Recon will investigate 94L in the Bay of Campeche, let us know if tropical depression or storm has formed

Graphical forecast map showing the low pressure and and associated high seas info for portions of the Bay of Campeche

Graphical forecast map showing the low pressure and and associated high seas info for portions of the Bay of Campeche

Despite the odds, it looks like the tropical wave and associated low pressure area that moved out of the Caribbean Sea and over the Yucatan may in fact develop later today, if not already.

You may recall just a few days ago, the NHC indicated only a 10% chance of development due to land interaction primarily. Yet, 10% is not 0% and the low pressure area, weak as it may be, has managed to remain over the warm water of the southern Bay of Campeche. As such, convection has blossomed overnight in to this morning and we could be dealing with another tropical system before the day is out.

The Hurricane Hunters are due to fly in and investigate later this afternoon, assuming the system doesn’t fall apart before then. Their information will help to determine just what is going on in the area and whether or not we have the next depression or possibly even a tropical storm. If it’s a storm, the name will be Danielle.

The primary threat will be very heavy rain for portions of eastern Mexico as the low approaches. There is a chance it will go on to become a tropical storm but the wind will not have a chance to ramp up much before landfall later tomorrow.

The rest of the tropics remain quiet for now although a vigorous tropical wave is moving in to the eastern Caribbean with quite a flare up of thunderstorm activity. This will bring squally weather to portions of the Windward and Leeward Islands today and tomorrow. Beyond that, we will have to monitor where the energy tracks as there are some indications in the long range models that the northwest Caribbean could get active within the next 10 days.

I’ll have more here later today, including a video discussion on the latest goings on with 94L and the rest of the tropics.

M. Sudduth 11:30 AM ET June 19

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Dry, sinking air keep tropics in check

Satellite analysis showing the Saharan Air Layer over the tropical Atlantic

Satellite analysis showing the Saharan Air Layer over the tropical Atlantic

The Atlantic Basin is fairly quiet as we start the new week. There is one area, invest 94L, that bears watching but I think that the odds of development anytime soon are slim. The reason? Dry, sinking air.

Tropical cyclones are driven by convection (thunderstorms). Without this convection, heat cannot be released and the process fails. One sure fire way to keep a lid on tropical convection, almost literally, is to have too much dry or sinking air around.

The dry air part is probably easy to understand. Moist air is lighter than dry air, believe it or not, and it lifts easier. This instability is essential in the development of convection, especially over the tropics. A stable layer of the atmosphere due to drier air keeps the convective process limited at best. In most cases, the dry air we see originates from Africa in the form of huge outbreaks of dust and warm, stable dry air from the Sahara. Thus, it is termed the Saharan Air Layer. As you can see in the image, the oranges and reds represent a dry and/or dusty air mass. Right now, the SAL is the dominant feature across the tropical Atlantic. Until and unless it abates, it will be extremely difficult to have anything develop in the area between Africa and the Lesser Antilles.

Velocity chart showing areas of upward motion (green) vs areas of sinking air or subsidence (brown)

Velocity chart showing areas of upward motion (green) vs areas of sinking air or subsidence (brown)

The other obstacle for tropical cyclone formation is subsidence or sinking air. Thunderstorms thrive in an upward motion environment where ascending air is favored over sinking air. Again, we’re talking about lift in the atmosphere and lift leads to cloud formation and ultimately, convection. Right now, the Atlantic is generally unfavorable in terms of lift in the atmosphere. The image shows this nicely with browns indicating sinking air and greens indicating rising air. This is an over-simplification of the process but that’s the general idea. As with the SAL issue, until we see a widespread change in the upward motion pattern, I doubt we will have much activity brewing in the deep tropics.

Vertical wind shear over the tropical Atlantic is actually quite favorable right now

Vertical wind shear over the tropical Atlantic is actually quite favorable right now

On the other hand, vertical wind shear, the difference in wind speed with height in the atmosphere, is running just a little bit below the long-term average for this time of year. This is a big plus for development but without an unstable, moist environment, tropical waves are going to have a very difficult time developing.

