The 2015 hurricane season saw a very strong El Nino event end of the Summer into the fall and a very evident negative Atlantic Multidecadal Oscillation (AMO) regime shift that made its presence felt across the Atlantic.
These are the main factors that led to the hostile conditions in the main hurricane development zone in the tropical Atlantic. The 2015 hurricane season helped prohibit a large majority of storm development across the region leading to the hurricane season in the Atlantic Basin only producing 55% of the normal amount of accumulated cyclone energy usually seen. 2015s was the third straight below average season seen in the Atlantic basin.
The period between 2012 and 2015 saw the ENSO as lackluster and the AMO turning from positive to negative. The AMO is going to be one of the question marks for the 2016 hurricane season. Will the AMO become more in the way of being permanently negative for a few years?
The El Nino Southern Oscillation (ENSO):
Last late fall early winter, I stated that we would enter a moderate to strong La Nina. The ENSO cycle clearly shows moderate to strong La Nina's follow strong El Nino's. After the retweak of the NECP coupled system model verson 2 (CFSv2); the American climate model has now joined the Japanese Weather Model (JAMTEC) and European weather model (ECMWF or EURO), in showing a La Nina by Fall 2016, most likely even sooner. La Nina would cool the Sea Surface Temperatures (SST) in the eastern Pacific to well below average. This cooling suppresses convective convergence in the upper atmosphere in the Eastern Pacific into South America; in other words cooler and dry air hinders thunderstorm and rainfall activity. The activity in the Pacific decreases vertical wind shear across the Caribbean Sea into the Atlantic. The decrease in the upper winds makes the environment in the Caribbean and Atlantic much less hostile to tropical cyclone development.
1906, 1973, 1988, 1995,1998, 2007, 2010, 2015
This year is going to be a transition between El Nino and La Nina. We saw the El Nino of 2009 transition to a strong La Nina in 2010. The 1997 El Nino flipped to a La Nina in 1998. 2016 will see the same thing happen. One thing that will have a impact this year is the much warm SST off the East Coast, then we saw in 1998. 2007 also looked very similar in the development of the La Nina.
The Jet Stream and Sahel:
The easterly Jet and the area known as the Sahel, have a lot to say about tropical cyclone formation in the Atlantic Basin. The Sahel is a region in Africa that lies between the Sahara Desert and the Sudanian Savanna.
As most of you know, tropical waves move off the West Coast of Africa. As the waves move into the Atlantic, they look for conditions were they can develop. Cape Verde Hurricanes are storms that form near the Cape Verde Islands. If they can't form here, they keep heading west, until they can find a more favorable environment. During the 2015 hurricane season the Sahel became wetter than average. Because of this Fred, Grace, and Ida became strong, in spite of hostile conditions due to the strong El Nino.
The Sahel looks to be once again wetter than average. So this will keep the amount of Saharan Dust lower, which will lower the amount of dry dusty air in the tropical formation zone of the Atlantic. The eastern African jet looks to be active this year. The strength of high pressure (Azores High) in the Atlantic, will be a inhibiting factor for development in the eastern Atlantic. But the higher precipitation over the Sahel, active African jet, and the warmer SST in the western Atlantic Basin will help counter that issue.
One thing all the analog years had a deep trough in the Gulf of Alaska during the winter. Which lead to ridging over North America during the Summer and Fall. This lead to displacing the Azores high to the north. Which increased the chances of a landfalling tropical cyclone on the CONUS.
The eastern Atlantic is warmer than last year, but still not as warm as it could be. But the western Atlantic, Caribbean, and Gulf are very warm. If I'm right on the Azores High being more to the north....this upcoming season looks to be above average in the number of tropical cyclones. If the Azores High is real strong it could slingshot tropical systems across the Atlantic, not giving them a lot of time to develop.
This season looks to see a ACE value of 90%-130% percent of average. Based on the things I just outlined, I think (at this time) we will see 13 named systems, 9-12 named systems, 7 hurricanes, 3 of which will be major. The development zone looks to be in the Gulf, Caribbean, and off the East Coast of the CONUS. This increases the worry of East Coast landfalling hurricanes.
I will come out with my final outlook end of April or the first couple of days of June......