Two tropical waves are set to move across Trinidad and Tobago over the next 72 hours, while the National Hurricane Center is monitoring an area off the southeastern United States coast for tropical cyclone formation but chances remain low.
What you need to know
— Tropical Wave 19: This tropical wave is just east of Barbados and Trinidad and Tobago, along 57W, moving west at 15-20 knots, producing some widely scattered showers generally north of T&T. Dry air at the low and mid-levels will limit shower and thunderstorm development associated with this wave as it moves across T&T overnight.
— Tropical Wave 20: This wave is located along 42W, moving west at 15 knots, and is forecast to move across T&T and the Lesser Antilles on Friday, producing showers and thunderstorms across T&T. However, the northern half of this wave is engulfed in high concentrations of Saharan Dust, which will limit shower/thunderstorm development across the northern Windwards and Leewards.
— Tropical Wave 21: This tropical wave is located at 28W, moving west at 10 knots. Currently, significant Saharan Dust is limiting shower and thunderstorm activity.
— AOI off the southeastern U.S.: A broad trough of low pressure is being monitored off the southeastern United States with low chances of development over the next several days before moving inland this weekend.
— Hazards for T&T: Mainly Friday through Saturday, isolated to scattered showers and thunderstorms are forecast to affect Trinidad and Tobago as Tropical Waves 19 and 20 interact with the Intertropical Convergence Zone. There is the potential for locally intense rainfall on Friday afternoon through Saturday morning.
Tropical Waves 19 and 20
Two large but weak tropical waves are analyzed at 57W (Tropical Wave 19) and 42W (Tropical Wave 20), east of Trinidad and Tobago.
Tropical Wave 19 is forecast to move across Trinidad and Tobago overnight tonight with little fanfare. Very dry low—and mid-level conditions inhibit the development of shower and thunderstorm activity. However, widely scattered showers are being observed on radar imagery, mainly north of Trinidad. Some isolated showers are possible overnight, favoring Tobago.
Tropical Wave 20, on the other hand, has a significant plume of deep tropical moisture across the southern half of the wave axis, while the northern half is engulfed in a dense plume of Saharan Dust. This wave is forecast to move across Trinidad and Tobago on Friday, with forecast models showing a generally saturated atmosphere and favorable mid to upper-level conditions. As a result, locally intense rainfall is possible in isolated to scattered showers and thunderstorms, with generally cloudy skies from Friday afternoon through Saturday morning. Model guidance also shows that wind shear will be very light, less than 10 knots, which will allow for some persisting rain and favorable conditions for isolated strong convection.
Across Trinidad and Tobago, generally, 15 to 25 millimeters of rainfall is forecast through Saturday night, with isolated totals up to 50 millimeters, favoring Trinidad, particularly across eastern and northern areas and localized areas of western coastal Trinidad. Wind gusts up to 45 KM/H are likely in heavy showers and thunderstorms, with higher gusts possible.
Tropical Wave 21
The 21st tropical wave analyzed by the National Hurricane Center is located well east of Trinidad and Tobago, along 28W, moving west at 10 knots (18 KM/H). Based on current model guidance, this wave is forecast to move across the region early next week, between Tuesday and Wednesday, bringing showers and isolated thunderstorms.
Currently, significant Saharan Dust is hindering any shower or thunderstorm activity from forming, but as it moves across the area next week, a deep-layered plume of moisture is forecast to accompany the wave across the Windwards.
Development Southeast of the U.S.
The National Hurricane Center is monitoring a broad trough of low pressure several hundred miles off the coast of the southeastern United States, with low chances of tropical cyclone formation over the next seven days. The NHC gives this system a low chance, 10%, of tropical cyclone formation over the next 48 hours and seven days, respectively.
According to the NHC, “Environmental conditions appear only marginally favorable for some additional development of this system over the next couple of days before it moves inland over the southeastern U.S. by this weekend.”
Based on the latest forecast guidance from the U.S. National Weather Service, parts of Florida and from South Carolina to New York could see between 1.5 and 3 inches of rainfall, with isolated higher totals across parts of North Carolina as a result of both this system and a flow of moisture from the south to north along the periphery of a high-pressure ridge in the west Atlantic Ocean.
Not Every Tropical Wave Brings Severe Weather
Tropical waves vary in intensity as they travel westward across the Atlantic. This variability can be in the order of days or as short term as hours. Sometimes, you may see satellite imagery that shows heavy thunderstorms and deep convective activity east of Trinidad and Tobago during the late night and early morning, but by daybreak – nothing.
This is due to diurnal (daily) variations in convective showers whereby convection peaks overnight and wanes during the day for already occurring convective systems (i.e., not triggered by daytime heating).
Activity can be enhanced by its proximity to upper-level troughs and the ITCZ but can also be degraded by hostile upper-level conditions and Saharan Dust.
A perfect example is Tropical Wave 19, which is set to move across T&T overnight tonight with little fanfare, but Tropical Wave 20 on Friday will bring more showers and thunderstorms – typical of a tropical wave.
