Tropical Wave 55 Key Messages:
— Although Tropical Wave 55 is already producing near-gale-force winds (sustained at 55 KM/H, gusts to 74 KM/H), upper levels winds are not forecast to be conducive for development as this active tropical wave nears the Windward Islands.
— Much of the heaviest showers, thunderstorms, and winds are forecast to move north of T&T later this week.
— Between 1 to 2 inches (25 to 50 mm) with isolated totals up to 4 inches (100 mm) are possible across the Southern Windwards, mainly north of Trinidad and Tobago. There is the threat of street flooding and flash flooding Wednesday into Thursday.
— Moderate seas with waves generally near 2.0 meters and up to 2.5 meters are possible in open waters east of T&T on Wednesday into Thursday.
— Gusty winds in excess of 65 KM/H possible. Winds of this strength will produce wind damage, including downed trees, utility poles and roof damage. Localized power outages possible.
— Due to unfavorable upper-level winds, thunderstorm activity associated with Tropical Wave 55 is forecast to diminish as it nears the Lesser Antilles. However, because of the widely scattered, but disorganized, convective activity associated with this wave, as well as the near-gale-force winds the weak low pressure is already producing, it is worth monitoring.
There are NO alerts, watches or warnings in effect for Trinidad and Tobago at this time.
As of 2:00 PM Sunday, the National Hurricane Center began monitoring an area of low pressure associated with Tropical Wave 55 moving across the Atlantic.
From the National Hurricane Center’s Tropical Weather Outlook, as of 2:00 PM, “A tropical wave located over the central tropical Atlantic is producing disorganized thunderstorm activity and strong gusty winds to near gale force in the northern portion of the wave. Upper-level winds are expected to be only marginally conducive for development to occur during the next few days while the system moves westward at around 15 MPH. By late Wednesday as the disturbance approaches the southern Lesser Antilles, upper-level winds are forecast to become quite hostile for any significant development to occur.“
What We Know
A tropical wave is in the Central Atlantic from 04N to 15N with axis along 45W, moving west at 10 knots/15 MPH/24 KM/H. Scattered moderate convection is from 10N to 14N between 40W and 47W.
Recent satellite-derived surface wind data indicate that the disturbance is producing winds to near-gale-force in the northern and eastern portion of the low pressure.
The approximate center of this low-pressure system is at 10.9°N and 44.9°W, moving west 24 kilometers per hour. This places the center of Invest 99L approximately 1700 kilometers east of Trinidad and Tobago
Based on our counts, this is the 55th tropical wave of the 2019 Atlantic Hurricane Season.
As of the 2:00 PM Tropical Weather Outlook, this system has a low chance, 10%, of tropical cyclone formation over the next 48 hours and a low chance, 20%, of tropical cyclone formation over the next 5 days.
This wave is yet to be designated as an invest, but the next invest will be called Invest 95L. 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 and mid-level vorticity (spin). There is a good amount of heavy thunderstorm and shower activity, which was scattered in intensity and areal coverage on Sunday afternoon, as seen on satellite imagery.
However, unfavorable wind shear continues across the entire tropical wave and is forecast to remain unfavorable throughout the week. This will be its main impediment to development. The other detriment will be dry, Saharan Dust surrounding the system on all quadrants, which will limit convection.
What We Forecast For Invest 99L
Due to a strong high-pressure system to the north of Tropical Wave 55, this system is forecast to remain on a mostly westward path. As it nears the Windward Islands, a more west-northwestward path is forecast. Much of the active weather associated with this system is already on the northern half of the low-pressure. Hence, further deviations northward would result in lesser impacts to T&T, beyond the usual impacts of a tropical wave passage.
This system has no model support for development at this time, based on the 12Z runs of the EMCWF (European), GFS (US) and UKMET (UK), ICON (German) and ARPEGE (French). But, there is notable consistency in the forecast track of the weak low pressure and the heaviest rain totals.
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, just north of Tobago, with the strongest sustained winds remaining north of Tobago and South of Barbados. The possible center of circulation is forecast to move north of Tobago at this time.
This system is not forecast at this time to produce widespread severe weather across T&T.
As mentioned above, there is no model support for the development of this system as of 12Z Sunday 13th October. However, small scale features such as this are difficult to pick up on global models. In addition, much of the models, at their point of initialization, did not pick up and properly resolve the winds and pressure of the low-pressure system associated with Tropical Wave 55.
As we move into the 18Z and 00Z runs later this evening, this post will be updated.
Based on present model guidance, upper-level winds are forecast to remain unconducive for development. Models, although they show little organization, do bring heavy rainfall to parts of the Windwards but not much of an organized wind threat.
Hence, as of Sunday afternoon, we continue to expect an active tropical wave to traverse the region onWednesday into Thursday, bringing locally heavy rainfall, gusty winds and agitated seas to the Southern Windward Islands.
Impacts From Invest 99L
The Southern and Central Windwards are forecast to be affected by this strong tropical wave. As mentioned, regardless of development, this system will be a locally heavy rain threat above all else.
All models, the EMCWF (European), GFS (US), UKMET (UK), ICON (German), ARPEGE (French) and CMC (Canadian) bring locally heavy rainfall and wind gusts in excess of 65 KM/H to the Southern Windwards, particularly Wednesday into Thursday,
Peak sustained surface winds of 25 KM/H to 55 KM/H with gusts in excess of 65 KM/H are possible in heavy showers or thunderstorms across the Southern Windwards, mainly north of Tobago. These peak sustained winds are forecast to occur Wednesday into Thursday.
With wind gusts in excess of 65 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. Localized power outages expected.
Across much of the Southern Windwards, including Trinidad and Tobago, we expect rainfall totals between 1 to 2 inches (25 to 50 millimeters) with isolated totals up to 4 inches (100 millimeters). Across Trinidad and Tobago, the heaviest rainfall is forecast to begin during the second half of Wednesday, lingering into Thursday.
Because of the particularly wet period we’ve had last week, and again at the beginning of this week, there is an elevated threat of street flooding, flash flooding and even possible riverine flooding upcoming.
Thunderstorms and Lightning
With thunderstorms, locally severe wind (in excess of 65 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
Throughout the week, seas are forecast to be moderate in open waters with waves up to 2.0 meters mainly east of Trinidad and Tobago and 1.5 meters elsewhere. Between Wednesday and Thursday, waves may occasionally near 2.5 meters in open waters and choppy in sheltered areas.
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.
Always check the National Hurricane Center for the latest information for tropical cyclones and your local meteorological offices for country-specific advisories concerning this low-pressure system.
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. However, as repeatedly mentioned, the main threat is flooding. Adequate preparations should be made to safeguard life and property. Create a safety plan in case of emergency.
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.