Since 2:00 AM Wednesday, the National Hurricane Center has been monitoring a Tropical Wave, soon to be designated Invest 99L, for tropical cyclone development. Though there was some model support for the development of this wave Tuesday and Wednesday, over the last 24 hours, these models have not shown any development of this system as it traverses the islands on Sunday into Monday.
From the National Hurricane Center’s Tropical Weather Outlook, as of 8:00 PM, for Future Invest 99L, “A tropical wave located about 1000 miles west of the Cabo Verde Islands is producing disorganized cloudiness and showers. Some development of this system is possible while the system approaches the Windward Islands this weekend or when it moves across the eastern Caribbean Sea early next week.“
What We Know
The tropical wave is located in the East Atlantic with its axis along 44W S of 19N is moving W at 15 knots. Scattered showers are within 100 nautical miles of the wave from 04N-16N. However, the approximate center of future Invest 99L is at 10.5°N and 44°W.
Based on our counts, this is the 49th tropical wave of the 2019 Atlantic Hurricane Season.
As of the 8:00 AM Tropical Weather Outlook, this system has a low chance, near 0%, of tropical cyclone formation over the next 48 hours and a low chance, 30%, of tropical cyclone formation over the next 5 days.
This wave is yet to be designated Invest 99L by NHC as of Thursday morning. The system is located in an area of favorable upper-level divergence and low-level convergence. It also had a good deal of low-level spin, but at mid-levels, this vorticity is more elongated. There is a modest amount of heavy thunderstorm activity, which was slowing increasing in intensity and areal coverage on Thursday morning, as seen on satellite imagery.
Conditions appeared favorable for development, with the SHIPS model diagnosing light wind shear 5 – 10 knots and warm SSTs near 28°C and a fairly supportive moisture envelope.
What We Forecast For Future Invest 99L
Future Invest 99L is forecast to move mostly westward over the next 3-4 days, forecast to move directly across the Southern Windward Islands, including Trinidad and Tobago on Sunday into Monday. However, the weather ahead of this system is forecast to begin affecting Trinidad and Tobago beginning on Saturday.
Based on present model guidance, the core (i.e. where the heaviest showers and thunderstorms may occur) is forecast to track across the Southern Windwards. The possible center of circulation (if any forms) is forecast to move across anywhere between Northern Trinidad and South of Barbados.
There is still great uncertainty on any potential track and intensity of a system that has not even formed. Islands as far north as Martinique to as south as Trinidad should remain aware of this system over the next several days.
There is remarkable consistency in the forecast track of this system. Based on model guidance, an expanding high-pressure, building behind Hurricane Jerry is forecast to move future Invest 99L west to the west-southwest, directly across Trinidad, Tobago, and the Southern Windwards.
Of the EMCWF (European), GFS (US) and UKMET (UK) all bring this system across the Southern Windwards. Other top models, like the ICON (German) and ARPEGE (French), have similar outputs to the EMCWF and UKMET.
This system is then forecast to move into the Caribbean Sea on Tuesday, with showers tapering off across the Windwards, but may then move northwestward toward the Greater Antilles later next week.
Regardless of any development, the primary threat from this system will be heavy rainfall between Sunday and Monday across T&T.
There are no models that bring this system, as of Thursday morning, to tropical storm strength, or even a tropical depression with a closed low-level low-pressure center.
Reiterating: there is great uncertainty on any potential track and intensity of a system that has not even formed.
However, nearly all models (EMCWF (European), GFS (US), UKMET (UK), ICON (German), ARPEGE (French) and CMC (Canadian)) bring heavy rainfall and winds between 40-55 KM/H and gusts in excess of 55 KM/H to Trinidad, Tobago and the remainder of the Southern Windwards, particularly Sunday into Monday.
Hence, as of Thursday morning, we are expecting a very strong tropical wave to traverse the region on Sunday into Monday, bringing locally heavy rainfall, gusty winds and agitated seas to all Southern Windward Islands.
Impacts From Future Invest 99L
The Southern and Central Windwards are forecast to be affected by this strong tropical wave, with most impacts across the Southern Windwards. This area includes St. Lucia, St. Vincent and the Grenadines, Barbados, Grenada, and its dependencies, and Trinidad and Tobago.
