Tropical wave likely to develop but remain over open Atlantic

Computer model track forecasts for 98L over the far eastern Atlantic.

Computer model track forecasts for 98L over the far eastern Atlantic.

A strong tropical wave situated far out in the eastern Atlantic is slowly organizing and should become a tropical depression later in the week. The wave of low pressure, also known as invest 98L, is currently positioned at a fairly low latitude – around 10 degrees north. This is keeping it at a safe distance from the otherwise detrimental effects of the Saharan Air Layer or SAL. With ocean temps warm enough and upper level winds favorable, 98L is likely to become the next tropical storm in the Atlantic. If so, the name will be Fiona. No, there is no Shrek on the list 😉

It is interesting to see development taking place right now because the overall lack of upward motion (favorable MJO) tends to keep things quiet. Most of the Atlantic is dominated by generally sinking air and cyclone flow aloft – unfavorable for tropical storm formation. However, 98L has managed to find a sort of safe haven and has a real shot to become a named storm.

No matter how strong this system becomes, it will only add to the overall seasonal ACE count. ACE or accumulated cyclone energy is the score we track to determine the true intensity of a season. The higher the wind speed, the higher the ACE output. A typical season has an ACE score of anywhere from 95-100 points or so. Right now we sitting at roughly 10 ACE units.

Steering currents are such that almost all of the model guidance suggests a track farther out in to the open central Atlantic in the coming days. This is somewhat unusual given the low latitude of the system right now but with the lack of deep layered high pressure to the north and west, it’s likely to turn on out to sea without ever affecting land.

Elsewhere, the tropics are of no concern right now and I do not see any additional development potential over the next few days. In the longer term, the usual “now you see it, now you don’t” tropical systems show up in the various models but nothing stands out just yet as being consistent. The later we go in to August, the greater the odds of development – perhaps 98L is the first solid sign of change. We shall see.

I’ll have more here tomorrow.

M. Sudduth 8:45 AM ET Aug 16

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The “real” hurricane season is about to begin…maybe

We should all know by now that the official hurricane season is June 1 – November 30. That’s what the powers that be designated as the most likely time to see tropical storms and hurricanes form in the Atlantic Basin. Within that 6-month window (hard to believe hurricane season takes up half the year) there is a pronounced uptick in activity that many refer to as “the real hurricane season”. It usually begins around mid-August and lasts until roughly the end of October. Some years, like 2005, are exceptional for the amount of activity spread out over the entire season. Other years, like 2013, it seemingly never comes. On average, however, today is generally thought of as the beginning of the real hurricane season and if it’s going to be active, this is when we begin to find out.

Before jumping in to what to look for in the coming days and weeks, let’s examine a few of the larger pieces of the puzzle that could help to shape the peak months of the season.

Sea surface temperature anomalies showing the obvious difference between 2015 and 2016 with a much colder tropical Pacific this year along with a warmer tropical Atlantic as well

Sea surface temperature anomalies showing the obvious difference between 2015 and 2016 with a much colder tropical Pacific this year along with a warmer tropical Atlantic as well

ENSO or El Niño Southern Oscillaion

This one is quite simple. El Niño tends to kill Atlantic hurricanes, especially in the deep tropics. It did a great job of that last year (Joaquin formed outside of the deep tropics from a non-tropical area of low pressure). The prediction was for there to be no El Niño this season and that has come to pass. In fact, the tropical Pacific is generally a lot colder now than it was last August. This is regarded as a plus for Atlantic hurricane development. While we are not seeing a true La Nina just yet, at least according to official standards, the Pacific has cooled significantly and you can see this clear as day in the two images I have posted here.

Atlantic Sea Surface Temperatures

While the Pacific has cooled, most of the tropical Atlantic, Caribbean and Gulf of Mexico has warmed to above normal levels. In fact, areas in the western Atlantic are as warm as I have ever seen them with anomalies (departure from normal) running several degrees above the long term average. This provides more fuel for hurricanes but not just at the surface. The upper ocean heat content is also very rich right now in areas close to land. The amount of available energy is somewhat astounding and if a hurricane comes along under the right atmospheric set-up, we could see intense development and not the weak, lop-sided storms we’ve observed in recent years.

