2019 Atlantic Hurricane Season Incoming
Updated May 30, 2019 @ 6:59 pm EST
It is that time of year once again. Sea surface temperatures (SSTs) are rising and wind shear is beginning to lessen. We have one factor so far, the SSTs are prime for hurricane development and survival, but we are experiencing a Spring season with high wind shear values in the atmosphere. This is good news if you do not want to see the formation of hurricanes; bad news if you are not a fan of tornadoes. Two of nature’s most formidable disasters rely on opposite wind ingredients. Hurricanes cannot survive in an environment of high wind shear where winds of different directions and speeds help to tear the structure and convection of the storm apart. Hurricanes prefer a calm wind environment so that thunderstorms can grow without disruption. The warm, moist air over the ocean rises upward leaving less air at the surface. So as this warm-moist air rises and fuels the building thunderstorms, an area of low pressure forms below. The more warm air that travels upward, the stronger the storm, and this powers up the low pressure beneath and allows it to “suck in” surrounding warm-moist air to continue to strengthen.
Tornadoes, on the other hand, thrive on wind shear. In order for a tornado to form it needs warm, moist air (from the Gulf of Mexico, for example) and cool, dry air from the opposite direction (for example, Canada). When these two air masses meet and interact they create instability in the atmosphere. These different winds, from two different directions (this is wind shear) also helps to create a spin in the clouds which produces tornadoes. So while hurricanes are primarily reliant on warm-moist air and very little wind shear; a tornado needs both warm and cold air to create an unstable environment, and powerful wind shear to create that spin in the atmosphere.
What we have been experiencing this past Spring is an active tornado season. There is so much energy and wind shear in the atmosphere that supercell thunderstorms are producing so many tornadoes across the United States. As of this writing, the United States has reported over 750 tornadoes this year of which over 500 of them have been confirmed by the National Weather Service. To put that in perspective, we only had about 470 tornadoes reported during this time last year. With so much tornado activity this year many are wondering if this is a sign as to how active the 2019 Atlantic Hurricane Season will be. There are so many factors to determine that there can never be a precise answer for how active this season will truly be, however, statistically speaking, years that saw an active tornado season yielded a less active hurricane season. This is because of the intense amount of wind shear in the atmosphere which is helping to produce all of these tornadoes. There is another ingredient at play here though, and that is the potential development of an El Niño over the next few months.
An El Niño is a long period change in the climate that can last 2-3 years on average. An El Niño event begins off the west coast of South America where SST’s begin to rise above normal. This large scale change affects weather patterns worldwide, especially hurricane formation. The Pacific becomes warmer and we typically see a surge in tropical storm development because of these hotter SSTs. However, in the Atlantic we have the opposite; SSTs become cooler than normal and wind shear values begin to increase for large portions of the Atlantic preventing the formation of hurricanes.
The National Oceanic and Atmospheric Administration (NOAA) says that “a weak El Niño is underway in the tropical Pacific, and it’s likely to continue through summer (70% chance) and fall (55-60% chance). Weak events can still produce moderate or strong impacts in some places, but such impacts are less likely overall.”
Images above: Global SST’s currently. First image is the current SSTs for May 30 (Courtesy Weather Underground). Second image is the change in the average temperature of sea water compared to the 1981-2010 time frame (Courtesy NOAA).
As a whole, Earth’s SSTs are higher compared to the 20 year period from 1981-2010. So yes, we are experiencing warmer than average SSTs across the world. However when identifying an El Niño event, we are not seeing a strong indication of warmer SST’s off the west coast of South America compared to the Pacific Ocean as a whole at this current time (see first image above). Extending from the northwest coast of South America we see a swirl of orange and yellow colors pushing their way westward towards Asia. This is the area we look at to confirm an El Niño taking place, and because these waters are cooler than the surrounding waters we can say that we are in a very weak El Niño stage for the moment. It is possible that these waters will continue to warm over the Summer and Fall and this will indicate a stronger El Niño. However, climatologists and meteorologists are in a general agreement that this year will see more of a weak El Niño taking place. So what does this mean for the upcoming Atlantic Hurricane Season?
