Complicated forecast for 99L, easy one for 90L

Convection or thunderstorm activity has increased substantially over night with 99L. You can also see here that invest area 90L is well on its way to becoming a tropical depression.

Convection or thunderstorm activity has increased substantially over night with 99L. You can also see here that invest area 90L is well on its way to becoming a tropical depression.

As I mentioned yesterday in my blog post, it looks as though invest area 99L will continue to struggle and not be much of an issue for land areas anytime soon. However, the recent development of convection or deep thunderstorms suggests that perhaps things are changing, even if only a little bit right now.

The very latest info from the NHC indicates that development chances are going up slightly – now up to 50% in the five day time frame. It appears the warmer sea surface temperatures and a better overall environment are slowly playing in to favor of this system developing.

One aspect that I cannot get over is the large size of the overall envelope of energy with 99L. It is not a small, weak and fragile tropical wave. It’s quite the opposite in fact with a large area of circulation and deep precipitable water profile. What this means is that this feature is not just going away despite the marginal conditions in the atmosphere. As we have seen in the over night hours, convection actually began to increase and persist with 99L and this morning, the satellite shot indicates continued slow organization. If this continues, we may have something to deal with in the coming days as it moves generally WNW towards the Caribbean Sea. Interests in the northern Leeward Islands, Puerto Rico and Hispaniola need to monitor 99L closely. At the very least, it could bring periods of heavy rain and gusty winds as the week progresses.

5 day tropical weather outlook grpahic showing the likely development areas and tracks for 99L (orange) and 90L (red)

5 day tropical weather outlook grpahic showing the likely development areas and tracks for 99L (orange) and 90L (red)

The longer term outlook for 99L is tough to call right now. So much is based on whether or not it goes on to fully develop in to a tropical depression or a storm. Generally speaking, the weaker and shallower in the atmosphere a system is, the farther west it tracks under the low level flow pattern. For now, the NHC is showing a potential track area extending up in to the Bahamas by later this week. There are some indications that the track could be farther south but we will have to wait and see about that. Very warm water temps await this system and if conditions improve aloft, it could be an interesting week ahead with not much time to prepare should this threaten land areas from Florida northward to the Carolinas. While this is not indicated by any particular solid forecast right now, it goes without saying that the closer this gets to the U.S. the shorter the time frame for reacting will be.

As for the short term, I want to emphasize again that this large wave energy should bring heavy rain and squalls to portions of the Caribbean Sea over the next few days. Do not count 99L out just yet. It’s late August, water temps are very warm and we have a large system heading westward. Let’s not get caught off guard.

Meanwhile, what should become the season’s next hurricane, and a strong one at that, is developing in to a tropical depression right now far out in the eastern Atlantic.

The NHC should begin advisories on TD7 later today. The model guidance is in excellent agreement that it will strengthen quickly in to TS Gaston and eventually become a hurricane. I see nothing to suggest that this will ever affect land but it will add to the seasonal ACE score, something that is tracked to help size up the quality of the storms/hurricanes that form.

In the eastern Pacific, a pair of disturbances well off the coast of Mexico both have a shot to develop as they move west to west-northwest out in to the open Pacific. No other areas of concern are seen over the next several days for Pacific Mexico or the Baja peninsula.

I’ll have more here in my daily video discussion. Also, you can follow all of my updates using our app, Hurricane Impact, available in the App Store. This blog, social media posts, video updates and field mission reports/data all goes in to the app. We’ve had it since 2012 as a great way to keep up with info while on the go. Search “Hurricane Impact” on the App Store.

M. Sudduth 8:15 AM ET Aug 22


False alarm looking likely for 99L but tropical wave off Africa, 90L, is on its way to developing

99L and its proximity to the Saharan Air Layer compared to 90L to the east.

99L and its proximity to the Saharan Air Layer compared to 90L to the east.

It has been an interesting few days to say the least. A lot of attention was placed on invest area 99L in the eastern Atlantic. By all accounts, it looked like it had a good chance of becoming a tropical storm and possibly even a hurricane. Long range models suggested a possible landfall somewhere in the United States, others did not. It was back and forth but the bottom line appeared to be that “Gaston” was destined to form from this large, sprawling tropical wave.