These three aspects of tropical cyclone formation are just part of the overall picture that includes other elements such as vorticity, sea surface temperatures and heat content, etc. However, as we can clearly see, the dry air is an overwhelming factor and one that apparently trumps the other positive parameters that are in place. So the question then becomes, will the dry air ever let up? It should in due time. We are still a couple of weeks away from the traditional start to the busiest part of the hurricane season. There is a reason for that and it’s not just about warm sea surface temperatures. After the 15th of the month, we typically see a seasonal shift in pressure patterns that helps to limit the amount of dry air outbreaks from Africa. We also note that over time, we usually have a period of favorable upward motion in the atmosphere that could allow for development. None of these things are guaranteed to happen and we could keep on going right in to September with no changes in sight. For now, the tropics are not an issue. Enjoy the quiet while it lasts.

I’ll have more tomorrow.

M. Sudduth 9:17 AM ET Aug 11

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Atlantic beginning to show signs of activity as east Pacific remains quite busy

Tropical weather outlook map showing more activity now in the Atlantic

Tropical weather outlook map showing more activity now in the Atlantic

First, let’s take a look at what’s going on in the east Pacific this weekend. We have hurricane Erick situated just off the coast of Mexico, moving parallel to the region. Heavy rain, gusty winds and rough seas will be in store for the area over the next couple of days as the hurricane moves past. Fortunately, these impacts will not be severe since Erick is not going to make landfall.

In a few days, the track shows Erick getting close to the southern tip of the Baja peninsula where tropical storm conditions are possible. It looks like Erick will have weakened by then and perhaps it can turn westward just enough to keep any significant weather away from the Baja. There are no other areas to monitor this weekend in the east Pacific.

Our next area to cover is the Gulf of Mexico where a weak low pressure area, labeled 94L, is situated southeast of Brownsville, Texas. Upper level winds are not very favorable to support rapid development but a large plume of moisture is gathering in the region and is expected to move north towards Texas and Louisiana. This means a good deal of rain is likely headed that way over the next few days along with an increase in wind and rough seas. The chance of this developing in to a tropical depression is slim right now but wind will not be the biggest impact from this system. It looks like a majority of the rain will be headed more towards Louisiana than Texas and in fact, it could spread farther east in to Mississippi and Alabama. Hopefully it will not make it as far east as the Florida panhandle where more than enough rain has fallen recently. We’ll need to watch this closely over the next couple of days.

Satellite photo showing 95L with the SAL or Saharan Air Layer (indicated by the yellow and orange color) to its north

Satellite photo showing 95L with the SAL or Saharan Air Layer (indicated by the yellow and orange color) to its north

Meanwhile, the deep tropics are beginning to become a bit more active with a strong tropical wave (designated 95L) located well to the east of the Windward Islands. The strongest convection, or shower and thunderstorm activity, is located south of 10 degrees north latitude and this is keeping it away from the crushing effects of the SAL or Saharan Air Layer. This phenomenon is like a giant hurricane killer. It’s a large mass of warm, dry air that spreads out over the tropical Atlantic from Africa, squashing the development of tropical convection. The SAL is often accompanied by dust and even insects that get blown off the African coast and pushed westward over the Atlantic. So far, 95L is showing signs of increased organization as convection remains intact despite the hostile conditions to its north. It is possible that this system could encounter a better environment in a few days if it can survive that long. Interests in the Lesser Antilles should monitor the progress of this low pressure area as it will bring, at the very least, an increase in showers and thunderstorms as it passes through in a few days.

It looks as though July could be fairly active from here on out as we are seeing a favorable MJO pulse of upward motion move in to the region. This period of rising motion in the tropics has been predicted by several of the global computer models for the past couple of weeks and appears to be coming to fruition. In fact, those models suggest that the pulse could remain in the Atlantic Basin for a couple of weeks, possibly supporting development all across the tropics. This would fit in with the forecasts of a very busy season, especially since water temps are running quite a bit above average across much of the tropical Atlantic.

