A weak tropical wave, Tropical Wave 54. is forecast to move across Trinidad, Tobago, and the Lesser Antilles on Friday into Saturday. Much of the showers and thunderstorms associated with the wave will mainly stay north of T&T and occur on Saturday. However, light winds and abundant moisture on Friday will aid in developing strong, afternoon thunderstorms.
As of 5:00 PM Thursday 8th October 2020, the axis of this wave was analyzed along 56W, moving west very slowly, at 5 to 10 knots.
Higher rainfall accumulations are forecast to favor the northern and western halves of Trinidad.
There are no alerts, watches, or warnings from the Trinidad and Tobago Meteorological Service at this time.
Forecast For Friday Into Saturday
Thursday Night: Until midnight, mostly settled conditions with clear to partly cloudy skies across both islands.
Friday: From 12:00 AM onwards, isolated showers and thunderstorms are possible, initially favoring Tobago as well as northern and eastern areas of Trinidad, moving west to southwest. Heavier activity is forecast to remain offshore generally. By daybreak, a mostly sunny start to Friday is forecast, with a few isolated showers favoring Tobago and northeastern Trinidad.
By the late morning through the afternoon, partly cloudy skies will give way to showers and thunderstorms developing across Western and Northern areas of Trinidad, as well as Tobago. Shortly after midday, severe thunderstorms are possible across the western half of Trinidad, moving towards the southwest. Conditions will gradually settle through the late afternoon, but isolated showers and thunderstorms are forecast to return after nightfall.
Isolated showers and thunderstorms are generally forecast to remain offshore during Friday night, mainly affecting northern and eastern areas of Trinidad as well as Tobago through midnight.
Saturday: Another round of showers and thunderstorms are forecast after 12:00 AM, this time in the Gulf of Paria. Frequent lightning may be spotted across Trinidad, with variably cloudy skies and breezy conditions. Showers and thunderstorms are also possible across Tobago and Eastern parts of Trinidad until daybreak when conditions initially settle.
By daybreak, a mostly sunny start to Saturday is forecast, with a few isolated showers favoring Tobago and northeastern Trinidad. Similar to Friday, by the late morning through the afternoon, partly cloudy skies will give way to showers and thunderstorms developing across Western areas of Trinidad and Tobago. Shortly after midday, severe thunderstorms are possible across the western half of Trinidad, favoring west-central Trinidad, moving towards the northwest to north. Conditions will gradually settle through the evening, with any isolated activity favoring the northern half of Trinidad.
Hazards: The main hazards include heavy rainfall, which may reduce visibility and gusty winds up to and in excess of 55 KM/H. Street or flash flooding will be possible in violent showers and thunderstorms, particularly across western areas of Trinidad during the afternoon Friday and Saturday. In thunderstorm activity, frequent lightning is also possible. Gusty winds may cause power dips/outages, downed trees, and localized wind damage. Conditions will be favorable for funnel cloud development on both days.
Marine: Seas are forecast to be slight, with waves below 1.25 meters in open waters. Swells are forecast to be from the northeast, with a swell period between 6 and 7.5 seconds. In sheltered areas, near calm. However, in areas where thunderstorms occur, seas can become choppy and locally rough.
Winds are forecast to be light to moderate offshore, between 10 and 15 knots prevailing from the east to northeast on Friday and the east to southeast on Saturday.
Forecast Discussion: A weak tropical wave will be moving across the Lesser Antilles on Friday night. Deep, tropical moisture will begin moving across T&T on Friday through Saturday. Though much of the activity directly associated with the tropical wave is forecast to remain north of T&T, our localized climatic effects combined with the wave’s influence will allow for strong afternoon thunderstorms to develop. In addition, a marginally favorable upper-level environment will allow for enhancement of convection (showers and thunderstorms) on Friday.
Across Trinidad, by the late morning through the afternoon on both Friday and Saturday, light winds, daytime heating, and sea breeze convergence will act as triggers for shower and thunderstorm development across western parts of Trinidad, with orographic lift triggering/enhancing showers along hilly topography of both islands.
Note that on Friday, weather will be moving to the southwest while on Saturday, weather will be moving towards the northwest.
A weak surface to low-level confluent pattern behind the wave axis may initiate some brief shower activity on Saturday, as an induced surface to low-level trough will be approaching the region. This feature lacks significant concentrated instability and with moderate to strong wind shear from the northeast will keep activity brief and weaker on Saturday.
Across both islands, even with the forecast showers and thunderstorms, hot and humid mornings are anticipated. The maximum high for Trinidad is forecast to be near 34.0°C, up to 37.0°C in urban and built-up areas, particularly between 9:00 AM and 3:00 PM. In Tobago, the maximum high is forecast to be near 33.0°C.
Temperatures in cities, such as Port of Spain, tend to be much higher than surrounding locations due to a phenomenon called the Urban Heat Island Effect. There are several causes, but the main instigator for this phenomenon tends to be increased dark surfaces such as roads and pavement in cities, which absorb solar radiation more than surrounding areas.
The Heat Index
The heat index will be near dangerous levels on Friday and Saturday across Trinidad and Tobago. The heat index is a combination of air temperature and relative humidity, determining what the air feels like to a person, i.e., how hot it actually feels.
Across Trinidad, the maximum heat index is forecast to be between 35°C and 45°C and even higher in urbanized areas. In Tobago, the maximum heat index is forecast to be between 35°C and 42°C
The heat index is important because of sweating. Your body sweats to cool the skin and maintain a constant, healthy body temperature. This cooling process means that the sweat has to evaporate off the skin to remove heat. However, if the sweat is unable to evaporate, the body isn’t able to regulate temperature.
Heat index is generally classified into four categories: caution, extreme caution, dangerous, and extremely dangerous. On Friday and Saturday, the heat index is forecast to be near dangerous levels! Remain hydrated!
Sustained surface winds will be light, peaking during the afternoon. By the afternoon, sustained winds between 20 KM/H and 35 KM/H with gusts up to and in excess of 55 KM/H are possible.
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 most areas of Trinidad and Tobago, low rainfall accumulations are anticipated, with maximum accumulation totals less than 20 millimeters during the forecast period, with daily accumulations less than 10 millimeters possible.
Across Western and Northern halves of Trinidad, rainfall accumulations between 20-50 millimeters are possible, with isolated totals over the forecast period up to 75 millimeters. Note that in daily heavy showers and thunderstorms, rainfall accumulations in excess of 25-50 millimeters are possible within a short period (1-2 hours). This will trigger street and flash flooding, particularly along the south-facing slopes of the Northern Range and West-Central Trinidad.
Generally, with heavy showers and thunderstorm activity, street flooding, particularly in flood-prone areas or areas with poor drainage, is possible as well as flash flooding in areas where more prolonged heavy rainfall may occur.
Frequent Lightning: Frequent lightning is possible in thunderstorm activity. Lightning can cause power outages, voltage dips, damage to life and property, particularly during cloud-to-ground lightning strikes.
Why I May Not/Will Not See Rainfall?
A frequent complaint is the forecast is wrong because I didn’t experience any rainfall. Scattered showers mean that you, individually, may experience some showers intermittently throughout the day and there is a higher chance for this activity than isolated activity. Widespread showers mean that nearly all persons and areas may experience rainfall.
Isolated to scattered rainfall is forecast on Friday and Saturday. Most will experience very hot and sunny conditions.