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

Jonathan Belles
Published: August 24,2016
We're watching an area of storminess that has moved into the Caribbean, 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 in the Caribbean
The broad area of low pressure associated with a tropical wave will continue to bring locally heavy rain to the Lesser Antilles into early Thursday morning and Puerto Rico, Hispaniola, and the Bahamas throughout Thursday.
Islands with higher terrain and those that see more sunshine-induced thunderstorms on Thursday could see rainfall amounts closer to four inches. Mudslides and flash flooding are possible on some islands.

Forecast Rainfall

2. This Disturbance Will Trek Near Land Toward the Northwest
Current computer model guidance solutions are very tightly packed initially, which improves our confidence that this system will move through the northeast Caribbean Islands the next couple of days and into the Bahamas by Friday or Saturday.
(MORE: What is an Invest?)
The forecast gets less clear after about three to five days, but the system should be near the Bahamas and possibly Florida by that time. The spread in the models at that time is large, and thus our confidence is LOW. Anything beyond that is more suitable for the "things we don't yet know" section below.

Forecast Track Models

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 into Thursday, and is likely already hampering short term development.
Wind shear and dry air can slow or prevent the development of tropical systems.
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. Sea surface temperatures in the Bahamas range from the mid-80s to near 90. 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. On Wednesday evening, multiple centers could be located by satellite imagery, which means models could latch on to different centers and thus show different solutions.
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 system, but it is always a good time to get prepared. It only takes one.
(MORE: 11 Years and Counting: Florida's Lucky Streak)
3. Ridge of High Pressure May Steer This System Into the Gulf
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.

If this system develops, the clockwise flow around the ridge of high pressure would send it toward the Gulf of Mexico. This would, of course, put parts of the U.S. Gulf Coast in play for possible impacts.
We do not yet know how strong this ridge will be when 99-L gets to the Bahamas. The strength of the ridge will dictate where this system goes exactly.
(MORE: 3 Things You Should Know About Spaghetti Models)
That said, there are other possible outcomes, and this is far from certain at this point. For more details, see our full forecast article at this link.
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