Note that warm water alone does not yield hurricanes. It is certainly a must-have ingredient but it is not the catalyst by itself. Despite the record warm water temps, other factors need to be favorable or nothing of note happens. I’ll go over some of that as I continue on…

Wind Shear

Shear analysis showing favorable (green) in the east Atlantic but quite unfavorable (red) in the Caribbean and Gulf of Mexico

Shear analysis showing favorable (green) in the east Atlantic but quite unfavorable (red) in the Caribbean and Gulf of Mexico

Shear analysis showing favorable (green) in the east Atlantic but quite unfavorable (red) in the Caribbean and Gulf of Mexico (click to enlarge)

Wind shear or the change of wind direction and/or speed with height in the atmosphere is a very important piece of the hurricane puzzle. Too much strong wind blowing against a developing or already developed hurricane usually leads to its demise. In 2005, for example, shear values over the Gulf of Mexico were close to zero for much of the season, especially when Katrina and Rita formed. These were ideal conditions, hard to duplicate (thank goodness) but it does happen.

Right now, the signal is mixed. Shear values over the eastern Atlantic are favorable for development. However, for the time being, the farther west one looks, the more the shear increases, literally screaming out of the west across the Gulf and Caribbean. This is a deviation from what we’ve seen for a good chunk of the season as shear has generally been favorable until recently. The pattern right now is such that anything tracking west will run in to this shear zone and be torn apart – unless the pattern changes, which it can but so far, I don’t see it doing so right away. This is something we will have to monitor almost daily since things can evolve rather quickly and change the outcome in a hurry.

Overall, compared to 2015 especially, shear is down and for the most part, this is a favorable sign for Atlantic hurricanes.

Instability

Tropical Atlantic vertical instability (blue line) is quite below where it should be (black line)

Tropical Atlantic vertical instability (blue line) is quite below where it should be (black line)

The lack of an unstable atmosphere is something that has been in place for several years in a row. Simply put, warm, dry air has been capping thunderstorm development in the MDR or Main Development Region of the deep tropics. Moist air, filled with energy, needs to lift in to colder air, if warm air is present over warm air, then there is little in the way of convection and thus we don’t have showers and thunderstorms developing which are THE mechanism for developing hurricanes. No convection = no hurricanes. For some reason, dry air, even when the famed SAL or Saharan Air Layer is not present, has been dominant for the past several hurricane seasons. This mid-level layer of stability has resulted in very little action in the MDR – the area between Africa and the Lesser Antilles. If memory serves, I think that Ike in 2008 was the last of the long-track hurricanes. Others such as Irene in 2011 struggled despite forming in the MDR. It is something new that we’ve been seeing and needs further study since it seems to be rather persistent.

So far this season, instability has been generally lacking again across the tropics and unless this changes, tropical waves will struggle until reaching more unstable air farther west.

This brings up an interesting scenario. If the tropical waves struggle out in the open Atlantic, everyone seems happy and safe since hurricanes have a hard time in dry air. Ok, well, what happens when those same tropical waves struggle all the way to say, 70 degrees W longitude? At that point, they blossom under a much more favorable environment and become hurricanes much closer to land areas. Earl was a classic example of this. It “waited” until right before landfall and sprung to life. Ask the people in Belize and southern Mexico about the “struggles” of the parent tropical wave that became Earl. Yes, it could have developed much sooner and become an intense hurricane but my point is, the later they wait to develop, the better the odds they hit land. So while the dry air may be impeding development out in the deep tropics, don’t be fooled by people who say this is a uniformly good thing. Sometimes the opposite is true.

Sea Level Pressure

Air has weight. We call this air pressure. High pressure squashes cloud formation generally (especially convection or thunderstorms) and low pressure tends to foster storminess. In the tropics, lower surface pressures helps to make the air slow down and converge, allowing it to pile up and promote thunderstorm development. Higher surface pressures typically doesn’t allow this set up and is thus a negative factor for development. So far this season, surface pressure in the deep tropics has been higher than normal more so than lower than normal. It’s not outright terrible for development but it hasn’t helped much for sure. This, like shear values, needs to be monitored on a weekly basis as it can change and lead to a burst of activity when pressures lower.

