Conditions across the tropical Atlantic are just not very favorable right now. There is simply too much mid-level dry air and pockets of unfavorable upper level winds are widespread. For these reasons, it looks as though, once again, the global models will be correct in forecasting what will likely turn out to be a very weak system in TD7.
Looking at the latest satellite photos, there is very little convection and the envelope of energy with the depression is fairly small. As the NHC noted on their early morning discussion, this makes it vulnerable to effects such as dry air and shear more so than a larger, more potent circulation would. I do not see TD7 being much of a problem for anyone unless of course there is a sudden and unexpected change in the environmental conditions ahead of it. I doubt it.
Meanwhile, something remarkable is going to happen. Think about this…the tropical wave that became hurricane Ernesto has traveled from Africa, all the way across the tropical Atlantic, through the gauntlet of the eastern Caribbean Sea, made landfall twice in Mexico and is now poised to emerge in the east Pacific where it can live another day. That’s right, Ernesto, or at least a bulk of its energy, is about to finish quite an incredible trek across the mountainous terrain of Mexico to cross in to the east Pacific. Now, it will not be named Ernesto if it does in fact regenerate, which is very likely to happen. Instead, it will take on the next name of the east Pacific, Hector. It is quite rare to have a tropical cyclone cross over land from one distinct basin to another. What’s even more interesting about this, there is a possibility that the regenerated system could eventually affect the Baja region. Who would have thought this to be the case a week ago or more when we were tracking something that, at one point, could have ended up making landfall anywhere from Florida to Texas. Now, it’s eventual final landfall could easily be along the Pacific coast of Mexico. Needless to say, folks in that region need to monitor what happens and I’ll post updates about it here along with video blogs in our HurricaneTrack app throughout the upcoming weekend.
The remainder of the Atlantic is somewhat busy with invest area 93L off the coast of Africa. Here again we see that conditions are only marginal for development and the global models show next to nothing over the next week to 10 days anywhere in the Atlantic, Caribbean or Gulf. I am not sure if it’s climatology (i.e. we are simply still just a little too early in the season to see prolific, sustained development) or if something else is going on related to the growing El Nino in the Pacific. I’ll take a closer look in today’s video blog to be posted in our app this afternoon. What ever the reason, it’s great news for coastal dwellers who will not have to deal with any hurricanes this weekend for sure and probably all of next week as well.
The mark of a busy hurricane season usually has one element missing from it: El Nino. That is to say, El Nino conditions in the Tropical Pacific tend to suppress Atlantic hurricane activity. This is due mainly to strong upper level winds that cut across the breeding grounds for hurricanes, thus limiting their numbers and intensities. However, one must remember infamous exceptions to this rule such as Andrew in 1992, an El Nino year. There are others as well which remind us of the adage “it only takes one”.
What about neutral years? What defines a neutral year anyway? Basically, when we see the sea surface temperature (SST) anomaly in the Tropical Pacific between .50 Celsius above or below normal, it is a neutral year (ENSO neutral). The scale is not tipped in one direction or another. Easy enough, right?
Subsurface Temps of the Tropical Pacific
So far this winter, the La Niña that has been in place since last fall continues to hold strong. As the graphic from the Bureau of Meteorology in Australia indicates, subsurface temperatures across the tropical Pacific remain much colder than average over a large area. There is a growing region of subsurface warmth beginning to pool in the western Pacific but it lacks a real mechanism to drive it eastward- a so-called westerly wind burst. We typically don’t see those unless there is a significant pressure change across the Pacific and that shows up in the SOI or Southern Oscillation Index. When it is substantially negative, and persistently so, the trade winds often slow or even reverse, allowing the warm water gathering in the western Pacific to migrate eastward.
The latest update from the BOM also points out that long range climate models suggest a gradual warming of the tropical Pacific as the La Niña fades. This means it is likely that we’ll see a return to more average, or neutral ENSO conditions (ENSO stands for El Niño Southern Oscillation) by the time summer arrives in the Northern Hemisphere. There is also the possibility that the warming will continue and a weak El Niño could set in by next fall. I do not see any evidence yet to suggest that a strong El Niño is coming. However, this time of year, it is difficult to predict what will happen several months down the road but the large subsurface cold pool coupled with a fairly strong SOI signal over the past 30 to 90 days tells me that La Niña is going to be the rule for a few more months at least.
Why does any of this matter? Aside from the effects outside of the hurricane season, which are far too detailed to get in to in this post, we typically see a more active hurricane season when El Niño is not present. This is due to the stronger and more numerous instances of wind shear, the change of wind speed and/or direction with height, over the deep tropics. El Niño events promote this negative impact to tropical cyclones where as La Niña events usually do not.
For now, the La Niña pattern will continue but we’ll watch for signs that it is breaking down and then we’ll see how much warming takes place in the tropical Pacific. The end result could have an impact, one way or another, on the upcoming Atlantic hurricane season. I’ll post more about the ENSO state next month.