The National Ocean and Atmospheric Administration (NOAA), is forecasting an above normal hurricane season for the 2017 season. Already one tropical storm has formed in the Atlantic Ocean this year back in April with Tropical Storm Arlene.
The forecast is focused on the fact that El Nino is very slow to develop which means that the potential for atmospheric shear will be reduced. The other factor is the potential for above normal sea surface temperature anomalies (SSTA) in the Caribbean Sea and Tropical Atlantic. The combination of low shear values and expected above normal sea surface temperature anomalies supported a 45% chance for above normal tropical development and a 35% chance for near normal tropical development.
This forecast from NOAA is in contrast to the going forecast by NY NJ PA Weather, which was issued early in May and can be seen here. The primary reasoning why a below normal Atlantic Tropical Season is expected.
First, the Atlantic Ocean is in a process of change from a positive Atlantic Multidecadal Oscillation (AMO) to a negative AMO. A negative AMO features below normal SSTA which typically leads to below normal activity for the Tropical Atlantic. These phases can last 25 to 40 years. The last cold phase was from 1971 to 1994, followed by the warm phase from 1995 to present. The uncertainty in the forecast comes down to how fast the transition from the warm phase to the cold phase.
The most pressing factor in these season will be the influence of Saharan dust coming off the African Coast. This dust is a strong inhibiting factor for the development of tropical low pressure systems. The dust leads to a drier mid and upper level atmosphere which limits tropical low pressure development. The evolution of El Nino, though very weak, will help to enhance the transport of dust from the Sahara. As a result, tropical development off the African coast and around the Bahamas will likely be significantly limited this year.
Regardless if the tropical cyclone activity is above normal or below normal, only one hurricane is needed to have a significant impact on the Eastern United States as we learned back in 1992 with Hurricane Andrew.
Trust in NY NJ PA Weather to keep you ahead of the storms!