Going forward – the next 60 days

If you add it all up, the ingredients are there for a busy hurricane season but not so much so that it will set records. There are still other aspects that are more difficult to go in to or that I myself don’t quite understand well enough yet. However, the larger, more obvious pieces to the puzzle indicate enough positives for an active season to warrant concern – more so than the past few seasons for sure.

For me, the single ingredient that worries me the most is the very warm water in the western Atlantic. While it is obvious that if no hurricanes track in to this warm water it won’t matter, what if they do? Remember what I said about the weak, struggling tropical waves? If even a few survive to form later and farther west, it could mean they make it in to the area of very warm water. It’s something we will just have to wait and see about.

So that brings me to the current set up.

Current area of interest, 98L, southwest of the Cape Verde Islands

Current area of interest, 98L, southwest of the Cape Verde Islands

Right now, we do have a strong tropical wave in the deep tropics. It emerged from the African coast a couple of days ago and is moving generally westward. The NHC gives it fairly low odds of developing further but some of the computer models are more favorable for continued development.

Warm water is plentiful but the dry air is not far away from the system. If it manages to survive the next few days, shear awaits unless it tracks north of the Caribbean. It’s going to be one of those “wait and see” situations. However, I find it ironic and perfectly timed since today is typically the beginning of when we look out across the tropical Atlantic for signs of activity. Right on cue, we have something to watch. Whether or not it becomes noteworthy remains to be seen.

The next 60 days will probably define the hurricane season. Will it end up being a non-event for U.S. interests once again? Or, will the 10+ year streak of no category three or higher hurricanes making landfall come to an end? The stage is set, maybe not for an award-winning performance so to speak, but certainly more so than in recent years. Right now, it is still quiet. There is time to prepare if you feel so inspired. The historic flooding in Louisiana should serve as a reminder that we’re not talking about only wind or surge here. It’s hurricane season and the peak months are just beginning. I’d say “be ready” because it sure seems like all that warm water won’t go untouched.

I’ll have more on the current goings on in the tropics with my video discussion to be posted later this afternoon.

M. Sudduth 9:20 AM ET Aug 15

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Danny no longer a tropical cyclone while 98L gathers strength

The NHC issued the last advisory on Danny this morning as the one-time category three hurricane fully succumbed to the hostile conditions of the Caribbean Sea. The remnants of the storm are moving through the region now with a few squalls and not much else. Unfortunately, the much needed rain will be hard to come by and short lived.

We’ll continue to track the left overs of Danny but odds are nothing more will come of the system as it heads west across the Caribbean this week.

Satellite photo showing 98L over the tropical Atlantic. It is likely going to become a tropical depression later today

Satellite photo showing 98L over the tropical Atlantic. It is likely going to become a tropical depression later today

The next area of interest is invest 98L out over the tropical Atlantic. It is almost certainly going to be classified as a tropical depression later today or tonight.

Water temps are plenty warm, shear is light and dry air is not much of an issue right now and as such most intensity guidance suggests that 98L will go on to become the second hurricane of the season.

I find this to be extremely interesting because of where this would happen. Most of the expert predictions for the season made their case for the MDR or Main Development Region to be very hostile tropical storms and hurricanes this year. Until Danny, that was very much the case. However, in recent weeks, water temperatures across the MDR have warmed to at least normal levels if not slightly above. I believe this has allowed for what we saw with Danny and will soon see with 98L as it ramps up and becomes our next named storm: Erika.

Latest forecast plots from the various computer models for 98L

Latest forecast plots from the various computer models for 98L

The forecast models indicate a general west to west-northwest track over the next five days putting it in a position fairly close to the northeast Caribbean Sea. This system is moving a lot faster than Danny was so it will cover more distance over the next several days. Interests in the northeast Caribbean should pay close attention to the progress of 98L over the next few days. We’ll know a lot more once the NHC upgrades it to TD #5 which I think will happen later today.

Elsewhere, the Atlantic Basin has no other issues to be concerned with.

Meanwhile, the east Pacific remains quite busy but any areas that develop will be far from land and remain that way for the time being.

I’ll have a video blog posted later this afternoon along with a separate blog post looking back at Katrina 10 years ago and how we handled this very important event.