I guess that’s what probabilities are all about. Unless it’s 100%, it’s not a guarantee – ever. The highest probability that I saw from the NHC regarding 99L developing in to a tropical depression or stronger was only 60%. That’s notable but not very high compared to say, 90%. In this case, for the next few days anyway, it looks like the 40% portion will win out and 99L will not develop much further.

I think the reason can be attributed to the large size of the tropical wave. It needs a lot of energy to keep going and to thrive. Right now, despite warm water temps, the atmosphere just isn’t providing. The ever-present Saharan Air Layer might be playing a role as well. But how can that be? Invest area 90L, which is just off the coast of Africa, is almost a shoe-in to become a tropical storm early next week. Isn’t its proximity to Africa enough to keep it from developing? One would think, after all, looking at the SAL analysis map I have posted here, you can see there is much more dry air and dust to the north of 90L than is surrounding 99L to the west. I just don’t know sometimes but the end result is that while we certainly won’t ignore 99L, it doesn’t look like much of an issue for now. It should bring some showers and thunderstorms, along with gusty winds at times, to portions of the Lesser Antilles early next week but beyond that, no development seems like the most likely outcome right now. We will see what happens when the energy makes its way in to the southwest Atlantic later next week. Until then, 99L will not become Gaston.

That leads me to discussing 90L which, as I mentioned, is situated just off the African coast, not far off from Senegal. The NHC and indeed most of the computer guidance, is telling us that 90L will go on to develop over the coming days. And true to what I posted yesterday about how soon systems develop and how that relates to their eventual impact to land, it looks as though the track will be out over the open Atlantic. Indeed, the sooner they develop, the less likely they are to ever reach the United States or other land masses in the western Atlantic. We can’t say for sure that this will have zero impact but odds are it will be a big ACE producer (that is the measure of energy output from tropical storms and hurricanes during a single season) and little more.

The negative phase of the MJO, outlined in red, dominates the Atlantic Basin right now. Unless this changes, hurricane development will be tough to come by.

The negative phase of the MJO, outlined in red, dominates the Atlantic Basin right now. Unless this changes, hurricane development will be tough to come by.

One other note. The lack of uplift or what we call upward motion is probably also partly aiding in the anemic look to the Atlantic Basin as of late. The favorable phase of the Madden-Julian Oscillation, which is a fancy way of saying that widespread favorable conditions exist, is no where near the Atlantic right now. In fact, it seems semi-stuck over in the west Pacific where a couple of storms spin off the coast of Japan. Tropical storms and hurricane can form without the MJO being favorable but its enhancing effects really seem to help when it is present. So far, none of the long range models show it reaching the Atlantic Basin anytime soon. This could make it tough to see much in the way of hurricane activity except in certain spots where favorable conditions exist – but those will be few and far between.

M. Sudduth 9:40 AM ET Aug 21


Slower development means more of a chance for impact later

Recent satellite shot showing invest 99L and the limited convection associateed with it currently. This will allow the tropical wave to move farther to west since it will not be influenced by any weakness in the subtropical ridge, allowing it to turn out to sea.

Recent satellite shot showing invest 99L and the limited convection associated with it currently. This will allow the tropical wave to move farther to the west since it will not be influenced by any weakness in the subtropical ridge.

It looks as though the Main Development Region or MDR is still struggling in terms of the ability for tropical cyclones to take shape. The area between Africa and the Lesser Antilles is usually fertile grounds for development this time of year but it seems that for the past several years, dry air has been the rule. The result is we see vigorous tropical waves move off of Africa, various computer models over-develop them and then nothing much happens. It’s like the models (some, not all) are simply not “aware” of the dry, more stable environment that has become a semi-permanent feature of the deep tropics.

However, this is not necessarily a good thing in the end. I’ll explain why…

It is actually quite simple. The longer a tropical wave takes to develop, the farther west it will track. The low level easterly flow which is dominant in the tropics this time of year pushes the tropical waves generally westward. If they don’t develop at all, they often end up in the southeast Pacific and try to develop there. It’s when they don’t develop until they get past about 60 degrees west longitude that is problematic for land areas.

Think about it, a larger storm or hurricane in the atmosphere will more than likely feel the effects of the mid-ocean trough that is usually waiting to allow systems to turn north and eventually northeast and away from land. Sometimes, like 2008, the subtropical ridge of high pressure is so well established that even hurricanes such as Ike can make it from Africa to Texas. Obviously this is rare – otherwise no one would want to live on the coast of Texas or anywhere else for that matter – the hurricanes would be too numerous year after year.

