Graphic from Colorado State University’s July hurricane season forecast outlook showing the below avg wind shear (blue color) across the MDR for the month of June. Click for full size.
The update from Colorado State University to the 2017 Atlantic hurricane season forecast made mention of the fact that, during the month of June, sea-level pressures were well below average across the deep tropics – also known as the MDR or Main Development Region. This is the area between Africa and the Lesser Antilles and has seen its share of powerful hurricanes over the decades.
In recent years, however, the MDR has been notably quiet. Dry air, strong upper level winds and generally higher than normal pressures have kept the region much more benign – resulting in far less hurricanes such as what we saw in 2004 with Frances and Ivan, as examples.
This year, it is becoming more and more obvious that the sleeping giant is awakening, so to speak. Water temps across the MDR are above normal, wind shear is below normal and surface pressures are below normal. The result thus far has been the formation of tropical storm Bret last month (extremely rare to have MDR tropical storms in June) and now, most recently, tropical depression four – technically a tropical cyclone though below tropical storm intensity. The only significant mitigating factor keeping TD4 in check has been a large Saharan Air Layer or SAL event that has pushed ample dry air in to the deep tropics, smothering the depression and keeping it from strengthening further. This SAL outbreak is typical for July, having a tropical depression in the MDR is not.
ECMWF model at day 5 from last night’s run showing energy or vorticity at the 850mb level of the atmosphere (circled in green). Image courtesy of Levi Cowan – tropicaltidbits.com. Click for full size image.
Now comes the next chapter in this story. Both the GFS and the ECMWF are now indicating the development of a tropical storm originating from a tropical wave that is about to emerge from the African coastline. I want to be clear, the development happens beyond the 5-day time frame but well within the next 10 days. Since both of these global models now indicate this happening, it has my attention. In fact, both models go on to develop the system in to what would likely be a hurricane later on in their forecast periods but again, not at some ridiculous time frame such as 10 to 14 days out – what many consider to be “model fantasyland”.
What concerns me about this is the mere fact that it is still early July, several weeks ahead of the traditional beginning to the normal run-up to the peak of the season and we’re talking about yet another MDR system trying to develop. In other words, if it’s this busy now, when climatology says it should not be, how busy will it be when the natural background state is inherently favorable? That usually sets in around August 15-20 and lasts until the end of October.
I make it a point to refrain from being an alarmist – those who have followed my blogs and video discussions know this and I stand firm behind that belief. At this point, I am beginning to worry that this season could end up exceeding all of our expectations in a bad way. The time-tested saying of “it only takes one” remains intact but this is the kind of season where we could be looking at multiple “it only takes one” events. Please keep in mind too that I am not talking about just the United States in terms of impact. The Lesser Antilles are front and center for any action that rolls out of the MDR and west of there we have Puerto Rico, Hispaniola and Cuba. This is the kind of season that could affect a lot of people across the Atlantic Basin and in areas that can least afford such bad luck.
I am going to say it, the signs are ominous right now. We’ve gone a long time without experiencing a category three or higher hurricane in the United States. They’ve also been somewhat rare elsewhere with the exception of Matthew and its devastating impacts on Haiti, eastern Cuba and the Bahamas last year (Joaquin in 2015 also impacted portions of the Bahamas). It is time to take notice and be ready to act.
Needless to say I am going to be watching the evolution of this next potential system very closely over the coming days. Perhaps it is just a blip in the models and subsequent runs will drop the storm/hurricane completely and we can all breathe a sigh of relief. I will post a detailed video discussion concerning this potential development later this afternoon once the morning model runs complete and are available.
M. Sudduth 7:45 AM ET July 7