El Niño, a warming of waters in the equatorial central and eastern Pacific ocean, has begun but it is not behaving typically. As El Niño has developed the North Atlantic ocean has warmed more rapidly than the equatorial eastern and central Pacific heating the north Atlantic to unprecedented highs.
A rapid warming of global temperatures in the early months of El Niño is a known phenomenon caused by the slowing of the trade winds that cool the subtropical and tropical oceans and seas. What’s unusual about this El Niño is that the trade winds slowed more in the tropical Atlantic than in the tropical east and central Pacific. Normally, the opposite is true. This spring, trade winds have stayed strong along the coastline of Baja California, keeping the California current strong and the waters cool between Baja California and Hawaii. Moreover, the slowing of the trade winds has led to less dust formation over Africa and very little dust blown over the eastern north Atlantic. This lack of dust has amplified the warming of the North Atlantic according to Professor Michael Mann.
The strong trade winds are not only keeping the waters cool between California and Hawaii, but they are also pushing the intertropical convergence zone (ITCZ) , the line where strong tropical thunderstorms form, towards the equator and they are reducing the potential for tropical storms to form in the eastern and central Pacific. The strong winds are keeping the line of strongest convective activity in the western Pacific ocean. Strong convection in the tropical western Pacific ocean this spring has generated high level westerly winds across the Pacific and a strong subtropical jet stream that has brought cool weather across the southern tier of states in the U.S. and heat to the north. It’s a very unusual weather situation. Notably, this is the source of the wind shear that would, in a normal El Niño, diminish hurricane activity in the north Atlantic, but this year the shear is north and west of it’s typical track in an El Niño year. This year, the Atlantic main development region for tropical storms has less shear than normal for this date, and this low shear situation is likely to continue through the hurricane season. And the heat in the upper ocean that fuels the strongest storms has built up to record levels in the main development region.
A tropical wave is presently moving off of the west coast of Africa which the National Hurricane Center gives a 60% chance of becoming a tropical storm over the next 5 days. If this tropical wave becomes a storm it is most likely to recurve harmlessly out to sea well before becoming a threat to land, but climate models and long range weather models are all showing conditions that will be very favorable to tropical storm formation this hurricane season, despite El Niño. The cold water situation along the California coast can last for years because it is self reinforcing. An index of this pattern, the Pacific Decadal Oscillation index was near record cold levels this spring and will hold the hurricane season in the eastern and central Pacific down along with wind shear that would affect the Atlantic.
Strong tropical convergence in the main development region forecast by multiple models for the peak of hurricane season combined with record ocean heat content create the potential for an extremely destructive hurricane season. This set up is similar to the one that led to hurricane Andrew. The lesser Antilles, the Bahamas and Florida are on the highest risk potential region.
If you live in Florida you need to be ready for the worst.