I’ll post another update tonight on all three systems.

M. Sudduth

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Gulf free of tropical troubles for now as we wait for 94L to develop

The Hurricane Hunters investigated 95L off the coast of Mexico in the western Gulf and found basically nothing. Winds were light and the system is losing organization. It appears that any chance of tropical storm formation is quickly dwindling. However, the overall pattern is somewhat unsettled across the region and periods of squally weather will persist across the region for a few more days.

Meanwhile, 94L continues to struggle to put up any deep thunderstorms. The dry air mass is simply too overpowering right now. It is interesting to note that the global models seem to want to ramp this system up after it passes through the Lesser Antilles. While I do not see anything intense coming out of the models just yet, it is possible that 94L will wait and wait and wait until it reaches the Caribbean Sea before developing. And the weaker it remains, the more west it will track. Some of the longer range models forecast the slowly developing system to move up towards Florida via the Greater Antilles first. This means that it could get tangled up in the high terrain of Haiti and Cuba if in fact it takes the track. So any threat to Florida should be considered minimal right now. I just don’t see this developing much over the next day or two. After that, we’ll see. The season has just been so hostile for deep tropical development that for it to all of a sudden change would be a surprise to me. This is why we have to just watch and see what happens. So far, there is nothing to indicate a major problem coming up for the Lesser Antilles or beyond. If that changes, we will still have plenty of time to react accordingly.

I’ll have more here tomorrow morning.

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Tropics look busy but it’s all bark so far

Tropical Weather Outlook Map

Tropical Weather Outlook Map

Taking a look at the latest Tropical Weather Outlook map from the National Hurricane Center, one might think that things were really busy. In one sense, things are busy, with plenty of suspect areas to monitor. On the other hand, with the exception of Gordon, which passed through portions of the Azores as a hurricane, looks can be somewhat deceiving as there is nothing brewing right now that poses any significant threat to land areas.

As I mentioned, Gordon moved through the Azores last night as a hurricane and continues to move eastward where it will weaken over cooler waters, falling short of affecting Portugal.

The system that has the most attention right now within the hurricane blogosphere is 94L. It still lacks any deep convection and is surrounded by an awful lot of dry air which has been the calling card of the deep tropics this season. Neither the GFS or the ECMWF strengthen it much as it passes through the Lesser Antilles and in to the eastern Caribbean. It is also worth noting that the GFDL and HWRF both keep it weak as well. Granted, the statistical SHIP model does make 94L a hurricane but it has not done so well with intensity this season, so I discount that for now.

I think the environment is just too hostile right now, mainly the lack of deep moisture and resulting absence of vertical instability. This is a major factor and even though wind shear is light and we’re in the latter part of August, if the atmosphere is too dry, convection cannot commence and sustain and the entire process will never really get a good start. So until and unless we see a change in the thermodynamics of 94L’s surroundings, it will likely be a weak area of low pressure as it moves westward. I would think that we will begin to see an increase in convection as it moves towards higher ocean heat content in a day or so. Keep in mind too that 94L has a large envelope of energy that it has to bundle and focus around a common area of low pressure. In other words, it has a lot of work to do before becoming much of an issue for anyone. This is good news and for now, it should stay that way.

Elsewhere, 95L is along the eastern Mexican coast and poses little more than a rain threat for portions of Mexico. I doubt it will ever get back out over water enough to amount to anything and none of the reliable models indicate much happening.

Then we have 96L out near Africa. All I can say is read back about 94L and there you go. Anything coming out of the deep tropics so far has struggled and I see no reason why that will change anytime soon. Obviously, it bears watching as it tracks steadily westward but I would not worry about it for at least a week.

I’ll cover all of these areas and more on today’s video blog which will be posted to the HurricaneTrack iPhone app this afternoon. Then, I’ll have another blog post here early this evening, sooner if need be.

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