First Image: The National Hurricane Center’s forecast for the 2019 Atlantic Hurricane Season (Courtesy NOAA). Second Image: Colorado State University’s 2019 Atlantic Hurricane Season forecast (Courtesy CSU).
Both the National Hurricane Center and Colorado State University are calling for a near-average hurricane season this 2019 in the Atlantic. Likely the factors taken into consideration were the developing El Niño and the warmer SSTs as a whole around the world. Even if this weak El Niño persists into the Summer and Fall it will likely not have enough strength to affect the development of hurricanes as a whole. With the Atlantic already being above average in temperature the past few years the cooling affect that an El Niño would generally delivers to the Atlantic Basin will probably not be enough to bring down the temperatures very much. Therefore, even though we are classified to be in a weak El Niño phase we are currently not seeing any strong effects from this climatological pattern, hence why forecasters are likely going with a near-average hurricane season. However, I have stated this for many years: It only takes one hurricane. We can forecast hurricane numbers each year but we cannot forecast the track of these systems. Agencies may “only” be calling for 2-4 major hurricanes this year but that does not mean they will stay out at sea and not bring any impact to us. The past three years have been deadly for the United States and reminded many of us that we are very vulnerable to these powerful systems. Hurricane’s Matthew, Irma, Florence, Maria, Harvey, and Michael, have all shown us these past few years how deadly a hurricane can be and that we must always be prepared no matter what forecasts say.
However, another topic to quickly discuss was the formation of Subtropical Storm Andrea (ignore the subtropical part, it is still a “tropical storm”).
Images above are the track and satellite imagery of Subtropical Storm Andrea
For the fifth straight year in a row we have had our first named system take place outside of the official Atlantic Hurricane Season (June 1 – November 30). Andrea was a weak system just to the southwest of Bermuda when it gained enough strength to be dubbed a “subtropical storm” on May 20. Unfortunately it only lasted about 0.75 days before it dissipated from intense wind shear on May 21, 2019. Andrea is an example that even though a weak El Niño is in place, there is still enough energy in the atmosphere to have a storm form, even if it was “alive” for less than a day.
The official start of the Atlantic Hurricane Season is less than two days away and meteorologists across the United States, Mexico, and Caribbean will have their eyes on the Atlantic and Gulf of Mexico as the season begins. Currently the Atlantic is quiet partly due to the intense wind shear in the atmosphere across the warm tropical regions hurricanes generally like to grow and develop in:
Image above: Current wind shear areas in the North Atlantic Basin (Courtesy CIMSS)
Referring to the image above, red areas indicate high wind shear and thus “unfavorable” for tropical cyclone development. It is clear that most of the tropical regions and the Gulf of Mexico are experiencing high wind shear at this time. This is generally typical for the month of June as we are phasing from Spring into Summer. However, this also gives a clear indication on why the United States, and especially The Plains have been experience one tornado after the next. With so much of the United States under high wind shear these thunderstorms are getting plenty of wind energy to help form these tornadoes.
Image above: Typical tropical tracks and origins for Tropical Storms that form in the month of June.
Over the next month we could see wind shear die down slightly giving a chance for a couple of storms to develop. However, June is a quiet month usually for tropical storm development, as well as the month of July. Since 1951, only 13 percent of tropical storms formed in June and July combined. August, September, and October (the active months) have accounted for 24, 36 and 21 percent of all tropical storms on record, respectively (Dolce, 2019). If a storm does form, however, they are usually found in the Gulf of Mexico where the SSTs remain warm for most of the year and do not need as much time to continue to warm as we transition from a cool Spring into a hot Summer. We will have to wait and see how the month of June plays out and what this hurricane season will have in store for us this 2019. Weather Goddess, Dr. Athena Masson will be keeping a close eye on the Atlantic for the next storm.