As mentioned, regardless of development, this system will be a heavy rain threat above all else.
All models, the EMCWF (European), GFS (US), UKMET (UK), ICON (German), ARPEGE (French) and CMC (Canadian) bring heavy rainfall and winds between 40-55 KM/H and gusts in excess of 55 KM/H to Trinidad, Tobago and the remainder of the Southern Windwards, particularly Sunday into Monday.
Peak sustained surface winds of 25 KM/H to 55 KM/H with gusts in excess of 55 KM/H are possible in heavy showers or thunderstorms across the entirety of the Southern Windwards, including Trinidad and Tobago. These peak sustained winds are forecast to occur Sunday into Monday.
With wind gusts in excess of 55 KM/H, whole trees are expected to be in motion and there may be some inconvenience when walking against the wind gusts. Light outdoor objects may topple or become airborne such as garbage cans, potted plants, loose galvanize or construction material and other outdoor furniture. Tents may jump. Older/weaker trees may fall, bringing down utility poles and lines.
Across much of the Southern Windwards, including Trinidad and Tobago, we expect rainfall totals between 2 to 4 inches (50 to 100 millimeters) with isolated totals up to 6 inches (150 millimeters). The heaviest rainfall is forecast between Sunday and Monday across Trinidad and Tobago.
Thunderstorms and Lightning
With thunderstorms, locally severe wind (in excess of 55 KM/H), violent rainfall rates (in excess of 50 millimeters per hour) and lightning are all possible.
Gusty winds and lightning pose a threat to our power grid, causing localized power outages. Lightning may also strike trees, homes or utility poles causing damage to property. Lightning can also be deadly to persons outside during a thunderstorm.
Seas and Surf
By Saturday night, seas are forecast to be moderate to rough with long-period swells between 2.0 to 3.0 meters in open waters, battering the Atlantic Coasts of the Southern Windwards.
On Sunday, seas are forecast to be rough in open waters with long-period swells between 2.5 and 4.0 meters in open waters, continuing to batter the Altlantic Coasts of the Southern Windwards.
On Monday, seas are forecast to be moderate to rough with long-period swells between 2.0 to 3.0 meters in open waters, with the third day of battering the Atlantic Coasts of the Southern Windwards.
Seas will return to a moderate state by Tuesday as whatever system comes out of future Invest 99L. However, between late Saturday and early Tuesday, large waves and dangerous near-shore conditions will make marine conditions unsafe for mariners and sea bathers. Large, battering waves may pose a threat to life and property within the surf zone.
But this model shows…
Individual model runs are just one possible outcome from a myriad of outcomes. Weather does not always follow what is modeled, and even what may be forecast. Beware of individual model runs being posted on social media, especially since this tropical wave still 4 days away from moving across the Windwards.
Always check the National Hurricane Center for the latest information for tropical cyclones and your local meteorological offices for country-specific advisories concerning Future Invest 99L.
What is an Invest?
It sounds ominous, but from the outset, it really isn’t. Invest is short for investigation, followed by the numbers 90 through 99 and either the letter “L” for the Atlantic basin systems or “E” for the Eastern Pacific Systems.
This naming convention is used by the National Hurricane Center to identify features they are monitoring for potential future development into a tropical depression or a tropical storm.
According to the National Hurricane Center, by designating a tropical weather system as an “Invest”, the collection of specialized data sets and computer model guidance on the area of interest can begin. This collection and processing of data are shown on a number of government and academic websites for analyzing.
That said, the “Invest” assignment does not correspond to how likely a system may develop into a tropical depression or storm.
What should I do?
Firstly, don’t panic. There is a high likelihood of this area of disturbed weather, future Invest 99L, remaining a strong tropical wave moving across our region in 3-4 days.
Secondly, if you are a risk-averse person, now is a good time to check your inclement weather, flood or hurricane season plan, ensuring your preparedness supplies are not expired, stocked and in a safe location.
The Office of Disaster Preparedness and Management has put together a comprehensive guide for preparing for the 2019 Wet and Hurricane Season.