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.
Analog
years:
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......
