Here is a simple graphic that explains why we tend to deal with average to above average seasons in La Nina, and more with below average seasons in El Nino where conditions Conditions often become less favorable for tropical cyclone formation in the Atlantic Ocean. We typically see an active Eastern Pacific hurricane season during an El Niño, as this is where most of the increased motion occurs while in the Atlantic we see increased longitudinal fault up and drier air from Africa. The graphic below is for reference in this blog and why it is relevant in the future.
Currently, we have a number of unfavorable factors for tropical cyclone formation in the Atlantic basin. First, there will be some Saharan dust emanating from Africa. This dry, dusty air plays a big role in inhibiting vertical movement from thunderstorms, along with several other major causes that generally hinder tropical cyclones in general. original text of this animation by Model of NASA’s GEOS-5 takes us to mid-July below, and we see no shortage of this dust.
Second, from a sub-seasonal forecasting perspective, (i.e. using the MJO circulation and its position at one point in time along the Equator which has a large impact on jet flows globally), let us dive into a hovmoller where we can see general forecast areas of upward and downward movement through EPS. As a reminder, it’s the same as the supplement when reading this graphic: the vertical axis is time and the bottom axis is longitude, so we’re seeing where the areas diverge (blue/green) and converge convergence (orange/yellow) occurs at a certain time in the near to long term.
Literally, we see that most of the upward-internal motion are “CCKW’s” (convection-coupled kelvin waves) like “small MJOs” as they propagate tropical disturbances along the Equator with can trigger up/down movement – occurring over much of the Pacific Basin. This brings us to the second half of July, where uncertainty in that range plays a larger role and we know changes will arise; however, note here that the divergence seems to stand “still” between the prime meridian – 80*W. Along with that, convergence (submerged air) is shown mainly in the Indian Ocean. If you look at the first image I put together now, does this look familiar to you? Above, we have rising motion in the Pacific and air sinking over the Indian Ocean/Maritime Continent. Compare that graphic with hovmoller again, and we see classic El Nino circulation (or more technical Walker Cell circulation). This is why we will see unfavorable conditions for hurricane development over the Atlantic due to increased vertical wind shear from such elevated motion in the Pacific and Increased wind shear from tropical cyclones will develop in the Eastern Pacific. Along with this, we should see increased stability across the Major Development Area and a continuation of the Sahara Dust with an increase in Atlantic trade winds (cooling and enhancing stability). The GIF below helps to show such areas of rising and falling motion, and to visually “see” why we’re missing any tornadoes forecasted through HIRES ECMWF and EPS.
Note the stark contrast between the paths of the spaghetti storm forecast in the Eastern Pacific and the dreaded Atlantic that will enter early July. RENT ECMWF.
Even the storyline of GEFS spaghettio absolutely nothing happens in the middle of the month. Compare that to the EPS rails, and we see the Atlantic basin is empty.
I should also mention that during El Nino from a climate standpoint we usually don’t see this activity (even if it’s a below average season) until the second half of August through September and October. However, from a long-range forecasting perspective, this is how we can gain greater confidence in whether we will see a “bump” in tropical activity by analyzing the signals. subtropical tropics that I have discussed a few times, especially last time. summer. Hopefully this will help give you some insight into how large-scale patterns and circulations become favorable or unfavorable for certain types of weather phenomena; in this case tropical cyclone!
About the author
Hello! My name is Armando Salvadore and I am a Mississippi State graduate with a Bachelor of Professional Meteorology and an Activity Meteorologist working in the Private Sector. Stay tuned if you like technical, exotic, and general weather tweets! Also big on long-range forecasting as well! Twitter: @KaptMands