Invest 97-L Could Develop into a Tropical Depression or Tropical Storm This Week

July 31,2016
An area of disturbed weather that is moving through the eastern Caribbean Sea has the potential to develop into a tropical depression or tropical storm this week.
The National Hurricane Center (NHC) said that the system - designated Invest 97-L - has a medium (50 percent) chance of developing during the next two days, and a high (70 percent) chance of developing during the next five days.
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?)

Invest 97-L Satellite and Position

The unsettled weather is currently associated with a tropical wave, which means it does not have a center of circulation near the ocean's surface at this time.
Tropical waves are batches of energy and general spin in the atmosphere that develop due to temperature contrasts on either side of Africa's Sahel region. They then move west across the Atlantic Ocean.
Sometimes tropical waves develop into a closed area of surface low pressure with collocated shower and thunderstorm activity. Once this occurs, a tropical depression or storm can develop, and that's what we'll be monitoring Invest 97-L for.
(MORE: What is a Tropical Wave?)

The NHC said that this system's fast movement was a negative to development in the near term. The dry air in the region also may be playing a role in keeping convection rather disorganized.

Once Invest 97-L reaches the western Caribbean Sea in a few days, it will have a greater chance to develop into a tropical depression or tropical storm.

Computer Model Track Forecast For Invest 97-L

Regardless of development, showers and some gusty winds will continue to affect the eastern and central Caribbean Islands into Monday. This will include areas as far west as Hispaniola.

Puerto Rico Radar

A flash flood watch has been issued for Puerto Rico and the U.S. Virgin Islands into Monday afternoon. Rainfall amounts of 2-4 inches are possible in the Antilles through mid-week. Some higher totals are possible in more mountainous areas.

Forecast Rainfall Associated with 97L

How well organized Invest 97-L is by the time it reaches the western Caribbean Sea will dictate what impacts to expect there and possibly in the Yucatan Peninsula. Much uncertainty remains, however, so stay tuned for updates.
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)

August and September: More Favorable For Development

Tropical waves that emerge off the African coast often develop around or after passing 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.

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

There are so many "mouse traps" (unfavorable conditions) in the Atlantic that very few of these Cape Verde 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
• The orientation of ridges (high pressure) and troughs (low pressure) 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 winds that are roughly the same speed and direction through a depth of the atmosphere for maximum development. Wind shear - changing winds with height - tends to break up tropical systems that are trying to develop, displacing convection away from a center of circulation.
This often occurs when a trough of low pressure aloft is to the west of a tropical weather system, such that west to southwest winds aloft combine with the typical tropical east-northeast trade winds to produce wind shear.
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 Sea 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