaits a pattern change that should spring it loose and eject it out to the northeast. Exactly when this happens remains to be seen but none of the guidance shows it impacting Florida. However, the impacts to Jamaica, Cuba and Hispaniola could be significant, especially with the aforementioned rain event.

In the longer term, the models suggest that what is almost certain to become “Sandy” will strengthen in to a hurricane. When it does so is tough to say, it could be after it tracks out of the Caribbean which would be good news. My only concern is all of the warm water available and the inability of the models to do well with intensity forecasting historically. Interests in the entire area need to monitor 99L’s future progress very closely.

I’ll have another post here tomorrow. If you have our iPhone app, be sure to check the video section for today’s video blog as it has been posted recently.

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