On the other hand, a shallow tropical wave, void of deep convection or thunderstorms, can sail along with the easterly trades and gain longitude day after day. Eventually, conditions improve and a tropical depression forms. By now, the system is nearing the eastern Caribbean and it will most certainly bring squalls, heavy rain and brief high seas to the region.

Hurricane Earl is an example of this scenario. The parent tropical wave struggled as it raced westward across the tropical Atlantic and in to the Caribbean Sea. It was not until it reached the western Caribbean that it developed and became a hurricane. It made landfall in Belize instead of developing early, way out in the MDR, and turning out to sea.

So what does this have to do with anything currently going on in the tropics? Perhaps it has huge relevance. This is because as we watch the recent trends with 99L, we have seen some of the models delaying development until it is only a day or so away from the Caribbean Sea. This ends up sending a slowly strengthening tropical system in to the region, bringing heavy rain and other hazards to the region. Beyond that time frame, anything seems possible, including threats to the United States.

Even though we expect development out in the open Atlantic, just because it doesn’t happen there doesn’t mean it won’t happen at all. The farther west these tropical waves track, the warmer the sea surface temps get. It’s only a matter of time, I believe, until we see something strengthen quickly and close to home. I just don’t know whose home yet.

Bottom line – over the coming days we will see a lot of variations of the “end result” for 99L and perhaps even Fiona and soon-to-be 90L coming off Africa now. The down side to delayed development is that more people take notice when a hurricane is coming from seven to ten days out. It makes sense, the hurricane is there longer and it gets more attention and more people know about it. If it blossoms later, like Katrina did in 2005 (5 days from tropical storm to landfall) then it gives us all less time to react.

The next few weeks will likely be very busy with one named storm after another forming in the Atlantic Basin. Some will be possible impact threats, others will not. It will be important to keep up with what’s going on at least daily if not more. The advantage of seeing a hurricane coming from a week out might not be there and as such, being ready in case one pops up with only 72 hours to prepare will be more important than ever.

I will go over this topic in greater detail on today’s video discussion which I will post here. You can also follow along in our app, Hurricane Impact, available on the App Store. All of our blog posts and video discussions are posted to the app for easy access on the go. Plus, the app has incredible landfall features which I will talk about more when and if the time comes.

M. Sudduth 12:20 PM ET Aug 20


Plenty to monitor over the next several days but beware of “scary maps”

NHC map showing potential for development in the eastern Atlantic, spreading towards the Caribbean, as the days progress

NHC map showing potential for development in the eastern Atlantic, spreading towards the Caribbean, as the days progress

We have several areas to monitor in the Atlantic Basin and one area in the east Pacific. Fortunately, none pose a direct threat to land for the time being but one area, in particular, warrants close scrutiny in the days ahead.

First up, tropical storm Kay in the eastern Pacific. Not much to say here except that it will weaken as it tracks well off of the Baja peninsula and eventually turns westward over cooler water. I do not see any appreciable impacts from this storm for the southern Baja except some added moisture. Once Kay dissipates early next week, that should do it for the time being in the eastern Pacific with no additional areas of development seen.

Next we have tropical storm Fiona in the open central Atlantic. Top winds are only 45 mph with limited deep convection noted on satellite imagery. Overall the dry mid-level air, partly due to the incessant Saharan Air Layer (SAL), is keeping Fiona from strengthening and this will likely remain the case over the next five days. In fact, the NHC is forecasting the storm to weaken as it moves farther to the north and west, well to the southeast of Bermuda. While I do not anticipate any issues arising from this storm, we never just ignore them until they dissipate or are headed away from land areas.

Of greater concern, especially for the eastern Caribbean islands, is invest area 99L deep in the eastern tropical Atlantic. The NHC gives it a 50% chance of becoming a tropical depression or stronger within the next five days.

The overall envelope of energy with the tropical wave is impressive. The large sprawling size makes me believe that development will be gradual at best. The SAL is far enough to the north to allow for slow but steady organization and it should go on to become the next named storm. If so, it will be “Gaston”.

Computer models are very aggressive with strengthening, perhaps a little too much so. Most of the intensity guidance suggests 99L will become a hurricane but I think its large size and overall state of the deep tropics will limit intensification until later in the period.

