El nino could impact hurricane season and Mid-MO weather

Photo: NASA

NEW BLOOMFIELD, MO â?? Hurricane season has begun and the move toward El Nino conditions will likely have an impact on the number of tropical storms this season.

June 1 is the official start of hurricane season in the Atlantic basin and the number of storms that develop could be lower this season due to the strengthening El Nino conditions in the tropical portions of the Pacific Ocean.

What is El Nino?

El Nino is classified as above normal warming of ocean waters in the Pacific Ocean, particularly the water near the equator. El Nino is the oscillation of ocean temperatures that is a part of the ocean-atmosphere system which is termed ENSO. This oscillation can cause fluctuation in weather patterns all across the globe, including a change in the anticipated number of hurricanes this season.

Currently, Pacific Ocean temperatures are slightly above normal, but not warm enough (when looking at the average temperature) to be considered to be in an El Nino phase. However, Pacific Ocean sea surface temperatures appear as if they will continue to warm slowly this summer and into the fall to a threshold that would be considered El Nino. The threshold to be considered El Nino is sea-surface temperatures that are 0.5°C above average. In the picture below, the red outline in the Pacific Ocean shows the area where temperatures are above normal. This is the area where we look for signs of developing El Nino conditions.

How does El Nino impact hurricane season?

As the waters warm in the Pacific Ocean, it causes air to raise and form a large area of low pressure over the ocean. This raising air turns into upper level winds in the atmosphere. El Nino increases the speed of these upper level vertical wind in the atmosphere, especially over the middle and deep Atlantic. This acts to shear, or blow apart, hurricanes in the upper parts of the atmosphere, effectively shutting down tropical cyclone development. As a reference point, severe thunderstorms that form over land require vertical wind shear to help them produce severe weather like large hail and tornadoes, which is opposite of favorable conditions for hurricane development. El Nino also leads to faster trade winds in the Atlantic Ocean which can aid in suppressing tropical cyclone development.

Another reason tropical development could be down this season (especially strong hurricanes) is because the waters off the coast of Africa and the Cape Verde Islands are slightly cooler than average. This is the area where tropical storms develop and strengthen into stronger hurricanes as they move toward the Caribbean Islands and North and Central America. This area of cooler than average sea-surface temperatures can be seened in the outlined blue oval in the picture below. Cooler waters have less energy that can be used to help strengthen tropical storms. Climatologically, the peak of hurricane season is September 10.

NOAAâ??s 2014 hurricane forecast is listed below with the average number of events per year in parentheses from 1966-2013. Overall, tropical activity is expected to be slightly below average.

8-13 Named Storms which includes subtropical storms (12)

3-6 Hurricanes (6)

1-2 Major Hurricanes (2)

*Major hurricanes are defined as a Category 3 or stronger on the Saffir-Simpson Scale.

Below is the average number of hurricanes (from 1900 to 2013) that make landfall in the United States each year.

Hurricanes: 2

Major Hurricanes (Cat. 3 and higher): 0.6

Here is a list of the 2014 hurricane names for the Atlantic Basin:

How does this possible lack of tropical activity impact Mid Missouri?

While tropical activity in the Atlantic does not directly impact our weather, remnants of tropical storms and hurricanes can bring beneficial rains over the summer and early fall when rainfall has been sparse. These rains can often break droughts in our area and break intense summer heat waves.

The way a lower than average hurricane season will impact is if there are less tropical storms and hurricanes, there is less of a chance that we get remnant rainfall from a tropical storm.

In Missouri, El Nino will would favor slightly cooler temperatures and above average moisture. A look at the long range Mid-Missouri forecast for June, which explains how El Nino will play a role in our weather can be found below:

Dan Ebner's June 2014 weather outlook for Mid-Missouri