Forecast: Tropical Wave 01 To Bring Rainfall, Gusty Winds & Saharan Dust

The 2022 Wet Season is on the cusp of officially being declared as Tropical Wave 01 moves across Trinidad and Tobago on Sunday, May 15th, 2022. The wave is forecast to bring in a surge of high winds and fast-moving showers and thunderstorms.

The Wet Season is yet to be declared by the Trinidad and Tobago Meteorological Service but is generally done once there is measurable rainfall from either a tropical wave or the Intertropical Convergence Zone.

However, rainfall is expected to be short-lived as a dry and dusty atmosphere plagues the country this weekend as Saharan Dust returns.

The Forecast

Sunday night into Monday: Partly cloudy to occasionally overcast periods, interrupted by light to moderate showers. Brief, isolated heavy showers or thunderstorms are possible, generally favoring eastern areas of the country initially, then across southern Trinidad. Conditions are forecast to become increasingly settled, hazy, and windy through Monday. Gusty winds are likely, and street/flash flooding is possible.

Tuesday: Mostly hazy, breezy/windy conditions interrupted by brisk, isolated showers. Gusty winds are likely. Night to be mostly settled, barring the odd shower.

Wednesday: Mostly hazy, breezy/windy with the odd shower. Warm. A mostly settled night.

Thursday: Mostly hot, hazy, and breezy with the odd shower. A mostly settled night.

Friday: Mostly hot, hazy, and breezy with the odd shower. A mostly settled night.

Marine: Seas are forecast to be moderate to occasionally rough, with waves generally between 2.0 meters and 2.5 meters, occasionally above during the forecast period in open waters. In sheltered areas, waves are forecast to be near 1 meter but occasionally choppy due to increased winds.

Temperatures

Through the forecast period, the minimum low in Trinidad and Tobago is forecast to be between 24.0°C and 26.0°C, trending warmer across Tobago.

Maximum highs across the country are forecast to be generally up to 32.0°C in Trinidad and Tobago. In urbanized areas like Port of Spain, Scarborough, San Fernando, and Chaguanas, the maximum high temperatures could exceed 34.0°C.

Forecast Impacts

There are several hazards across Trinidad and Tobago over the next five days.

This week’s main hazards would be gusty winds through Tuesday night, while Saharan Dust is set to reduce air quality from late Monday through the week.

Mainly overnight Sunday into Monday afternoon, street/flash flooding is possible, mainly in heavy showers or thunderstorms. Riverine flooding is very unlikely based on current model guidance for accumulated rainfall over the next five days.

With the potential for thunderstorms, cloud-to-ground lighting can pose hazards for both on land and mariners. Landslides are also possible, particularly if heavy rainfall falls across elevated areas like the Northern Range and southwestern areas of Trinidad.

Even with favorable upper-level conditions, strong winds at low levels of the atmosphere will limit the development of severe thunderstorms, funnel clouds, waterspouts, and tornadoes.

Rainfall & Flooding

Through the forecast period, wind shear is forecast to remain unfavorable for persisting heavy rainfall. However, with the passage of Tropical Wave 01, favorable overall atmospheric conditions may allow deeper pockets of convection to develop, producing heavy/violent rainfall rates in showers and thunderstorms.

Putting the rainfall forecast into context, rainfall rates in excess of 50 millimeters per hour or areas that receive in excess of 25 millimeters within an hour tend to trigger street flooding across the country or flash flooding in northern Trinidad. For riverine flooding to occur, a large area of the country (not just in highly localized areas of western coastal Trinidad) would have to record upwards of 75 millimeters within 24 hours, and rainfall would have to fall across major rivers’ catchment areas.

Gusty Winds

Stronger wind gusts can cause power dips and outages, fallen trees, utility poles, lines, and isolated areas of wind damage.

With wind gusts up to and 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.

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 Sunday night into Monday, with highly isolated rainfall throughout the week.

Forecast Discussion

Tropical Waves: Based on the Tropical Analysis and Forecast Branch’s 18Z surface analysis, their first tropical wave for 2022 is along 62°W, south of 17°N, moving west at 15 knots (27.8 KM/H).

The first tropical wave for the 2022 Atlantic Hurricane season has moved across Trinidad and Tobago without much fanfare. As with most tropical waves, the activity tends to follow the wave axis, and this first wave seems to be struggling. Due to unfavorable wind shear and a significant encroaching surge of Saharan Dust, little notable convection is noted with the wave axis.

However, there is still abundant moisture following the axis of the wave and, more impactful – a surge of tradewinds. Winds between 15 to 20 knots have been detected following the wave axis, with gusts up to 30 knots possible. For the non-mariners, these are sustained winds up to 37 KM/H and gusts to 55.6 KM/H.

Generally, over the next 12-18 hours, this wave is forecast to progress westward. Under favorable upper-level conditions, its moisture is forecast to fuel isolated to scattered showers, with highly isolated and brief thunderstorms and heavy shower activity. Rainfall is set to mostly subside by Monday afternoon, with a surge of Saharan Dust drying out the low to mid-levels of the atmosphere as the Atlantic high-pressure system becomes dominant.

Saharan Dust is forecast to remain across the Windwards through the week with fluctuating high to significant concentrations, limiting further rainfall and leading to mostly hazy and sunny conditions from Tuesday onward. Low-level cloud patches could bring brief cloudy periods with brisk (lasting no more than 5 minutes) showers.

Overnight Thursday into Friday, a fresh surge of deep, tropical moisture associated with the BMS-analyzed tropical wave is set to begin moving across the Windwards and T&T. Showers and thunderstorms will be shortlived associated with this trough/tropical wave as the axis is on the leading edge of a forecast trade wind and Saharan Dust surge, set to arrive on Friday night.

Strong westerly to southwesterly wind shear will continue to keep overall heavier rainfall east and north of Trinidad and Tobago through the five-day forecast period.