M. Sudduth 12:30 PM ET Aug 24

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Danny will bring some rain (not nearly enough), a little wind but not much else

Recent satellite photo of TS Danny. You can clearly see the low level center becoming exposed on the southwest side of the storm

Recent satellite photo of TS Danny. You can clearly see the low level center becoming exposed on the southwest side of the storm

Danny is getting closer to the Lesser Antilles and will pass through over the next day with little more than some passing squalls and increased surf. The one-time category three hurricane is now fully engaged with stronger upper level winds than it can handle, coupled with drier mid-level air. This has led to quite a weakening trend which was exactly what was forecast to happen as of late.

For interests in the Caribbean, Danny will bring much needed rain but it won’t even begin to put a dent in the long-term drought that has affected the region. I suppose every drop counts and it’s better than nothing and certainly better than say, a category three hurricane bearing down.

I think it is safe to say that Danny will be all but gone by mid-week, chewed up by strong upper level winds and running over land that will further gut the storm down to little more than a low level swirl. That’s the circle of life in the tropics sometimes.

Meanwhile, we will need to be watching invest area 98L quite closely in the coming days as it looks to be well on its way to becoming a tropical depression. The models are not much help. One run can show a significant hurricane heading west while another run has barely anything at all. The only sure thing is that it is far from land and we have plenty of time to monitor its progress as the new week begins.

In other news, it was 10 years ago today that I began my planning for what would become hurricane Katrina. There is a lot that will be said by many people who had to deal with not only that historic hurricane but also the unprecedented 2005 season as a whole. I will have a separate blog post on this topic later in the coming week.

M. Sudduth 4:50 PM ET August 23

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Several areas to talk about

NHC five day outlook indicates several areas to monitor

NHC five day outlook indicates several areas to monitor

The tropics are quite busy with one hurricane and three additional areas to watch in the coming days. Let’s begin with Cristobal…

As of this morning, hurricane Cristobal had winds of 80 mph. Not much change in strength is expected although it could become a little stronger before undergoing transition in to a powerful extratropical storm over the North Atlantic. In fact, interests in the United Kingdom should keep watch over the post-tropical version of Cristobal as it tracks across the Atlantic over the next several days.

In the Gulf of Mexico, the NHC has increased slightly the chance of development for what is now invest 98L. Deep convection developed over night around the northern part of the broad low pressure area. However, upper level winds are quite brisk out of the west and west-southwest and this is helping to push the convection away and not let it organize much around the low. In any case, there is a small window of opportunity for this system to develop further before it moves inland over south Texas later tomorrow.

The biggest impact from 98L will be periods of heavy rain and occasional gusty winds. Local effects such as an increase in waves with any of the heavier thunderstorms will impact boating interests. Hopefully some much needed rainfall will come out of this for parts of south Texas – just as long as it’s not too much of a good thing all at once.

A Hurricane Hunter crew is scheduled to investigate 98L later today if conditions warrant. We’ll know more then about the structure and wind field but again, this is only if the NHC feels the flight is needed.

Farther east in the tropical Atlantic, what was once invest area 97L has now become a non-issue, for now anyway. It appears that the tropical wave energy is likely to to track in to and across the Caribbean Sea over the next several days. Computer models are indicating the chance of development either in the western Caribbean or perhaps the southern Gulf of Mexico early next week. This will be something to keep an eye on but for now, the tropical wave is not organizing but it will bring a brief period of squally weather to parts of the Lesser Antilles as it moves through over the next day or two.

The last area to discuss is a tropical wave forecast to move off the coast of Africa in a day or so. Most computer model guidance suggests that this will develop rather quickly and should become a tropical storm over the far eastern Atlantic. I do not know how many people actually live in the Cape Verde Islands but it appears that they will be impacted by this strong low pressure area and could experience tropical storm conditions as it passes by. Beyond that, it is obviously too soon to even speculate on where it may end up. However, most of the time when something develops that far east, it has no trouble finding a weakness in the high pressure area over the Atlantic and turning north and eventually out in to the open Atlantic.

So there is quite a bit going on as we end August. Things can change quickly this time of year so keep up to date with the latest. I’ll post updates on Twitter as they come in and will have another full blog post either late tonight or certainly by early tomorrow morning.

M. Sudduth 10:00 AM ET Aug 27

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