Invest 99-L May Become a Tropical Depression or Storm in the Atlantic, Possibly Threaten Lesser Antilles Next Week

Jon Erdman
Published: August 19,2016
A tropical disturbance in the eastern Atlantic Ocean, Invest 99-L, may develop into the next tropical depression or storm in the days ahead.
Unlike Tropical Storm Fiona, this system may pose more of a threat to the Lesser Antilles.
(MORE: Latest on Fiona | Hurricane Central)
Beyond that, it's possible this future Gaston -- the name it would receive if it reaches tropical storm-strength -- may threaten other parts of the Caribbean Sea, then eventually some portion of the U.S.
Here's what we know now and what is far too early to determine.

Will It Develop at All?

At this early stage, there's uncertainty whether a tropical depression or storm will even form.
Invest 99-L is currently a tropical wave -- an area of low pressure without a closed, counterclockwise surface circulation -- several hundred miles southwest of the Cabo Verde Islands off the west coast of Africa.
(MORE: What is an Invest?)

Invest 99-L Infrared Satellite Image

This tropical wave's convection looks fairly ragged and disorganized for now, according to infrared satellite imagery.
(MORE: Why Tropical Waves Are Important During the Hurricane Season)
For a tropical cyclone to form, there's needs to be persistent convection near a surface low-pressure circulation. None of those two conditions are there yet.
Dry air and perhaps some wind shear may interfere with Invest 99-L's attempt to organize.
This shear and dry air is currently taking a toll on Fiona. Sometimes the first system becomes a sacrificial lamb, helping to prime the atmosphere behind it for the next system.
The National Hurricane Center says this system has a moderate chance of development into a tropical depression or tropical storm over the next five days.

Will It Threaten the Antilles?

Invest 99-L was about 2,000 miles east of the Lesser Antilles on Friday.
Given that and the uncertainty of development, it's no surprise there's question about the track.
This uncertainty is, in part, due to the fact we don't yet have a closed circulation with which numerical guidance can use as a starting point. It's hard to know where you're going if you don't know where you are.
For now, the consensus of our guidance suggests the disturbance should continue in a general west or west-northwest trajectory across the Atlantic and may reach the Lesser Antilles by the middle of next week.
(MORE: Three Things to Know About Spaghetti Model Forecasts)

Forecast Model Tracks: Invest 99-L

But there are some scenarios that turn the center of the wave northwest or even north before it ever reaches the Lesser Antilles.
Assuming it does reach the Antilles, what intensity will it be? The range of solutions are wide ranging: from a tropical wave that never develops to a tropical storm or hurricane.
It's just too early to determine.

Will It Threaten the Caribbean and/or U.S. ?

There's a reason some of the world's best hurricane forecasters at The National Hurricane Center only issue forecasts and outlooks five days out.
To put it bluntly...

Numerical forecast models don't yet have the sufficient skill to determine the eventual track and intensity of a tropical cyclone that hasn't even formed yet while it's still thousands of miles and over a week away.

Keep that important point in mind if you see any social media posts in the days ahead suggesting any landfall more than seven days out. We wrote an example of this overhype two years ago regarding what eventually became Hurricane Cristobal.
It's far too soon to determine if this system will pose any further threat to any Caribbean or U.S. interests.

Typical tropical storm and hurricane origin areas and tracks in August. This is **not** a forecast for this current system, merely a representation of August climatology.

For now, this is something to monitor the next few days. We'll keep you updated with the latest at weather.com and let you know if and when a threat materializes for these areas.
(MORE: Hurricane Season Outlook Update)
This is another sign that we're headed into the climatologically most active time of the Atlantic hurricane season.
(MORE: When Atlantic Season Peak Arrives | Where Every U.S. Hurricane Has Hit Since 1985)
Regardless of whether this system becomes a threat, now is a good time to make sure you have a plan before a hurricane hits.
Jonathan Erdman is a senior meteorologist at weather.com and has been an incurable weather geek since a tornado narrowly missed his childhood home in Wisconsin at age 7.