Interests in the Lesser Antilles should be watching 99L closely. Almost all of the track models indicate a general westward movement in to the eastern Caribbean early next week. As we have seen time and time again, it does not take a strong tropical storm or a hurricane to cause life-threatening flooding. The people in parts of Louisiana know this all too well and we need only to look back at Erika last season as a reminder for the Caribbean. There’s not much you can do to prepare for heavy rain, just being aware and making sure there is safe haven is at least something as opposed to nothing.

There is no doubt going to be a lot of speculation about where 99L and its eventual transition in to a tropical storm (or hurricane) will end up. In today’s world, computer model forecast maps can be shared with literally millions of people at a moment’s notice. Under the wrong context, this can be harmful. Not everyone has the weather geek know-how to realize that a 5, 7 or 10 day map has extreme limitations. On top of that, graphs showing intensity will only lead to more anxiety when it is probably unwarranted.

My point is, we are likely going to have to deal with a tropical storm and possibly a hurricane some time next week. The first area of concern is for the eastern Caribbean Sea. Beyond that, it’s wait and see just like it has been since I began this site back in 1999. Sure, the Internet has made things a lot faster, more weather models are available and so forth but with great access comes great responsibility (sorry Spiderman, had to borrow your uncle’s catch-phrase). Staring at a map that shows a giant hurricane on it 10 days out is not helpful to most people. If you see such things in social media, say to yourself, “Hmmm, guess I better keep an eye on that one”. Worrying about it this soon is futile – instead, maybe do a little more to prepare in case this, or any future storm/hurricane, comes your way. I’ve said my piece on this issue but just know, it’s coming (the scary weather maps) and you’ve been warned. Be smart and don’t spread the fire by sharing such images.

Last in my list of things to cover, the NHC has highlighted the area just off the African coast, out in to the eastern Atlantic by a few hundred miles for possible development next week. This too is just something to monitor but hey, if you live in the Cape Verde Islands, you could be impacted by squally weather as this tropical wave moves by.

It’s getting towards late August and we were told this hurricane season could be the busiest in four years. So far, it has generally lived up to that expectation. We are headed in to a busy period with a lot to keep up with. Considering the world around us and the inherent, constant distractions, it will be more important than ever to stay aware and be ready….just in case.

I’ll have more in my video discussion later this afternoon followed by another blog post in the morning.

M. Sudduth 2:30 PM ET Aug 19



Tropics about to get quite busy as we head deeper in to August

Satellite image of the eastern Atlantic where TS Fiona is moving out over open water. We are also watching for more tropical wave energy just off the coast of Africa for possible development.

Satellite image of the eastern Atlantic where TS Fiona is moving out over open water. We are also watching for more tropical wave energy just off the coast of Africa for possible development.

There are indications that things are going to be busier and busier over the coming days and weeks as far as the Atlantic Basin goes. You may recall that the east Pacific was producing storm after storm, with a few hurricanes thrown in too, back in July? While I do not see that much activity coming, I do think there is potential for several more development areas over the next two weeks.

First up is tropical storm Fiona. Obviously this system poses no threat to land and probably won’t as it moves generally northwestward over the open Atlantic.

The combination of dry mid-level air being ingested from time to time and some stronger upper level winds will likely keep Fiona from becoming too strong. Water temps gradually increase out ahead of the storm and if the background environment changes enough, the chance for it to become a hurricane is there. However, this would only affecting shipping lanes and add to the ACE score for the season. I just don’t see any reason right now to be concerned with Fiona directly impacting land.

As we watch Fiona, we also need to monitor activity just off the African coast for possible development down the road. Computer models are suggesting the possibility of additional development from one or two more tropical waves over the next five to seven days. This would be the most active the MDR or Main Development Region has been for quite some time. It also fits in perfectly with the time of year we are in as the latter part of August tends to see an increase in potential for development across much of the tropical Atlantic.

Meanwhile, the east Pacific will likely have a new named storm before too long. The NHC is tracking invest area 97-E well off the coast of Mexico. Conditions appear favorable for this to continue to develop and become a tropical storm as it moves northwest but off shore of Mexico and the Baja peninsula.

I will have more in my video discussion which will be posted here and to our app, Hurricane Impact, later this afternoon – followed by more blog coverage here tomorrow morning.

M. Sudduth 10:20 AM ET Aug 18