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.
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