Invest 96-L Designated as Atlantic Basin Warms Up For Peak of Hurricane Season

Tom Moore
Published: July 27,2016
This time of year, we begin to look farther east in the Atlantic Basin for possible tropical development. Right on cue, there's an area of disturbed weather to monitor near the coast of Africa.

A strong tropical wave – a batch of energy and general spin in the atmosphere that develops due to temperature contrasts on either side of Africa's Sahel region – has emerged off the coast of Africa and is attracting more interest as it moves westward. On Wednesday, the National Hurricane Center (NHC) began highlighting this area for a medium chance of development during the next five days.

(MORE: What is a Tropical Wave?)

Area of Interest in the Atlantic

Designated Invest 96-L, the NHC indicated that the disturbance was producing a disorganized area of showers. This naming convention is used by the NHC to identify features that are being monitored for potential future development into a tropical depression or a tropical storm.

(MORE: What is an Invest?)
Environmental conditions are somewhat favorable for this wave to become more organized in the days ahead. The NHC gives Invest 96-L a 30-percent chance of becoming a tropical cyclone over the next two days and a 40-percent chance in five days.

Computer Model Track Forecast

Farther west in the Atlantic, some wind shear and dry air are present, which can hinder development of this system.
This is the first tropical wave in the eastern Atlantic Ocean to have a chance to develop this season, which is why it has our attention. However, it has a long way to go, and there's plenty of time to monitor the disturbance as it tracks west, so there's no need to have any major concerns at the moment.
Technically, the Atlantic hurricane season runs from June 1 through Nov. 30. Much of the tropical activity occurs between the second week of August and the second week of October. In late July and early August, we begin to keep an eye on the eastern Atlantic as it begins to show signs of life.
(MORE: Gulf of Mexico Hurricane Drought Likely to Become the Longest in 130 Years)

Why We Begin Looking Farther East Into the Atlantic This Time of Year

In July, a series of tropical waves often form across the Sahel area of Africa and move westward toward the Atlantic coast. The Sahel area lies between the Sahara Desert to the north and wetter areas to the south.
Tropical waves can develop into tropical storms and hurricanes once they emerge into the Atlantic, but because of some unfavorable environmental factors, they tend to not develop in July.
Meteorologists observe trends, however, that can frequently give us a sneak peek of what the heart of the tropical season could look like.
Over the past couple of weeks, we have noticed a series of weak tropical waves that have moved westward, emerging off the African coast. These waves have dissipated rapidly due to lots of dry air, cool ocean temperatures and wind shear in this region.

NOAA satellite photo (July 27, 2016) shows a series of tropical waves moving west across Africa.

Now that we are moving toward August, ocean temperatures have risen to about 80 degrees along the African coast – more favorable for tropical development. Each preceding wave has added moisture to the atmosphere in the eastern Atlantic, and the amount of dry air that can inhibit development is eroding.

The latest satellite photograph clearly shows a number of tropical waves in the Sahel region of Africa, which are moving westward.

 

(MORE: Eastern Pacific Hurricane Season Sees Record Start to July After a Slow Start)

August and September: More Favorable For Development

Tropical waves that emerge off the African coast often develop around the Cape Verde Islands.
Meteorologists make frequent references to the "Cape Verde" season, which is essentially a season within the overall hurricane season. Most Cape Verde storms develop from mid-August until late September.
There are so many "mouse traps" (unfavorable conditions) in the Atlantic that very few tropical storms and hurricanes ever make it all the way to the United States. But there have been some notable Cape Verde storms that made it to the East Coast of the U.S., such as the 1938 Hurricane, Hurricane Hugo in 1989 and Hurricane Andrew in 1992.
Development of tropical waves into tropical storms or hurricanes is determined by several environmental factors that can range from somewhat favorable to extremely favorable, including:

• Ocean temperatures
• Ridges and troughs aloft
• A moist environment

In general, the ocean temperature needs to be around 80 degrees for tropical cyclones to develop. Off the coast of Africa, that doesn't usually occur until late July.
Tropical systems like to have calm winds aloft for maximum development. Winds aloft (wind shear) tends to break up tropical systems that are trying to develop.
This often occurs when a trough of low pressure aloft is in close proximity to a tropical weather system.

Expanding high pressure ridge creates a more favorable environment for tropical systems to develop and move westward in the Alantic

In August and September, a high-pressure ridge aloft, known as the Bermuda-Azores high, often expands and creates a more favorable environment for development. Atlantic systems are often steered toward the western Atlantic, Caribbean and sometimes all the way to the U.S.
Since the area from Africa to the eastern Atlantic looks quite active already and we now have a tropical system of interest, it'll be interesting to see what the rest of the hurricane season will have in store.
MORE: Retired Atlantic Hurricanes and Tropical Storms