3 Things We Know About Invest 99-L and 3 Things We Don't Know Yet

Jonathan Belles
Published: August 23,2016
We're watching an area of storminess approaching the Lesser Antilles, and this one could bring impacts closer to home.
But Invest 99-L is still in development, and there are a few questions we still have, in addition to the things we already know about this system.
(FORECAST: The Latest on 99-L) 

What We Know So Far

1. Invest 99-L Will Be A Rainmaker
This strong tropical wave is currently forecast to bring upwards of an inch of rain to the Antilles north of St. Lucia and including Hispaniola and areas to the east. Islands with higher terrain and those that see more sunshine-induced thunderstorms on Wednesday could see rainfall amounts closer to four inches.
Mudslides and flash flooding are possible on some islands, including Puerto Rico and the U.S. Virgin Islands.

Forecast Rainfall

2. This Disturbance Will Trek Through Land Toward the Northwest
Current computer model guidance solutions are very tightly packed, which improves our confidence that the tropical wave will move through the northern Leeward Islands, including the British Virgin Islands, Anguilla and surrounding islands with showers and thunderstorms in and around those islands.
(MORE: What is an Invest?)
Showers and storms will overspread Puerto Rico and Hispaniola Wednesday and Thursday, but the tropical wave axis or center of Invest 99-L should pass toward the north.

Forecast Track Models

The forecast gets less clear after about three to four days, but the system should be north of the Bahamas by that time. Anything beyond that is more suitable for the "things we don't yet know" section below.
3. Invest 99-L Will Fight Dry Air and May Use Atlantic Heat Content To Its Advantage
A large dusty pool of dry air exists over the eastern Caribbean and southwestern Atlantic. So far, 99-L has done a good job of plowing the dry air forward and out of the way.
This system may pull in some of this dry air as it gets north of the Greater Antilles on Thursday. Some shear will be present Wednesday night into Thursday.
Deeper, warmer ocean temperatures are ahead of this tropical wave. A few patches of cooler waters do exist, but the general trend will be for waters to warm throughout the next five days. This effect alone should enhance thunderstorm activity, but dry air and shear could hamper this.

Conflicting conditions that 99-L will have to face. Water Vapor Image: Orange designates dry air, which is not hospitable for tropical cyclones. Heat content image: Yellow and red are areas that tropical cyclones can pull energy from for extended periods of time.

(MORE: The Most Intense Landfalls Have Happened in this 17-Day Period)

What We Are Trying to Figure Out

1. How Strong 99-L Will Get?
There remains a large array of possible outcomes in terms of intensity. At one end of the spectrum, this disturbance could run into the Greater Antilles or get dried out and remain weak throughout its lifespan. On the other end, many favorable conditions could come together in the Bahamas or east of the Bahamas, and a hurricane is possible.
Part of this variation is due to our lack of understanding in where the current center is located and the environment that exists around it. Remember, this is coming from an area with very few observations over the open Atlantic.
Scheduled Hurricane Hunter missions over the next couple of days should prove helpful.
(MORE: What is a Tropical Wave?)
2. When Will Florida's Hurricane Drought End?
Florida has seen numerous tropical storms in the last decade, but the state's lucky hurricane streak is up to 11 years. We don't know if this will be the storm, but it is always a good time to get prepared. It only takes one.
(MORE: 11 Years and Counting: Florida's Lucky Streak)
3. Will 99-L's Interaction with Fiona's Remnants Change Its Course?
Once 99-L gets closer to the Bahamas and the western Atlantic, the main steering feature will become a ridge of high pressure that is forecast to be parked over the Carolinas.

This ridge will not only be a major player in the steering of 99-L, but it may also capture the remnants of Fiona.
Although Fiona just ceased to be a tropical cyclone on Tuesday, its legacy may be two-fold. Numerous computer models, including the HWRF hurricane model, show that Fiona may get entwined somehow into this possible future cyclone's larger circulation.
(MORE: 3 Things You Should Know About Spaghetti Models)
The forecast at this point beyond four days is highly uncertain. How this interaction will take place and what happens if it takes place has yet to be seen. There are numerous other possible solutions.
This interaction, if it takes place, is at least six days away.
Other solutions slow 99-L down in the Bahamas and let it linger there for some time, or even bring this system closer to the United States.
MORE: Hurricanes, By The Numbers